title: Anthrax spores make an essential contribution to vaccine efficacy.
abstract: Anthrax is caused by Bacillus anthracis, a gram-positive spore-forming bacterium. Septicemia and toxemia rapidly lead to death in infected mammal hosts. Currently used acellular vaccines against anthrax consist of protective antigen (PA), one of the anthrax toxin components. However, in experimental animals such vaccines are less protective than live attenuated strains. Here we demonstrate that the addition of formaldehyde-inactivated spores (FIS) of B. anthracis to PA elicits total protection against challenge with virulent B. anthracis strains in mice and guinea pigs. The toxin-neutralizing activities of sera from mice immunized with PA alone or PA plus FIS were similar, suggesting that the protection conferred by PA plus FIS was not only a consequence of the humoral response to PA. A PA-deficient challenge strain was constructed, and its virulence was due solely to its multiplication. Immunization with FIS alone was sufficient to protect mice partially, and guinea pigs totally, against infection with this strain. This suggests that spore antigens contribute to protection. Guinea pigs and mice had very different susceptibilities to infection with the nontoxigenic strain, highlighting the importance of verifying the pertinence of animal models for evaluating anthrax vaccines.
authors.affiliation: Unité des Toxines et Pathogénie Bactérienne (CNRS URA 2172), Institut Pasteur, 75725 Paris Cedex 15, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Brossier
authors.forename: Martine
authors.initials: M
authors.lastname: Levy
authors.forename: Michèle
authors.initials: M
authors.lastname: Mock
mesh_terms: D000818:Animals; D000881:Anthrax / Q000517:prevention & control*; D022122:Anthrax Vaccines / Q000276:immunology*; D000942:Antigens, Bacterial / Q000276:immunology*; D001408:Bacillus anthracis / Q000187:drug effects / Q000276:immunology*; D001427:Bacterial Toxins / Q000276:immunology*; D005260:Female; D005557:Formaldehyde / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D051379:Mice; D013171:Spores, Bacterial / Q000187:drug effects / Q000276:immunology
chemical_list: D022122:Anthrax Vaccines; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C030325:anthrax toxin; D005557:Formaldehyde