Evidence for T cell nature and heterogeneity within natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) effectors: a comparison with cytolytic T lymphocytes (CTL).

Three monoclonal antibodies (Ab) to human T lymphocytes (9.3, 9.6, and 10.2), a monoclonal Ab to the human la antigen (7.2), and a monoclonal Ab recognizing a monocyte-associated antigen (OKM1) were used to characterize 3 cytolytic effector types: CTL, NK, and ADCC. Activity was measured after treatment with Ab plus C. T cell antigen 9.3 was expressed on all CTL but gave only minimal reduction in NK or ADCC activities in the presence of C. T cell antigen 10.2 was expressed on all CTL and, in the presence of C, reduced by one-half the NK or ADCC activities. CTL were heterogeneous in expression of 9.3 and 10.2 antigens on days 5 and 7 of MLC, whereas all CTL were positive on day 9. T cell 9.6 antigen, closely associated with the E receptor, was found on all CTL and NK cells and the great majority of ADCC effectors. Our finding with 9.6 confirms by independent and more direct means the findings of others that NK and ADCC effectors reside within the sheep rosetting population. Further experiments were performed with Ab in the absence of C. Ab 9.6 was able to partially block CTL and NK activities but not ADCC effectors. Ab OKM1 was unable to block NK or ADCC activities, despite its ability in the presence of C to ablate the majority of NK and ADCC lytic activity. Ab 9.3 was capable of blocking CTL activity but not NK or ADCC activity. Treatment with Ab 10.2 had no blocking activity against CTL, NK, or ADCC effectors. In sum, these results indicate that NK and ADCC effectors express, at least in part, differentiation antigens recognized by 3 monoclonal Ab to T lymphocytes, thus suggesting that some of these effectors may derive from a T cell origin. Although NK and ADCC effectors were identical based on cell surface phenotype, Ab blocking experiments could distinguish these activities.