Feedback suppression of the immune response in vivo: III. Lyt-1+ B cells are suppressor-inducer cells

We previously demonstrated that injection of a high dose (4 × 109) of sheep erythrocytes (SRBC) into C57L/6 mice results in the generation of splenic B cells (plastic nonadherent, Thy-1− and Ig+) which, when transferred to normal syngeneic recipients, subsequently induce antigenspecific suppressor T cells to suppress the recipient's plaque-forming cell (PFC) responses to SRBC. In the present study we characterized the suppressor-inducer B cells phenotypically. Cytotoxic treatment of the donor's immune spleen cells with anti-Lyt-1 antibody plus complement (C′) but not with anti-Lyt-2 antibody plus C′, relieved the suppression of PFC responses in recipients. The FcRr+ population separated by EA-rosette formation showed enriched suppressorinducing activity, whereas the FcRr− population showed no activity. Our findings, taken together with the previous ones, suggest that suppressor-inducer cells are Thy-1−, Lyt-1+, Lyt-2−, FcRr+, and Ig+.