Immunoperoxidase localization of alpha bungarotoxin: a new approach to myasthenia gravis.

The IPBT method has made it possible to precisely visualize the AChR. Normal distribution of AChR is at the peaks of the postjunctional folds of the muscle sarcolemmal membrane with a small amount present on the axonal tip as well. Denervated muscle fibers have extrajunctional AChR. In MG, there are also denervated-appearing fibers but these do not have extrajuctional AChR with the IPBT stain. To explain this, we have been able to demonstrate a serum factor capable of blocking the binding of alpha-BuTx to the AChR and have shown for the first time that this factor is capable of acting at the neuromuscular junction itself. This blocking factor may play a major role in causing the weakness of MG.