Acetylcholine receptor antibody in myasthenia gravis: purification and characterization

Acetylcholine receptor antibody was measured in serum and IgG fractions from patients with myasthenia gravis using different analyses for antibody interfering with the toxin binding site and for antibody directed against other sites. No correlation was found between the concentration of receptor antibody as measured with the two assays. The different antibody activities also showed different isoelectric spectra. Receptor antibody was purified about 1000 times from IgG by affinity chromatography on a partially purified human skeletal muscle receptor preparation. The purified antibody was homogeneous in SDS-gel electrophroesis and showed a polyclonal pattern in agarose gel electrophoresis and isoelectric focusing. Both kinds of light chains were demonstrated. The results imply that the acetylcholine receptor antibody found in myasthenia gravis is heterogeneous and of multiclonal origin.