CD11b is the integrin alpha M chain. Integrinsare heterodimeric integral membrane proteins composed of an alphachain and a beta chain. This I-domain containing alpha integrincombines with the beta 2 chain (ITGB2) to form a leukocyte-specificintegrin referred to as macrophage receptor 1 ('Mac-1'), orinactivated-C3b (iC3b) receptor 3 ('CR3'). The alpha M beta 2integrin is important in the adherence of neutrophils and monocytesto stimulated endothelium, and also in the phagocytosis ofcomplement coated particles.