Antibodies to motor endplates demonstrated with the immunofluorescence technique.

Antibodies to acetylcholine receptors (AChR) are probably directly responsible for the pathogenesis of myasthenia gravis (MG). Methods for the demonstration of these antibodies are complicated. The present study shows that the antibodies can also be revealed by the use of the simple indirect immunofluorescence technique with rat diaphragm as substrate. Antibodies were demonstrated with FITC-labelled anti-human Ig. The location on the motor endplates was confirmed by using a TRITC-labelled anti-alpha-bungarotoxin system. Antibodies to motor endplates were only demonstrated in MG and not in either twenty-two patients with neuromuscular disorders or fifty normal subjects. Antibodies to motor endplates were found in only twelve out of fifty-seven MG patients. In fifteen of the other forty-five patients, antibodies were found of the classical anti-skeletal muscle type, 'overluminating' the anti-motor endplate antibodies.