Antigen Pretreatment and Mechanisms of the Resulting Temporary Tolerance. ∗

Summary

Three factors were studied in animals showing prolonged homograft survival as a result of donor antigen pretreatment. The possible contribution of a grafts-host reaction to prolonged homograft survival, wasting, or lymphoid depletion was eliminated by using irradiated donor blood for conditioning, and irradiated transplants, and finding no significant change in homograft survival or in degree of lymphoid depletion. Any role the thymus may play as a source of lymphoid repopulation when conditioned animals reject homografts was ruled out by finding no increase in homograft survival in animals conditioned and transplanted after thymectomy. The importance of primary vascular contact between conditioned recipient and transplant was shown by the absence of wasting and lymphoid depletion on conditioned animals which receive massive skin homografts, rather than kidney transplants.