Functional analysis of human T cell subsets defined by monoclonal antibodies. II. Collaborative T-T interactions in the generation of TNP-altered-self-reactive cytotoxic T lymphocytes.

In previous reports we have demonstrated that human T cells, responding to soluble and alloantigens, release helper factor(s) that amplify primary in vitro hapten-altered-self-reactive CTL responses. In the present studies, we have employed complement-fixing monoclonal antibodies (OKT4 and OKT8) that recognize functionally distinct human T cell subsets to investigate the role of T-T interaction in the generation of these killer cells. In all experiments, purified OKT4+ responder T cells were deficient in cytotoxic activity, whereas responder populations containing OKT8+ T cells generated substantial cytotoxicity; demonstrating that TNP-altered-self-reactive CTL precursors are contained within the OKT8+ T cell subset. Further, optimal cytotoxic responses were obtained from responder populations containing both OKT4+ and OKT8+ T cells, suggesting that cooperative interaction between these subsets may result in an amplification of killer cell activity. This interpretation was supported by the following observations: (1) the amplifying effect of soluble antigen required the presence of both OKT4+ and OKT8+ responders; (2) during MLC, OKT4+ but not OKT8+ responder T cells generate helper factor(s) that amplify TNP-altered-self-reactive CTL responses; (3) helper factor(s) bypass the requirement for direct OKT4-OKT8 T cell interaction, triggering a CTL response that is proportional to the percentage of OKT8+ T cells present within the responder population. In additional studies, we determined that the TNP-altered-self-reactive effector CTL maintain the OKT3+, OKT4-, OKT8+ surface phenotype displayed by the CTL precursor.