Complement receptor (specifically, this refers to a family of receptors; the most relevant for leukocytes are Complement receptor type 1, 3, and 4) (CR (with specific members abbreviated as CR1, CR2, CR3, and CR4))

Complement receptors are membrane-bound proteins expressed on various immune cells—including monocytes, macrophages, neutrophils, B lymphocytes, NK cells, and activated T lymphocytes—that bind fragments of complement proteins generated during activation of the complement system. These interactions mediate key processes such as phagocytosis of opsonized pathogens or immune complexes and regulation of inflammatory responses. There are several types—most notably Complement receptor type 1 (CR1), type 2 (CR2), type 3 (CR3), and type 4 (CR4)—each with distinct expression patterns and functions. For example: • **CR1** is found on erythrocytes and leukocytes; it mediates clearance of immune complexes from circulation. • **CR3** (*CD11b/CD18*, also known as Mac‑1) is highly expressed on myeloid lineage leukocytes where it facilitates phagocytosis and cell adhesion. • **CR4** (*CD11c/CD18*) shares structural similarity with CR3 but has different ligand preferences. Deficiencies or mutations in these receptors can contribute to susceptibility to infections or autoimmune diseases such as systemic lupus erythematosus. While they represent potential therapeutic targets for modulating inflammation or autoimmunity, there are currently no widely approved drugs that specifically target these molecules[1][2][3].

Other names

Complement receptorsCRsCD35 (for CR1)CD11b/CD18 or Mac-1 (for CR3)CD11c/CD18 or p150/95 (for CR4)

therapeutic mechanisms would include inhibition of ligand binding to block immune complex clearance or modulation of inflammation