Thyroid-Stimulating Activity in the Serum of Rabbits Immunized with Thyroid Microsomes

Abstract

Rabbits were immunized with human thyroid microsomes in an effort to determine if thyroid-stimulating activity would develop in their serum. Twenty-four of 32 rabbits so immunized developed significant amounts of thyroid-stimulating activity, while only 1 of 8 control animals, immunized with liver or adrenal microsomes, had such a response. Peak thyroidstimulating activity appeared in most instances one week after the course of immunization; it usually declined thereafter. Repeated courses of immunization resulted in the appearance in serum of larger amounts of thyroid-stimulating activity. Active rabbit serums generally caused a murine blood ¹³¹I response which was slightly higher at 2 than at 8 hr and was intermediate in time course between thyrotropin and the longacting thyroid stimulator. The serum of thyroidimmunized rabbits showed an elevated PBI and thyroxine, balanced by markedly reduced resin uptake of ¹³¹I-triiodothyronine (T₃). Thyroidal ¹³¹I uptake and serum PB¹³¹I and conversion ratio were unaffected by immunization. The serum of thyroid-immunized rabbits contained precipitating and hemagglutinating antibodies against human thyroglobulin and antibodies which fixed to both colloid and cytoplasm of thyroid tissue sections. These serums also contained complement-fixing antibodies against human thyroid microsomes, but serums from liverimmunized rabbits also caused complementfixation. The immunofluorescent reaction in thyroid cytoplasm was also nonspecific. It is concluded that serum thyroid-stimulating activity does develop, along with various antithyroid antibodies, in rabbits immunized with human thyroid microsomes; the affected rabbits appear to remain euthyroid.