Precipitation of autoantibody in serum from patients with myasthenia gravis.

Suitable means have been developed for the preparation of extracts of human or monkey skeletal muscle, which give precipitation with certain sera from patients with myasthenia gravis. These extracts are prepared in three solvents, namely, water, saline or sucrose. The water and saline extracts are the best for precipitation in fluid systems, conveniently carried out in capillary tubes. While all three types can be used for precipitation in gel diffusion, either double diffusion or immunoelectrophoresis, the sucrose extract is more convenient. In all these tests, the systems are to be incubated at 4°, and the results are to be read at 24 hours. This time limit is particularly important for the fluid precipitation, in order to avoid non-specific precipitation. With these precautions, it was found that no precipitation occurred with a large number of normal sera. Furthermore, only two out of about 100 sera from patients with various other diseases gave any precipitation. The precipitation antigen could not be found in extracts from a large number of other tissues, including heart, thymus and smooth muscle. Gel diffusion analysis revealed two major antigens and a minor antigen. Different precipitating myasthenic sera differ in their content of the respective antibodies. The antigenic material has not yet been chemically characterized, but the data suggest that it is not myosin or actomyosin.