Thyrotropin Receptor T Cell Epitopes in Autoimmune Thyroid Disease

The human TSH receptor represents the primary target of thyroid-stimulating immunoglobulins responsible for the hyperthyroidism of Graves’ disease. In the present series of investigations, the distribution of T cell epitopes has been mapped using synthetic peptides spanning the entire extracellular region of the human TSH receptor. In vitro proliferatire responses of the mononuclear cells were measured using flow cytometric analysis of bromodeoxyuridine incorporation into nuclei. In 8 of 11 samples from patients with Graves’ disease, at least one (and up to 9) regions of the human TSH receptor induced proliferation, with the mean stimulation index being 39.8 ± 47.3. No single universal stimulatory peptide was identified. In contrast, stimulation was not observed in three control subjects, while one control subject showed minimal stimulation (index of 5.7) to peptides encompassing a limited area (amino acids 31-65). The immunodominant epitope of patients with recent-onset Graves’ disease was localized between amino acids 271 and 365, whereas the immunodominant epitope of patients with disease duration greater than 1 year localized between amino acids 91 and 215. We conclude that the bromodeoxyuridine incorporation method is a useful and important tool for detecting antigen-induced lymphocyte proliferation. The TSH receptor-specific T cells from different Graves’ disease patients recognize variable distinct sites within the extracellular region of the TSH receptor, and the immunodominant epitope apparently shifts toward the N-terminus of the receptor protein during the course of treated Graves’ disease.