Measurement of thyroid cell surface antibodies by radioassay using human cultured thyroid cells

The present report describes a sensitive and quantitative binding radioassay for measurement of thyroid cell surface antibodies (TCSAb). Enzyme-dispersed thyroid cells from surgical specimens of human normal thyroid tissue were used after 7 days of culture. 125l-labelled Graves’ IgG was shown to bind to cultured thyroid cells. The binding was time- and temperature-dependent and increased linearly with the number of thyroid cells. Evidence for specificity was provided by the lack of binding of radioiodinated Graves’ IgG to human fibroblasts and by the negligible binding of 125l-labelled normal IgG to thyroid cells. A dose-dependent inhibition of binding of 125l-labelled Graves’ IgG to thyroid cells was produced by the addition of graded amounts of the unlabelled original Graves’ IgG preparation, but not by normal IgG. Assays for TCSAb were performed on IgG preparations from patients with and without thyroid autoimmune disorders using the original Graves’ IgG preparation as reference stadard. Results were expressed in terms of arbitrary units/100 μg IgG, 1 unit corresponding to the minimum amount of the standard IgG producing a significant inhibition of binding. Negative tests were found in most normal subjects (15/18) while low TCSAb levels (≤1.8 U/100 jug μG) were detected in 3 cases. I ncreased TCSAb levels were found in the majority of the patients with Graves’ disease (14/21), in most of the patients with idiopathic myxedema (9/10) and in all of those with Hashimoto’s thyroiditis (10/10). © 1981, Italian Society of Endocrinology (SIE). All rights reserved.