CD11b (integrin alphaM subunit) is a 165-170 kDa type I transmembrane glycoprotein that non-covalently associates with integrin beta2 subunit (CD18), expression of the CD11b chain on the cell surface requires the presence of the CD18 antigen. CD11b/CD18 integrin (Mac-1, CR3) is highly expressed on NK cells, neutrophils, monocytes and less on macrophages. CD11b/CD18 integrin is implicated in various adhesive interactions of monocytes, macrophages and granulocytes, facilitating their diapedesis, as well as it mediates the uptake of complement coated particles, serving as a receptor for the iC3b fragment of the third complement component.Synonyms: CD11 antigen-like family member B, CR-3 alpha chain, CR3A, Cell surface glycoprotein MAC-1 subunit alpha, ITGAM, Integrin alpha-M, Leukocyte adhesion receptor MO1, MAC1, Neutrophil adherence receptor