TSH receptor sequences recognized by CD4+ T cells in Graves' disease patients and healthy controls

Twenty-nine overlapping synthetic peptides, twenty residues long, representing the entire extracellular sequence of the human thyroid stimulating hormone receptor (hTSHr), were used to test the epitope repertoire of CD4+ T lymphocytes from patients with Graves' disease and from healthy subjects. The peptides were used to propagate and test short term CD4+ T cell lines specific for hTSHr epitopes, and to directly test CD8+ depleted, CD4+ enriched peripheral blood lymphocytes. Analysis of the response of short-term CD4+ T cells lines and CD8+ depleted peripheral blood lymphocytes to the individual peptides revealed that 14 of the 15 patients and nine of the ten controls responded to at least one hTSHr peptide. There was no common response pattern, nor any region of the hTSHr sequence that was predominantly recognized. Several peptides were recognized by both patients and controls. These results support the notion that immunological tolerance to hTSHr is due to peripheral tolerance of potentially autoreactive CD4+ T cells, not their clonal deletion. The presence of self-reactive, hTSHr-specific CD4+ T cells in healthy individuals implies that these cells are not permanently anergized, since they can be activated in vitro.