Regions recognized on the light chain of botulinum neurotoxin type A by T lymphocytes of SJL and BALB/c mice primed with inactivated toxin

Lymph node cells (LNC) from SJL (H-2^s) and BALB/c (H-2^d) mice primed once with inactivated botulinum neurotoxin type A (BoNT/A) were examined for their T-cell responses to each of 32 synthetic overlapping peptides (19 residues each, L1–L32) that encompass the entire L chain (residues 1–448) of BoNT/A. LNC of SJL gave strong responses to 6 regions on, L2 (residues 15–23), L10/11/12 (127–173), L19 (253–271) and L21 (281–299), and moderate to weak responses to L9 (113–131), L14/15 (183–215) and L27 (365–383). In BALB/c, LNC gave a substantial T-cell response only against peptide L12 (residues 155–173), and responded very weakly to 9 other peptides. The results were compared with the recognition profiles determined previously in these two strains after multiple BoNT/A injections. Overall responses to the L-chain peptides of T cells in later profiles were found to be somewhat weakened in SJL and stayed essentially at a similar level in BALB/c, although responses to BoNT/A increased. In SJL, response to L10 (127–145) remained the highest in the later profile. Strong responses against L12 (155–173) observed in both strains at early stage were reduced to an insignificant level. Cross-reactivity to tetanus neurotoxin by BoNT/A-specific T cells was observed in SJL but not in BALB/c. Design of an effective synthetic peptide vaccine will require incorporation of both T cell- and Ab-recognition elements of the BoNT molecule. Significance and possible implications of these results on BoNT/A-specific T-cell responses of BoNT-treated patients are discussed.