Monoclonal antibodies to human LFA-1 and T8 surface structures act synergistically to inhibit the recognition phase of cytotoxic T cell killing

A long term human alloimmune cytotoxic T cell line (LFA-1⁺, T3⁺, T8⁺, T11⁺, T4^-) was studied as a model system to investigate the mechanism of inhibition of effector function by several anti-LFA-1 and anti-T8 monoclonal antibodies (MAb). Several anti-LFA-1 MAb, reactive with unique epitopes, by themselves or pooled, inhibited cytolysis 40 to 60% in a 4 hr ⁵¹Cr-release assay. Similarly, several anti-T8 MAb blocked lysis by only 30 to 60%. However, when anti-LFA-1 MAb and anti-T8 MAb were pooled, cytolysis was inhibited 70 to 100% and the effective dose of either MAb was decreased 10 to 50 fold. Several other MAb to T cell surfaces structures, when combined with anti-LFA-1, showed no synergistic effects in blocking cytolysis. Ca⁺⁺ pulse experiments indicated both anti-LFA-1 and anti-T8 blocked lysis during the pre-Ca⁺⁺ dependent phase. The kinetics of lysis was reversibly inhibited by anti-LFA-1 or anti-T8, but anti-LFA-1 and anti-T8 MAb in combination irreversibly blocked cytolysis. Neither anti-LFA-1 or anti-T₈, alone or in combination, modulated its respective surface structure. These results suggest the necessary participation of LFA-1 and T8 structures in the recognition phase of cytolysis. One possibility, suggested by the synergistic effects of anti-LFA-1 and anti-T8 in blocking cytolysis is that a functional linkage between LFA-1 and T8 molecules occurs during the recognition of allogeneic targets by cytotoxic T lymphocytes. Supported by PHS grant No ROI CA 35638 awarded by the NCI, DHHS.