CR 1 Complement Receptor CD35

CRl is present on a number of blood cells including polymorphonuclear leukocytes, monocytes/macrophages, follicular dendritic cells, glomerular epithelial cells, T and B cells. The receptor binds C3b, iC3b, and C4b. Interactions between complement fragments and the cellular receptors initiate endo-cytosis and phagocytosis of bacteria. In addition, the CRl receptor serves to regulate complement activation via its role as a cofactor in the cleavage of Factor I (Thomsen, 1988).

There are four different polymorphic forms of CRl that range from 190 to 280 kDa. All members of the family are single-chain membrane proteins with multiple, arranged, short consensus units (SCRs) of65-70 amino acids. Binding of C3b and C4b is associated with the second SCR. This ensures that binding of the complement fragments to CRl occurs at a distance from the cell surface (Berger etal., 1981).

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