CD11b is implicated in various adhesive interactions of monocytes, macrophages and granulocytes as well as in mediating the uptake of complement coated particles. It is identical to CR3, the receptor for the iC3b fragment of the third complement component.CD11b is also a receptor for fibrogen, factor X and ICAM1.It recognizes P1 and P2 peptides of fibrogen gamma chain.The Mac1 CD11b antigen is present on macrophages, granulocytes, natural killer cells, blood monocytes.CD11b is expressed on 8% spleen cells, 44% bone marrow cells and less than 1% thymocytes and is commonly used as a microgial marker in nervous tissue.CD11c encodes the integrin alpha X chain protein.This protein combines with the beta 2 chain (ITGB2) to form a leukocyte-specific integrin referred to as inactivated-C3b (iC3b) receptor 4 (CR4).The alpha X beta 2 complex seems to overlap the properties of the alpha M beta 2 integrin in the adherence of neutrophils and monocytes to stimulated endothelium cells, and in the phagocytosis of complement coated particles.CD11b/c gene lead to systemic lupus erythematosus.
