Proliferative responses of peripheral blood mononuclear cells from patients with Graves' disease to synthetic peptides epitopes of human thyrotropin receptor.

In Graves' disease thyrotropin receptor (TSH-R) autoantibodies cause hyperthyroidism. Production of TSH-R autoantibodies must be controlled by specific T cells. In this study we investigated T cell responses to 33 peptides corresponding to the sequence of the extracellular domain of human TSH-R. Peripheral blood mononuclear cells (PBMC) from 12 patients with Graves' disease and 9 healthy subjects were cultured with peptides for 3 days. The proliferative responses of PBMC were analyzed by measurement of [3H]thymidine incorporation. A stimulation index (SI; mean cpm in the presence of peptide/mean cpm in culture medium alone) of more than 3 was considered a positive response. When PBMC were stimulated with a pool containing all synthesized peptides, the mean SI of patients was significantly higher than that of controls (4.50 +/- 3.95 vs. 1.44 +/- 0.60; p < 0.05). When PBMC were cultured with individual peptides, PBMC from patients responded predominantly to two peptides, corresponding to sequence segments 152-157 (5 patients) and 207-222 (4 patients). No PBMC from controls responded to these two peptides. There was no clear correlation between the HLA-DR or HLA-DQ genotype and the stimulatory sequence segments. These results suggest that (a) TSH-R-specific T cells are present in peripheral blood of patients with Graves' disease, and (b) sequence segments 152-157 and 207-222 may be T cell epitopes of the human TSH-R in Graves' disease.