Mapping functional epitopes of the human LFA-1 glycoprotein: Monoclonal antibody ingibition of NK and CTL effectors

Anti-LFA-1 monoclonal antibody (MoAb) was originally identified by screening antibodies for their ability to inhibit cytolysis in the absence of complement. Anti-LFA-1 MoAb has been shown to inhibit both natural killer (NK) and cytolytic T lymphocyte (CTL) mediated cytolysis. To further define the utilization of this molecule in cell-mediated cytolysis, we used a panel of MoAb to functional epitopes on both the α and β chains of the LFA-1 heterodimer. The panel was used to compare OKT3^- NK effectors and OKT3⁺ CTL clones. As expected, function-associated MoAb to CTL antigens (T3, T8, LFA-2) and target cell antigens (HLA, LFA-3) blocked only CTL clones and not NK effectors. In contrast, anti-LFA-1 MoAb blocked both NK effectors and CTL clones. In addition, the panel of anti-LFA-1 MoAb demonstrated an identical hierarchy of functionally relevant LFA-1 epitopes. Given the similar utilization of LFA-1 in NK and CTL mediated cytotoxicity assays, we explored the ability of MoAb to different epitopes on LFA-1 to inhibit conjugate formation. Anti-LFA-1 MoAb inhibition of NK-target binding paralleled the inhibition of CTL-target binding. Thus, functional epitopes on the LFA-1 molecule have been defined for NK and CTL effectors. The identical hierarchy of functional epitopes indicates that the LFA-1 molecule is similarly utilized in NK and CTL mediated cytotoxicity and that the relevant epitopes are involved in effector-target conjugate formation. The common involvement of the LFA-1 molecule in both NK and CTL mediated cytotoxicity suggests a potential role for anti-LFA-1 MoAb in the treatment of human allograft rejection.