Immunization of rats with polypeptide chains from torpedo acetylcholine receptor causes an autoimmune response to receptors in rat muscle.

Four polypeptide chains were purified from acetylcholine receptor of Torpedo californica electric organ. Their apparent molecular weights were 64,000, 57,000, 49,500, and 38,000. Rats immunized with any of the four chains produced antibodies that crossreacted with rat muscle receptors in vivo. Specificities of anti-chain sera were evaluated in vitro by reaction with native receptor solubilized from electric organs and muscles of several species and by inhibition of this reaction with the purified polypeptide chains. The chains are immunologically distinct from one another. Antigenic determinants comparable to each chain of torpedo receptor are found in receptor from both rat and human muscle. At least part of each of these determinants is exposed on the extracellular surface of the muscle membrane. The most immunogenic determinants on native receptor are lost on denaturation to polypeptide chains. Its component peptides are much less immunogenic than native receptor, and induce antibodies of different specificity. Anti-receptor antibodies of many specificities can cause experimental autoimmune myasthenia gravis.