DETECTION OF ANTIBODY CLASSES AND SUBPOPULATIONS IN MYASTHENIA-GRAVISPATIENTS USING A NEW NONRADIOACTIVE ENZYME-IMMUNOASSAY

To investigate the presence of antibodies in myasthenia gravis (MG) pa tients, we have developed a new reproducible and sensitive enzyme immu noassay (EIA-AChR), in which a beta subunit-specific monoclonal antibo dy (mAb 73) immobilizes fetal calf acetylcholine receptors (AChRs). We tested 92 MG patients (42 with positive and 50 with negative antibody titers), 60 healthy controls. and 40 controls with other autoimmune d iseases. EIA-AChR detected immunoglobulin G (IgG) titers in all of the seropositive samples, with a significant correlation between these an d those obtained using the traditional immunoprecipitation method. Mor eover, 5 seronegative patients at immunoprecipitation assay were posit ive at EIA-AChR. EIA-AChR was also useful in revealing: (1) a seroposi tive patient subpopulation with generalized MG who had Abs directed ag ainst alpha-Bungarotoxin binding sites; and (2) patients with IgM dire cted against fetal calf AChR (detected in 13 seronegative and 16 serop ositive WIG patients, and in 6 of the patients with other autoimmune d iseases). (C) 1997 John Wiley & Sons, Inc.