Heterogeneity of acetylcholine receptors in denervated muscle: interactions of receptors with immunoglobulin from patients with myasthenia gravis

The interaction of immunoglobulin G fractions from the sera and thymus glands of patients with myasthenia gravis with acetylcholine receptors from denervated rat muscle was studied using a combination of immunoprecipitation and an assay for binding to concanavalin A-Sepharose. Results showed that myasthenic IgG distinguishes 2 different α-bungarotoxin-binding components, each associated with approximately half the total receptor toxin binding capacity. The receptor components can be separated as immune complexes by different properties of binding to concanavalin A and are characterized by different kinetics of toxin binding. The majority of myasthenia gravis sera contain at least 2 antibodies, directed against determinants on 1 or both components of the receptor, which do not affect the total binding capacity for α-bungarotoxin. A few sera contain a third antibody type, which prevents the binding of α-bungarotoxin to receptors.