Thymic expression of the main immunogenic region of titin in thymomatous myasthenia gravis.

Antititin antibody occurs in the serum of myasthenia gravis (MG) patients with thymoma (MGT), and is a diagnostic marker for the disease. The mechanism that triggers MGT development is, however, unclear. This study evaluated the role of the main immunogenic region (MIR) of titin in MGT pathogenesis. Titin MIR antiserum (antibody titre 1:16) was obtained and an in situ immunohistochemical study of thymomatous tissue samples was performed. Strong immunostaining for titin MIR was observed on epithelial cell membranes in MGT patients, and the degree of immunostaining was directly proportional to the number of epithelial cells in thymomatous tissue. Serum antititin antibody levels were closely related to titin MIR levels in thymoma cells; however, titin MIR levels did not appear to be related to MG severity. Antititin antibody may be a good surrogate marker for thymoma but is probably not involved in the pathogenesis of MGT.