Direct and quantitative measurement by immunoprecipitation assay of anti-thyrotrophin receptor antibodies in sera of patients with Graves' disease.

The presence of anti-TSH receptor antibodies in the sera of 32 patients with untreated Graves' disease, 21 patients with euthyroid autonomous multinodular goitre, nine patients with Hashimoto's disease and 22 normal controls, was investigated by means of a direct and quantitative immunoprecipitation assay (IPA). A comparison was made between the IPA anti-TSH receptor antibody titres, the thyrotrophin-binding inhibitor immunoglobulins (TBII) index determined by radio-receptor assay and the presence of circulating immune complexes (CIC); no correlation was found. Twenty-six (81%) of the 32 untreated patients with Graves' disease were IPA-positive; 16 (50%) had a positive TBII index. None of the patients with euthyroid autonomous multinodular goitre and none of the normal controls were IPA-positive and their TBII index was normal in all cases. Of the nine patients with Hashimoto's disease seven were IPA-positive and three had a positive TBII index. Of ten patients with Graves' disease still in remission none was IPA-positive and their TBII index was normal. Of 18 patients who relapsed after treatment, 13 were IPA-positive and only five had a positive TBII index. In seven patients with Graves' disease studied serially, anti-TSH receptor antibodies remained present in the sera of four, although the TBII indices normalized. For the five patients who relapsed, a rise in the anti-TSH receptor antibody titre at the time of the relapse was observed. It is concluded that not all anti-TSH receptor antibodies cause TSH-binding inhibition in the radio-receptor assay, and further evidence has been obtained that anti-TSH receptor antibodies are the cause of the hyperfunctioning of the thyroid gland in Graves' disease.