Epithelial cells and macrophages in myasthenia gravis thymus culture.

Monolayer culture of thymic nonlymphoid cells derived from female patients with myasthenia gravis (MG) and individuals who underwent heart surgery was established to investigate the cellular composition of the thymic microenvironment and the interaction of nonlymphoid cells with autologous thymocytes. Thymic epithelial cells were identified by immunoperoxidase staining using monoclonal antibodies (mAbs) specific for cytokeratin and MR6 and MR19 antigens expressed on cortical and medullary epithelial cells, respectively. Macrophages were characterized by determination of alpha-naphthyl acetate esterase activity and detection of M1 antigen by mAb. It was demonstrated that in MG thymus cultures the number of cortical MR6+ epithelial cells is significantly reduced, and the ability of the remaining MR6+ cells to bind autologous thymocytes is markedly affected. On the other hand, the number of macrophages and the interaction of those cells with thymocytes were similar in MG and control thymus cultures. Since MR6+ epithelial cells are numerically and functionally affected in MG, maturational events of T cells occurring in the inner cortex may be altered. The mechanisms underlying the induction and expansion of T helper clones in MG are discussed.