Different mechanisms of two anti-anthrax protective antigen antibodies and function comparison between them

Siping Xiong,Zhengqin Feng,Feng Zheng,Qi Tang,Jin Zhu,Yongping Cao,Tingting Zhou,Xudong Liang,Chunhui Wang

doi:10.1186/s12879-019-4508-z

Abstract

BackgroundBacillus anthracis causes a highly lethal infectious disease primarily due to toxin-mediated injury. Antibiotics are no longer effective to treat the accumulation of anthrax toxin, thereby new strategies of antibody treatment are essential. Two anti- anthrax protective antigen (PA) antibodies, hmPA6 and PA21, have been reported by our lab previously.MethodsThe mechanisms of the two antibodies were elucidated by Electrophoresis, Competitive Enzyme-linked immune sorbent assay, Western blot analysis and immunoprecipitation test, and in vitro, in vivo (F344 rats) treatment test. The epitopes of the two antibodies were proved by Western blot and Enzyme-linked immune sorbent assay with different domains of PA.ResultsIn this study, we compared affinity and neutralization of these two antibodies. PA21 was better in protecting cells and rats, whereas hmPA6 had higher affinity. Furthermore, the neutralization mechanisms of the two antibodies and their recognition domains of PA were studied. The results showed that hmPA6 recognized domain IV, thus PA could not bind to cell receptors. Conversely, PA21 recognized domain II, thereby limiting heptamer oligomerization of PA63 in cells.ConclusionsOur studies elucidated the mechanisms and epitopes of hmPA6 and PA21. The present investigation can advance future use of the two antibodies in anthrax treatment or prophylaxis, and potentially as a combination treatment as the antibodies target different epitopes.

Highlights

Bacillus anthracis causes a highly lethal infectious disease primarily due to toxin-mediated injury
J774A.1 cells were used to assess the ability of hmPA6 and PA21 to protect against LeTx
We studied the mechanism in the following aspects: inhibition of protective antigen (PA) binding to cell receptors, interference with PA proteolytically cleavage by furin protease, inhibition of the heptamer assembly of the remaining PA63 on the cells, and interference with the PA63 heptamer combined lethal factor (LF)/edema factor (EF) [22, 23]

Summary

Introduction

Bacillus anthracis causes a highly lethal infectious disease primarily due to toxin-mediated injury. Two anti- anthrax protective antigen (PA) antibodies, hmPA6 and PA21, have been reported by our lab previously. The pathogenesis of B. anthracis is mainly caused by anthrax toxin which is a tripartite protein complex. The three-protein toxin consist of a cellular receptors binding component, the protective antigen (PA), and two catalytic components, lethal factor (LF) and edema factor (EF) [5, 6]. PA binds to cell surface receptors (the tumor endothelial marker 8, TEM-8; the capillary morphogenesis protein-2, CMG-2) [7, 8]. The amino-terminal 20-kDa region of PA is cleaved by furin protease and released. LF is a zinc-dependent protease specific for the

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Discussion

Conclusion