IgG Subclass and Heavy Chain Domains Contribute to Binding and Protection by mAbs to the Poly γ-D-glutamic Acid Capsular Antigen of Bacillus anthracis

PLoS Pathogens

Peter Thorkildson¹  Thomas R. Kozel¹  William H. Welch¹  Mark A. Hubbard¹  Maria Hovenden²  David P. AuCoin²  Dana E. Reed²  C. Rick Lyons²  Julie A. Lovchik² 

[1] Cell and Molecular Biology Graduate Program, University of Nevada School of Medicine, Reno, Nevada, United States of America;Department of Microbiology and Immunology, University of Nevada School of Medicine, Reno, Nevada, United States of America

关键词: Antibodies;    Enzyme-linked immunoassays;    Bacillus anthracis;    Mouse models;    Antigen encapsulation;    Anthrax;    Polymerase chain reaction;    Polysaccharides;   

DOI  :  10.1371/journal.ppat.1003306

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Bacterial capsules are common targets for antibody-mediated immunity. The capsule of Bacillus anthracis is unusual among capsules because it is composed of a polymer of poly-γ-d-glutamic acid (γdPGA). We previously generated murine IgG3 monoclonal antibodies (mAbs) to γdPGA that were protective in a murine model of pulmonary anthrax. IgG3 antibodies are characteristic of the murine response to polysaccharide antigens. The goal of the present study was to produce subclass switch variants of the γdPGA mAbs (IgG3→IgG1→IgG2b→IgG2a) and assess the contribution of subclass to antibody affinity and protection. Subclass switch antibodies had identical variable regions but differed in their heavy chains. The results showed that a switch from the protective IgG3 to IgG1, IgG2b or IgG2a was accompanied by i) a loss of protective activity ii) a change in mAb binding to the capsular matrix, and iii) a loss of affinity. These results identify a role for the heavy chain constant region in mAb binding. Hybrid mAbs were constructed in which the CH1, CH2 or CH3 heavy chain constant domains from a non-protective, low binding IgG2b mAb were swapped into the protective IgG3 mAb. The IgG3 mAb that contained the CH1 domain from IgG2b showed no loss of affinity or protection. In contrast, swapping the CH2 or CH3 domains from IgG2b into IgG3 produced a reduction in affinity and a loss of protection. These studies identify a role for the constant region of IgG heavy chains in affinity and protection against an encapsulated bacterial pathogen.

【 授权许可】

CC BY