beta-Bungarotoxin binding protein is immunogenic but lacks myasthenogenicity in rats

Myasthenia gravis is an autoimmune disease resulting from autoaggressive immunity to the nicotinic acetylcholine receptor (AChR) of the neuromuscular junction. Immunization with AChR leads to experimental autoimmune myasthenia gravis (EAMG). AChR binds to alpha-bungarotoxin, and this property is utilized to purify AChR. The utilization of beta-bungarotoxin (beta-BGT) allows the purification of a different protein of striated muscle. To examine the myasthenogenic activity of the beta-BGT binding protein, we immunized Lewis rats with the beta-BGT binding protein or AChR from Torpedo. While AChR-immunized rats developed typical signs of EAMG, beta-BGT binding protein immunized rats showed no definite clinical signs of muscular weakness during observation periods up to 14 weeks after immunization. High levels of anti-AChR IgG antibodies and low levels of antibodies against beta-BGT binding protein were present in the AChR-immunized rats, while high levels of IgG antibodies to the beta-BGT binding protein and low anti-AChR IgG antibody levels were found in the rats immunized with the beta-BGT binding protein. No relationship was observed between antibody levels and severity of EAMG. The anti-AChR and anti-beta-BGT binding protein IgG antibodies showed only low degrees of cross-reactivity. We conclude that the beta-BGT binding protein is immunogenic also in EAMG, while it is still an open question whether it also has myasthenogenic properties.