Protection against alpha-bungarotoxin poisoning by immunization with synthetic toxin peptides

The purpose of the present work was to determine the ability of BgTX peptides, corresponding to the various loops and exposed regions of alpha-bungarotoxin (BgTX) and representing regions that are recognized by B and/or T cells, to stimulate protective immunity in mice against in vivo challenge with BgTX. The BgTX LD50 values in non-immune mice or mice that had been immunized with proteins and peptides unrelated to BgTX were: Balb/c, 0.128 microgram/g; SJL, 0.156 microgram/g. Immunization of Balb/c and SJL mice with each of the synthetic peptides in its free form afforded considerable protection against BgTX poisoning. Peptides L1 (residues 3-16), L2 (residues 26-41) and C-tail (residues 66-74) of BgTX were the most protective and mice immunized with these peptides survived LD50 values that were three times higher than control mice. Immunization with an equimolar mixture of the three peptides was even more protective and these mice survived even higher challenge doses of BgTX (4.6-fold higher than LD50 of controls; i.e. protection index, PI = 4.6). An OVA conjugate carrying all three peptides, when used as an immunogen, conferred extremely high protection (PI > or = 18.1) which was almost double the protection obtained by BgTX immunization (PI = 9.7). Thus, the conjugate of the three peptides should serve as an effective vaccine against BgTX poisoning. Furthermore, these results with BgTX peptides should serve as a prototype for the design and synthesis of peptide vaccines against other members of this large family of toxins which include both long and short neurotoxins as well as cytotoxins.