Thyroid transplantation developing autoimmune thyroiditis following thymectomy and irradiation.

Post-irradiation transplantation of normal thyroids under the renal capsule of syngenetic thymectomized and irradiated (Tx-X) rats leads to the development of thyroiditis in the ectopic grafted thyroids. A close correlation was observed between the extent of the lesions in the grafted and recipient's own thyroid. The histopathology of both grafted and recipient thyroid was similar and was characterized by infiltration with mononuclear cells together with some plasma cells. Conversely, grafting of affected thyroids from Tx-X rats to normal animals resulted in the regression of the lesion in the graft and no evidence thyroiditis was observed in either the graft or the recipient's thyroid when these were examined 60 days post-grafting. Thyroids derived from normal animals grafted to syngenetic normal rats were found to remain healthy and intact over a 60-day period. In contrast to normal animals, Tx-X rats were unable to reject totally in transplanted allogeneic thyroids by 28 days post-grafting, suggesting that some impairment of cell-mediated immunity follows this treatment. These findings indicate that the pathological change occurring in the thyroid gland of Tx-X rats is not attributable to the local effect of irradiation of the thyroids and adds further support to the concept that the process is immunologically mediated by thyroid-specific circulating components in the absence of normal immune regulatory function.