Skip to Main contentScienceDirectJournals BooksRegisterSign in Sign inRegisterJournals BooksHelpSensitized CellRelated terms:PhotovoltaicsQuantum DotTitanium DioxidePower Conversion EfficiencySolar CellsDye-Sensitized Solar CellSensitizerView all TopicsDownload as PDFSet alertAbout this pagePhotovoltaic Solar EnergyL.L. Kazmerski, in Comprehensive Renewable Energy, 20121.03.3.3 Revolutionary Photovoltaics: The Chase Toward the Next GenerationsSome of the possible contenders for the next PV generations have started their journeys in the laboratory. Martin Green [78] brought attention to this future when he classified first-generation PV as crystalline Si, second generation as the thin films, and third generation as a host of evolving devices, upstarts, and wild ideas that have lined up in the race to meet the performance and cost goals needed to deliver those 15–30 TW by mid-century. Whereas the second generations might be competing in the analogue of the 100 m dash to surpass Si in the current to near-term technologies, the third generations are in a marathon struggle that must not only bring them to commercialization, but also demonstrate their abilities to generate voltage and current for the very first time.This is the PV researcher’s field of dreams. It is also the parking lot of nightmares for the near-term real business of PV – with worries about delaying or inhibiting the adoption of real and working technologies that will serve for the next 20–30 years to wait for one that might not have even been demonstrated to generate electricity yet, but that theoretically promises performance beyond Olympic levels. (This is something many of us have experienced awaiting the next, then the next, speed bump up in computer microprocessors – and we may never purchase a computer!) There must be understanding and patience, knowing that the investment in these research areas is important for both future technology ownership and readying the next generation(s) of solar electricity for many generations of consumers to come. These third-generation contenders include the following.1.03.3.3.1 Fooling mother natureDye-sensitized cells (Grätzel cells [79]) have efficiencies that are 11% in the laboratory and 15% in tandem with an inorganic cell. Although the visibility of this technology was lowered from its high point in the 1990s, it has started to advance again, largely due to technology investments and innovation from the Asian sectors. Increased understanding and improvements in processing have helped the status of this truly nanoscale-based technology.1.03.3.3.2 Just one word – ‘plastics’Organic PV (or OPV) [80–82] also operate through excitonic processes, with small molecule (  104 molecular weight) to polymer or large molecule (  106 molecular weight) approaches under development. The best single-junction confirmed cell has 10.0% efficiency (Mitsubishi Chemical), followed by Konarka (8.3%). Several tandem approaches have been reported now, including the record 9.8% cell by Heliatek in Germany (December 2011) followed by UCLA’s 8.6% device. These OPV cells are currently the hotbed of progress in the efficiency chase. A single-junction large-area (almost 2 cm2) cell was confirmed at 5.9% by OSOL in Dresden, Germany. Overall, the progress is now exceeding that for the inorganic thin films in the early 1980s, and it is bolstered by an incredible population of scientific researchers working in this area. The organic solar technology has reached some initial commercial stage (really qualifying it as a disruptive technology that could have some impact in the mid-term), and the device lifetimes have started to improve substantially in work reported in the past year. \"Dustin Hoffman, stay tuned … .” (The Graduate, 1967). Recently the first greater than 10% organic tandem was verified at 10.6% for a UCLA-Sumitomo Chemical.1.03.3.3.3 Using more sun, less real estateMultiple-junction cells have been developed, but those with ‘multi-multijunctions’ – four to six such devices – are in the research stage. Europe is leading the efforts [83], but some work has now been reinstated in this area in the United States. Others include the recent split-spectrum reported under the US DARPA program, with a module confirmed at 37.5% [84]. There are also several metamorphic designs under investigation. Polycrystalline tandems are also in this category, with the first reported devices using CIGS and CdTe thin films. This area is of immense technical interest – high risk, but potentially high payoff with the dual promise of high performance and low cost. Again, look to Asia … .Silicon also has been evolving quickly in this area based upon Si micro- or nano-wire technology [85–89]. ‘Single-wire cells’ with excellent electrical properties (e.g., minority carrier diffusion length Ln ≫ 30 μm) have been fabricated with unconfirmed efficiencies in the 17% range (under low concentration). However, the goal is to use this high-quality wire aligned on a substrate, leading to large-area cell with similar or greater performances. Aligned micro- and nanowires for these PV applications have been reported with enhanced absorption and carrier collection. These devices have not only demonstrated enhanced performance, but also are coming with positive material utilization – perhaps using as little as 1/100 of the Si needed using conventional technology at the same efficiency level.1.03.3.3.4 Hot flashesBoth thermophotovoltaics (TPV) and thermophotonics incorporate the infrared in their conversion schemes. The latter uses two thermally isolated diodes operating at the radiative limit which are optically coupled. The efficiency can approach the Carnot limit for conversion between the temperatures of the warmer and cooler devices. This has been modeled, but not yet confirmed. The TPV device has been confirmed, and uses very low-bandgap semiconductors [90]. However, the terrestrial use has been confined to niche applications.1.03.3.3.5 Retro-voltaicsIn the quest for solar cells that are devoid of materials supply and potential toxicity problems, a host of materials are being resurrected that initially evolved in the 1950s to the 1980s. These materials have optimal bandgap properties in addition to be fabricated from earth-abundant and/or nontoxic elements. These include CuxS, Cu2O, Zn3P2, CdSe, Cu2Se, SnSe2(S2), and FeS2 [91, 92]. The most advanced of these was the Cu2S/CdS cell, confirmed above 10% efficiency in the early 1980s [93] – and was actually first reported as a thin-film solar cell in 1955 [94]. Despite many groups representing six continents and being commercialized, stability issues surrounded its further development. The 30 or more years that separate these approaches from those 1970s–1980s rapture with new materials (and funding!) have brought about an expanded understanding of materials and device engineering, improvements in processing and deposition control, and an incredible new arsenal of characterization techniques that will provide new insights and guidance toward better performance (efficiency and stability). The Center for Inverse Design, a Department of Energy (DOE) Office of Science Energy Frontier Research Center (EFRC), has recently reported an example of implanting improved science, techniques, and methodologies that were not possible when one of these ‘retro’ materials was first considered. Using their inverse design approach (www.centerforinversedesign.org) to design materials according to specified target functionalities, they have recently reported new results by incorporating Si and Ge in the FeS2 to control the defect density at the surface (device interface) that promises to provide gains in open-circuit voltage needed to continue with this earth-abundant semiconductor. It may well be time for ‘something old and something borrowed’.1.03.3.3.6 The far sidePV science and technology have always included higher-risk approaches in their R D portfolio: alternatives to the conventional that are near or at the outer fringes of science and engineering and that might provide breakthroughs, significant progress leaps, or even new technologies. These alternatives center on nanotechnology and hot-carrier approaches resulting in multiple-exciton generation from a single photon, including quantum dot solar cells and intermediate-band solar cells [95–98]. Multiple-exciton generation (MEG) has been demonstrated in several materials; however, no solar cell has yet been confirmed. There is some question relating to the MEG results [99], but these approaches are new and need time to develop – patience is needed to let these quantum dots provide watts. Just when some skeptics were ready to write off these ‘more for the price of one’, two events occurred. First, the the first ‘quantum dot’ solar cells have been reported (Figure 8); PbSSe cells (reaching 5.1%, reported by the University of Toronto [100]). And more spectacularly, the first confirmed report of the multiple-exciton generation (MEG) process occurring in a PV quantum dot device [101]. Photocurrent enhancement was reported in lead selenide quantum dot solar cells, with a peak external quantum efficiency (QE) of 114% and a corrected internal QE of 130%. Ready for the manufacturing world? Not yet, but this does provide the proof of concept needed for continuing R D investment in this approach. And, like all nascent technologies, stability is an issue. Of course, the payoff for these technologies is a conversion efficiency that, at least on paper, can exceed 60% and perhaps even approach 80%; a summary is shown in Table 1 [96, 98]. They are the cells for our next–next generations of consumers, and they need the investment now to establish the R D for realizing these very high-value technologies. These are at the most radical fringe in the PV technology revolution.Table 1. Predicted efficiencies for ideal revolutionary: second- and third-generation solar cells compared to limits (Carnot, Landsberg, and Shockley-Queisser)Converter or limit (Tsource = 6000 K, Tdevice = 300 K, isotropic illumination)Efficiency (%)Carnot limit95.0Landsberg93.3Multijunction (infinite number of junctions)86.8Impact ionization (best Q)86.8Hot electron85.4Solar thermal85.4Thermophotovoltaic85.4Thermophotonic85.5Intermediate band (quantum dot or alloy)63.2Multiple quantum well (second photon pumped)63.2Shockley-Queisser limit40.3Based on Honsberg CB and Barnett AM (2004) 20th European Photovoltaic Solar Energy Conference, Valencia, Spain. Germany, WIP-Energies [96]; Honsberg CB (2004) U.S. DOE Solar Energy Technologies Program Review. Denver [98].View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780080878720001013Blood Group ImmunoglobulinsF.J. BAKER F.I.M.L.S., F.I.S.T., R.E. SILVERTON F.I.M.L.S., L.I.Biol., in Introduction to Medical Laboratory Technology (Fifth Edition), 1976The anti-human globulin (Coombs) testThis test was introduced by Dr Coombs in 1945 and is also known as the Coombs test or antiglobulin test. It is considered one of the most sensitive techniques in the detection of IgG antibodies or incomplete antibodies, which are antibodies which will not cause direct agglutination of red cells suspended in saline. Apart from its other important uses it is one of the essential tests in the crossmatching of blood to ascertain that the donor blood is compatible with the recipient s serum, and does not react with antigens in the donor s red cells.The principle of the test is that as all antibodies are globulins an antibody against human globulin will attach itself to the specific blood group antibody which itself is attached to the red cell. In effect an antibody is prepared against another antibody and the red cells are used as an indicator of this reaction (Figure 38.3).Figure 38.3. Diagrammatic representation of the principles of the antiglobulin testThe anti-human globulin serum is prepared by injecting whole human serum into rabbits to produce what is called a ‘broad-spectrum’ serum which will contain IgG antibody and also anti-complement fractions. Specific antisera to IgG, IgM and IgA can also be produced against the heavy chains of these immunoglobulins. It is essential that group O serum is used to prepare antiglobulin sera because anti-A and anti-B sera contain A and B antigens which may well stimulate the production of a large amount of unwanted anti-A or anti-B.After an initial screening test to determine that the produced antiglobulin serum is potentially suitable for routine use, a full series of standardization tests is undertaken. The serum is inactivated to destroy complement and mixed with group A and group B cells to remove unwanted agglutinins. Doubling dilutions (1 in 2, 1 in 4, 1 in 8, etc.) of the antiglobulin serum are prepared and each dilution is tested against red cells which have been sensitized with varying amounts of IgG antibody; this is usually anti-D, as this antibody is freely available. The complexity of this standardization is to ensure that the antiglobulin serum will detect small amounts of IgG antibody and will not detect any red cell antigens causing a falsely positive reaction.The detection of cells sensitized with IgG antibodies using anti-human globulin serum may be performed in two ways.1.The direct antiglobulin test, also referred to as the direct Coombs test or DCT. This test is performed directly on the patient s washed red cells to establish if they have been coated with IgG antibody in vivo, i.e. antibody attaching itself to the patient s own red cells whilst still circulatng in the vascular system. This test is often positive in haemolytic disease of the newborn, incompatible transfusion reactions and in some cases of auto-immune haemolytic anaemia.2.The indirect antiglobulin test or indirect Coombs test. This test is used to detect antibody in a patient s serum by incubating fully grouped red cells with the patient s serum at 37 °C to establish if any antibody present will sensitize the red cells in vitro. After incubation the red cells are washed, antiglobulin serum is added and the presence or absence of agglutination is noted. By using a ‘panel’ of fully genotyped red cells and incubating the patient s serum with each, it is possible to determine the specificity of the antibody if an IgG antibody is present. Any red cells which do not agglutinate after the addition of antiglobulin serum will not contain the antigen to the specific antibody. The cells which do agglutinate will have been sensitized by the antibody and will contain the specific antigen to this antibody. By a series of eliminations the specificity of the antibody may be determined.As all human serum contain globulins, it is essential that any globulin not attached to the red cells is removed by washing in copious volumes of saline before the addition of antiglobulin serum. If these are not removed the antiglobulin serum will be neutralized by the ‘free’ globulins and false negative reactions obtained. The cells are washed at least three times, and in laboratories which perform large numbers of antiglobulin tests this procedure is tedious and use is made of a cell-washing centrifuge which automatically washes the cells, and in some models automatically adds the antiglobulin serum.All the common Rhesus antigens, with the apparent exception of d, are able to stimulate the production of their corresponding specific antibody in both the complete and incomplete forms. Mixtures of antibodies do occur with anti-C + D and anti-D + E being likely combinations.A patient who has developed Rhesus antibodies from a previous blood transfusion, pregnancy or abortion and is given Rhesus incompatible blood will have a ‘transfusion reaction’. This reaction, if detected at an early stage, may cause little damage, but if the patient is anaesthetized, the reaction may be masked and severe renal damage occur due to the large haemoglobin molecule being released into the blood stream, and being unable to pass through the kidney. The breakdown of red cells in this way is called ‘intravascular haemolysis’.