Sequential B-Cell Epitopes of Bacillus anthracis Lethal Factor Bind Lethal Toxin-Neutralizing Antibodies

• Published in: Infection and Immunity 2009-01, Vol.77 (1), p.162-169
• Main Authors: Nguyen, Melissa L, Crowe, Sherry R, Kurella, Sridevi, Teryzan, Simon, Cao, Brian, Ballard, Jimmy D, James, Judith A, Farris, A. Darise
• Format: Article
• Language: English
• Subjects: Animals; Anthrax - prevention & control; Anthrax Vaccines - immunology; Antibodies, Bacterial - blood; Antibodies, Bacterial - immunology; Antibodies, Monoclonal - immunology; Antigens, Bacterial - immunology; Bacillus anthracis; Bacillus anthracis - immunology; Bacterial Toxins - immunology; Bacteriology; Biological and medical sciences; Cell Line; Epitope Mapping; Epitopes, B-Lymphocyte - immunology; Female; Fundamental and applied biological sciences. Psychology; Immunoglobulin G - blood; Immunoglobulin G - immunology; Macrophages - drug effects; Mice; Mice, Inbred A; Microbial Immunity and Vaccines; Microbiology; Miscellaneous; Neutralization Tests
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00788-08

The bipartite anthrax lethal toxin (LeTx) consisting of protective antigen (PA) and lethal factor (LF) is a major virulence factor contributing to death from systemic Bacillus anthracis infection. The current vaccine elicits antibodies directed primarily to PA; however, in experimental settings serologic responses to LF can neutralize LeTx and contribute to protection against infection. The goals of the present study were to identify sequential B-cell epitopes of LF and to determine the capacity of these determinants to bind neutralizing antibodies. Sera of recombinant LF-immunized A/J mice exhibited high titers of immunoglobulin G anti-LF reactivity that neutralized LeTx in vitro 78 days after the final booster immunization and protected the mice from in vivo challenge with 3 50% lethal doses of LeTx. These sera bound multiple discontinuous epitopes, and there were major clusters of reactivity on native LF. Strikingly, all three neutralizing, LF-specific monoclonal antibodies tested bound specific peptide sequences that coincided with sequential epitopes identified in polyclonal antisera from recombinant LF-immunized mice. This study confirms that LF induces high-titer protective antibodies in vitro and in vivo. Moreover, the binding of short LF peptides by LF-specific neutralizing monoclonal antibodies suggests that generation of protective antibodies by peptide vaccination may be feasible for this antigen. This study paves the way for a more effective anthrax vaccine by identifying discontinuous peptide epitopes of LF.