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

Abstract

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