Functionally distinct human T cell clones that produce lymphokines with IL-2-like activity

Various functionally distinct human T cell clones derived from in vitro mixed leukocyte cultures are found to secrete lymphokines with detectable Interleukin-2 (IL-2)-like activity upon antigenic stimulation. These lymphokine producing clones are not only dependent on exogenous growth factors provided in the form of crude phytohemagglutinin (PHA)-induced spleen conditioned medium for growth but can themselves be driven to proliferate by their own lymphokines. The induction of lymphokine production appears to be antigen-specific and the lymphokines secreted are believed to contain nonantigen and nonspecies specific IL-2-like activity. We show here that IL-2-like lymphokines are produced by a subset of T lymphocyte clones, i.e., the help-independent cytotoxic T cells clones that have the capacity to proliferate to, as well as to lyse, the original sensitizing cells. In addition, other T cell clones capable of producing active lymphocytes include those clones that have the T helper cell characteristics, i.e., can undergo antigen-induced proliferation but are not cytotoxic; in the presence of lectin (PHA), however, some helper T cells (Th) but not others, can express lectin-dependent cell-mediated lysis. Finally, yet another subset of T lymphocytes, the help-dependent cytotoxic T cell clones that cannot proliferate to antigenic stimulation, was found to produce no detectable IL-2-like activity.