A radioimmunoassay for the quantitative evaluation of anti-human acetylcholine receptor antibodies in myasthenia gravis.

A radioimmunoassay was developed for the quantitative evaluation of antibodies to the acetylcholine receptor in the serum of myasthenic patients. AcChR was extracted from human muscle. A detailed preparation of the 125I-labelled alpha-Bgt-AcChR complex used as antigen is reported. Usually, an average of 20 pmol were obtained form 100 g muscle. This preparation is stable for 1 month in presence of an inhibitor of proteolysis and sufficient for performing about fifteen assays. The labelled complex was incubated with increasing amounts of sera and precipitated with anti-human IgG serum. Titres were expressed in pmol 125I-labelled alpha-Bgt-AcChR complex precipitated per ml serum. Out of thirty-nine sera tested thirty-six had positive titres ranging from 0-1-46 pmol/ml. No anti-AcChR were detected in the sera from twenty-seven patients used as controls.