ABSTRACT
We have previously demonstrated that incubation of splenic lymphocytes from an unimmunized mouse with IL-2 IFN-α or γ resulted in the development of a population of nonspecific regulatory cells (Ts). These cells were shown to block the ability of lymphocytes to generate mixed-lymphocyte responses in vitro. In the studies reported here, we have investigated the cell populations involved in this phenomenon. The Ts cells develop over a period of 2 or more days in culture with IL-2. Antibody to the 55-kD chain of the IL-2 receptor blocks Ts generation while stimulating T-cell proliferation. Although NK activity develops in these cultures, the mechanism of suppression is not via a lytic mechanism. Generation of the Ts in culture in the presence of IL-2 requires adherent cells as well as CD8+ cells. In studies using Con-A as the stimulus, the generation of Ts clearly requires both CD4+ T cells as well as CD8+ T cells and adherent cells. The evidence suggests that the CD4+ T cells serve as a source of IL-2 that is necessary in the activation of the IL-2-responsive CD8+, nonspecific Ts.