The effect of donor-specific blood transfusion (DST), in combination with pretransplant immunosuppression with deoxyspergualin (DSG), on hamster-to-Wistar rat cardiac xenograft survival was assessed. While DST given on day -6 sensitized the recipients, resulting in hyperacute xenograft rejection, the addition of 5 mg/kg/k/day DSG from the day of transfusion to the day of grafting not only prevented hyperacute rejection but resulted in prolongation of graft survival from 3.4 +/- 0.5 days in untreated controls to 7.0 +/- 0.7 days (P less than 0.01). In contrast, DSG alone as pretransplant immunosuppression had no beneficial effect and rejection occurred in 4.0 +/- 0.7 days. This effect appears to be at least donor species-specific, in the sense that ACI cardiac allograft survival was not prolonged when transplanted into xenotransfused and DSG-treated Wistar recipients. DST alone resulted in marked increase in antibody titers, showing the value of 1:512 or more on transplantation day. On the other hand, combined treatment suppressed the titers to 1:1-1:4 on that day. An adoptive cell transfer system was used to analyze the mechanisms underlying this effect. When sublethally irradiated secondary hosts were transferred with 5 x 10(7) lymph node cells (LNCs) harvested on day 0 from xenotransfused and DSG-treated rats, the test heart xenograft survived longer than the irradiated and nontransferred controls, suggesting the presence of suppressor cells. Further in vitro studies demonstrate that LNCs from DST+DSG-treated rats response less in a mixed lymphocyte reaction to hamster LNCs (41% on day 0 [P less than 0.01]), compared with the controls. In coculture experiments, the LNCs from treated recipients suppressed the response of unmodified Wistar LNCs to hamster LNCs by 76% on day 0 compared with the positive controls (P less than 0.01). On the other hand, the transfer of serum taken from treated rats on day 0 did not lead to prolongation of test heart xenografts in syngeneic naive hosts. These findings suggest that the mechanisms underlying the hyporesponsiveness induced by pretreatment with DST and DSG include the induction of suppressor cells, although a degree of clonal deletion can not be ruled out. The generation of serum suppressor factors seems to have no role in this phenomenon.