Antipeptide antibody specific for the N-terminal of soluble immune response suppressor neutralizes concanavalin A and IFN-induced suppressor cell activity in an in vitro cytotoxic T lymphocyte response.

Soluble immune response suppressor (SIRS) is a nonspecific immunosuppressive lymphokine produced by Lyt-2+ lymphocytes after exposure to Con A, IFN-alpha, or IFN-gamma. The N-terminal 21 residues of SIRS have recently been elucidated and antisera specific for this sequence have been raised in rabbits by using a synthetic peptide coupled to an immunogenic carrier protein. In a series of experiments, we have established that this antiserum blocks the suppressive activity of Con A- or IFN-activated suppressor cells. These data establish that Con A- or IFN-activated suppressor cells exert some or all of their suppressive effects via SIRS. Further studies show that SIRS acts primarily during the induction of CTL and not at the effector phase. Last, we show that SIRS is not involved in the radiation-resistant Ag-specific suppressor cell circuit that can be induced during the in vitro MLR.