Cell types required for anti-acetylcholine receptor antibody synthesis by cultured thymocytes and blood lymphocytes in myasthenia gravis.

In most young myasthenia gravis patients, the thymic medulla contains germinal centres. Thymocytes from these cases spontaneously synthesize anti-acetylcholine receptor autoantibody (anti-AChR) in culture; after irradiation they may also selectively stimulate anti-AChR antibody production by autologous blood lymphocytes. By depleting cortical or mature thymic T cells by complement killing, we now show that neither of these responses depends on thymic T cells, unlike the total IgG response to pokeweed mitogen which is T cell-dependent and shows T/B cell synergy. The results suggest that much of the spontaneous anti-AChR production is by autonomous thymic plasma cells, which may be HLA-DR-. The ability to stimulate autologous blood lymphocytes does not require viable HLA-DR+ thymic cells but appears to depend on rare antigen presenting cells from the germinal centres. In preliminary experiments, blood T cells were apparently also necessary.