CD35/CR1
CD35, or complement receptor 1 (CR1), is a large single-pass glycoprotein whose longest isoform carries 30 complement control protein (CCP) modules. It binds C3b and C4b opsonins and acts as a cofactor for factor I in cleaving these fragments, making it a central regulator of complement activation. On erythrocytes, CD35 binds immune complexes and shuttles them to liver and spleen macrophages for clearance, the basis of immune adherence. The receptor is also present on neutrophils, monocytes, B cells, and follicular dendritic cells. Polymorphic size variants exist, and the Knops blood group antigens reside on CD35. Plasmodium falciparum-infected erythrocytes exploit CR1 for rosetting.
