CD11/CD18 (LFA-1) are beta 2-type integrins. The leukocyte integrins are a family of heterodimeric receptors that mediate divalent cation-dependent cellular adhesion reactions. T cells use integrins in essentially all of their functions. Integrins become active following signalling through other membrane receptors, which cause both affinity alteration and an increase in integrin clustering. The monoclonal antibody 24 recognizes a structural feature and is strictly dependent upon the presence of Mg2+. The epitope is located within, or in close proximity to, the three conserved cation binding domains and therefore a measure of Mg2+ bound to the leukocyte integrins and thus reflects functionally active molecules. The epitope can be induced on polymorphonuclear leukocytes and on monocytes. Glu173 and Glu175 of the beta(2) I domain are identified as critical for antibody 24 binding. The monoclonal antibody 24 inhibits monocyte-dependent, antigen specific T cell proliferation and IL-2- activated natural killer cell assays. The antibody does not interfere with mitogen-stimulated T cell proliferation. Furthermore the monoclonal antibody 24 prevents deadhesion of receptor/ligand pairs, possible locking leukocyte integrins in an active conformation.
integrin, alpha L (antigen CD11A (p180), lymphocyte function-associated antigen 1; alpha polypeptide); integrin, beta 2 (complement component 3 receptor 3 and 4 subunit)