ITGB2 gene, also known as CD18, codes for the beta 2 integrin subunit. Integrins are integral cell membrane glycoproteins composed of an alpha chain and a beta chain. Beta 2 integrin, the product of ITGB2, pairs noncovalently with at least four different alpha chain subunit L, M, X and D encoded by the CD11a, CD11b, CD11c, or CD11d gene, forming distinct functional heterodimers complexes: LFA-1 (CD11a/ CD18), Mac-1 (CD11b/CD18), gp150,95 (CD11c/CD18), or CD11d/CD18, respectively. These complexes play major roles in the immune system by mediating important leukocyte adhesion reactions. They are critical for the recruitment of circulating leukocytes to inflammatory sites, in that they are responsible for the establishment of firm adhesion and transendothelial migration. Each complex also has additional distinct functional profiles. For example, CD11a/CD18 plays an important role in lymphocyte proliferation, cell-mediated cytotoxicity, monocyte-lymphocyte and B-T-cell adhesion, and T-helper activity. CD11b/CD18 is an oligospecific receptor that is primarily involved in neutrophil adhesion-dependent functions, such as chemotaxis, phagocytosis, homotypic and heterotypic adhesion, and antibody-dependent cytotoxicity. It shares many of these functions with CD11c/CD18.