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780407001541500427FUELS – HYDROGEN PRODUCTION | Photothermally and Thermally-Assisted PhotovoltaicS. Licht, in Encyclopedia of Electrochemical Power Sources, 2009Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis. An overview of solar direct, solar indirect, and hybrid thermal processes for the generation of hydrogen is presented, and compared with non-thermal solar-based alternatives. The energy source (sun) and reactive media (water) for solar water-splitting are readily available and provide a renewable source, and the resultant fuel (hydrogen) and its discharge product (water) are each environmentally benign. In particular, a hybrid solar–thermal plus electrochemical process substantially increases the hydrogen that can be produced with solar energy via a decrease in the water-splitting voltage that occurs with increasing temperature. Unlike other processes, this uses the complete solar spectrum to increase solar efficiency, i.e., both the visible light to drive photovoltaics and also solar–thermal radiation that would normally be wasted as sub-bandgap energy. The hybrid process combines photovoltaics with the excess sub-bandgap heat to deliver efficient, elevated-temperature, solar water electrolysis to produce hydrogen. High-temperature electrolysis components are available, and solar concentration can provide the high temperature and diminish the surface area of the components for solar conversion to electrical energy.Fundamental thermodynamics are used to show that solar-to-hydrogen conversion efficiencies of about 50% are accessible over a wide range of insolation, temperature, pressure, and photovoltaic band-gap condition.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B978044452745500318XPhoto-Functional Applications of Semiconductor Nanomaterials☆Yoshio Nosaka, Atsuko Y. Nosaka, in Comprehensive Nanoscience and Nanotechnology (Second Edition), 20195.06.4.1.2 Quantum dot solar cellsFor applying semiconductor quantum dot (QD) to solar cells, typical device architectures are quantum dot sensitized solar cell (QDSSC), colloidal quantum dot Schottky junction solar cell, and colloidal quantum dot heterojunction solar cell as shown in Fig. 14 [115,116]. Other challenges are quantum dots dispersed in organic semiconductor polymer matrices, fullerenes, graphene, or carbons [117].Fig. 14. Comparison of three colloidal QD photovoltaic architectures (a) QD sensitized solar cell (b) The depleted heterojunction design combines the advantages of the other two cells, and (c) the Schottky design solar cell.Reproduced from Pattantyus-Abraham, A.G., Kramer, I.J., Barkhouse, A.R., et al., 2010. Depleted-heterojunction colloidal quantum dot solar cells. ACS Nano 4, 3374–3380.In QDSSC, dye molecules of DSSC are replaced by semiconductor nano particles or quantum dot, which produce excitons by the absorption of light. The wavelength of the absorption threshold depends on the size as well as the band gap of the semiconductor. Weller and co-workers [20] presented for the first time a method for sensitization of highly porous TiO2 electrodes by in situ prepared quantum-sized CdS particles (4–20 nm). A photocurrent efficiency of more than 70% was achieved by visible light illumination, but a photovoltage was as low as 400 mV. Adsorption of CdSe QDs onto nanostructured TiO2 films was attempted by Toyoda and coworkers [118]. Coating of ZnS onto the CdSe QDs improved the photovoltaic conversion efficiency remarkably. Nozik suggested that efficient inverse Auger effects in QDSSCs could produce much higher conversion efficiencies than those possibly attained with DSSCs [119]. Hodes compared semiconductor-sensitized SCs with DSSCs and discussed the differences between the two types of cells in terms of typical charge transfer times for various current generating and recombination processes [120]. He suggested that the large improvements in efficiency of the liquid junction semiconductor-sensitized SC are very feasible [120].Single-crystal ZnO nanowire arrays grown on a conducting glass substrate were applied as a new type of QDSSC that consisted of CdS [121] and CdSe [122] semiconductor nanocrystals as light-collecting materials. Fig. 15(a) illustrates the cell structure of CdSe QD solar cell with ZnO nanowire. The significant enhancement of the photocurrent of a bare ZnO nanowire array is demonstrated by using CdSe NPs as a sensitizer [122]. Fig. 15(b) shows the hollow core-mesoporous shell carbon counter electrode causes fast mass transfer with less resistance with having highly enhanced catalytic activity toward the reduction of the mediator [123]. The efficiency of QDSSC was increased with polymer or organic HTM in place of redox solution [115].Fig. 15. (a) Schematic illustration of the quantum-dot-sensitized solar cell. An array of ZnO nanowires, grown vertically from an F-doped SnO2/glass substrate and decorated with CdSe quantum dots. Reprinted from Leschkies, K.S., Divakar, R., Basu, J., et al., 2007. Photosensitization of ZnO nanowires with CdSe quantum dots for photovoltaic devices. Nano Letters 7, 1793–1798. (b) Hierarchical nanostructured carbons counter Electrodes for CdS Quantum Dot Solar Cells.Reprinted from Paul, G.S., Kim, J.H., Kim, M.S., Do, K., Ko, J., Yu, J.S., 2012. Different hierarchical nanostructured carbons as counter electrodes for CdS quantum dot solar cells. ACS Applied Materials and Interfaces 4, 375–381.For intermediate-band solar cells using self-assembled QDs, suppression of a reduction of open circuit voltage presents challenges for further efficiency improvement. In QD sensitized cells and QD heterojunction cells using colloidal QDs, well-controlled hetero-interface and surface passivation are key issues for enhancement of photovoltaic performances [124]. The ZnS surface passivation was found to play important roles on the stability and the photovoltaic performance of the QDSSCs as illustrated in Fig. 16;Fig. 16. Schematic illustration of the effects of surface passivation on QD adsorbed photoelectrodes in QD sensitized solar cells: (1) prevention of photocorrosion; (2) prevention of reverse electron transfer; and (3) reduction of surface trap states.Reprinted from Sogabe, T., Shen, Q., Yamaguchi, K., 2016. Recent progress on quantum dot solar cells: A review. Journal of Photonics for Energy 6, 040901 (27 pp).(1)preventing photocorrosion of QDs in electrolyte and improving the stability,(2)preventing reverse electron transfer from TiO2 to electrolyte and increasing charge collection efficiency, and(3)reducing surface trap states of QDs and thus increasing electron injection efficiency.Recent review works may be helpful for preparation of colloidal quantum dot [116,125,126] and for the architecture of QDSCs [127–130].Nozik reported that QD solar cells have a potential to increase the maximum attainable thermodynamic conversion efficiency of solar photon conversion up to about 66% by using hot photogenerated carriers to produce higher photovoltages or higher photocurrents [119]. However, the potential high efficiency configurations are theoretical and there have been no experimental results yet that demonstrate actual enhanced power conversion efficiencies in QD solar cells [103]. The maximum power conversion efficiency for QD solar cells at present is 13.4% according to the chart of NREL [103].View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780128035818112366FACTORS AND ACTIVITIES PRODUCED IN VITRO BY LYMPHOCYTESH. Sherman Lawrence, in In Vitro Methods in Cell-Mediated Immunity, 1971B RNA-Transfer Preparations and Leucocyte Lysate Transfer PreparationsThese materials, studied now in guinea pig, monkey and man, do not appear to have the same properties as dialyzable human transfer factor. Their relation to it remains a problem.Thus we are faced with a dilemma particularly appropriate to this workshop: Transfer Factor has been easily demonstrated repeatedly in diverse systems of cellular immunity (bacterial, fungal, viral, denatured protein, homograft rejection) under a variety of experimental circumstances as unquestionably the most potent initiator of delayed type reactions or cellular immune responses in vivo. – And yet despite this abundant reality, transfer factor is still in search of an adequate, reproducible assay system in vitro. In sharp juxtaposition, the mediators or effector molecules of cellular immunity that are so readily revealed and potently expressed in vitro are still in search of an in vivo function. (Lawrence and Valentine, Am. J. Path. 60: 437, 1970).DR. THOR: We initiated studies at the University of Illinois to investigate RNA fractions that might be related to transfer factor in an attempt to clarify several problems. We were interested in differences between a dialyzable and non-dialyzable transfer factor, both of which appear to have similar activities. We extracted RNA from human lymph nodes which had a molecular weight very similar to the non-dialyzable transfer factor. The biological activity resided in species between an 8 to 18 S RNA with the majority of activity at 18 S. To date, we have been unable to isolate from this higher molecular weight RNA any type of dialyzable transfer factor piece, despite the use of a number of enzyme systems in an attempt to produce such a low molecular weight transfer factor. Several of the activities that Dr. Baram has reported seem to be similar to our material. Both are RNA extracts, and sensitive to pancreatic ribonuclease sensitive. Phosphodiesterase destroys the activity of our high molecular weight transfer factor.DR. LAWRENCE: Will you also tell us your assay of the dialyzable material, Dr. Thor?DR. THOR: The dialyzable material was assayed by an in vitro method, namely, the production of migration inhibition factor by normal cells treated with RNA plus antigen. One of the big problems in evaluating the activity of the RNA extracts is in getting the RNA into the test cell. In the human system, migration assay requires a 72 hour tissue culture suspension of lymph node cells to obtain a migrating cell source. We have been unable to activate fresh human peripheral lymphocytes with the RNA extracts. However, if peripheral lymphocytes are placed in tissue culture for four to five days, they can be activated with the RNA extract but only in the presence of antigen to produce MIF. Perhaps I should qualify that to say that they then produce a factor in the supernatant fluid which will produce migration inhibition of guinea pig macrophage.DR. LAWRENCE: With regard to the non-dialyzable transfer factor that Dr. Baram has worked with in vivo and its relationship to dialyzable transfer factor, I would suggest that unless large volumes of fluid are used outside the dialysis sac and frequent fluid changes made, some dialyzable transfer factor will remain within the sac as equilibrium is achieved with the dialysis fluid. The inside contents of the sac will then transfer delayed sensitivity. In our early studies when a 1:1 ratio of fluid inside to fluid outside the sac was used, we could dialyze the inside of the sac once, do a transfer with the dialysate, transfer the inside contents to another sac, dialyze again and get out more transfer factor. (cf Lawrence, et al. Trans. Assoc. Amer. Phys. 76: 84, 1963).DR. HIRSCHHORN: You assume that what transfer factor does is to convert non-sensitive cells into antigen responsive cells. I wonder, in view of the low number of cells that appear to respond in the in vitro assay system, whether or not you are simply amplifying a very small number of preexisting antigen recognition cells which we presumably all have.DR. LAWRENCE: Burnet may be correct in his suggestion, that we do hold in reserve a clone of cells set aside for tuberculin responsiveness, for example, which remain dormant until such times as we meet either the tubercle bacillus in nature or transfer factor in the laboratory.DR. SMITH: That makes transfer factor an antigen, does it not?DR. LAWRENCE: This was the conclusion Dr. Uhr reached at the Brook Lodge Symposium.DR. AMOS: I wonder if it isn t possible that during the process of dialysis, you pick up endotoxin. Do you think endotoxin could contribute to the stimulating effect?DR. LAWRENCE: This could be, except the amounts used were so small. Do you want to speak to that. Dr. Valentine?DR. VALENTINE: One of the surest things in this system in our hands is that the material itself, dialyzable transfer factor, without antigen, did not stimulate the cells.DR. LAWRENCE: I would emphasize that the dialysate did not even stimulate tuberculin sensitive cells. We found no evidence for antigen when looking in the dialysate for a possible antigen-polynucleotide fragment in the transformation system that Dr. Valentine perfected, where one can detect as little as 0.001 gamma PPD.DR. AMOS: I am not sure that answers it, Dr. Lawrence, because if it were a stimulating effect of endotoxin, it would augment the response to antigen.DR. BACH: If transfer factor were something like endotoxin, you must assume that the endotoxin effect is specific, since Dr. Lawrence finds that his material, whatever it is, is specific. He will only get activity to the specific antigen to which the donor was sensitive.DR. DRAY: Has transfer factor ever been described for any other species than man?DR. LAWRENCE: And monkeys. I propose to call on Dr. Adler, shortly, to inform us that human dialyzable transfer factor can convert mouse lymphocytes to a specific antigen responsive state. But you are quite correct. There have been no successful, reproducible transfers, with extracts in vivo in animals other than primates to date.DR. DRAY: With regard to RNA, which is extracted by the hot phenol technique, we have shown that this will transfer the capacity to produce MIF to guinea pigs. Further, we have almost sufficient evidence to prove that this RNA will also transfer the skin test in guinea pigs.DR. BENACERRAF: I would like to state that certain laboratories are not as fortunate as Dr. Thor and Dr. Dray in their ability to transfer immunological activity with RNA. We attempted to find out how best to do it from Dr. Thor, and we could never manage to achieve such a transfer. That does not mean it is not true; it