HETEROGENEITY OF TSH RECEPTOR-BINDING ANTIBODIES IN HASHIMOTOS-THYROIDITIS AND GRAVES-DISEASE

The possible heterogeneity of TSH receptor antibodies in Graves' disease (GD) and Hashimoto's thyroiditis (HT) with respect to the binding site on the receptor and corresponding biological effect was studied. Employing an immunoprecipitation assay (IPA), the sera of 80% of the patients with GD (24 out of 30) and 76% of the patients with HT (16 out of 21) contained TSH receptor-binding antibodies, compared to none of the sera from 17 normal volunteers and 8 patients with non-toxic multinodular goiter. TSH inhibited immunoprecipitation by GD and HT sera. In HT sera (n = 9), but not in GD sera (n = 5), heterogeneity of the TSH-induced inhibition was observed. Four HT sera showed complete inhibition of immunoprecipitation at a saturating concentration (19.8 nM) of TSH. Five HT sera, like the 5 GD sera, showed partial inhibition of immunoprecipitation by 19.8 nM TSH. Thyroid stimulating immunoglobulins (TSI) were found in four of the five GD sera and in only one of the nine HT sera. The results suggest that different subpopulations of TSH receptor antibodies, characterized by other receptor binding sites or different affinities, are associated with autoimmune thyroid disease.