Integrins are cell adhesion molecules that can mediate bidirectional transfer of signals across the plasma membrane. The cytoplasmic domains of integrin family members interact with components of the signal transduction apparatus within cells. Integrin receptors contain noncovalently associated alpha and beta subunits that consist of a large extracellular region (the ligand-binding domain), a short transmembrane region, and a cytoplasmic domain of varying length. In mammals, at least 17 alpha subunits and 8 beta subunits have been identified and these proteins can heterodimerize to form at least 22 different receptors. The integrin beta2 subunit associates with integrin alphaL to form a receptor for ICAM family members. Integrin beta2/alphaL is involved in a variety of immune phenomena including leukocyte-endothelial cell interaction, cytotoxic T-cell mediated killing, and antibody dependent killing by granulocytes and monocytes.
