title: Sequential B-cell epitopes of Bacillus anthracis lethal factor bind lethal toxin-neutralizing antibodies.
abstract: 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.
authors.affiliation: Department of Microbiology & Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Nguyen
authors.forename: Sherry R
authors.initials: SR
authors.lastname: Crowe
authors.forename: Sridevi
authors.initials: S
authors.lastname: Kurella
authors.forename: Simon
authors.initials: S
authors.lastname: Teryzan
authors.forename: Brian
authors.initials: B
authors.lastname: Cao
authors.forename: Jimmy D
authors.initials: JD
authors.lastname: Ballard
authors.forename: Judith A
authors.initials: JA
authors.lastname: James
authors.forename: A Darise
authors.initials: AD
authors.lastname: Farris
mesh_terms: D000818:Animals; D000881:Anthrax / Q000517:prevention & control; D022122:Anthrax Vaccines / Q000276:immunology; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000276:immunology; D000942:Antigens, Bacterial / Q000276:immunology*; D001408:Bacillus anthracis / Q000276:immunology*; D001427:Bacterial Toxins / Q000276:immunology*; D002460:Cell Line; D018604:Epitope Mapping; D018985:Epitopes, B-Lymphocyte / Q000276:immunology*; D005260:Female; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology; D008264:Macrophages / Q000187:drug effects; D051379:Mice; D008805:Mice, Inbred A; D009500:Neutralization Tests
chemical_list: D022122:Anthrax Vaccines; D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D018985:Epitopes, B-Lymphocyte; D007074:Immunoglobulin G; C030325:anthrax toxin