[Autoimmune myasthenia: recent physiopathological data].

AUTOIMMUNE DISEASE: Myasthenia gravis is a one of the rare autoimmune diseases with a well-defined antigen. Autoantibodies directed against the muscular acetylcholine receptor (AChR) play a key role, blocking the acetylchoroquine binding site and provoking accelerated receptor degradation; complement destroys the post-synaptic membrane. Disease severity is correlated with extent of AChR loss. THYMUS: Involvement of the thymus is suggested by the beneficial effect of thymectomy and by histological and functional anomalies (modified cellular composition, abnormally activated lymphocytes, sensitivization of certain lymphocytes to AChR). "ANTIBODY NEGATIVE" DISEASE: The lack of anti-AChR antibodies detectable at immunoprecipitation, evidences the complexity of myastenia gravis pathogenesis. These "antibody-negative" forms are distinct from seropositive forms which have a high frequency of pure occular involvement and from infantile forms where the thymus regresses. "Antibody-negative" myastenia gravis might be mediated by antibodies directed against other endplate tardets. CLINICAL DIVERSITY: Our understanding of mechanisms responsible for the diversity of the clinical expression highlight the role of the AChR polymophism (with and adult and fetal expression). GENETIC PREDISPOSITION: Several factors involved in disease pathogenesis have been identified, including genetic factors: the HLA system, AChR alpha chain gene polymorphism, and immunoglobulin and T-cell antigen-receptor gene polymorphism.