The effect of xenotransplantation of human thyroid tissue following radioactive iodine-induced thyroid ablation on thyroid function in the nude mouse.

We have attempted to determine whether xenotransplanted human thyroid tissue into nude mice would act as a physiological substitute for the mouse thyroid gland after the mice had been rendered hypothyroid, using radioactive iodine (131I). The dosage of 0.2 millicuries of 131I was given to each mouse. The xenotransplantations of human thyroid tissue, i.e., normal, Graves' and nontoxic multinodular goitre, were carried out three weeks after radioactive ablation. The values of TSH in all mice rose to high levels (71 +/- 15.6 ng/ml, +/- SD) by three weeks after 131I administration. The TSH values in the mice declined rapidly and reached normal levels by 3-5 weeks after xenotransplantation. In addition, the serum T4 values were generally in the euthyroid range by 3-6 weeks after xenotransplantation. There were no marked differences in the changes of serum T4 and TSH when the three groups were compared. These results indicated that the xenografted human thyroid tissue permitted a return to a normal feedback system as reflected by normal serum TSH and T4 values in the animals. The Graves' thyroid tissue reverted to normal physiological function when removed from its human (abnormal) immune environment, signifying that Graves' thyrocytes are mere passive captives to immune events. This model should prove to be useful in the study of human thyroid physiology and pathophysiology.