Induction of suppressor cells by donor-specific blood transfusions and heart transplantation in rats.

In the BN/Rij to WAG/Rij rat donor-host combination, a single injection of 1 ml of donor blood 7 days before transplantation leads to permanent acceptance of BN/Rij hearts. In this model of specific unresponsiveness, it was investigated whether suppressor cells were present in the steady-state phase at 5 to 6 weeks after transplantation. Thymocytes, spleen cells, peripheral blood lymphocytes, and lymph node cells from blood-conditioned recipients were adoptively transferred to WAG/Rij recipients irradiated with 450-rad X-rays. BN/Rij heart transplantation was performed after 14 days. It was found that suppressor cells were present in the spleen and thymus of unresponsive recipients but not in the peripheral blood or lymph nodes. Adoptive transfer of 25 x 10(6) spleen cells led to permanent survival of BN/Rij hearts in four of nine cases, whereas transfer of 25 x 10(6) thymocytes always resulted in permanent graft survival. Fractionation of suppressor spleen cells into T and B cell-enriched populations and macrophages revealed that the suppression was mediated by T cells.