just means we could not do it.DR. THOR: I would like to respond to Dr. Benacerraf s challenge.DR. BENACERRAF: That was not a challenge, but simply a statement of fact. The methods we used were those given to us by Dr. Thor himself on a variety of occasions. That we may not have been able to reproduce them properly, is our failure; it is not the case that we did not know them. I also know that Dr. Schlossman attempted to repeat some experiments which had been done with Dr. Thor at one time by himself in his own laboratory, and was unable to do so again using the same methods. I don t say that it is not possible to do so; I simply must state that we were not able to do it, and, therefore, it must require a very special technique or other things which have not been yet published with clarity.DR. THOR: There are a number of difficulties in the guinea pig system, many of which I have described to some of the people in Dr. Benacerraf s lab. I am not convinced yet that in the way their methods were set up, they followed exactly our technique. The method I report in the second section of this book spells out these methods in better detail than previously published elsewhere.DR. LAWRENCE: That is the purpose of this book.DR. COOPER: Since the pandora s box has been opened on RNA, what I have to say may be germane. In my experience, it is virtually impossible for somebody in one laboratory to take a detailed technique, involving RNA extractions, and go and do it in another laboratory, without one or two years failure!More specifically, and perhaps more usefully to this meeting, Dr. Robert Stern, working in my laboratory, has found two very interesting things. The possibly double-stranded RNA piece apparently associated with transfer factor may be more vulnerable in the assay system than people may think. It appears that there is a measurable amount of ribonuclease activity of a very special type, directed specifically to double-stranded RNA, present in the sera of all animals and in other body fluids such as saliva. It is produced in virtually all tissue culture cells of human origin that Dr. Stern has looked at. This enzyme is very effective in degrading double-strand RNA, i. e., - RNA resistant to pancreatic RNA ase. As a purely technical point, people working with these materials may want to eliminate this activity, for example, by leaving out the serum from their incubation mixture.The other point I wish to make is that all of the cells that we have studied (lymphocytes, Burkitt s lymphoma cells, and HeLa cells) continuously synthesize small but detectable amounts of double-stranded RNA. This is actinomycin-resistant production.DR. VALENTINE: Dr. Thor mentioned the difficulty of getting RNA into cells. I wonder if he has tried or if he knows of others that have tried changing the tonicity of the medium in the fashion that the virologists do on occasion to get viral RNA material into cells?DR. BENACERRAF: We performed experiments, using DNA to increase the RNA uptake, which we could accomplish without difficulty, but without successful transfer of specificity.DR. THOR: In some of the early reports on activity of RNA in the cellular immune system, Mannick and Egdahl used the osmotic effect of sucrose to get RNA into cells. We tried sucrose initially and had difficulty getting the same effect with sucrose. Recently Werner Braun has suggested that heparin would increase RNA uptake by cells. I believe that it isn t just a simple problem of getting RNA into cells. The problem is to get it in in the right way or form. I personally don t know what that right way is, except that non-sensitized, or non-activated macrophages seem to be an effective way. Perhaps it is the most natural method. Further, using a hypotonic medium does not always bring about the effect one is looking for.DR. LAWRENCE: I would now ask Dr. Adler to present his experience on the effect of dialyzable human transfer factor on mouse spleen lymphocytes.DR. ADLER: We have two sets of experiences with transfer factor on mouse spleen cells. Human transfer factor extracted from peripheral lymphocytes, dialyzed, lyophilized and then reconstituted with medium, when added to mouse spleen cells, permits the cells to be stimulated by PPD when it is added to the culture. The same sort of extraction procedure applied to mouse spleen cells taken from mice which have been previously immunized with BCG results in the production of a transfer factor which causes non-immune cells to respond to PPD. But there is a difference between these two types of transfer factor. As the amount of human transfer factor in the medium is increased, you find concomitant depression of tritiated thymidine incorporation. Conversely, as the amount of mouse transfer factor, without antigen, in the medium is increased, there is non-specific stimulation and an increase in tritiated thymidine incorporation. In other words, the mouse transfer factor is itself a mitogen.Dr. Amos has suggested that there may be endotoxin contamination and, therefore, an adjuvant effect. This is a possibility. We reported in the Federation Proceedings last April that endotoxin is a potent mitogen for mouse spleen cells. In this sense, the major problem with the PPD stimulation of mouse spleen cells is the PPD itself; some preparations of PPD are in themselves mitogenic for non-immune cells. We believe this is due to endotoxin contamination of the PPD.Our observations are similar to those of Dr. Lawrence s on the point that very few cells are involved in the response to PPD in the spleen cell cultures treated with transfer factor. The background stimulation and the nonspecific mitogenic effect of PPD makes the system very much of a problem to deal with and impossible to determine exactly the number of cells involved in response to PPD,DR. LANDY: I would only point out that there is good data on record to indicate that the transformation of human peripheral lymphocytes in vitro by endotoxin involves only a few percent of cells. In seeking to account for the high degree of transformation of murine cells by endotoxin, Dr. Adler has wisely reminded me that we are comparing human peripheral cells with murine spleen cells and consequently, additional factors may be operative. All experiments should really include at least two antigens assayed in a crossed manner to assure that there is immunologic specificity for each antigen.DR. LAWRENCE: In experiments that Dr. Valentine and I did, we used tuberculin positive, diphtheria toxoid negative transfer factor and the cells responded to tuberculin but not to diphtheria toxoid in the presence of the tuberculin positive transfer factor.DR. DRAY: Dr. Paque in our laboratory, in collaboration with Peter Baram, has shown that whole transfer factor would convert normal cells to a state of competence as assayed by migration inhibition. Now, working with dialyzable and non-dialyzable transfer factors, we have been able to show that the non-dialyzable factor transfers cell migration inhibition activity, but have not been able to get the dialyzable factor to accomplish this. The situation is human TF is added to normal human lymphocytes for release of MIF, but the assay eventually uses the inhibition of guinea pig macrophages.DR. VALENTINE: In the experiment Dr. Lawrence referred to involving transfer factor from a person sensitive to PPD and not sensitive to toxoid, put on double negative cells, and the cells respond to PPD, but not to toxoid, I must point out that we did not do the reverse experiment.DR. LAWRENCE: We now move on to discussion of \"New Factors.” Before those who would get up to propose new acronyms, we would like to be assured that they really represent new factors and not rediscovery of the old.DR. BACH: I believe we have a new factor (Janis and Bach, Nature 225: 238, 1970). The factor is produced in the same way the blastogenic factor is produced, i. e., it is obtained in the cell-free supernatant medium of a stage I leucocyte culture. That cell-free medium is assayed in a stage II culture for the presence of potentiating factor activity. Table 9. shows results of an experiment. Lymphocytes from both individuals A and B responded to PPD (compare reactions 2 and 6 with control reactions 1 and 5 respectively). Cell-free medium obtained from stage I cultures of PPD-stimulated leucocytes from individual A, i.e., A cells and PPD, caused little or no stimulation of lymphocytes from individuals A or B, alone, i.e., stage II cultures (compare reactions 3 and 7 with 1 and 5 respectively). The response was more than additive when stage II lymphocytes were stimulated with PPD in the presence of cell-free medium obtained from stage I cultures treated with PPD. In reaction 4 there were approximately 85, 000 c.p.m. above the added contributions of the stimuli provided by antigen and stage I cell-free medium separately; in reaction 8 there were approximately 8, 000 cpm.TABLE 9. Potentiating Activity in Leucocyte Culture Cell-free MediumStage IStage IICellStage ICellStage IIStage IIExper.React.DonorTreatmentDonorTreatmentc. p. m.I1NoneNoneANone4672NoneNoneAPPD48, 5943APPDANone1, 5914APPDAPPD134, 8185NoneNoneBNone5386NoneNoneBPPD5,4507APPDBNone4878APPDBPPD13,463Potentiation signifies a response which is greater than the sum of the responses due to the stimulating antigen alone and to the cell-free medium alone (blastogenic factor activity). Data indicate that potentiating activity is nonspecific, for cell-free medium from leucocyte cultures stimulated by one antigen potentiates the response of isogeneic or allogeneic leucocytes to the same antigen or to a second antigen. This factor has not been purified to the extent that it can be recognized by any other means than the in vitro activity described. To clarify the distinction between the factors, let me reiterate that blastogenic factor is demonstrated by testing the response of an individual s cells to cell-free medium of stage I cultures in the absence of added antigen or allogeneic cells; potentiating factor is assayed by testing the response of one individual s lymphocytes to the combination of stage I cell-free medium and antigen or allogeneic-stimulating cells. It is only by testing the antigen and the cell-free medium separately, as well as in combination, that it is possible to delineate blastogenic factor from potentiating factor. The presence of these two operationally defined activities, however, should not lead to the conclusion that there are necessarily separate molecules responsible for each activity. Let me just mention that we have several preparations which have no blastogenic factor activity but do have potentiating factor activity. Still, I do not think that this proves that they are different molecules.DR. CHASE: Were individuals A or B sensitive to tuberculin? What concentration of PPD was used?DR. BACH: Both these individuals are sensitive to tuberculin in vitro. I don t think we ever tested them in vivo. I don t remember the concentration of PPD used here - it is in the same range which we ordinarily use to get the maximum stimulation.I would also like to mention a factor that has to do with the adherent cells which several investigators have shown are necessary for a mixed leucocyte culture reaction to proceed. This work has been done principally by Miss Barbara Alter and Mr. David Zoschke. Several authors have suggested that \"macrophages” or adherent cells are needed in a mixed leucocyte culture reaction for stimulation to proceed. We have repeated this work attempting to get very high purity of lymphocytes, using a two-stage procedure in which the cells are first purified on either nylon wool or on a Rabinowitz glass bead column and these prepurified cells are then separated on a Shortman density gradient. This latter method of purification, while yielding rather low numbers of cells (approximately 10% of the original cell number), has provided populations in which, of more than 35, 000 cells evaluated morphologically, not a single cell resembled a classical monocyte.An adherent cell population can be obtained by incubating peripheral blood leucocytes in plastic Petri dishes for several hours, washing off the non-adherent cells, and then incubating the adherent cells for an additional 2 to 3 days. These cells can then be released from the dishes and used. It must be remembered that in addition to macrophages (monocytes) such cell preparations contain both adherent lymphocytes and occasional polymorphonuclear leucocytes. If one mixes purified lymphocytes of two individuals, these cells do not respond in the mixed lymphocyte culture. The addition of either isogeneic or allogeneic adherent cells treated with mitomycin C to a mixture of purified lymphocytes allows a response in that mixed leucocyte culture (14, 545 c.p.m. and 16, 951 c.p.m. where background is 66 c.p.m.). If instead of the adherent cells we simply use the supernatant from an attached cell monolayer which has been incubating for three days and add this conditioned medium reconstituting factor (CMRF) to a mixture of purified cells, the response is also reconstituted (Table 10). Approximately 60% of the preparations of CMRF which we have analyzed have been active in reconstituting a response. The degree of reconstitution, as compared with the mixed leucocyte culture of unpurified cells, has varied, but in many cases reconstitution has been in the same range as the mixed leucocyte culture of unpurified cells. It must be stressed that the adherent cells are incubated in the presence of autologous plasma and have never seen the allogeneic cells which are subsequently used for stimulation in the mixed leucocyte culture.TABLE 10. Reconstitution of Purified Lymphocyte Reactivity in Mixed Leucocyte Cultures with Conditioned Medium Reconstituting Factor (CMRF)aCell TypesRespective cell concentration per ml × 10−6CPM in fresh 199-SCPM in CMRFAup.219121456Ap.262491Aup Bupm.2 - .41806323000Ap Bpm.2 - .410419030aGuide to abbreviations: Aup = unpurified cells of donor A Aup Bupm = unpurified cells of donor A mixed with mitomycin C treated unpurified cells of donor B Ap = Shortman bead purified cells of donor A Ap Bpm = purified cells of donor A mixed with mitomycin C treated purified cells of donor B CMRF = conditioned-medium reconstituting factorDR. GRANGER: Have you tried the supernatant from other kinds of cells, preferably non-lymphoid?DR. BACH: We have not looked as to whether or not other cells can produce CMRF.DR. VALENTINE: I think Dr. Bach has found something that perhaps has been recorded in many other tissue culture systems off and on for the past thirty years. It is derived from the observation that cell density must often be at a certain critical level before cells will grow. Conditioned medium usually facilitates the survival of cells and their proliferation. This phenomenon has been investigated by H. Rubin (The Harvey Lectures, Series 61: 117-143, 1967) quite extensively, who demonstrated that large molecules put into the medium by high-density cell cultures of fibroblasts and other cells facilitate the growth of smaller densities of cells in the tissue culture. An