THYMIC B LYMPHOCYTE CLONES FROM PATIENTS WITH MYASTHENIA GRAVIS SECRETE MONOCLONAL STRIATIONAL AUTOANTIBODIES REACTING WITH

Myasthenia gravis (MG) ' is an autoimmune disease of skeletal muscle that is characterized by prominent thymic pathology (reviewed in 1). Lymphoid follicles in the medulla are increased in number, often with germinal centers, and B lymphocytes (2) and DR ' cells are numerous (3). The thymus in MG is a site for the production of antibodies to nicotinic acetylcholine receptors (AChR) (4), the serologic hallmark of acquired MG and the cause of impaired neuromuscular transmission. Thymoma, a slowly growing epithelial tumor that rarely metasta-sizes, occurs in ^-15 % of patients with MG, and more impressively, it has been estimated that 35 % of patients with thymoma either have MG or will develop MG (5). The basis of this striking association between thymoma and MG is not known. In 1960, Strauss et al. (6) reported that sera of patients with MG contained antibodies that reacted with cross-striations of skeletal muscle. Although these striational autoantibodies (StrAb) were the first organ-specifc autoantibodies found in MG, the pathogenic significance of StrAb, if any, is unknown. The