Immunohistological studies of the thymus in myasthenia gravis. Correlation with clinical state and thymocyte culture responses.

In frozen sections of thymus from 9 out of 12 myasthenia gravis patients, the medulla contained follicles of B lymphocytes with germinal centres showing the same immunofluorescence staining pattern as is seen normally in reactive lymphoid tissues. Only 1 similar follicle was seen in 9 normal thymus samples. There was a positive association between the extent of germinal centres, plasma anti-acetylcholine receptor (AChR) titre, and spontaneous anti-AChR production by thymocytes in vitro. These thymic changes were not universally found, and are thus probably not central to the initiation of myasthenia. Between the follicles, in 9 cases, there was an apparent increase in interdigitating cells with closely associated 'inducer' (OKT4+)T lymphocytes. Thymic antigen presenting cells--either here or in the germinal centres--could be involved in breaking self-tolerance, or in perpetuating the autoimmune response, and it may be their removal that is therapeutic.