important difference, of course, would occur if this factor is present, as in part of your cultures, only when the macrophage layer has been exposed to antigen. That would distinguish it from Rubin s factor.DR. BACH: This is, of course, why we refer to it as conditioned medium reconstituting factor (CMRF). If you take unpurified cells and incubate them from one person alone, you do get a certain number of cells which incorporate thymidine without having an overt stimulus. We don t find that to any great extent in our system. It takes an adherent cell population, and I prefer not to think of macrophages exclusively in this case, an adherent cell population for the response to occur. Others have suggested this; our studies are simply confirmatory with perhaps much purer cells.DR. SMITH: I would like to direct my comments to Bach s first new factor, which appears to have some of the same effects as the mitogenic factor which is produced in continuous lymphocyte cultures. For example, when the mitogenic factor from continuous cultures, or from transforming cells is put on mixed cell cultures, higher levels of incorporation occur than the sum of one-way blocked mixtures. Essentially, it enhances the number of cells which presumably enter into the reaction.DR. BACH: That is the potentiating factor. The reason I spoke about specificity was that we have cells which will not respond to given antigen in vitro, at least at the concentrations of antigen which we test, that, in the presence of potentiating factor do respond to that antigen, the potentiating factor itself not being stimulatory.DR. WILSON: Dr. Bach, have you obtained this potentiating factor with mixed cultures?DR. BACH: Yes, we find a potentiating factor in mixed culture, but can also get it from unpurified cells incubated alone.DR. WILSON: Is there some possibility that potentiating factors obtained with human cultures are due to the large number of PMN s in human cultures? The reason I ask is that, with rat mixed cultures, I tried to confirm you report on potentiating factor, but could note.DR. BACH: I honestly don t know, and that is why I said they are unpurified cells. We don t know if we can get it from purified cells, but we can get potentiating factor from adherent cells.DR. GLADE: I am interested in the kinetics in this response, because this appears to be the same system that Granger uses to demonstrate lymphotoxic activity.DR. BACH: We see an inhibitory material as well in these culture supernatants and I don t suggest that it is a new factor. Nevertheless, we have found one way to study blastogenic factor activity and potentiating activity predominantly and avoid the inhibitory activity. We avoid getting inhibitory material by keeping the concentration of cells in the stage 1 culture rather low, e. g., a total of 200, 000 or less mononucleated cells, compared to a million we used to use. If you increase the concentration of cells in stage 1, you will not demonstrate blastogenesis or potentiating factor, but will get inhibitory factor.DR. OPPENHEIM: I have a question that is a corollary of what Dr. Glade asked, namely, if you serially dilute lymphotoxin, does this LT then manifest potentiating activity or blastogenic activity?DR. BACH: We have done this work with Dr. Granger, who sent us a preparation which had lymphotoxic activity and another preparation which was his control supernatant with the PHA added to the cell-free medium. Both these preparations at a 1: 100 dilution were very highly inhibitory to lymphocytes cultured with PHA. They were inhibitory and in fact, the control was a little more inhibitory. There was little or no inhibition at dilutions beyond one to 1, 000. We found no potentiating factor activity. I can t answer critically whether we saw blastogenic activity, since we did not have the appropriate control.DR. LAWRENCE: I would like now to ask Dr. Benacerraf if he will discuss for us the status of cytophilic antibody in relation to the kind of cell-cell interaction we have been considering.DR. BENACERRAF: I would like to say that I am not speaking of my own free will, but at Dr. Lawrence s request. I think it proper to start this with some historical background. The first observation suggesting cytophilic antibody was made by Nelson and Boyden who demonstrated that peritoneal macrophages in animals already sensitive when challenged with the antigen could not be washed from the peritoneal cavity. They apparently stuck on a variety of surfaces. They proposed that the adherence of peritoneal cells resulted from receptors on macrophages, probably cell-bound antibodies, which were being bridged by the antigen. This was the state of affairs for 6 or 7 years. In the meanwhile, it has become clearer that most of the events that we regard as cellular immunity can be explained on the basis of mediating factors which are produced by lymphoid cells. Nevertheless, the question still arises, \"Is there an antibody which can bind to macrophages and in some way be responsible for the production of some of the manifestations of cell-mediated reactions?”The answer is that there are indeed humoral antibodies which bind to macrophages, and also to polymorphs. They are largely of the IgG type, although in some species some antibodies may be IgM. Nevertheless, affinity is for all macrophages irrespective of the specificity of the antibody. The binding is usually weak, and in competition with all the other immunoglobulin molecules competing for the same binding site, which can displace it. In vitro, however, one can easily demonstrate or put together a system where immune complexes, or, shall we say, cytophilic antibody at certain concentrations in the presence of antigen, will indeed cause sticking together of macrophages. These cell experiments have been carried out in many laboratories, and all that is required is to have the proper concentration for the various reactions. In my opinion, and this is an opinion not a fact, it is highly improbably that it plays an important role, or at least as an important a role as that of the lymphocyte-mediated macrophage information response in vivo.DR. OPPENHEIM: In addition to the possible role of the aggregation of the antigen by the antibody, I wonder if you would agree that such antibodies may also have a role in the induction of the lymphocyte stimulation. They may effectively enhance the degree to which lymphocytes can respond to antigens, since in some situations, antigen-antibody complexes stimulate lymphocytes much better than do the uncomplexed antigens. Alternatively, if present in excess, they may even inhibit the lymphoid proliferative reaction to antigen.DR. BENACERRAF: I think you are right to raise that point. I was in a sense somewhat guilty in being narrow in the way I attempted to tackle the problem, but I was concerned primarily in clarifying the point of whether cytophilic antibody had a role to play in the formation of the mononuclear inflammatory exudate. Cytophilic antibody may have an extremely important physiologic role to play in vivo in many ways, particularly in defense mechanisms. One of them, perhaps, is to act as a bridge between an antigen and a macrophage, an opsonin. Another may be to accumulate antigen at certain sites. You might say that antibody which exists on the cells of the germinal lymphoid follicle, the cells that make up the reticulum, is indeed concentrating antigen by virtue of its being there. In systems where macrophages help to bring antigen to lymphoid cells, it may indeed act again as a concentrating mechanism. In such sites, however, the antibody must be in extremely high concentration with respect to the gamma globulins which are normally there.DR. BLOOM: I wonder if Dr. Granger would comment on his work and the work of Dr. Heise and Weiser on rejection of tumors in mice with purified macrophages presumably containing cytophilic antibodies.DR. GRANGER: About five years ago, Dr. Weiser and I demonstrated that preparations of purified peritoneal macrophages obtained from C57 B1 K mice that were in the process of rejecting an ascities tumor (sarcoma I from A/Jax donors) would cause specific destruction in vitro of target fibroblasts. This reaction could be blocked by trypsinizing the macrophages. We also found that an antibody which was specific for the antigens on the fibroblasts could be eluted off the surface of the \"immune” macrophages by the heat technique of Boyden. In additional studies Dr. Weiser demonstrated that the heat eluate would \"rearm” trypsin-treated macrophages. I don t believe this would rearm a \"non-activated” macrophage from a non-stimulated animal.DR. LAWRENCE: Would someone answer for me, for the record, whether or not there is such a beast as an immune macrophage?TUTTI: No.DR. LAWRENCE: This has been my private persuasion.DR. BENACERRAF: The observations of Dr. Mackaness and Dr. Cohn on factors produced by lymphocytes which affect macrophages should be considered. While these factors have not been characterized as well (and in an optimistic sense, I say as well) as the ones which have been described this morning, nonetheless they may play an extremely important role in defense mechanism involving infectious processes of obligatory intra-cellular organisms. The phenomenon described many years ago by Shwartzman, whereby an anamnestic response could be observed for nonspecific antigens in the general defense capacity of macrophages may be explained on the basis of factors being manufactured by sensitized lymphocytes in contact with antigen which are able to stimulate macrophages to become \"super macrophages” with large lysosomes.DR. LAWRENCE: As a follow-up to Dr. Benacerraf s comment, I wonder if any of the participants who have been working with MIF and other factors that affect macrophages have tried to link those studies with the Mackaness study either by determining whether these factors confer on macrophages in vitro resistance to intracellular infection, or whether such factors injected into the peritoneal cavity with micro-organisms on first challenge cause normal animals to behave like Mackaness s animals sensitized with antigen.DR. DAVID: For several years we have tried to relate our work to the findings of Dr, George Mackaness in his extensive studies of cellular immunity. He has shown a relationship between delayed hypersensitivity and the activation of macrophages, and more recently has demonstrated that lymphocytes are the cells involved in the immunological recognition step of the reaction. The manner in which the lymphocytes affect the macrophages in this cellular immunity model is not known. Naturally, we have considered the possibility that MIF might be the missing link. In the past few years, we have noticed that the macrophages at the periphery of an inhibited fan of cells seemed more spread out than those in cultures without antigen. This also occurred inconsistently when monolayers of guinea pig macrophages were studied. Carl Nathan has been working intensively on this problem for the past year. He started with unfractionated supernatants, and found that more macrophages were stuck to the culture dish when cultured in supernatants from antigen-stimulated lymphocytes than in control cultures. However, he also found that when antigen was added to the control supernatants, there was an increase of macrophages stuck to the dishes, although not quite as much as in the stimulated supernatants. As there was some effect of antigen itself, and since we knew that these lymphocyte cultures also contained some newly formed antibody, Nathan decided to use Sephadex fractions to eliminate the antigen, the antibody, and any complexes which might have formed. He has studied the effect of fractions which contain molecules smaller than albumin (less than 55, 000 mol. wt.). After 24 hours of incubation, there was no significant increase in the number of macrophages stuck to the petri dish, as measured by the total cell protein stuck to the dish. After 72 hours there was a 2-4 fold increase in residual cell protein on petri dishes from cultures in MIF- containing fractions as compared to controls. When he measured phagocytosis, using the uptake of radioactive starch, he found considerably more starch in the macrophages which were cultured in stimulated fractions than control. Although much of this is nevertheless an increased number of starch granules per cell in the stimulated cultures. This difference is even greater when dead tubercle bacilli are used. We are presently studying the effect of active supernatants on the bactericidal capacity of such macrophages.We are now more hopeful that a link to cellular immunity from lymphocytes and macrophages via a soluble mediator will be found. Recently, Nathan has also used cinematography to follow his cultures and has found macrophages which markedly resemble the \"activated macrophages” demonstrated by Dr. Zanvil Cohn and Dr. Mackaness with widespread ruffled membranes and granules.There were several papers at the Federation Meetings in Atlantic City, April 1970, dealing with the effects of MIF-containing whole supernatants on macrophages, by Mooney and Waksman and by Adams et al., both of which showed increased spreading of macrophages. Dr. Salvin has also been studying this process by cinematography.DR. CHASE: At the recent meeting of the American Society for Microbiology, a paper by Patterson and Youmans (Bacteriological Proc., 1970, page 106, Abstract M213) presented pertinent results. The test system was, first, normal macrophages which had ingested mycobacteria and, second, lymphocytes from sensitive animals. When the lymphocytes were mixed with the macrophages and H37Ra mycobacteria were added, the macrophages disposed of the ingested organisms. The same result was then seen when crude culture supernatant of stimulated lymphocytes was added to the mixed cells. The report by Mackaness would predict this type of result. It is simply another important example of lymphocytes serving as mediating cells.DR. RUDDLE: The studies of Drs. Mooney and Waksman, using HSA sensitized rabbits, confirm the findings of Dr. David. They added supernatants, obtained from the 24 hour incubation of sensitized cells with antigen, to normal peritoneal exudate cells, and observed a macrophage spreading effect. They see an increase in the number of ameboid cells, cells with ruffled membranes, and cells attached to plastic. There are fewer cells in the supernatant of those cultures which have received the macrophage spreading factor than cultures which received supernatants from normal lymph node cells1. (S. J. Mooney and B.H. Waksman. Fed. Proc. 29: 359, 1970). In addition, we have shown that the method of induction of peritoneal exudate, influences how cytotoxic a macrophage preparation is. If we used nothing to induce rat peritoneal exudates, we got a very inactive population, non-cytotoxic to normal fibroblasts and without very much acid phosphatase, but very phagocytic. When we used beef heart infusion broth, we got a strongly activated population which was very cytotoxic. Other agents, such as glycogen, gave intermediate effects.DR. RUDDLE: After addition of these macrophages to fibroblast monolayers, plaques of destruction are seen.DR. GRANGER: We should mention observations made by Drs. Heise and Weiser (J. Immunol. 