Production and characterization of monoclonal anti-CD18 anti-idiotype antibodies

Three leukocyte adhesion receptors have been described which mediate intercellular binding of leukocytes: LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and p150/95 (CD11c/CD18). We have previously reported the production of several monoclonal antibodies against the common subunit of these receptors (CD18). We here describe the production of monoclonal anti-idiotype antibodies against one of the anti-CD 18 antibodies (H52) which has been shown to inhibit potently the function of leukocyte adhesion receptors. Three IgG1 and two IgM anti-idiotype antibodies were derived which recognized private idiotopes on the H52 molecule. Two of these antibodies blocked the binding of H52 to purified LFA-1 and to cell surface expressed antigen. One of the antibodies (AIM.6) was shown to be an internal image-type (Ab2β) antibody based on inhibition of its binding to H52 by purified LFA-1 and by its ability to induce Ab3 which recognize LFA-1 when used as immunogen. The AIM.6 Ab2β antibody was tested for recognition of leukocyte adhesion ligands in LFA-1-mediated leukocyte adhesion and activation assays. The AIM.6 antibody did not block intercellular adhesion of leukocytes or mitogen stimulation of T cells, functions which were completely inhibited by low concns of H52. AIM.6 Ab2β antibody bound to H52 very well at 0°C but bound very poorly or not at all at 37°C. Binding studies on a panel of anti-CD18 monoclonal antibodies showed that the idiotope defined by AIM.6 was unique to H52 and an antibody recognizing the same epitope on CD 18 (H5B9). This result showed that inhibitory anti-CD 18 monoclonal antibodies utilize at least two distinct paratopes in binding to CD18. The above results are in contrast to those obtained in other systems in which Ab2β antibodies against receptor-specific Ab1 antibodies recognize receptor ligands and are discussed in the context of ligand recognition by leukocyte adhesion receptors.