The failure of a combination of thyroid and thymus allografts to prevent the development of autoimmunity in thyroidectomized foetal lambs.

Previous experiments have shown that surgical removal of the thyroid gland from the foetal lamb one third of the way through gestation prevents the development of self tolerance towards thyroid-specific determinants. As a result, self thyroid tissue reintroduced into the foetal lamb after maturation of the immune system is not recognized as self and is subject to autoimmune thyroiditis. Furthermore, the transplantation of a thyroid allograft into a foetal lamb immediately after extirpation of its own gland has been shown not to direct the development of self tolerance to thyroid determinants. In the present experiment, foetal lambs were submitted to removal of the entire thyroid gland and the majority of the thymus gland, at 51-54 days of gestation followed by the immediate implantation of thyroid and thymic allografts. The additional implantation of thymus tissue did not affect the previously observed incapacity of a thyroid allograft to facilitate induction of organ-specific tolerance by the thyroid allograft. It was inferred that any T lymphocytes generated within the thymus graft and tolerant of thyroid-specific determinants had not had the capacity to suppress the activity of autoreactive cells generated in the host's thymus.