A comparative study of three vehicles on antibody responses against elapid snake neurotoxin immunogens.

A study was undertaken to compare the effects of three vehicles (incomplete Freund's adjuvant, IFA; bentonite and squalene/Arlacel A) on the antibody responses to various elapid neurotoxin immunogens. Three neurotoxin immunogens were prepared using purified principal postsynaptic neurotoxin(s) of Naja naja siamensis (NNS), Ophiophagus hannah (OH) and Bungarus fasciatus (BF). Glutaraldehyde (GA) or a carbodiimide (ECDI) was used as a coupling agent while diphtheria toxoid (DT) was used as a protein carrier. The immunogens (NNS-OH-BF-GA, NNS-DT-ECDI and NNS-OH-BF-DT-ECDI) were characterized in terms of percentage of toxin polymerized, mol. wt and abundance and toxin density by SDS-PAGE using 125I-NNS neurotoxin 3. The immunogens, with crude NNS venom as control, were immunized in groups of eight rats with either of the three vehicles given above. Serum titres of specific antibodies against NNS, OH and BF neurotoxins were determined by ELISAs. Multiple comparisons of the results showed IFA to enhance significantly higher antibody titres than the other two vehicles for all immunogens. All the chemically modified immunogens stimulated higher antibody titres against NNS neurotoxin 3 than the crude NNS venom in most vehicles. The two multispecific immunogens also stimulated high antibody titres against OH and BF neurotoxins. These results should lead to the preparation of potent, polyvalent antivenoms against these elapid snakes.