Transplantation tolerance in primates after total lymphoid irradiation and allogeneic bone marrow injection. III. Lymphocyte responsiveness and suppressor cell activity.

After total lymphoid irradiation (TLI), allogeneic bone marrow (BM) injection, and organ transplantation in baboons, there is a prolonged period of reduced lymphocyte proliferative responsiveness to polyclonal mitogens and allogeneic lymphocytes. The effect observed is greater with the use of fractionated TLI than after single doses of irradiation. Suppressor cell activity can be demonstrated in vitro in most animals by inhibition of mixed lymphocyte reactivity (MLR) by mitomycin-treated recipient lymphocytes harvested after TLI, with or without allogeneic BM injection, and organ transplantation. Preliminary data suggest the presence of both donor-specific and nondonor-specific suppression, although other interpretations are possible, and suppressor phenomena may not be responsible for the transplantation tolerance observed.