Immune responses to ER stress have been closely related to the pathogenesis of autoimmune diseases. Using an immunoprecipitation assay, 24 (7.1%) of 336 MG serum samples immunoprecipitated a 90-kDa protein from the muscle cellular extracts, but none of the disease or healthy control sera. The 90-kDa protein was affinity-purified and found to match to ER chaperon GRP94 by matrix-assisted laser desorption/ionization-time of flight mass spectroscopy analysis. The frequency of associated autoimmune diseases was much higher in the anti-GRP94-positive than the -negative patients (71% versus 11%, p<0.001). Autoimmunity to ER chaperone GRP94 is associated with a subset of MG patients who have additional autoimmune diseases.
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