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Infection and Immunity, November 2009, p. 4859-4867, Vol. 77, No. 11
0019-9567/09/$08.00+0     doi:10.1128/IAI.00117-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Neutralizing Monoclonal Antibodies Directed against Defined Linear Epitopes on Domain 4 of Anthrax Protective Antigen{triangledown}

Cassandra D. Kelly-Cirino and Nicholas J. Mantis*

Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, and Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York 12208

Received 30 January 2009/ Returned for modification 6 March 2009/ Accepted 15 August 2009

The anthrax protective antigen (PA) is the receptor-binding subunit common to lethal toxin (LT) and edema toxin (ET), which are responsible for the high mortality rates associated with inhalational Bacillus anthracis infection. Although recombinant PA (rPA) is likely to be an important constituent of any future anthrax vaccine, evaluation of the efficacies of the various candidate rPA vaccines is currently difficult, because the specific B-cell epitopes involved in toxin neutralization have not been completely defined. In this study, we describe the identification and characterization of two murine monoclonal immunoglobulin G1 antibodies (MAbs), 1-F1 and 2-B12, which recognize distinct linear neutralizing epitopes on domain 4 of PA. 1-F1 recognized a 12-mer peptide corresponding to residues 692 to 703; this epitope maps to a region of domain 4 known to interact with the anthrax toxin receptor CMG-2 and within a conformation-dependent epitope recognized by the well-characterized neutralizing MAb 14B7. As expected, 1-F1 blocked PA's ability to associate with CMG-2 in an in vitro solid-phase binding assay, and it protected murine macrophage cells from intoxication with LT. 2-B12 recognized a 12-mer peptide corresponding to residues 716 to 727, an epitope located immediately adjacent to the core 14B7 binding site and a stretch of amino acids not previously identified as a target of neutralizing antibodies. 2-B12 was as effective as 1-F1 in neutralizing LT in vitro, although it only partially inhibited PA binding to its receptor. Mice passively administered 1-F1 or 2-B12 were partially protected against a lethal challenge with LT. These results advance our fundamental understanding of the mechanisms by which antibodies neutralize anthrax toxin and may have future application in the evaluation of candidate rPA vaccines.

* Corresponding author. Mailing address: Division of Infectious Diseases, Wadsworth Center New York State Department of Health, 120 New Scotland Ave., Albany, NY 12208. Phone: (518) 473-7487. Fax: (518) 486-7971. E-mail: nmantis{at}wadsworth.org

{triangledown} Published ahead of print on 24 August 2009.

Editor: J. B. Bliska

Infection and Immunity, November 2009, p. 4859-4867, Vol. 77, No. 11
0019-9567/09/$08.00+0     doi:10.1128/IAI.00117-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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