THYMOMAS EXPRESS EPITOPES SHARED BY THE RYANODINE RECEPTOR

Myasthenia gravis (MG) patients with thymoma have antibodies against r yanodine receptor (RyR) of skeletal and heart muscle. In this study, t hymomas were examined for reactivity with a panel of polyclonal rabbit antibodies against various short peptides of RyR. An antibody against peptide C2 in the transmembrane region of RyR stained thymoma epithel ial cells in cryosections of 17/23 thymomas, and detected a 4O-kDa pep tide in Western blotting of a thymoma membrane fraction. The other RyR antibodies did not react with thymoma tissue. The anti-C2 RyR antibod y did not react with normal thymus, tonsil or carcinoma of colon. The results strongly indicate that epithelial thymoma cells express an epi tope shared by the transmembrane region of skeletal and cardiac muscle RyR.