A new mediator (suppressor cell induction factor) activating T cell-mediated suppression: characterization of suppressor cells, kinetics of their generation, and mechanism of their action

Abstract

Human T cells precultured in MLC supernatant (SIF) could suppress responder cells in MLC. SIF-activated cells expressed suppressor effects equally on both autologous and allogeneic responder cells in MLC. The suppression observed was not due to cell crowding, cell death, depletion of nutrients, absorption of IL 2, alternation in the kinetics of MLC response, production of soluble inhibitory factor, or generation of cytotoxic cells. In this system, suppressor cells were generated after 5 days of culture, and Ia-positive cells were required in the induction of suppressor cells. Suppressor cells themselves, however, were characterized as Ia-negative subsets of T cells; they could be derived from both Fc-IgG receptor-positive and -negative subsets of T cells. Suppressor activity of SIF-treated cells on the MLC response was sensitive to mitomycin C treatment. They apparently exerted their suppressor effect on some early phase of the MLC response. This early event was almost complete within 48 hr after the initiation of MLC. The possibility that SIF may be involved in T-T interactions required in the generation of effective suppression is discussed.