The inability of thyroid allografts to induce self-tolerance of organ-specific antigens in foetal lambs.

Foetal lambs in the eighth week of gestation were submitted to thyroidectomy followed by the immediate implantation of a thyroid allograft from a donor of similar age. Excised thyroid glands were transplanted to nude mice and maintained there for approximately 2 months, after which they were re-implanted in the original donor. Some foetuses also received second allografts of thyroid tissue from the original donors at this time. Several weeks later, foetuses were killed to permit histological examination of the original thyroid allografts and of subsequent autografts and allografts. Examination revealed heavy lymphocytic infiltration, interpreted as autoimmune thyroiditis, in reimplanted autografts. Thyroid allografts which had been transferred in the eighth week occasionally showed limited areas of lymphocytic infiltration but their most notable feature was a highly abnormal follicular morphology. Whilst these primary allografts had not been rejected, second thyroid allografts from the same donors were all rapidly destroyed. The failure of foetal lambs which had experienced thyroidectomy and receipt of a thyroid allograft to acquire self-tolerance to thyroid tissue was attributed to the inadequacy of thyroid-specific antigens to achieve this when presented exclusively on allogeneic thyroid cells.