Expression of Titin Epitope in Normal Thymus, Thymoma and Thymus Carcinoma

  Objective  To investigate the expression of titin epitope in normal thymus, thymoma, and thymus carcinoma and explore the correlation of titin expression in thymus with the clinical manifestation of myasthenia gravis (MG).

  Methods  Thymoma tissues from four thymoma patients with MG, thymus carcinoma tissue from one patient, hyperplastic thymus tissue from one thymoma patient with MG, and normal thymus tissue from one patient were obtained. Each specimen underwent HE staining and immunohistochemistry staining using anti-cytokeratin (CK) and anti-titin antibodies. Surum anti-titin antibody level of thymoma patients with MG was also examined.

  Results  In MG-associated thymoma, the expression of anti-titin antibody was strongly positive, and its distribution was consistent with that of epithelial cells. However, the lymphocytes and other structures were not stained. In the tissue of thymus carcinoma, the expression of anti-titin antibody was negative. In normal thymus tissue, only the expression of Hassall body was weakly positive, while other structures were not stained. Serum anti-titin antibody was detected in three of the four thymoma patients with MG.

  Conclusions  Titin epitope is expressed only on the epithelial cells in thymoma patients with MG. In normal thymus, titin epitope is expressed only in the area of Hassall bodies. These findings indicate pathogenic change of immune microenvironment in the thymoma patients with MG.