C3 is the most abundant protein of the complement system and predominantly synthesized by hepatocytes. C3 can be cleaved in two divalent fragments, where the letter “b” always indicates the larger fragment. C3b binds covalently to glycoproteins scattered across the cell surface. Macrophages and neutrophils have receptors for C3b and can bind the C3b-coated cell or particle preparatory to phagocytosis. This effect qualifies C3b as an opsonin. C3a is the smaller fragment that is released into the surrounding fluids. It can bind to receptors on basophils and mast cells triggering them to release their vasoactive contents (e.g., histamine). The quantitation of C3a corresponds to the level of complement activation in a test sample.
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FC = Flow Cytometry, Intracellular Staining/Flow Cytometry; ELISA = ELISA, ELISPOT; Multiplex = Multiplex Immunoassays; ICC = Immunocytochemistry; IHC = Immunohistochemistry, Immunofluorescence, Microscopy, Imaging, In Vivo Imaging; IHC-F = Immunohistochemical Staining of Frozen Tissue Sections; IHC-P = Immunohistochemical Staining of Formalin-Fixed Paraffin Embedded Tissue Sections; FA = Functional Assays, Bioassays, Neutralization, Depletion Studies, Biomolecule Conjugation; IP = Immunoprecipitation; WB = Western Blotting
RUO = Research Use Only; GPR = General Purpose Reagent; ASR = Analyte Specific Reagent. Analytical and performance characteristics are not established; CE = CE-marked reagents