In Vitro Generation of Suppressor Cell Activity: Suppression of in vitro Induction of Cell-Mediated Cytotoxicity

Abstract

Abstract It was observed that when normal mouse spleen cells were cultured alone in vitro (precultured) for 3 to 7 days, these cells lost the ability to generate cell-mediated cytotoxicity (CML) during subsequent in vitro sensitization with allogeneic spleen cells, trinitrophenyl (TNP)-modified syngeneic spleen cells, or syngeneic tumor cells. These precultured cells, which were themselves unable to generate CML, were also shown in mixing experiments to suppress, actively, the generation of CML by freshly explanted spleen cells. Suppression occurred at the sensitization phase of CML, and not at the effector level; supernatants from suppressive precultured cells were not suppressive. Suppression was totally abrogated by the treatment of spleen cells with a T cell-specific rabbit anti-mouse brain serum and complement (RαMB + C) either before or after preculturing, suggesting that a T cell was essential both to the generation of suppressor activity and to its expression. Suppressor activity was entirely absent in precultured nylon wool column-nonadherent spleen cells, a T cell-enriched population containing most of the RαMB + C-sensitive cells in the spleen. Precultured nylon column-adherent cells (T cell-depleted) did have suppressive activity, and a mixture of nylon-adherent and nylon-nonadherent cells was as suppressive after preculture as the precultured unseparated spleen. Moreover, the ability of nylon-adherent spleen cells to generate suppressive activity during preculturing was abrogated by treatment with RαMB + C. Thus, the “spontaneous” generation of CML-suppressive activity was dependent upon a limited subpopulation of splenic T cells isolated in the nylon columnadherent fraction. The relationship of these data to a previously described synergy between subpopulations of normal mouse spleen in the generation of CML is discussed, and the findings related to other suppressor systems described in the literature.