HUMAN MEMORY T CELL ACTIVATION EFFECTS OF MONOCLONAL ANTIBODIES DIRECTED AT INTERLEUKIN-2, RECEPTORS FOR INTERLEUKIN-2, OR INTERFERON-γ

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Abstract
Several polyclonal T cell activators can induce the differentiation of quiescent antigen-specific memory T cells (memory cells) into specific secondary cytotoxic T cells, in the absence of the original priming alloantigens. Such activation represents a potential pathway by which immunologically nonspecific signals can elicit specific antiallograft immunity. We therefore investigated the molecular basis for antigen-independent activation of memory cells using as probes recombinant interleukin-2 and monoclonal antibodies directed at IL-2, IL-2 receptors (IL-2R), or interferon-.gamma. (IFN-.gamma.). Antigen-specific memory cells, generated in human longterm-primary mixed lymphocyte cultures, were induced to proliferate, exhibit antigen specific secondary cytolytic activity, or produce IFN-.gamma. by recombinant DNA human IL-2 produced in E. coli. Monoclonal antibodies directed at the IL-2R or at IL-2 inhibited IL-2-mediated proliferation, cytolytic activity, or production of IFN-.gamma.. Monoclonal antibodies directed at IFN-.gamma. did not inhibit alloantigen or IL-2 mediated activation of memory cells. Our findings suggest that successful interaction between IL-2 and its receptor expressed on memory cells represents a plausible pathway by which an immunologically nonspecific signal might elicit specific antiallograft immunity. Moreover, therapeutic strategies that include antibodies directed at the IL-2 and/or IL-2R and not antibodies directed at IFN-.gamma. will inhibit IL-2-dependent alloimmunity.