[Role of the thymus in the physiopathology of myasthenia].
In myasthenia gravis (MG), the frequency of histologic abnormalities (hyperplasia in young patients, thymoma in older cases) and clinical improvement after thymectomy indicate involvement of the thymus in the pathophysiology of the disease. MG patient thymuses are characterized by the following features: increased amount of B cells (in hyperplasia) and functional abnormalities, mainly activation of B, T and epithelial cells. Moreover, thymic lymphocytes are sensitized to acetylcholine receptor (AChR): first, AChR specific T and B lines can be grown from MG thymus cultures, second, cultured thymic lymphocytes proliferate in the presence of AChR and produce anti-AChR antibodies. AChR molecules are expressed in thymic myoid cells and AChR-like molecules could be displayed at the surface of other cell types. Thus, autosensitization conditions are combined in MG thymus, and potential mechanisms are discussed. It could be a primary event, autosensitization of lymphocytes to AChR taking place initially in the thymus. Or it could be a secondary process, lymphocytes sensitized to AChR in the periphery could be trapped by myoid cells and restimulated in the thymus. In thymoma, autoimmunization occurs differently: the autoimmune process could be initiated by the tumor epithelial cells which express an AChR-like protein. The possible role of severe architectural disturbance in MG thymus (particularly in thymoma), altering thymic lymphocyte selection and maturation is also discussed.
Eymard
B
B
Division Risler, Hôpital de la Salpêtrière, Paris.
Berrih-Aknin
S
S
D005260:Female; D006801:Humans; D008297:Male; D009157:Myasthenia Gravis / Q000209:etiology / Q000503:physiopathology*; D013945:Thymoma / Q000503:physiopathology; D013950:Thymus Gland / Q000276:immunology / Q000502:physiology / Q000503:physiopathology*; D013952:Thymus Hyperplasia / Q000503:physiopathology; D013953:Thymus Neoplasms / Q000503:physiopathology
Rôle du thymus dans la physiopathologie de la myasthénie.