Myasthenia gravis. Antibodies to skeletal muscle cell surface antigens

Sera from 28 of 137 patients with myasthenia gravis (MG) (i.e. 20%) contained antibodies which stained the surface of skeletal muscle cells in an indirect immunofluorescence test. Forty of the 137 sera (i.e. 30%) contained cross-striational antibodies. Absorption experiments showed that the antibodies staining the muscle cell surface were different from those staining the cross-striational bands. Twenty of the sera (i.e. 15%) contained antibodies which agglutinated sheep erythrocytes (SE) coated with a citric acid extract of skeletal muscle (CAE). These antibodies were closely associated with the presence of a thymoma. There was a positive correlation between the antibodies agglutinating CAE-coated SE and those staining the muscle cell surface. Absorption experiments indicated that the antibodies to CAE were directed against muscular antigens located in or near the sarcolemma.