Macrophage-1 antigen
Macrophage-1 antigen (or integrin αMβ2 or macrophage integrin or Mac-1) is a complement receptor ("CR3") consisting of CD11b (integrin αM) and CD18 (integrin β2).
Complement receptor 3 (CR3)(CD11b/CD18) is a human cell surface receptor found on polymorphonuclear leukocytes (mostly neutrophils), NK cells, and mononuclear phagocytes like macrophages. CR3 is a pattern recognition receptor, capable of recognizing and binding to many molecules found on the surfaces of invading bacteria. CR3 also recognizes iC3b 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.
Upregulation of Mac-1 in the presence of certain factors such as IL-2 may cause a prolongation of the life of the immune cell while the presence of TNF-α induces apoptosis and selective removal of the cell.
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. In human mononuclear phagocytes, phagocytosis of Mycobacterium tuberculosis is mediated in part by human monocyte complement receptors including CR3.
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