Integrins are heterodimeric integral membrane proteins consisting of an ? chain and a ? chain. CD11b is an I-domain including ? integrin combines with the ? 2 chain (ITGB2) to form a leukocyte-specific integrin referred to as macrophage receptor also called MAC1. The ? M beta 2 integrin is crucial in the adherence of neutrophils and monocytes to stimulated endothelium, and also in the phagocytosis of complement coated particles. Multiple transcript variants encoding different isoforms have been found for this gene.