Product Description

Rat C1q is purified from pooled normal rat serum. C1q is part of the C1 complex, which is thefirst complement component in the classical pathway of complement. The C1 complex is a non-covalent assembly ofthree different proteins (C1q, C1r, and C1s) bound together in acalcium-dependent complex. C1q has sixextended arms with domains at the end of each arm that bind to the Fc domainsof immunoglobulins such as IgG or IgM.When antibodies bind to antigens, forming immune complexes, they clusterallowing two or more of the six C1q arms to bind to the Fc domains ofantibodies. Rat IgG2 is very efficientwhen compared to IgG1 in activating complement (Medgyesi, G.A et., al., 1981).This is in contrast to the human system in which IgG1 activates complement butnot IgG2 (Redpath, S. et. al., 1998). Thebinding of multiple arms of C1q to immune complexes causes the two C1r proteinsin the complex (protease zymogens) to auto-activate. The activated C1r proteasescleave and activate the two C1s protease zymogens in the complex. The activated C1s cleaves complementcomponent C4 releasing C4a and initiating covalent attachment of C4b to theactivating surface. Activated C1s alsocleaves C2 and the larger fragment of C2 binds to the surface-attached C4bforming C4b,C2a, the C3/C5 convertase of the classical pathway.

Rat IgG1 cannot activate complement whereas rat IgG2 does.

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