Acetycholine receptor antibody characteristics in myasthenia gravis: Fractionation of α-Bungarotoxin binding site antibodies and their relationship to IgG subclass

Abstract

Anti-acetylcholine receptor (anti-AChR) antibodies from two myasthenia gravis (MG) patients, known to have anti-AChR to the α-bungarotoxin (α-BuTx) binding site on the AChR (anti-α-BuTx site), were fractionated on an affinity column of human AChR fully saturated with α-BuTx. More than 80% of the anti-AChR in the pass-through fractions was directed against the α-BuTx site, whereas anti-AChR eluted from the column was mostly directed at other site on the AChR. Recovery of anti-AChR was greater than 60%. Anti-α-BuTx site antibodies varied from 0 to 33% of the total anti-AChR antibodies in 12 MG sera. Fractionation on Sepharose-Protein A showed that anti-α-BuTx was only restricted to IgG3 in two patients. Anti-α-BuTx site antibody, which can be separated from antibodies binding to other antigenic determinants on the AChR, is variable in amount and heterogeneous in its subclass distribution. Although it may play an important pathogenic role in some patients, our results do not support the existence of an anti-α-BuTx site antibody common to all MG patients.