Antibody-induced degradation of acetylcholine receptor in myasthenia gravis: clinical correlates and pathogenetic significance.

Sera of myasthenic patients containing anti-AChR antibodies increase the rate of degradation of mammalian AChR. This phenomenon, antigenic modulation (AMd), was tested on AChR of rat myotubes in serum from 48 myasthenic patients. Sixty-six percent of the sera increased AChR degradation. AMd activity was higher in more severely affected patients, paralleled clinical evolution in individual patients, and was related to AChR-antibody titer. Steroid treatment and thymectomy did not affect AMd activity. Patients who had a thymoma always had greater AMd activity.