The rejection of thyroid allografts in the ovine testis

The survival of thyroid autografts and allografts in the ovine testis has been investigated. Thyroid autografts survived and concentrated iodine 4 weeks after transplantation. Healthy colloid-containing follicles were found in the graft at this time, although no response of the grafts to a thyrotropin releasing hormone (TRH) challenge could be detected and there was no detectable basal thyroxine secretion into testicular venous blood or lymph. Thyroid allografts, however, were effectively rejected within 4 weeks of transplantation and did not concentrate iodine. No healthy tissue in the allografts could be found at 4 weeks after transplantation. Thus, in contrast to rodents and related species, the ovine testis does not appear to be an immunologically privileged site. This suggests that the immune privileged status of the rodent testis is not necessarily a general mammalian characteristic.