Difference in species specificity of TSH receptor antibodies in Graves' disease and Hashimoto's thyroiditis

TSH receptor antibodies have been detected in the sera of patients with Graves' disease (GD) and Hashimoto's thyroiditis (HT). Since non-human thyroid tissue fractions or cells are used in the majority of assays, the species specificity of TSH receptor antibodies in GD or HT could be important. The species specificity was evaluated by means of an immunoprecipitation assay (IPA) using Triton X-100 solubilized TSH receptors prepared from human, porcine and rat thyroid as well as guinea pig fat cells (GPFC). In each assay the majority (4 or 5) of the 6 patients with GD were IPA-positive. In contrast, 9 out of 11 patients (82%) with HT had a positive human and rat IPA, while only 3 out of 11 (27% p less than 0.05) sera were positive in the porcine and GPFC assays. Conclusions: no species specificity of TSH receptor antibodies was detected for patients with GD; a selective species specificity for human and rat TSH receptors was found for HT sera. This suggests that TSH receptor antibodies in HT either recognize different determinants on the receptor than the antibodies in GD or are of lower affinity. Furthermore, the use of porcine thyroid tissue or GPFC may lead to an underestimation of the presence and level of TSH receptor antibodies in patients with HT.