Functional role of HLA class I cell-surface molecules in human T-lymphocyte activation and proliferation

This investigation addressed the role of major histocompatibility complex-encoded class I molecules in the activation and proliferation of human lymphocytes. We studied the effect of antibodies specific for HLA-A and HLA-B locus gene products on mitogen-stimulated peripheral blood mononuclear cell (PBMC) subpopulations. Three individually derived, well-characterized anti-HLA class I monoclonal antibodies were demonstrated to inhibit the proliferation of human PBMC stimulated by either OKT3 or the calcium ionophore ionomycin. The antibody directed against HLA-A, -B, and -C locus gene products (W6/32) and the antibody directed against HLA-B locus gene products (4E) inhibited proliferation induced by either mitogen by 70-90%. The HLA-A locus-specific antibody (131), though inhibiting ionomycin-induced proliferation by 80-90%, was much less effective when OKT3 was the stimulus. The inhibition affected T4⁺ and T8⁺ cells and was not mediated by DR⁺ accessory cells. The inhibitory effect of these antibodies was associated with a decrease in the level of interleukin 2 activity present in culture supernatants, decreased interleukin 2 receptor expression, and decreased transferrin receptor expression and was not overcome by the addition of exogenous interleukin 2. Our results suggest that HLA class I molecules are directly involved in the early critical events of human lymphocyte activation and proliferation.