101: 1004, 1968) and Pincus (R.E.S. 7: 220, 1970) who demonstrated that guinea pig macrophages release cell toxins in vitro that will kill other cells, and cause migration inhibition. In our laboratory, Mr. J. Kramer has found that purified monolayers of macrophages taken from tumor-immunized animals exposed to the tumor antigen release activity into the medium which is nonspecifically toxic for cells. This can be fractionated on Sephadex-G 100 and G 150 into two components, one about 70, 000 molecular weight, and one about 150, 000 molecular weight. The material is released in small quantities in the absence of antigens. Specific antigen causes much more toxic material to be released.DR. CEROTTINI: Since the present discussion might be construed to suggest that cytotoxic activity of sensitized lymphoid cell preparations may be due to the presence of macrophages, I would like to mention that removal of macrophages from spleen cell suspensions obtained from mice immunized with tumor allografts did not affect the in vitro cytotoxicity displayed by the lymphoid cells.DR. RUDDLE: I would agree with you. We have purified lymph node cells with glass beads, plastic plates, and nylon columns, and we still got cytotoxicity in this system (sensitized lymph node cells and specific antigen).DR. SALVIN: We stimulated lymphocytes with specific antigens in a manner similar to that used in production of MIF. In addition to looking for inhibition of macrophage migration, we have added killed tubercle bacilli to the macrophage (we have also done this with supernatants from candida sensitized animals). We found that the macrophages which were inhibited in their migration did not phagocytize these specific organisms as readily as normal cells. Therefore under conditions parallel to MIF formation, phagocytosis is inhibited, both in terms of the number of macrophages that are actually engaged in phagocytosis as well as the number of pathogens per cell. MIF did not enhance phagocytosis, but rather inhibited it at 48 hours.DR. DAVID: I would say that this is quite different from the results of our phagocytosis studies which were carried out at 72 hours using radioactive starch or dead tubercle bacilli.DR. WILSON: With the Mackaness system, as I understand it, lymphocytes sensitized to one pathogen, in the presence of this pathogen produce something which makes macrophages resistant to other microorganisms. Is there any information on the range of differences of the two antigens, and on possible relationships of one to another? In the presence of lymphocytes sensitized to any antigen and stimulated by that antigen, will macrophages be resistant to intracellular infection? Dr. Bloom, at the recent Brook Lodge meeting (\"Immunological Surveillance, Smith Landy, Eds.), discussed the premise that some of these \"nonspecific mediators” seemed to be acting quite specifically, especially when the antigen involved was a histocompatibility antigen. Suppose we were to use the Mackaness system with sensitization to histocompatibility antigens. In the presence of these antigens, would nonspecific resistance to Listeria or Brucella result?DR. FALK: If one takes the supernatant from a set of human lymphocytes sensitized to transplantation antigens and cultured with the appropriate antigen, and reacts it with fibroblast target cells, this supernatant is found not to be cytotoxic to the fibroblasts. If one cultivates the lymphocytes on the same target cells, the lymphocytes by themselves not being sensitized to the target cells, the fibroblasts are not killed. However, in the presence of the appropriate supernatant, a supernatant from activated lymphocytes, these non-sensitized lymphocytes will destroy the fibroblast monolayer.DR. VALENTINE: I am pleased that Dr. Wilson raised the question whether some of these mediators have specificity for antigens.Several years ago, Drs. Bennett and Bloom (Transplantation 5: 996, 1967) found that MIF produced by stimulating lymphocytes with antigen for 1 hour and then washing, had a greatly enhanced ability to inhibit the migration of macrophage when PPD was added to it. Johanovsky had similar findings; supernatants of sensitized lymphocytes incubated with 1 ug of PPD were not migration inhibitory but the addition of PPD to them converted them to full MIF activity.The paper by Amos and Lachmann (Immunol. 18: 269, 1970) raises again the point concerning the necessity of antigens for the activity of migration inhibitory factor. Supernatants were prepared using PPD - coupled to insoluble particles, and in this situation it was found that inhibition by supernatants was not obtained unless the soluble antigen was added. That this was not due to antibody, was indicated by its elution from G-100 column at about the 50-70, 000 region.A second mediator, of course, which seems to be dependent upon antigen concentrations for its activity is the lymphocyte transforming factor which in our hands can be produced in a way which by itself causes a relatively small amount of stimulation of non-sensitive cells, but then with addition of increasing doses of antigen it produces greater amounts of stimulation of non-sensitive cells. This system also works on cord blood cells, so it is not a question, I think, of pre-immunization.We have been considering these mediators only as pharmacological substances and, indeed, as far as David s MIF and the lymphotoxins are concerned, that is true. Clearly, this question of specificity requires further looking at.DR. BLOOM: I am pleased that Dr. Valentine raised the question of specific factors, as it is such a sticky one. Certainly there is clear evidence, in rejection of grafts across major histocompatibility barriers from the Klein s work, of exquisite specificity of the effector process.To answer the question whether there are really factors, with specificity for antigen, other than antibody, I will assert that one must have a well purified factor. For example, our observations and Johanovskys (Immunol. 15: 1, 1968), indicating specificity of MIF, were made on whole, unfractionated supernatants, and could easily have been due to antibodies secreted by the antigen-stimulated cells, cytophilic or otherwise. Similarly, Drs. Valentine and Lawrence s report used whole supernatants, and also autologous serum from the patients. Even though the studies are as well controlled as possible, until the work is done with a purified material, it is difficult to exclude antibodies.Secondly, it must be noted the evidence for antigen requirement for activity has been found only in one system - the tuberculin system. David has not found any specificity of MIF elicited by hapten-protein conjugates. Thus no true reciprocal experiment has been done, and perhaps we should speak only of antigen \"dependency” rather than \"specificity.”And lastly, in the MIF system in the guinea pig, there appear to be two MIF s, one large (˜50, 000) and one smaller (˜25, 000) that we (Am. J. Path. 60: 457, 1970) and Yoshida and Reisfeld (Nature 226: 856, 1970) have described. Assuming only one has specificity, one may get more or less of the specific MIF or blastogenic factor made, depending on the antigen used.Editors note: At this point, all available information on the parameters used in various laboratories for characterizing and comparing the different factors was collated. In an effort to establish what chemical and physical similarities and differences between factors are now clear, and to pin-point what further information is needed, the results, while far from complete, are presented in the appendix tables.DR. CHASE: It might be profitable at this time to get the consensus of the various workers regarding stability or lack of it in the supernatant fluids as they prepare these. Once, Dr. Bloom told me that he experienced trouble in holding activity until the fluids had been passed through Sephadex and part of the first effluent discarded. Recently, he stated that the whole supernatant was stable after lyophilization. What are other findings? For how long, for example, did Dr. Falk s supernatants retain activity, under what conditions did he hold them, and what recovery was noted after lyophilization and reconstitution? The experience of the workers here could well serve to direct us in handling materials during fractionation procedures, or during the times required to stimulate primary and secondary stimulation of rabbits for antibody formation.DR. GRANGER: Human cell toxins lose activity over the period of a month at 4°C. Activity however, remained at -20°C, and -70°C. We do not employ serum containing medium any more but find it helpful to add small quantities of protein or carbowax to help stabilize the effective molecules. We employ 0.2% non-purified commerical carbowax.DR. HIRSCHHORN: We used carbowax routinely to concentrate sera for lipoproteins analysis, and had found recently that you can do much better by simple vacuum dialysis. All that it does is pull water out.DR. GRANGER: Yes, people have used carbowax for concentration purposes for a long time. However, we use it as a medium additive. That is all.What I was going to say, when we make the cell-toxins in protein or carrier free medium, we find that unless it is concentrated, the material is very labile. We lose activity, up to 90%, during purification unless we have carrier present. The material, when freed of most protein, sticks to glass, plastic, and siliconized glassware.DR. DAVID: We found it easy to keep supernatants for three weeks, at either -4°C or -20°C without loss of MIF activity.DR. BLOOM: Let me add that we tested glass and plastic because I was sure that MIF would stick to glass like interferon does. We were not able to show any loss of activity by adsorption either to glass or plastic.DR. VALENTINE: The lymphocyte transforming material loses activity in one week at 4°C even with 15-20% serum.This same solution frozen at -70°C, will retain activity, but in a diminishing amount for as long as a year; for example, after a year, we might have, perhaps, half the activity left.DR. LAWRENCE: There are many evidences of the hardiness of Transfer Factor including the retention of full potency following storage. Whole blood leucocytes containing TF can be frozen (alcohol-dry ice) and stored at -20°C for 3-4 years without loss of potency following transfer. Similarly lyophilized dialyzable TF retains full potency for in vivo and in vitro transfer when stored at ordinary refrigerator temperatures (4°C) for as long as 5 years.DR. MERIGAN: I think that when workers talk about stability they must have quantitative assays which give sharp points. From these proceedings it does not sound as though that is the case of the mediators. I must say that in the interferon field, working with a quantitative biological assay, we have the problems of stability of materials and changes in assay sensitivity as well. We have attempted to establish internal working laboratory standards which are related through national and international standards. Hence, workers are beginning to publish results in terms of their relationship to international unitage. Of course the people in the hormone field have been doing things like this for many years. As you talk about working your way out of difficulties of cross reactivity of a given factor in several assays, it strikes me that laboratory working standards and replicate variability are critical. I don t have a good feeling of what the replicate variation is on a single technique in one person s laboratory when he runs it over and over. We, in the interferon field, are at a tremendous advantage in the sense that we can dilute our preparation several thousandfold and still have activity. That situation makes us less vulnerable to nonspecific things that might be present in our preparations at low concentration, influencing our assay.DR. CHASE: How do you dilute and standardize the interferon?DR. MERIGAN: We use both twofold dilutions or half-log dilutions. Assays are reasonably accurate and we can interpolate over a log-log dose-response curve. This is because the dose-response curve to interferon is quite reproducible. Hence, all we need is two points within 20% of the 50% plaque inhibition dilution to interpolate a result in the plaque assay (Method 32).DR. GRANGER: I believe Dr. Merigan has asked a most important question which we have attempted to answer in our laboratory. We have a set standard dilution system to which each new batch of medium and each step of physical chemical treatment is subjected. The number of these tests we have performed is now in the many hundreds, the same batch tested from day to day will routinely vary about 30%, but on occasion (1 of 10-20 times) as much as 75%.DR. LANDY: That was not quite Dr. Merigan s point. As I understand him, he was addressing himself to the essentiality of including a reference standard with each assay of additional material.DR. LAWRENCE: Perhaps we could profitably consider, for the remainder of this session, questions regarding the biosynthesis of these factors.DR. COOPER: There are several systems investigated, in which phenomena are described which parallel what happens during the induction of growth in lymphocytes. I have specifically in mind the regenerating rat liver or estrogen-stimulated rat uterus. When the rat is subjected to partial hepatectomy with 70% removal of the liver, there is released into the circulation a humoral factor which, from cross-circulation experiments, can be shown to induce a waive of DNA synthesis in the liver of the non-operated animal. This may be analogous to the blastogenic factor released from stimulated lymphocytes. It might be well for us to keep in mind that the release of factors may not be a series of phenomena related exclusively to the lymphocyte or even to immunology, but in fact may reflect more general aspects of the ways cells interact with one another and respond to environmental changes.DR. GLADE: We have used as controls for our investigations with human lymphoid cell lines other continuous cell lines of non-lymphoid origin. We began with HeLa cells, originally obtained from a uterine carcinoma specimen. Supernatants obtained from HeLa cells assayed for migration inhibitory activity both on guinea pig peritoneal macrophages and human lymphoid cell lines showed marked inhibition of migration. The same supernatants studied in HeLa monolayer systems with Granger s methods for the detection of cytotoxic activity demonstrated that HeLa cell supernatants may produce at least a 20% inhibition of the incorporation of labelled amino acids by the monolayer cells. We have studied six additional non-lymphoid cell lines, including human embryonic lung, primary human skin, rat lung, rat thymus, and several clones of mouse erythroblastic leukemia cells obtained from Dr. Charlotte Friend. Several supernatants showed inhibition of migration of guinea pig