Anti-TSH antibodies in Graves' disease and their failure to interact with TSH receptor antibodies

Abstract

Abstract. The occasional occurrence in sera of patients with Graves' disease of negative values in the assay for TSH receptor antibodies led to the discovery of endogenous antibodies to TSH. We examined the sera of approximately 2500 patients with Graves' disease. Eight positive sera were found. The IgG in all 8 sera showed higher binding with both bTSH and porcine TSH (pTSH) than with human TSH (hTSH). This means that autoantibodies to TSH in sera from patients with Graves' disease are rare and often directed towards heterologous bovine and porcine TSH. When hTSH levels were determined in sera of hyperthyroid patients with positive antibodies to hTSH, discrepancies in serum hTSH levels were observed when using different assay methods, i.e. hTSH levels were higher with the double-antibody technique, and lower with immunoradiometric assays. Antibodies in these sera showed higher binding to pTSH-α subunit than to -β subunit. The binding of the two pTSH subunits with antibodies could be displaced by intact bTSH. Neither stimulation in Graves' disease nor blocking in primary hypothyroidism of TSH receptor antibodies interfered with the binding of the anti-TSH antibodies to 125I-labelled pTSH, pTSH-α, and pTSH-β. Consequently, using this type of autoantibodies to TSH we were unable to obtain evidence that the TSH receptor antibodies of patients with Graves' disease was an anti-idiotype antibody against anti-TSH antibodies.