Heterogeneity of antibodies directed against the α-bungarotoxin binding site on human acetylcholine receptor and severity of myasthenia gravis

A rapid and sensitive radioimmunological method is described, using decamethonium (DC), which revealed antibodies which blocked α-bungarotoxin (α-Bgt) binding to human acetylcholine receptor (AChR) in 98% of myasthenia gravis (MG) patients' sera tested. These sera had anti-AChR antibody titres by the conventional assay. The titre of blocking antibodies (1 to 110 nM) could be measured and was found to produce from 1 to 54% inhibition of α-Bgt binding. No relationship was found between these titres and anti-AChR antibody titres. MG sera were divided into 2 major groups on the basis of their blocking effects, with and without DC, but there was no correlation between these and the clinical status, as defined by Osserman's classification. However, no sera from asymptomatic or ocular MG patients had the dual capacities of blocking α-Bgt binding, directly and in the presence of DC.