BETA-BUNGAROTOXIN BINDING-PROTEIN IS IMMUNOGENIC BUT LACKS MYASTHENOGENICITY IN RATS

Myasthenia gravis is an autoimmune disease resulting from autoaggressi ve immunity to the nicotinic acetylcholine receptor (AChR) of the neur omuscular junction. Immunization with AChR leads to experimental autoi mmune myasthenia gravis (EAMG). AChR binds to alpha-bungarotoxin, and this property is utilized to purify AChR. The utilization of beta-bung arotoxin (beta-BGT) allows the purification of a different protein of striated muscle. To examine the myasthenogenic activity of the beta-BG T binding protein, we immunized Lewis rats with the beta-BGT binding p rotein or AChR from Torpedo. While AChR-immunized rats developed typic al signs of EAMG, beta-BGT binding protein immunized rats showed no de finite clinical signs of muscular weakness during observation periods up to 14 weeks after immunization. High levels of anti-AChR IgG antibo dies and low levels of antibodies against beta-BGT binding protein wer e present in the AChR-immunized rats, while high levels of IgG antibod ies to the alpha-BGT binding protein and low anti-AChR IgG antibody le vels were found in the rats immunized with the beta-BGT binding protei n. No relationship was observed between antibody levels and severity o f EAMG. The anti-AChR and anti-beta-BGT binding protein IgG antibodies showed only low degrees of cross-reactivity. We conclude that the bet a-BGT binding protein is immunogenic also in EAMG, while it is still a n open question whether it also has myasthenogenic properties.