Purification and characterization of Yersinia enterocolitica envelope proteins which induce antibodies that react with human thyrotropin receptor

Graves' disease is an autoimmune disease mediated by autoantibodies to the thyrotropin receptor (TSHR). Several studies have suggested that the development of Graves' disease may be linked to infection with the enteric pathogen Yersinia enterocolitica. Using the purified recombinant extracellular domain of human TSHR (ETSHR), we have recently shown that immunization of mice with Y. enterocolitica results in the production of antibodies capable of reacting with the ETSHR. In this study, we identify two low molecular weight (5.5 kDa and 8 kDa) envelope proteins of Yersinia containing epitopes that are crossreactive with the TSHR. Identification of these crossreactive envelope proteins was achieved by Western blotting using affinity-purified anti-Y. enterocolitica antibodies that specifically react with the TSHR and, conversely, for envelope proteins of Yersinia. Confirmation that these Yersinia proteins contained crossreactive epitopes with the ETSHR was obtained by immunizing mice with partially purified envelope proteins, which resulted in the production of Abs that recognized the ETSHR. Further, some of the cross-reactive envelope proteins were purified with SDS-PAGE and HPLC. The crossreactive envelope proteins were shown to be chromosomally encoded, exposed on the surface of bacteria, and produced by virulent as well as avirulent strains of Yersinia (Y. pestis, Y. pseudotuberculosis, Y. enterocolitica VW⁺, and Y. enterocolitica VW^-). These results identify for the first time the Yersinia envelope proteins that are crossreactive with the ETSHR. Availability of these proteins will allow future studies to determine whether patients with Graves' disease have a unique immune response against these proteins when compared with healthy individuals.