Immune recognition of botulinum neurotoxin type A: regions recognized by T cells and antibodies against the protective H(C) fragment (residues 855-1296) of the toxin

Botulism toxicity is caused by botulinum neurotoxins (BoNTs), a group of protein neurotoxins produced by Clostridium botulinum. Recent studies have shown that immunization with a C-terminal fragment [H(C), residues 855-1296] of BoNT type A (BoNT/A) affords excellent protection against BoNT/A toxicity. The present work was carried out in order to map the molecular and cellular immunological recognition of H(C). We have previously described the synthesis of 31 overlapping peptides encompassing the entire H(C)-fragment of BoNT/A. These peptides were employed in this study to localize the continuous regions recognized by T cells and by antibodies (Abs) generated in two mouse strains against H(C). T cells from SJL that had been primed with H(C) gave a strong proliferative response to challenge in vitro with each of the six peptides spanning residues 897-985 and a lower response to peptide 1051- 1069. While H(C)-primed T cells of BALB/c recognized three regions residing within residues 939-957, 1009-1027 and 1135-1153 (strong). Recognition regions by Abs in SJL or BALB/c anti-H(C) antisera essentially overlapped. However, the level of Abs bound to each region differed between the two strains. These common or similar recognition regions by the two strains were: 855-915 (SJL) or 855-901 (BALB/c); 939-957; 967-1013 (BALB/c) or 981-1013 (SJL); 1051-1069; 1079-1111 (BALB/c) or 1093-1125 (SJL); 1177-1195; and 1275-1296. In addition, BALB/c recognized region 1135-1153. Some of these regions show considerable sequence similarity in BoNT types B and E and, therefore, H(C) of these two BoNTs might offer protection against the correlate clostridial toxins.