IgG subclass distribution of myasthenia gravis thymoma-associated antiskeletal muscle antibodies.

Myasthenia gravis patients with thymoma often have serum antibodies directed against human skeletal muscle. We have developed an enzyme-linked immunosorbent assay to investigate the subclass distribution of these antibodies. Five thymoma patients all had IgG4 antibodies, whereas a patient who developed myasthenia gravis after bone-marrow transplantation had only IgG1 antibodies. The data suggest that IgG1 is the first subclass to appear in the autoantibody response against skeletal muscle.