Studies on the radioreceptor assay of TSH: the properties of TSH-binding inhibitor immunoglobulins (TBII) in patients with Graves' disease (author's transl)

In the radioreceptor assay system for TSH, serum immunoglobulin G (IgG) from some patients with Graves' disease has been shown to inhibit the binding of labelled TSH to its receptor sites. In order to clarify the properties of these TSH-binding inhibitor immunoglobulins (TBII) in patients with Graves' disease, TBII were measured in sera from 31 untreated and 51 131I-treated patients, and their relation to clinical and laboratory findings was studied. TBII were detected in 18 (60%) out of 31 patients with untreated Graves' disease. TBII levels in these patients correlated well with thyroidal 99mTc uptake at 30 min and also with the grade of epithelial hyperplasia of thyroid follicles. There was no significant correlation between TBII and serum T3, serum T4, free T4 index, antibody titers against thyroglobulin and microsomes, or association of exophthalmos. There were many patients with Graves' disease whose sera contained high TBII levels but no detectable bioassayable thyroid-stimulating activity (LATS), and in these patients a close correlation was observed between serum levels of TBII and bioassayable LATS-protector activity. In patients with Graves' disease who had been treated by 131I from 5 to 17 years before, the incidence of TBII was very low at 20% (10/51). All except two cases having TBII were found to be still thyrotoxic. Thus, TBII were detected in 8 out of 10 thyrotoxic patients and in only 2 out of 18 euthyroid and none of 23 hypothyroid patients. These findings suggest that TBII in patients with Graves' disease were in close association with human thyroid stimulating activity, and that TBII might be useful as an indicator for checking the effectiveness of the treatment.