[Is permanent survival of kidney allograft receivers in weak histo-incompatible combinations dependent on...

To study the immunological status of indefinitely surviving recipients of histocompatible (minor histoincompatible) allografts we transplanted Fi or (Fi x LEW)F1-kidneys to LEW-rats. At the same time bilateral nephrectomy was performed. To examine the cellular immune response we carried out local GvHR, microcytotoxicity assay and allorosette-formation test with recipient cells. We also studied lymphocytotoxins in the serum of recipients. To detect a blocking serum factor we used allorosette-formation inhibition test and microcytotoxicity assay. A blocking serum factor could not be found. In spite of stimulation with donor specific skin graft the cellular immune response of prolonged surviving recipients was inhibited. Our results suggest that prolonged survival of minor histoincompatible renal allograft recipients was caused by suppression of cellular immune response.