Regulation of the immune response XII. Targets for suppressor cell activity in on in vitro cell-mediated immune response

Irradiated CBA anti-DBA/2 cells, produced in a CBA anti-DBA/2 mixed lymphocyte culture, inhibited a second in vitro CBA anti-DBA/2 cytotoxic cell response. Increasing the numbers of CBA responder cells in the second culture decreased suppression, whereas increasing the number of irradiated DBA/2 stimulator cells led to a lesser reduction in suppression. Preincubation of irradiated CBA anti-DBA/2 suppressor cells with CBA rcsponder cells gave a twofold greater suppression than preincubation of CBA anti-DBA/2 suppressor cells with stimulator cells. The inhibitory effect of CBA anti-DBA/2 suppressor cells on CBA responder cells was sensitive to alkaline storage whereas neither the interference with DBA/2 stimulator cell immunogenicity nor antistimulator cell cytotoxicity itself was sensitive to storage. The antiresponder mechanism for suppression predominated over the antistimulator effect when all three cell types (responder, stimulator, and suppressor) are put into culture simultaneously. Additional CBA responder cells corrected the defect in suppressed second cultures, caused by CBA anti-DBA/2 suppressor cells, to a greater extent than additional irradiated DBA/2 stimulator cells. We conclude from these experiments that these suppressor cells exert a major effect on responder cells and a minor effect on stimulator cells.