Thymic lymphocytes bear a surface antigen which cross-reacts with acetylcholine receptor.

Acetylcholine receptor (AChR) is a major antigen in the neuromuscular disease myasthenia gravis and it is clear today that the basic defect in this disease is brought about by an autoimmune attack on acetylcholine receptors at the neuromuscular junctions. The involvement of the thymus and its role in myasthenia have been widely investigated but are still poorly understood. A high incidence of thymic abnormalities is observed in patients with myasthenia and thymectomy is beneficial in many cases. Immunological studies have demonstrated the presence of humoral as well as cellular immune responses towards thymic tissues in myasthenic patients. There were also some reports that animals immunized with thymic extracts develop a partial defect in neuromuscular transmission. In spite of all these observations, the nature and origin of the association between the thymus and the neuromuscular junction in myasthenia gravis are still not known. We have previously demonstrated an immunological cross-reactivity, both humoral and cellular, between a thymic component and AChR; such a cross-reactivity could provide a molecular explanation for the involvement of the thymus in myasthenia gravis. In this study, we demonstrate, by using immunofluorescence and radioimmunological techniques, that thymic lymphocytes bear a surface antigen which binds specifically to antibodies against nicotinic AChR and is thus defined as an 'AChR-like' antigen. A preliminary report of this study has been published.