Establishment of a New Zealand White Rabbit Model for Lethal Toxin (LT) Challenge and Efficacy of Monoclonal Antibody 5E11 in the LT-Challenged Rabbit Model.

Duanyang Zhang,Bing Li,Weicen Liu,Zhonghua Wen,Jianmin Li,Shuling Liu,Wei Chen

doi:10.3390/toxins10070289

Abstract

Anthrax caused by Bacillus anthracis is a lethal infectious disease, especially when inhaled, and the mortality rate approaches 100% without treatment. The anthrax antitoxin monoclonal antibody (MAb) 5E11 is a humanized antibody that targets the anthrax protective antigen (PA). The efficacy of 5E11 needs proper animal models. However, anthrax spores are extremely dangerous, so experiments must be conducted under Biosafety Level 3 conditions. Considering the critical effects of lethal toxin (LT) on hosts during infection, we report the establishment of a LT-challenged rabbit model, which caused 100% mortality with a dose of 2 mg PA + 1 mg LF, while a 4 mg PA + 2 mg LF challenge could limit death to within three days. Then, we evaluated 5E11 efficacy against LT. A prophylactic study showed that the i.v. administration of 40 mg/kg 5E11 four days before lethal dose LT challenge could lead to 100% survival. In therapeutic studies, the i.v. administration of 40 mg/kg 5E11 10 min after lethal dose LT challenge could provide complete protection. Overall, we developed a new LT-challenged rabbit model, and our results indicate that 5E11 shows potential for the clinical application in anthrax treatment.

Highlights

Bacillus anthracis, a Gram-positive and spore-forming bacterium, is the etiologic agent of anthrax that can cause fatal human disease
In the lethal toxin (LT)-challenged rabbit model (LRM), the percentage of rabbits that succumbed to LT increased when challenge dose was higher (Figure 1A)
The 2 mg protective antigen (PA) + 1 mg lethal factor (LF) group showed no survival but the average survival time was longer than the 4 mg PA + 2 mg LF group. 2 mg PA + 1 mg LF was approximately confirmed as the minimal lethal dose (MLD)

Summary

Introduction

A Gram-positive and spore-forming bacterium, is the etiologic agent of anthrax that can cause fatal human disease. The virulence factors of this pathogen have two primary parts: the poly-D-glutamic acid capsule and anthrax toxins. The three toxin constituents generated by B. anthracis are protective antigen (PA), lethal factor (LF), and edema factor (EF). The two catalytic constituents, LF and EF, are transported into the cytosol through receptor binding of constituent PA in the form of the lethal toxin (LT) complex, which is made up of LF and PA, and the edema toxin (ET) complex, which is made up of EF and PA [4]. ET hinders neutrophil activity in vivo and impacts water homeostasis, causing edema, while LT disrupts many signaling pathways, influences cellular functions, induces cell death and is closely related to shock and death in severe anthrax infection [5,6,7]

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Results

Conclusion