Precipitations of thyrotropin receptor-related peptides by immunoglobulin G of patients with Hashimoto's thyroiditis.

In order to study whether specific binding sites for Hashimoto's IgG exist in TSH receptor, we have examined the TSH receptor binding activity of IgG of patients with Hashimoto's thyroiditis using synthetic peptides corresponding to the amino acid sequences in the extracellular domain of human TSH receptor. Eight different peptides were synthesized, radiolabeled and examined by immunoprecipitation assay. Among the peptides studied, peptide (352-378) was significantly precipitated by IgG of patients with Hashimoto's thyroiditis compared with control subjects. Ten out of twenty patients with Hashimoto's thyroiditis showed more precipitations of peptide (352-378) than mean + 2SD of those of control subjects. Peptide (352-378) was precipitated by IgG in a dose dependent manner and the binding of peptide (352-378) to IgG was displaced by the addition of increased amount of cold peptide (352-378). Precipitations of peptide (352-378) positively correlates with both TGHA and MCHA titers. Two out of fourteen patients with Graves' disease, one out of seven patients with subacute thyroiditis and none of eleven patients with thyroid tumor showed more precipitations of peptide (352-378) than mean + 2SD of those of control subjects. These results suggest that one of binding sites for Hashimoto's IgG is present in the amino acid sequence of 352-378 in the extracellular domain of TSH receptor.