Antibody and T-cell recognition of α-bungarotoxin and its synthetic loop-peptides

Abstract

Peptides representing the loops and surface regions of α-bungarotoxin (BgTX) and control peptide analogs in which these sequences were randomized were synthesized and used to map the recognition profiles of the antibodies and T-cells obtained after BgTX immunization. Also, the abilities of anti-peptide antibodies and T-cells to recognize the immunizing peptide and BgTX were determined. Three regions of BgTX were immunodominant by both rabbit and mouse anti-BgTX antibodies. These regions resided within loops L1 (residues 3–16), L2 (residues 26–41) and the C-terminal tail (residues 66–74) of the toxin. The regions recognized by BgTX-primed T-lymphocytes were mapped in five mouse strains: C57BL 6(H-2 b) , Balb c (H-2 d ), CBA (H-2 k ), C3H He (H-2 k ) and SJL (H-2 s ). The H-2 b and H-2 d haplotypes were high responders to BgTX, while the H-2 k and H-2 s were intermediate responders. The T-cell recognition profile of the peptides varied with the haplotype, consistent with Ir gene control of the responses to the individual regions. The submolecular specificities of antibodies and T-cells were compared in three of the mouse strains ( C57BL 6 , Balb c and SJL). In a given mouse strain, there were regions that were strongly recognized by both antibodies and T-cells as well as regions that were predominantly recognized either by antibodies or by T-cells. The peptides were used as immunogens in their free form (i.e. without coupling to any carrier) in two of the mouse strains, Balb c and SJL. In both mouse strains, the peptides gave strong antibody responses. Antibodies against peptide L2 showed the highest binding to intact BgTX. Antibodies against the other peptides exhibited lower binding activity to the intact toxin, and this activity was dependent on the peptide and the mouse strain. The response of peptide-primed T-cells to a given immunizing peptide was not related to whether this region was immunodominant with BgTX-primed T-cells. The ability of peptide-primed T-cells to recognize the intact toxin varied with the peptide and was dependent on the host strain. These results indicate that anti-peptide antibody and T-cell responses are also under genetic control and that their ability to cross-react with the parent toxin is not only dependent on the conformational exposure of the correlate region in intact BgTX.