Thyrotropin receptor epitopes and their relation to histocompatibility leukocyte antigen-DR molecules in Graves' disease.

Context: Graves' disease (GD) is characterized by autoimmunity to the TSH receptor (TSHR). Objective: We sought to identify T cell epitopes in TSHR that initiate this immune response and their interaction with human histocompatibility leukocyte antigen (HLA) molecules predisposing to GD. Design: We examined the affinity of 31 overlapping peptides spanning the TSHR extracellular domain for binding in vitro to five purified HLA-DR molecules; DRB1*0101 (DR1), DRB1*1501 (DR2), DRB1*0301 (DR3), DRB1*1101 (DR5), and DRB1*0701 (DR7). We scanned the TSHR extracellular domain using a T cell epitope-mapping algorithm, EpiMatrix. We compared these results with clinical studies of GD patients measuring in vitro T cell responses to the peptides. Setting: The study was conducted at a university laboratory. Patients: Patients included 200 serial adult clinic patients with GD. Intervention: There were no interventions. Main Outcome Measurements: Binding affinity of epitopes, predicted affinity, and reported T cell stimulation data were measured. Results: Most peptides bound with intermediate or high affinity to one or more HLA-DR molecule. Peptides binding to HLA-DR3 and HLA-DR5, which predispose to GD, exhibited moderate binding affinities overall, whereas most peptides binding to GD-protective HLA-DR7 bound with high affinity. These differences may relate to T cell selection in the thymus. Binding affinity of peptides correlated strongly with EpiMatrix-predicted affinity for HLA-DRB1* 0101, DRB1*1501, DR3, and DRB1*0701 but not HLA-DR5. Average IC50 values correlated significantly with clinical T cell stimulation data. Conclusions: Three different methods for identifying immunogenic peptides did not provide a uniform picture of important TSHR epitopes. However, peptide 132-150 (GIFNTGLKMFPDLTKVYST) was identified by three methods as an important epitope in GD; the possible importance of peptides 145-163, 158-176, 207-222, 248-263, 272-291, and 343-362 was also identified.