Integrin ?M, also designated complement component receptor-3 ?, CD11b (p170), macrophage antigen a polypeptide, cell surface glycoprotein Mac-1 a subunit, MAC1A, MO1A and ITGAM) is a cell adhesion molecule that acts as a receptor for cell surface ligands such as intracellular adhesion molecules (ICAMs) or soluble ligands. Integrins are heterodimeric proteins that contain an a chain and b chain. Integrin ?M combines with the Integrin 2 to form a leukocyte-specific integrin referred to as macrophage receptor 1 (Mac-1), or inactivated-C3b (iC3b) receptor 3 (CR3). Integrin ?M/2 is important in the adherence of neutrophils and monocytes to stimulated endothelium, and also in the phagocytosis of complement coated particles.