Spontaneous cell-mediated cytotoxicity by human peripheral blood lymphocytes in vitro

With isolated subpopulations of human peripheral blood mononuclear cells, spontaneous cell-mediated cytotoxicity (SCMC) and antibody-dependent cellular cytotoxicity (ADCC) were demonstrated to be functions of a population of surface immunoglobulin (sIg)-negative, Fc receptor-positive lymphocytes. Organ distribution studies revealed that SCMC and ADCC effector cell activity occurred in parallel, being present in spleen and absent in tonsils. Treatment of effector cells with trypsin significantly inhibited SCMC but not ADCC and this inhibition was not reversed by short-term incubation in autologous plasma. These results demonstrate that SCMC and ADCC involve different cytotoxicity mechanisms and are consistent with two subsets of effector cells with separate functional capabilities or a single effector cell mediating both forms of cytotoxicity through separate mechanisms.