title: Selection of human antibodies against cell surface-associated oligomeric anthrax protective antigen.
abstract: The protective antigen (PA(83)) of Bacillus anthracis is the dominant antigen in natural and vaccine-induced immunity to anthrax infection. Three human single-chain variable fragments (scFvs) against cell bound PA were isolated from an antibody phage display library. Specifically, the antibodies were evaluated for their ability to bind to cell bound heptameric PA and ultimately protect against the cytotoxicity of lethal toxin. In total, all three scFvs possessed neutralizing activity against the cytotoxic effects of lethal toxin in a macrophage lysis assay. The K(d) values of the Fabs were determined, interestingly their protective effects did not parallel their affinities; hence, a simple binding argument alone to PA(63) cannot be used as the distinguishing feature for the prediction of their neutralization abilities. Immunofluorescent microscopy experiments were conducted and provided strong evidence for Fab binding to oligomeric PA on the cell surface and thus a plausible mechanism for the toxin neutralization activity that was observed. The results of this study presented herein suggest that our antibodies compete with LF-PA cell surface interactions, and thus may provide potential application of human antibodies as passive immunization prophylactics in cases of B. anthracis exposure and infection.
authors.affiliation: Departments of Chemistry, Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Sebastian C J
authors.initials: SC
authors.lastname: Steiniger
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Altobell
authors.forename: Bin
authors.initials: B
authors.lastname: Zhou
authors.forename: Kim D
authors.initials: KD
authors.lastname: Janda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000737:chemistry / Q000276:immunology* / Q000302:isolation & purification / Q000494:pharmacology; D000915:Antibody Affinity; D000942:Antigens, Bacterial / Q000276:immunology*; D001427:Bacterial Toxins / Q000037:antagonists & inhibitors* / Q000276:immunology*; D001667:Binding, Competitive; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000276:immunology* / Q000302:isolation & purification / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D019151:Peptide Library
chemical_list: D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D007135:Immunoglobulin Variable Region; D019151:Peptide Library; C030325:anthrax toxin