Establishment and Characterization of an Antihuman Thyrotropin (TSH) Receptor-Specific CD4 + T Cell Line from a Patient with Graves' Disease: Evidence for Multiple T Cell Epitopes on the TSH Receptor Including the Transmembrane Domain

From the peripheral lymphocytes of a patient with Graves' disease, we established a T cell line using its reaction to a pool of 49 synthetic peptides corresponding to the entire human thyrotropin receptor (TSHR) sequence. This T cell line showed a specific response to the pool of peptides in a microproliferation assay (stimulation index: 4.8). Flow cytometry analysis revealed that the cell surface markers were CD4⁺CD8^-, T cell receptor (TcR) αβ⁺, and TcRγδ^-. To investigate T cell epitopes on TSHR, the 49 synthetic peptides were divided into 6 groups, and the responses of the T cell line to each group were tested. The T cell line reacted well against three groups: the N-terminal (amino acids 31-169) and C-terminal (338-420) regions of the extracellular domain and the N-terminal half (441-661) of the transmembrane domain of the receptor. This suggests a multiplicity of T cell epitopes on the TSHR, and was further supported by analysis of TcR gene expression in the cell line that showed the expression of 5 Vα genes: Vα-1, 2, 10, 20, and w25. In conclusion, the results of the present study indicated multiple T cell epitopes on the TSHR molecule including the transmembrane domain.