Integrin alpha M beta 2 (CD11b/CD18)

Integrin alpha M beta 2 (also known as CD11b/CD18 or Mac-1) is a heterodimeric adhesion receptor composed of alpha M (ITGAM/CD11b) and beta 2 (ITGB2/CD18) subunits, primarily expressed on leukocytes such as monocytes, macrophages, neutrophils, natural killer cells, and subsets of lymphocytes. It plays a central role in innate immunity by mediating leukocyte adhesion to endothelium via interactions with ICAM-1/ICAM-2, facilitating transmigration to inflammation sites, and enabling phagocytosis of complement-opsonized particles through binding to iC3b. The receptor exhibits conformational switching from inactive (bent) to active states upon stimulation (e.g., via Toll-like receptors), promoting high-affinity ligand binding including fibrinogen, microbial components, and denatured proteins, while its cytoplasmic tails support bidirectional signaling for cytoskeletal reorganization and cytokine regulation (e.g., IL-10, TGFβ production). In disease, dysregulation contributes to excessive inflammation in autoimmune conditions and cardiovascular pathologies, or immunodeficiency when deficient, as seen in leukocyte adhesion deficiency syndromes. Although no approved small-molecule drugs target it directly, its structure has guided development of blocking antibodies and inhibitors to modulate leukocyte recruitment, highlighting therapeutic potential tempered by risks of impaired host defense.

Other names

Mac-1complement receptor 3 (CR3)ITGAM/ITGB2CD11b/CD18

Inhibition of ligand binding (e.g., to iC3b, ICAM-1, fibrinogen), Blockade of integrin activation/conformation change, Prevention of leukocyte adhesion and transmigration