Complement Receptor 3 (CR3)

Macrophage-1 antigen (integrin alphaM/beta2) is a complement receptor "CR3" consisting of CD11b and CD18.CR3 is a human macrophage cell surface receptor that recognizes C3b when bound to the surface of foreign cells. Binding to the receptor causes phagocytosis and destruction of the foreign cell. CR3 belongs to a family of cell surface receptors known as integrins (because they share this particular β chain, they are referred to as β2-integrins), which are extremely widely distributed throughout nature and which generally are important in cellular adhesion and cell-cell interactions in a variety of cells and circumstances. CR3 (CD11b/CD18) is present exclusively on leukocytes, particularly on NK cells, monocytes and polymorphonuclear neutrophils. A fully activated neutrophil may express on its membrane 200,000 or more CR3 molecules. Absence of CR3 results in reduced binding and ingestion of Mycobacterium tuberculosis (in mice).