Characteristics of the second-set kidney allograft reactions in rats

Unlike skin allografts in rats, accelerated rejection of second-set kidney allografts was a rare occurrence. Host reactivity was generally suppressed as a consequence of first-set kidney rejection, resulting in prolonged survival of a second-set kidney bearing the same alloantigens. Three variables with potentially important clinical implications were critical for induction of extended survival of the second kidneys: (1) Longer first-set kidney retention or sensitization periods promoted prolonged second-set allograft survival; the longer the period (tested up to 50 days), the greater was the observed immunosuppression. (2) Shorter intervals between first set removal and second-set grafting greatly prolonged second-set survival times; the shorter the interval, the greater the immunosuppressive effect. The optimal timing for facilitation of second kidney survival may be assumed as the time of first kidney removal. (3) Lesser or weaker histoincompatibility of the second kidney clearly promoted prolonged or indefinite survival. Thus, the second kidney from semiallogeneic F1 hybrids survived far longer than fully allogeneic parental kidneys. Prolongation of second-set F1 kidney survival could be achieved under less strict conditions. Spleen lymphocytes from second kidney recipients showed suppressed alloreactivity in the popliteal lymph node graft-versus-host (GVH) assay. Prolonged survival of repeated renal allografts is attributable to intervention of an active immunoblocking process rather than acquired tolerance.