In order to determine the role of humoral factors in myasthenia gravis (MG) the anti-acetylcholine receptor antibody was measured in the sera of a series of patients and controls. A radioimmunoassay and a toxin-inhibition assay were used to assess the interaction of the autoantibody with receptor purified from denervated rat muscle. Antibody was detected in 88% of MG patients and was not present in controls. In some patients the antibody was assayed at different time during the course of the disease and after the drug-induced remission of symptoms. Antibody titre was found to increase with the progressive development of muscle weakness but remained very high after muscle strength returned to normal during steroid treatment. It is suggested that autoantibody may be necessary but is not sufficient to account for the pathogenesis of MG.
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