CRP binds and opsonizes apoptotic cells (6-8) as well as bacteria such as S. pneumoniae (9, 10). It subsequently enhances the phagocytosis of these opsonized cells (6, 8-10). CRP additionally binds several proteins in the complement cascade including C1q, C4BP, and Factor H (8, 11-13). It enhances activation of the classical complement pathway and the deposition of C3b (9). In later stages of the response, CRP inhibits complement-mediated cell lysis through its binding to C4BP and Factor H (8, 12). These interactions induce the upregulation of complement inhibitory proteins CD46, CD59, and CD55/DAF and inhibit assembly of the membrane attack complex (MAC) (8, 14).
CRP binds to Fc gamma RI, Fc gamma RIIA, and Fc gamma RIIB on macrophages and dendritic cells (15-17), and Fc receptors are required for the phagocytosis of CRP-opsonized target cells (6, 10, 18). CRP binding to Fc gamma RI induces Src activation which subsequently triggers the inhibitory Fc gamma RIIb and dampens the inflammatory response (15, 19). CRP additionally promotes dendritic cell maturation and humoral immunity (10). In cardiovascular disease, CRP binds to oxidized LDL, exacerbates tissue damage in coronary artery infarction, and inhibits the repair of injured vascular endothelium (7, 19, 20).
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