THE ANTIBODIES CAUSING THYROID-STIMULATING HORMONE-BINDING INHIBITION(TSH-BI) ARE NOT RESPONSIBLE FOR THE SPECIFIC-INHIBITION OF GONADAL STEROIDOGENESIS BY GRAVES SERA

Graves' disease is attributed to the presence of autoantibodies with a gonist activity which interact with the TSH receptor causing thyroid h yperstimulation and hyperthyroidism. The degree of TSH-binding inhibit ion (TSH-BI) caused by a Graves' serum in a TSH radioligand receptor a ssay is considered to be an index of the prevalence of anti-TSH recept or autoantibodies in that serum. We have previously shown that the spe cific inhibition by Graves' serum of hCG-stimulated steroidogenesis by Leydig cells was at a site distal to receptor binding and second mess enger activation. In this report, we have investigated whether the eff ect of Graves' serum upon Leydig cells is a property of the constituti ve antibodies. Immunoglobulin-enriched fractions were obtained from Gr aves' and normal sera using three increasingly rigorous procedures; am monium sulphate precipitation, caprylic acid treatment and Protein A o r G-affinity purification. The TSH-BI was determined for untreated and extracted sera in two radioreceptor assays developed for use with ser um, one using human thyroid membranes and the other using HeLa cells t ransfected with the human TSH receptor, and the results were compared with effects in the Leydig cell steroidogenesis bioassay. The specific inhibition of hCG-stimulated Leydig cell steroidogenesis by Graves' s era was not retained in the antibody fraction causing TSH-BI. Thus, th e inhibitory factor appears not to be an antibody and we are now attem pting to purify and identify the responsible factor from Graves' serum .