C-Reactive protein, human

Biochemical Physiological Actions : C reactive protein (CRP) is an acute phase protein. Serum levels in patients with atherosclerosis is predictive of increased risk of myocardial infarction (MI) and stroke. The cytokine IL-6 is thought to be the key mediator in hepatocyte secretion of acute phase proteins including CRP. CRP mediates innate immunity by binding to microbial polysaccharides and to ligands exposed on damaged cells. The binding activates the classical complement pathway (C1, C4, C2, C3 but not C5-9). Opsonization of the substrates leads to their uptake by phagocytic cells and limits the inflammatory response. CRP also binds to several nuclear components including chromatin, histones and snRNP, suggesting that it may play a role as a scavenger during cell necrosis. In addition, CRP binds, through the Ca2+-dependent PC-binding site, to many other body components including phospholipids, lecithin, sphingomyelin, a variety of monophosphate esters, low density lipoprotein, fibronectin and to the basement membrane protein laminin. CRP binding to polycations has also been demonstrated, but this binding does not appear to occur through the PC-binding site on CRP.