Effect of myasthenic IgG on degradation of junctional acetylcholine receptor.

We investigated the effect of the IgG from patients with myasthenia gravis (MG) on the degradation of normal rat junctional acetylcholine receptor (AChR) labeled with 125I-alpha-bungarotoxin (BuTx) and calculated the degradation rate (DR). The DR for the IgG from these patients was significantly higher than that from healthy volunteers and patients with other autoimmune diseases. For MG, DR was significantly correlated with the severity of the disease but not with anti-AChR antibody titer. DR was accelerated by IgG from patients with generalized MG whose antibody titers were in the normal range and by IgG from patients with ocular MG. These results indicate that measurement of the DR of junctional AChR in normal rats is more closely correlated with the severity of the disease than is measurement of anti-AChR antibody and that the former is a sensitive and confirmatory method for evaluating MG.