Production and characterization of monoclonal antibodies against Naja naja atra cobrotoxin.

Twelve monoclonal antibodies against cobrotoxin from Naja naja atra venom were tested for cross-reactivity with eight different snake toxins, binding to linear epitopes, prevention of cobrotoxin binding to acetylcholine receptor (AchR) in vitro, and protection in mice concomitantly given a lethal dose of cobrotoxin. The antibodies were highly specific, as evidenced by little reactivity with other snake toxins. None of the monoclonal antibodies bound to reduced cobrotoxin or synthesized 8-mer regions spanning the whole molecule, thus suggesting the recognition of conformational epitopes. The in vitro binding of toxin to AchR was competitively inhibited (23-79%) with a 1.66:1 mole ratio of antibody:AchR. Preincubation of monoclonal antibody with toxin before adding AchR (3:1 mole ratio of AchR:antibody) inhibited the in vitro binding of toxin to AchR by 20-80%. Monoclonal antibodies added after the preincubation of toxin with AchR did not dissociate the toxin-AchR complex. An antibody:toxin mole ratio of 2.5:1, with 6 micrograms of cobrotoxin, delayed the time to death of mice 3.7-23.8-fold over control mice. The monoclonal antibodies that most effectively prevented in vitro binding of toxin to AchR also provided the longest delay in time to death in mice.