Protective and immunochemical activities of monoclonal antibodies reactive with the Bacillus anthracis polypeptide capsule - Monoclonal Antibodies

Protective and immunochemical activities of monoclonal antibodies reactive with the Bacillus anthracis polypeptide capsule
2006 Oct 23
Kozel TR, Thorkildson P, Brandt S, Welch WH, Lovchik JA, Aucoin DP, Vilai J, Lyons CR.
Departments of Microbiology; and Immunology and Biochemistry; and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada, 89557 and Department of Internal Medicine, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131
Infect Immun.
Bacillus anthracis is surrounded by a polypeptide capsule composed of poly-gamma-D-glutamic acid (gammaDPGA). In a previous study, we reported that a MAb (MAb F26G3) reactive with the capsular polypeptide is protective in a murine model of pulmonary anthrax. The present study examined a library of six MAbs generated from mice immunized with gammaDPGA. Evaluation of MAb binding to the capsule by a capsular "quellung" type reaction showed a striking diversity in capsular effects. Most MAbs produced a rim type reaction that was characterized by a sharp increase followed directly by a decrease in refractive index at the capsular edge. Some MAbs produced a second capsular reaction well beneath the capsular edge, suggesting complexity in capsular architecture. Binding of MAbs to soluble gammaDPGA was assessed by a fluorescence perturbation assay in which a change in the MAb intrinsic fluorescence produced by ligand binding was used as a reporter for antigen-antibody interaction. The MAbs differed considerably in the complexity of the binding curves. MAbs producing rim type capsule reactions typically produced the more complex binding isotherms. Finally, the protective activity of the MAbs was compared in a murine model of pulmonary anthrax. One MAb was markedly less protective than the remaining five MAbs. Characteristics of the more protective MAbs included a relatively high affinity, an IgG3 isotype, and a complex binding isotherm in the fluorescence perturbation assay. Given the relatively monotonous structure of gammaDPGA, the results demonstrate a striking diversity in the antigen binding behavior of gammaDPGA antibodies.
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