peritoneal macrophages and human lymphoid cell lines, and blocked the incorporation of labelled amino acids into new protein by monolayer cells.DR. LAWRENCE: These cells produce the factors by growing and nothing else? Is there no stimulus akin to antigen added?DR. GLADE: Perhaps, like transformed lymphocytes, these cells which are rapidly dividing and in an accelerated synthetic phase, are capable of expressing more of their genetic potential with the production of factors usually ascribed to immunocompetent lymphocytes. We have little knowledge of the kinds of stimuli affecting these cells in vitro, or on what caused them to go into long term culture. We must be very clear, however, that the techniques now used for study are biologic assays and as such measure only biologic effects, not specific factors. We have no information whether these effects of lymphoid and non-lymphoid cells are mediated by the same or even similar molecular species.DR. UHR: There appear to be two distinct issues raised. Dr. Cooper s comment referred to the fact that the biosynthetic events accompanying replication and differentiation of lymphoid cells are not that different from those of other mammalian cells. I do not find this is very surprising. The second point concerns the relevance to delayed hypersensitivity lesions of the various products that are being \"milked out” of lymphocytes. This question can only be answered by relating the products to the lesion in vivo, not by considering their relationship to the biosynthetic events.DR. HIRSCHHORN: While I concur with Dr. Uhr that we should now compare these events to the in vivo situation, I would like to suggest that there is one step to consider before that. The common phenomenon about which we are concerned is the induction of protein synthesis. Whether this be by specific antigen, nonspecific mitogen, mixed lymphocyte culture, partial hepatectomy, or the transfer of a monolayer cell culture into a fresh nutrient medium, we are inducing protein synthesis. I agree these may not all be the same kind of induction but we do produce active protein synthesis. Among the proteins which are newly synthesized may be \"factors,” no matter what kind of cell types they come from. Whether or not this means that production of these factors is a general phenomenon involved in wound healing and in a whole variety of biological phenomena, or only in the case of cellular immunity, where the specific antigen is the stimulant, are questions that I believe worthy of careful investigation.DR. UHR: I agree with Dr. Hirschhorn s comments. This is protein synthesis, but it would be well for this group to pay attention to the use of the term elaboration of the molecules into the medium, which has been treated very casually and not really been discussed. It would be well to consider whether these factors are secretory proteins destined for export, or whether they reach the medium perhaps by some other mechanism. I think this is a significant aspect of the biology of the cells in mediation.DR. COOPER: There are many phenomena, especially the early events in lymphocyte growth induction (i. e., \"transformation” or response to mitogen) which are independent of protein synthesis and will occur with complete inhibition of protein synthesis. Acetylation of histones, increased uptake of acridine orange, increased phospholipid turnover in the cell membrane does not require protein synthesis. In fact, RNA turnover occurs in these cells in the absence of protein synthesis. This means you can produce a great many of the initial phenomena of transformation without reference to proteins, and it would not be hard to consider as well the release into the medium of small molecular weight materials.DR. HIRSCHHORN: This is perhaps where the lymphocytes or the immunological phenomena may be involved, but what happens after the cells have been turned on? Those factors that are newly synthesized proteins may be the same for all types of cells. Perhaps, agents such as a double-stranded small RNA molecule, are more specific and this may be the only specific factor which we are talking about that has anything to do with immunology.DR. LAWRENCE: What is the name of that factor?DR. HIRSCHHORN: Transfer factor.DR. LAWRENCE: Thank you.DR. GRANGER: I believe it is fair to say at this point, that there is no correlation between the release of the effector molecules and DNA synthesis. Nevertheless, both MIF and LT require protein biosynthesis, as judged by inhibitors of protein synthesis.DR. VALENTINE: In our study, the Lymphocyte Transforming Factor or whatever you wish to call it, is present in medium, but not in relation to the number of blasts that are present at that time. It appears early in culture and the amount of activity falls off slightly with time. At the beginning of culture the supernatant activity is greatest, and the number of blasts are smallest, and in the end the reverse situation is true. We are, however, measuring activities in a medium, and we are not measuring an amount of material present. If, for example, an inhibitor were produced at the end of the culture, that might explain the events observed, or if the material were destroyed by the culture or consumed by the culture, this also would explain a lack of increasing amount of material with an increasing number of blasts. My own prejudice would be that they would be released early, before transformation occurs, similar to the kinetics for MIF and LT.DR. BACH: The production of blastogenic factors by lymphocytes in mixed culture is dependent to some extent on the amount of activity in that mixed culture in terms of thymidine incorporation. MLC has on the average more blastogenic factor activity than cells of one individual cultured alone.DR. HIRSCHHORN: With relation to what Dr. Valentine said regarding the timing of the release of factors and their relationship to blastogenesis, the production of rather large quantities of lysosomal enzymes, among which are a number of degradative enzymes, may well interfere with or destroy the activity of these effector molecules.DR. LAWRENCE: All the enzymes I have used on cells do not seem to penetrate, or attack living cells. DNase can t get into a living cell, but once the cell becomes sick or is dead, then it is susceptible. How do the lysosomal enzymes function in this regard? If they attack living cells, they would be unique, relative to other enzymes.DR. HIRSCHHORN: Certain ones, for example, the phospholipi dases can attack the membrane and are able to destroy cells.DR. LAWRENCE: Is there anything to Dr. Granger s suggestion that the metabolic activity of the cell under attack determines the outcome? Does MIF produce its effect because it is acting on activated macrophages, whereas those cells that are in culture such as HeLa cells or L lines, are not at that extreme degree of metabolic activity?DR. GRANGER: We have found that cells differ widely in their sensitivity to LT based upon two mechanisms. 1) Some cells have the LT sensitive receptor expressed on the plasma membrane and other cells do not. 2) Certain cells are able to repair the membrane damage much more efficiently than others. This implies that the membranes of target cells are different in their molecular composition and this influences their susceptibility to destruction. Moreover, the physiologic state of the target cell also influences its susceptibility.DR. RUBIN: I feel the group has stampeded itself into a general feeling that these factors are elaborated by lymphocytes in a nonspecific fashion in association with cell growth and concomitant heightened protein synthesis. A statement was made by Dr. David this morning that there were certain situations in which cells would enlarge and divide without producing MIF. We have recently studied an interesting patient with a peculiar type of non-sex-linked agammaglobulinemia in which there was a good response to phytohemagglutinin with increased RNA and protein synthesis. However, there was no response to antigen. Is it possible that elaboration of these factors may not be such a nonspecific phenomenon? Might not some cells be inherently defective in producing the factors as well?DR. BLOOM: That there are diseases in which one aspect of cell function can be deficient is not terribly surprising, but perhaps not yet clearly related to what really occurs in the normal sensitized cells. Several basic problems require elucidation. Is there an increase in amount of material or factor when you use multiple antigens? Does one get additive effects? Do all factors, nonspecific and specific, attack all cells, or do certain antigens attack certain cells?DR. OPPENHEIM: These are very difficult questions to answer. If one stimulates cells with more than one antigen, you will get an additive effect, but not summative. If you use three, you will get a bit more of an additional reaction. If you, for instance, do cell mixes of twenty different people, you will get a response which looks like a PHA reaction with 50 to 60% blasts. But if you added all the individual pairs together, you should have had a 500% response.DR. LAWRENCE: Are you telling us there is a non-committed pool of lymphocytes finite in number that can be engaged in this sort of activity?DR. OPPENHEIM: I would not make such a claim. Cells are dying in vitro, cells are proliferating in vitro, and cells are probably not doing anything in vitro. It is very difficult to make up any statements about clones or overlapping effects from this sort of approach.DR. HIRSCHHORN: There are two sets of experiments that tend to answer your question. First, Carolyn Ripps and I, using blast transformation, found that there was an additive but not a summating effect with multiple antigens. When we reached four, we reached the upper limit. This was assayed by morphological criteria. Eijsvoogel Schellekens in Holland have recently done similar experiments using thymidine incorporation, and have also reached a ceiling, in their hands with three antigens.DR. BACH: Mr. Zoschke and I have looked at whether antigens are additive in their effect in leucocyte cultures. He has found that it is critical to test the antigens at many different concentrations, since at relatively low doses of antigens the further addition of the same antigen will increase the response, and thus the addition of two antigens will of course be additive. Further, as the dose of an antigen increases beyond a given point, the counts per minute of thymidine incorporated are actually decreased - i. e. \"inhibition” takes place. He has found that at optimal concentrations certain antigens are additive in their effect over and above that which will be expected from increasing the concentration of either antigen alone. A possible explanation for this summation effect by more than one antigen would be non-additivity of the \"inhibition” mentioned above. Mr. Zoschke also has shown that inhibition appears to be additive, and thus that the summation of response could be regarded as a real phenomena. I would, however, argue that this cannot be used as critical evidence for the existence of separate cell populations responding to the two antigens.Mr. Zoschke has adapted the use of BUdR in an attempt to obtain critical evidence that different cell populations do respond to different antigens. The response of peripheral blood leucocytes to an antigen, such as tetanus toxoid, can be eliminated if that culture is treated with BUdR and light. BUdR is added at a concentration between 10−5M and 10−6 Molar for 24 or 48 hours between 48 and 96 hours of culture. These concentrations of BUdR followed by exposure of the cells to light for approximately 60 to 90 minutes appears to be effective in virtually eliminating the response to the antigen. Mr. Zoschke has done these experiments in reciprocal cultures, e. g., a culture initially stimulated with antigen 1 and treated with BUdR and light will no longer respond to a subsequent dose of antigen 1 but will respond to an unrelated antigen 2. Similarly a culture initially stimulated with antigen 2, and treated with BUdR and light, while no longer responding to a subsequent dose of antigen 2 will respond to antigen 1. We believe that this is much stronger evidence that cell populations responding in lymphocyte culture to different antigens are, in at least some part, different.DR. WILSON: This system might provide important information for or against the premise that the lymphocytes which react to histocompatibility mixtures are multi-potential.DR. LANDY: Couldn t one approach this issue in a slightly different way by separating lymphocyte populations in terms of their buoyant density, for example on an albumin gradient. Would not this give sub-populations of lymphocytes with minor differences in cell size, specific gravity, etc., possibly with differences of response to these stimuli, particularly to plant mitogens?DR. WILSON: Actually, Smith s group and my colleague, Carol Newlin have used this approach. If one starts with a heterogeneous population of spleen cells, it is not surprising that fractionation on a density gradient will separate reactive from non-reactive cells. However, when something more pure, or at least more homogeneous, like peripheral blood lymphocytes, are used, they cannot be fractionated to reactive and non-reactive sub-populations. Some fractions may have more PMN s or RBC s than others, but all seem to react, by virtue of their lymphocyte content, to histocompatibility antigens.DR. CEROTTINI: Since we have been discussing the biosynthesis of mediators of cellular immunity, it would be worth while to determine whether the various factors described today are produced by thymus-derived cells or not. In the mouse species, one can take advantage of the fact that thymus-derived cells in spleen or lymph node carry a marker, the alloantigen theta (B), and are lysed when incubated with anti-B antiserum and complement. Using such an antiserum, we have investigated the origin of the sensitized lymphocytes displaying a cytotoxic activity in vitro. Previous studies showed that spleen cells from mice immunized with tumor allografts contained both cytotoxic lymphocytes and allo-antibody-producing cells (the latter cells were detected by a plaque assay developed by A.A. Nordin in our laboratory). Prior to the in vitro tests for cytotoxicity and antibody plaque formation, the immune spleen cells were treated with anti-B antiserum and complement. It was found that this treatment completely abolished the cytotoxic activity, but had no effect on alloantibody plaque formation. These results suggest that the cytotoxic activity measured in vitro in our system is due to thymus-derived cells and thus represents a correlate of cell-mediated immunity.DR. RUDDLE: We have been doing the same kind of experiment in rats, using KLH and PPD as antigens and finding to our horror that they are bone-marrow derived. I think this question is still very open.DR. SMITH: Two items of unpublished evidence from our laboratory seem pertinent to Dr. Ruddle s work: 1) all mouse lymphoreticular cells, whether they are bone-marrow