TwokeyfeaturesoftheimmunesystemaretheclonalexpansionofBcellsandTcellsinresponsetoantigens,andthepotentiationoffutureimmuneresponsesbylong-livedmemorycells.CD4expressingTcellsrequirecostimulatorysignalsalongwithantigenstimulationtomountaneffectiveimmuneresponse.CD28hasbeenwidelycharacterizedasacostimulatoryreceptorforCD4+Tcells.OX40,alsocalledCD134,isanothertransmembranereceptorproteinexpressedbyCD4TcellsthatprovidesacostimulatorysignalforTcellactivationbyantigen.TheOX40LligandforOX40isexpressedasatransmembraneproteinbyantigen-presentingcells,andisrequiredforfunctionofantigen-presentingcells.TheTcellcostimulatorysignalprovidedbytheOX40/OX40Linteractionincreasestheclonalamplificationofantigen-specificTcellsandthesurvivalofmemoryTcellsthatrespondtothisantigen. Contributor:GlennCroston,PhD. REFERENCES: