Evidence for two types of non-specific suppressor cells activated by the graft-versus-host reaction in mice.

In vitro experiments were carried out to investigate the immunosuppressive efect of different populations of spleen cells obtained from animal experiencing a graft-versus-host reaction (GVHR). To induce the GVHR, parental lymphoid cells were injected into adult F1 hybrid mice. GVHR-activated spleen cells (GVH-sc) taken at different times post-GVHR induction were separated into adherent and non-adherent fractions and treated with anti-theta serum plus complement. The different types of GVH-SC were added to either parental (donor-type) of F1 (host-type) normal spleen cells and cultured with sheep erythrocytes in a modified Marbrook chamber. It was found that both adherent and non-adherent 10-day GVH-SC significantly inhibited the plaque-forming cell response of F1 normal spleen cells but not that of parental normal spleen cells. Significant suppression of the parental response was observed following the addition of 15-day GVH-SC or anti-theta treated adherent and non-adherent 7-day GVH-SC. The results suggest that the non-specific immunosuppressive effect of GVH-SC is mediated by GVHR-activated macrophages and B lymphocytes found in the anti-theta treated adherent and non-adherent fractions of the GVH-SC suspensions respectively.