or thymus derived, are stimulated to transform and divide by endotoxin; 2) KLH, as obtained from most sources, contains endotoxin.DR. RUDDLE: This is the system we have used. Previously thymectomized irradiated (900 Rads) Lewis rats received DA x Lewis F1 thymus grafts, and Lewis bone-marrow cells. Seven days later, they were sensitized in the hind foot pad with tubercle bacilli in oil. Fourteen days after that, the animals were subjected to skin test, immunofluorescence test and tissue culture cytotoxicity test (Table 11). The animals are divided into two groups, those skin tested and those whose cells were checked by immunofluorescence and tissue culture test. In the immunofluorescence test we are looking for the DA antigen, i. e. the specific antigen on those cells in spleen, thymus grafts, bone marrow, which are supposedly thymus-derived. The tissue culture test is the Coulter counter cytotoxicity test (Method 20). These experiments have not been done with supernatants. What we do in the tissue culture test is try to wipe out a population of cells that is thymus-derived with an anti-DA antiserum. In other experiments using Lewis rats sensitized with egg albumin, anti-Lewis anti-sera, completely abolished this cytotoxic effect. There is no nonspecific cytotoxicity with this anti-DA anti-sera. What we have found was a great surprise to us and contradicts quite a bit in the literature, both from Dr. Waksman s lab and a number of other labs. Animals which receive thymus grafts and bone-marrow have delayed reactions of 18 mm. Animals which have received bone-marrow alone have delayed reactions of 18 mm and 14 mm. This particular skin test system has been repeated about ten times now. Histologically the animals are completely depleted of lymphoid cells in the thymic dependent areas in the spleen and lymph nodes. The skin test looks like the delayed reaction, it does not look like a Jones-Mote response. We can t find any basophils or mast cells stained with giemsa, toluidine blue and hematoxylin and eosin.TABLE 11. LEWIS THYMECTOMIZED HOST LEWIS BONE MARROW PLUS (DAXL) F1 THYMUS GRAFTA. Skin Test (24 hrs)TreatmentDiameter mmTG + BM1818BM1814B. ImmunofluorescenceOrgan% DA (Thymus-derived) cellsThymus grafts–Spleen11Draining lymph node3Cervical lymph node8Mesenteric lymph node2Bone marrow5C. Tissue Culture TestTreatment of lymph node cells% fibroblast survival in the presence of sensitized lymph node cells and PPDNormal Lewis serum44Lewis anti DA serum25The immunofluorescence in this particular experiment is not very good. There were not very many thymus derived cells in the spleen, mesenteric nodes, or any place else. In other experiments, these percentages have been much higher. With successful thymus grafting as much as 20% of the cells in the nodes are thymus derived. In the presence of sensitized cells treated with normal Lewis serum and antigen, we get 44% fibroblast survival. In the presence of anti-DA serum, which should destroy the cytotoxic effect, we get 25% fibroblast survival. In other replicate experiments with the same system, usually with the anti-DA and normal Lewis sera, we get the same number of fibroblasts surviving. We have, in addition, reversed conditions using DA by Lewis (DA × LF) bone-marrow and tried to determine if cytotoxic cells were actually bone-marrow derived.DR. SMITH: Are the thymectomized animals impaired in their capacity to reject skin grafts?DR. RUDDLE: It s difficult to do this, but it is a very good point. However, these experiments work with KLH as well as PPD. Dr. Waksman, I think, would like to consider it a new phenomenon.DR. WILSON: Isn t it true that KLH is a non-thymus dependent antigen?DR. CEROTTINI: KLH is an antigen which is highly thymus-dependent in the mouse.DR. TURK: It depends upon the way it is used as an immunogen. If it is put in Freunds adjuvant, it is highly thymus-dependent, and if it is used in the soluble form, it may be bone marrow-dependent in the same strain of mouse.DR. RUDDLE: We first did it with KLH, but repeated the studies with the tuberculin, with which we expected thymic dependency.DR. CEROTTINI: I would like to comment on Dr. Ruddle s results. For a correct interpretation of experiments using animals reconstituted with thymus and/or bone-marrow cells, one should remember that thymus cells are much less efficient than thymus-derived cells present in the blood, spleen or lymph node. For example, in the mouse graft-versus-host system, the number of reactive cells present in the thymus appears to be 10-50 times lower than in the blood or the peripheral lymphoid organs. Moreover, bone-marrow cell preparations might be contaminated with a small number of circulating blood lymphocytes which are very rich in thymus-derived cells. It is therefore important to establish whether a given activity displayed by bone-marrow cells is due to the contaminating cells or not. In a study of the origin of sensitized lymphocytes active in cell-mediated immunity, we found that cytotoxic lymphocytes, sensitized by transfer into heavily-irradiated allogeneic recipients, were present in mouse thymus cells, but not marrow cells. However, in a given strain combination, cytotoxic lymphocytes were found in transferred thymus cells as well as in transferred bone-marrow cells. To test the possibility that the marrow cell population included thymus-derived cells transported via the circulation, lymphoid cell donors were treated with small amounts of anti-lymphocyte serum (ALS) a few hours prior to collecting cells. The amount of ALS administered was just sufficient to reduce the total white blood count to 15% of the normal value. In this situation transferred bone-marrow cells from ALS-treated donors contained no cytotoxic lymphocytes, whereas thymus cells from the same ALS-treated donors produced as many sensitized lymphocytes as thymus cells from normal animals.DR. RUDDLE: This is one thing we are investigating now with those animals which are getting the marked type of bone-marrow (DA × L F). We still have not completely demonstrated the response is not coming from the host animal s residual cells.DR. WILSON: I think Dr. Cerottini s point is a good one. My colleague, Dr. Johnston, did an interesting experiment on this point. With the rat you can use sex chromosome markers, so that if thymectomized and irradiated animals are repopulated with male bone-marrow or female thymus, one can determine which cells are responding in mixed cultures by examining the sex chromosomes in the mitotic figures. About 90% of them are of the thymus-derived variety, but another 10% are clearly bone-marrow derived. They could well be from the thymus in the original donor, being temporarily located in the bone-marrow. They could be bone-marrow cells reactive to H antigens, or perhaps activated by a blastogenic factor.DR. OPPENHEIM: Rumor has apparently reached Drs. Lawrence and Landy to the effect that we have some cell membrane extracts, namely HL-A antigens prepared by Dr. Reisfeld from a human cell line, that are capable of stimulating the leucocyte cultures from unrelated donors but not those from closely matched donors to respond with increased DNA synthesis in vitro. We have measured the uptake of H3 thymidine and have calculated the ratio of the stimulated response to the unstimulated response. As shown in the Fig. 16, we tested a preparation with this particular type of HL-A phenotype on the leucocytes of closely matched and mis-matched individuals.Fig. 16. A comparison of the DNA synthesis by leucocyte cultures from closely matched and mismatched donors when stimulated by a soluble HL-A preparation extracted from a normal human lymphoid cell lines. The points represent the mean c. p. m. of duplicate cultures. The HL-A extracts were sterilized either by lyophilization, pasteurization or millipore filtration. The typing was performed by a standard cytotoxicity assay and a + indicates that a histocompatibility antigen was present, whereas a blank indicates that it was not detected.One caution at this time is that such HL-A matching is far from complete. The matched leucocyte donors were as similar to the HL-A type of the extract as we get in unrelated individuals. Therefore at times we also saw low grade reactions by so-called matched individual leucocyte cultures. There are several consistent promising findings, however. If we filter our extracts with 0.2 or 0.45μ filters to sterilize them, we only get very low grade reactions, with ratios to 3:1 in the mismatched leucocyte cultures. Most people would not accept these as significant responses. However, statistical analysis has shown that in comparison with the inhibitory effect of the HL-A extract on the matched leucocyte cultures, those from the mismatched individual are significantly stimulated. In order to improve the assay and get more impressive results, we decided rather than filter sterilizing our HL-A membrane preparation, to pasteurize them at 60° for a half hour, or to lyophilize the preparations. Characteristically, we find that pasteurization produces a milky, cloudy aggregation of the soluble membrane extract, and results in significant stimulation of mismatched but not the \"matched” leucocyte cultures. We have obtained three to seven-fold increases in stimulated over unstimulated cultures with such aggregated extracts. The third finding is that lyophilization also produces more stimulation than filtered soluble extracts, but not as high as pasteurized preparations. However, relative to the mixed leucocyte reaction, the response of these reactions are small. In an experiment in which the response to HL-A extracts will be 20, 000 counts of H3 thymidine incorporation, we see the incorporation of 100, 000 counts by mixed live leucocyte cultures. I think that the main point to be made is that we can in fact detect the in vitro equivalent of an immunogenic response, using soluble HL-A preparations. This permits us to assay the biologic activity of membrane preparations, and thus provides us with a physiologically more relevant test of these materials. The degree of the reactions at present is still too small, and the procedure too slow and arduous to be used for typing or screening studies.DR. BACH: Are these active on autologous cells?DR. OPPENHEIM: We have tested extracts containing such histocompatibility antigens on cells from \"matched” individuals. Also, the extract is obtained from Dr. Paper-master s cell line, and we have tested them on his own leucocytes, and they have not stimulated his cells.DR. BACH: You have a maximum of four-fold stimulation in everything there except for one culture combination. We find that this degree of difference is frequently not statistically significant. Could you tell me how you analyze your data?DR. OPPENHEIM: In our statistical analysis we do the same thing that you do, which is to normalize the data by changing the cpm to logs, and then doing the T test on this logarithmically transformed data. Furthermore, the points in the Figure represent the average response of duplicate cultures, so that when we have a dose response curve that shows three different points, this permits a comparison of six different cultures.DR. AMOS: You ve got an HLA-7 HLA-2 extract with a 5, 7, 2, 3 matched cell. For it to be compatible in the sense of having no antigens of the segregant series not present in the responding cell, it would have to be from a homozygous donor. The probability of homozygosity for this particular combination is extremely small since the 2-7 combination only occurs in 2% of haplotypes. The frequency of homozygotes is approximately 0.04%. I wonder whether the \"matched” extract is really much better matched than the mismatched one being used for comparison?DR. OPPENHEIM: When we repeatedly test this particular \"matched” individual we find that her leucocyte culture response is consistently lower than those from the mismatches. We have tested another \"matched” individual in whom we have a similar typing pattern to that of the extract, who differs at Torino 6 locus whose leucocyte cultures frequently manifest positive reactions.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780121077501500091Photovoltaic Materials, Physics ofBolko von Roedern, in Encyclopedia of Energy, 20046.1 Dye-SensitizedA solar cell efficiency greater than 10% has been reported by Michael Grätzel et al., who invented and optimized a dye-sensitized solar cell at the Swiss Federal Institute of Technology. The dye-sensitized cell is an electrochemical cell in which an electrolyte, rather than a conductor or semiconductor, is used to make one of the junctions of a solar cell. The absorber layer consists of a deliberately porous SnO2/titanium dioxide (TiO2) coating, for which the surface of the TiO2 is on the order of 1000-fold enhanced over the surface of a smooth film. This ∼100-nm-thick TiO2 is coated with a very thin (∼1-nm-thick) dye. The best performance has been achieved with ruthenium (Ru)-containing dyes, such as Ru bipyridyl or Ru terpyridine complexes that absorb near-infrared light. The contact is made with an iodine redox electrolyte and a second piece of SnO2-coated glass as the electrical contact. Note that this type of cell is not actually wet. The electrolyte simply has to wet the dye, requiring only drops of electrolyte per 100-cm2 device area. Nevertheless, when multiple cells are made on one substrate with monolithic interconnection, this device must be tightly sealed not only around the perimeter but also between adjacent cells. In an attempt to simplify fabrication, solid or gel electrolytes have been investigated but have resulted in inferior cell performance compared to cells with liquid electrolytes.The prevailing physical description of cell operation assumes that in this device the photogenerated electrons and holes are already separated upon generation in the physical phase boundary of the dye. This creates a photo-induced potential gradient that drives electrons and holes in opposite directions.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B012176480X003272THE METHODOLOGY OF MICROASSAY FOR CELL-MEDIATED IMMUNITY (MCI)M. Takasugi, Eva Klein, in In Vitro Methods in Cell-Mediated Immunity, 1971Publisher SummaryThe microassay for cell-mediated immunity detects histocompatibility and tumor-specific antigens with sensitivity and clarity. In this microassay, around 1000 target cells and a maximum of 50, 000 effect or cells are cultured in 10 microliters of medium in each well of the microtest tissue culture plate. Target cell destruction by sensitized cells has been observed with lymphocytes from human as well as mice and rats by this method. The condition of the target cells is most critical for consistent results. With cells in poor growing phase, survival is better toward the center of the plate and fewer cells are observed toward the edges and in the cornersafter several days of incubation. By dividing the plate in half, with test cells on one side and control cells on the other, this effect has the least influence on results. By placing the target cell controls on the outside edge, the effect works against the researcher an deliminates spurious reduction of target cells. With target cells in optimum condition, this effect is not observed.