B cells in thymomas.

Although previous studies demonstrated thymoma-associated lymphocytes to be T cells, six thymomas were identified with germinal centers (GC) inside the tumor capsule. Three were mixed lymphocytic and epithelial thymomas. These tumors contained GC interspersed throughout and were not associated with myasthenia gravis (MG) or with GC in adjacent thymus. Three other tumors were lymphocytic thymomas with subcapsular GC. These thymomas occurred in MG patients and were associated with GC in adjacent non-neoplastic thymus. Immunoperoxidase studies using antibodies LN1, LN2, and L26 confirmed the presence of B cells in thymomas, particularly those with germinal centers. The presence of B cells in certain thymomas must be considered when studying the association of Epstein-Barr virus with thymic tumors. Germinal centers in a thymoma are not necessarily associated with myasthenia gravis.