Complement receptor type 1 (CR1), Complement receptor type 2 (CR2), and Complement receptor type 3 (CR3) (CR1/CR2/CR3)

Complement receptors CR1 (CD35), CR2 (CD21), and CR3 (CD11b/CD18) are a group of cell surface glycoproteins that play essential roles in the innate and adaptive immune systems by interacting with complement activation products. Complement receptor type 1 (CR1) is a key regulator of the complement cascade, providing decay-accelerating activity for C3 and C5 convertases and acting as a cofactor for Factor I-mediated cleavage of C3b and C4b. Complement receptor type 2 (CR2) is primarily expressed on B cells and follicular dendritic cells, where it functions as a co-receptor that lowers the threshold for B-cell activation and facilitates the retention of antigens. Complement receptor type 3 (CR3), an integrin, mediates the phagocytosis of iC3b-opsonized particles and is involved in leukocyte adhesion and migration. These receptors are linked to various diseases, including systemic lupus erythematosus, rheumatoid arthritis, and Alzheimer's disease, where dysregulated complement activity contributes to tissue damage. Therapeutic approaches include the development of soluble CR1 (sCR1) to inhibit systemic complement activation and CR3 agonists to modulate inflammatory signaling. Additionally, CR2-based fusion proteins are being explored to target complement regulators specifically to sites of C3d deposition in tissues.

Other names

CD35CD21CD11b/CD18Mac-1C3b/C4b receptorC3d receptoriC3b receptorIntegrin alpha-M beta-2Complement component 3b/4b receptor 1Complement component 3d receptor 2Knops blood group antigen

Inhibition of complement activation via decay acceleration and cofactor activity; modulation of B-cell activation; enhancement of phagocytosis; regulation of leukocyte adhesion.