Complement Receptor 1
Complement receptor 1 (CR1, CD35) is a single-pass transmembrane glycoprotein composed almost entirely of complement control protein (CCP) repeats organized into four long homologous repeats. Expressed on erythrocytes, monocytes, granulocytes, B cells and follicular dendritic cells, CR1 binds C3b, C4b and their inactive fragments iC3b and C3d,g, and serves as a cofactor for factor I-mediated cleavage of C3b and C4b. On erythrocytes it ferries complement-opsonized immune complexes to the liver and spleen for clearance. CR1 also accelerates decay of C3 and C5 convertases, curbing complement amplification, and soluble CR1 is being explored as a complement inhibitor for transplant and inflammatory indications.
