Myasthenia gravis (MG) is a skeletal muscle disorder characterized by muscular weakness. In such cases, muscular weakness is due to anti-acetylcholine receptor (AChR) antibodies. Anti-AChR antibodies are present in approximately 90% of patients with MG. Anti-AChR antibodies could be: binding antibodies (multitudes of wide populations of antibodies directed to hydrophilic domains of receptors), blocking antibodies (preventing binding of acetylcholine to receptors), and modulating antibodies (accelerating endocytosis resulting in loss of receptors).

Anti-AChR antibodies are detectable by a radiobinding assay that’s followed by precipitation of the antibodies. Patient specimens and references are incubated with detergent-solubilized fetal and adult AChRs labeled with I125-alpha-bungarotoxin. The resulting bound complexes of labeled AChRs and antibodies are precipitated with anti-human IgG. After centrifugation, the supernatant is aspirated and the pellet containing labeled AChR-autoantibody complexes are counted in a gamma-counter. Counts are directly proportional to the amount of antibodies present.