Kinetic studies on neurotoxin-binding inhibitory antibodies in myasthenia gravis

A method for measuring antibodies which inhibit the binding of 125I-alpha-bungarotoxin to the acetylcholine receptor was developed. The procedure allows the detection of inhibitory activity in 70% of sera from the patients with myasthenia gravis. Kinetic analysis showed that (1) a linear dose-response exists between logarithmic concentrations of any test serum and inhibitory activity, (2) the slope of the inhibition line is identical among various myasthenic sera and, (3) the slope of line induced by various cholinergic ligands was comparable to that obtained by myasthenic sera. The inhibitory activity correlated with the titer of anti-acetylcholine receptor antibody measured by an immunoprecipitation method (r = 0.76, p less than 0.01).