Integrin ITGAM/ITGB2 is implicated in various adhesive interactions of monocytes, macrophages and granulocytes as well as in mediating the uptake of complement-coated particles and pathogens (By similarity). It is identical with CR-3, the receptor for the iC3b fragment of the third complement component. It probably recognizes the R-G-D peptide in C3b. Integrin ITGAM/ITGB2 is also a receptor for fibrinogen, factor X and ICAM1. It recognizes P1 and P2 peptides of fibrinogen gamma chain. Regulates neutrophil migration. In association with beta subunit ITGB2/CD18, required for CD177-PRTN3-mediated activation of TNF primed neutrophils (By similarity). May regulate phagocytosis-induced apoptosis in extravasated neutrophils (By similarity). May play a role in mast cell development (By similarity). Required with TYROBP/DAP12 in microglia to control production of microglial superoxide ions which promote the neuronal apoptosis that occurs during brain development (PubMed:18685038). Heterodimer of an alpha and a beta subunit. ITGAM associates with ITGB2. Found in a complex with CD177 and ITGB2/CD18. Interacts with JAM3. Interacts with THBD. Interacts with complement factor H/CFH; this interaction mediates adhesion of neutrophils to pathogens leading to pathogen clearance. Predominantly expressed in monocytes and granulocytes (PubMed:3887182, PubMed:8986723). Expressed in a subset of peritoneal mast cells (PubMed:9862668). Expressed in microglia (at protein level) (PubMed:18685038). Induced by lipopolysaccharide (LPS) in mast cells. The integrin I-domain (insert) is a VWFA domain. Integrins with I-domains do not undergo protease cleavage. Mice are born at the expected Mendelian rate (PubMed:8986723). The numbers of blood leukocytes are normal and neutrophils rolling on blood vessels is not affected (PubMed:8986723). Impaired LTB4-induced neutrophil adhesion to venules (PubMed:8986723). Numbers of mast cells in the peritoneal cavity, peritoneal wall and in the dorsal skin are reduced (PubMed:9862668). In an experimental model of thioglycolate-induced peritonitis, abnormal accumulation of recruited neutrophils due to impaired apoptosis (PubMed:8986723). In an experimental model of acute septic peritonitis, 5-fold increase in mortality rate, reduced neutrophil recruitment in the peritoneum, reduced histamine production and impaired bacterial clearence (PubMed:9862668). In experimental model of immune complex-mediated glomerulonephritis, reduced neutrophil accumulation without affecting their initial recruitment and reduced proteinuria (PubMed:9382884). Enhanced susceptibility to high fat diet-induced obesity characterized by a weight increase and higher levels of white and brown fat (PubMed:9207125). Reduced apoptosis in the hippocampus in neonates (PubMed:18685038). Belongs to the integrin alpha chain family.