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780121077501500364Energy MaterialsYun Hang Hu, Wei Wei, in Comprehensive Energy Systems, 20182.6.6.2.1 Portable chargingPortable charging was the largest application segment and accounted for 33.0% of revenue share in 2014 and is expected to grow at a CAGR of 12.6% from 2015 to 2022. To fulfill the requirement for such applications, some evolutions of the structure of solar cells are mandatory: to fully exploit their capabilities, devices have to be flexible and adaptable to complex shapes. The availability of lightweight flexible dye sensitized cells or modules are attractive for applications in room or outdoor light powered calculators, gadgets, and mobiles. Fig. 14 shows several applications of DSSCs as portable charger. For example, Fig. 14(B) shows the wireless sensors based on printable solar cell technology developed by Analog Devices Incorporated and Gas Sensing Solutions Limited and Fig. 14(C) shows a self-powered electronic shelf lable (ESL) module using DSSC developed by MKE Technology Co., Ltd. Fig. 14 shows the images of few commercial DSSC products on the market are indoor electronics by G24 ((A)–(C)), while (D) and (E) are developed by 3G Solar.Fig. 14. Images of few commercial dye-sensitized solar cells products on the market are indoor electronics by G24 ((A)–(C)), while (D) and (E) are developed by 3G Solar.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780128095973002169HLA RESTRICTION OF CYTOTOXICITY AGAINST INFLUENZA-INFECTED HUMAN CELLSA.J. McMichael, in Natural and Induced Cell-Mediated Cytotoxicity, 1979RESULTS AND DISCUSSIONOur previous results (12) have shown that cells from an individual homozygous for HLA-B7 and sensitized to influenza virus-infected autologous cells lysed only target cells that shared HLA-B7. The cytotoxic cells also showed specificity for the influenza virus-type A or B. Mouse cytotoxic T cells do not distinguish influenza virus haemagglutinin from neuraminidase subtypes, either in the sensitization phase or in the lytic phase (6). This may explain the relative ease with which cytotoxic cells were generated in man because it is probable that all individuals studied had been immunologically primed by natural infection with one or more of the cross-reacting influenza A viruses.The results of the experiment shown in Table 1 extend these findings using sensitized cells from a second individual FW, which is homozygous for HLA-A1 and B8. Lymphoid cells from FW, sensitized in vitro to autologous target cells infected with influenza virus A(31), lysed only influenza-infected target cells from donors that shared HLA A1 or B8.TABLE 1. Lysis of Influenza-Infected Target Cells by Sensitized Lymphocytes of Individual FW (HLA: 1, 8, W3 / 1, 8, –)Target cellsHLAaPercent Specific Lysisb(%)FW1,8, W3/1,8–41.7JF1,8, W3/W24, W35,–33.5JP1,8, W3/W24, W35,–32.5DW1, W32, W35,13,–,–35.3RG1,3,14,15,–,–33.0RD2,2,8,12, W3,–32.2CH9,11,7,39,W3, W27.2AT2,11,40,22,–,–10.2aHLA antigens are shown either as genotype (A,B,D/A,B,D) or as phenotype A, A, B, B, D, D,. Shared antigens are underlined.b5 hour 51Cr-release assay at killer : target ratio of 50 : 1.Sensitized FW cells have been tested on 20 influenza-infected target cells. None of the six that did not share HLA antigens gave more than 10.2% specific lysis.One target that shared only HLA-DW3 was not lysed, which is compatible with mouse data because HLA-D is probably equivalent to the H-2I region. Of 13 target cells that shared HLA A or B antigens, 12 were lysed by FW. The one exception was a target cell that only gave 6.1% lysis in spite of sharing HLA-A1.Table 2 summarizes results with other sensitized cell donors. These results are expressed as \"relative lysis” for ease of comparison. Each sensitized cell displayed a bimodal pattern of lysis with a group of target cells, and accordingly, one group of target cells was killed (relative lysis 58%), whereas another group was not as susceptible to lysis (relative lysis 0-32%). The lysed targets all shared HLA-A or B antigens with the killer cell. Targets that shared no HLA antigens were not killed, but each of the targets shown in Table 2 was lysed by at least one effector cell type. Thus, no target was intrinsically resistant to infection. In view of the reproducible infection in targets CW, FW, AM, the low levels of killing seen when HLA antigens were not shared probably reflect the failure of target cell recognition by effector cells.TABLE 2. Relative Lysis of Influenza-Infected Target Cells by Lymphocytes of Sensitized DonorsaLymphocyte donorsCWFWCHJRAM9,7,W21,8,W39,7,W22,12,–2,21,–Targets and HLA9,7,W11,8,–11,W16,–2,27,–32,W40,–PGFb3,7,W2/3,7,W2101–160218JD3,7,W2/2,7,W210015–––CW9,7,W2/9,7,W210022–––FW1,8,W3/1,8,–22100–––CH9,11,7,W16,W2,––3100––JR2,12,–/2,2713–010023AM2,21–/32,W40,–32–––100PM2,7,W2/85–60306ATc2,11,W40,–,–18250–0PF3,7,W2/24,8,–58–––0OD2,7,W2/2,13,–96–––30DH2,7–/3,7,W284–6422–JM2,2,27,140–076–aRelative lysis: Specific lysis expressed as a percentage of the lysis seen with autologous infected targets. Specific lysis values from which those calculations were made were: 42 and 32% for CW, 42% for FW, 24% for CH, 33% for JR and 32% for AM. Negative values are expressed as 0, – = not tested.bPGF is a lymphoblastoid cell line.cInfected AT has been lysed by autologous sensitized cells.The results are consistent with the phenomenon first described by Zinkernagel and Doherty (2) and may be explained by either of the models they proposed: dual recognition or recognition of an HLA-virus complex (altered self). There are some exceptions to the HLA restriction that deserve comment. All these have been in the direction of a greater specificity for self. Nonspecific cytolysis of all infected target cells, which has been reported for measles (13) and vaccinia-infected human cells (14), was not encountered. Of the effector cells tested, AM showed the utmost specificity as it failed to lyse any HLA-matched target cell. JR cells did not kill target cells that shared only HLA-A2; FW did not lyse one target that shared A1, and CW did not lyse one target that shared A9. These exceptions all occur in combinations with shared A locus antigens. It is unlikely that this represents an A locus effect simply because FW lyses two targets that share only HLA-A1.Three other explanations for these exceptions seem possible. There may be HLA antigen subgroups that are serologically silent and killer target interaction between the two subgroups are not discernible. This would be comparable to the results described by Zinkernagel (15) with H-2 mutants.A second possibility is that lysis is only seen when killer and target share an HLA haplotype. The instances in which lysis was seen with apparent single antigen sharing may reflect recent recombinations, where partial haplotype sharing did still occur. On the other hand, an individual such as AM could have a group of HLA antigens that are in linkage equilibrium such that unrelated target cells sharing an HLA haplotype would be hard to find and thus AM cells would display extreme specificity toward self. This explanation implies that other as yet unidentified HLA products, such as Ir genes (16), might play roles in target cell recognition.A third possibility is that certain HLA antigens fail to interact with the influenza virus. This would be comparable to the finding of Blank and Lilly (8) according to which Friend virus only interacts with H-2Db. HLA-A2 might fail to interact with the influenza virus because neither JR- nor AM-sensitized cells would kill infected targets that shared only HLA-A2. If this interpretation is correct, the effect would be antigen specific. Goulmy et al. (10) and Dickmeiss et al. (11) have shown that in the cytotoxic cell recognition of the H-Y antigen and dinitro-phenylated cell surface, respectively, HLA-A2 sharing was particularly effective.These explanations for the failure of sensitized cytotoxic cells to lyse particular target cells despite their HLA sharing are currently being tested. The results may be of consequence for the mechanisms of interaction between influenza viruses and the HLA system.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B9780125846509500262Optical coatings for automotive and building applicationsC.H. Stoessel, in Optical Thin Films and Coatings, 201320.7.2 Building applicationsIn architectural glazing, a specific coating or glazing solution is constrained by market conditions that quickly go beyond the simple question of which coating type or spectral performance is optimal to satisfy a certain application profile. It is important to understand the additional motivations or constraints the market imposes on a certain glazing solution.The purpose of a building determines many aspects of its glazing solution. A big distinction is the difference between commercial and residential dwellings, or the difference in motivation whether the building is owned by the operator or leased/rented.In an unregulated market, the owner/operator distinction highlights the different motivations of owners and operators: owners want to minimize construction cost whereas operators want to minimize operating cost. The resulting discrepancy between minimizing glazing cost and choosing an energy-efficient window is increasingly being resolved by regulatory requirements for energy efficiency, or – as is the case in Germany, for example – the need for a landlord to disclose the energy consumption of a rental building (especially residential).Another application related distinction between commercial and residential construction is the size of individual windows. Residential windows tend to be smaller and of much more varied size and operator type compared to commercial construction which tends to be more standardized for a given building, and generally of larger size.Another distinguishing concept of commercial buildings is the trend towards ‘curtain wall’ construction (especially in high-rises), which has a very different mounting system (the windows can become load-bearing members, so the structural integrity is important), and usually are fixed (non-opening). Commercial windows can also incorporate design elements where the exterior glass pane extends beyond the window opening to cover structural elements of the curtain wall structure or spandrels, which requires special window manufacturing techniques to accommodate the large setbacks (for multi-pane windows, removal of silver-containing low-e coatings, or additional printed aperture frames). Residential windows, in comparison, still follow the ‘hole-in-the-wall’ paradigm, are smaller, and typically require being opened for ventilation by the use of slider or turn/tilt operator types. It is important to recognize that the frame-to-aperture ratio influences the thermal properties of the overall window – multi-pane glazing can achieve significantly higher thermal insulation than common window frame systems, and for passive house windows that rely on large apertures, larger windows are desirable. This may sometimes create design conflicts – sliding windows typically have higher frame cross-sections than turn/tilt windows of similar window aperture, or historicizing muntins or grids that are embedded inside multi-pane cavities add to shadowing and can create undesirable thermal bridges that negate the benefits of advanced energy-efficient glazing coatings.Integration of coatings into multi-functional glazing requirementsA recent trend in window technology diversification is the combination of glazing with additional functionality such as photovoltaics or dimmable/ switchable glazing.Building-integrated photovoltaics (BIPV) offer many opportunities to utilize the building envelope for solar electricity generation.9 The combination of photovoltaic (PV) structures with (typically semi-) transparent glazing is a niche technology that is often a compromise between the desire for solar energy generation and design goals, most often shading (but possibly also infrared-blocking – from the transparent conductors in a PV element – and UV-blocking from the use of suitable laminating adhesives) because a semi-transparent solar cell will not utilize the full amount of available photons for energy conversion. Amorphous and crystalline silicon are the most common PV elements, and dye-sensitized cells (DSCs) may have future potential but currently show very small conversion efficiencies. Considering the significant ‘balance of system’ expense and infrastructure for converters and wiring, a strong architectural design justification is typically driving such implementation, while a more conversion-efficient PV function can be obtained with opaque building components (some curtain wall structures may combine clear non-PV windows with adjacent opaque PV panels). Another design constraint for BIPV windows is the lack of standardized window sizes, as the solar panels are very difficult and expensive to build in custom formats. Therefore, installations tend to favor curtain wall designs that take advantage of the standardized formats of the PV cells but demonstrate the creative potential, e.g., by laminating with colored and screenprinted glass (for example a semi-transparent amorphous silicon solar panel in a office building staircase façade).10Switchable glazing (or ‘smart windows’) is an attractive way to dynamically control the spectral properties of windows, and resolve the changing optical requirements during the day or the seasons.11,12 Although the fundamental concept of electrochromism is well established, development into robust, reliable, and lasting consumer products has been hampered by technical hurdles (mostly reliability for the two leading technical embodiments, thin film solid-state devices, and electrolyte exchange polymer-based devices), which translates into relatively high consumer prices that have moved little, and relegates electrochromic windows to niche applications. The need for electrical controls and thus supply of electrical power to windows is another hurdle that hinders broad adoption. Electrochromic windows, with their multilayer structures of transparent conductors, allow easy integration of several energy-efficiency functions beyond just-switchable shading (which primarily affects the visible spectrum), such as infrared reflection or ultraviolet blocking.View chapterPurchase bookRead full chapterURL: https://www.sciencedirect.com/science/article/pii/B978085709594750020XRecommended publicationsInfo iconSolar Energy Materials and Solar CellsJournalDyes and PigmentsJournalJournal of Power SourcesJournalCarbonJournalBrowse books and journalsAbout ScienceDirectRemote accessShopping cartAdvertiseContact and supportTerms and conditionsPrivacy policyWe use cookies to help provide and enhance our service and tailor content and ads. By continuing you agree to the use of cookies.Copyright © 2021 Elsevier B.V. or its licensors or contributors. 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