Graft survival is prolonged by pretransplant transfusion of the graft recipient. It has been postulated that graft rejection is associated with Th1-like cytokines. We tested whether transfusion shifts cytokine production from a Th1-type (gamma-IFN production) to a Th2-type (IL-4 production). Transfusion prolonged cardiac allograft (C3H/HeN donor to a C57BL/6 recipient) survival (10.4+/-0.5 versus 7.2+/-0.2 days for controls, P<0.0001). Splenocyte cultures from nontransfused recipients produced supernatant IFN-gamma concentrations of 13.4+/-1.4 ng/ml upon anti-CD3 stimulation; the same cells produced 32.3+/-3.5 pg/ml IL-4 stimulated with Con A. Spleen cells from transfused animals did not produce gamma-IFN with or without stimulation; (P<0.0001) and produced 21.5+/-3.2 pg/ml IL-4 without stimulation (P<0.0001 compared with controls). C57BL/6 CD8+ lymphocytes isolated from rejected C3H grafts were adoptively transferred (6.7+/-1x10(6)/animal) to pretransfused, C57BL/6 recipients of a C3H graft. Graft survival for these recipients was 7.8+/-0.3 days compared with 10.4+/-0.5 days for recipients pretreated with transfusion only (P<0.005). Transcripts of the gamma-IFN gene were present in unmodified grafts but not in the grafts from transfused recipients given the CD8 cells. In conclusion, transfusion downregulated gamma-IFN production and up-regulated IL-4 production and slowed (but did not abrogate) rejection; CD8 graft-infiltrating cells given adoptively restored normal rejection but not IFN-gamma. Further studies are needed to elucidate the role of cytokines in cardiac allograft rejection.