In vivo dynamics of active edema and lethal factors during anthrax.

Clémence Rougeaux,Jean-Nicolas Tournier,Pierre L Goossens,François Becher,Eric Ezan

doi:10.1038/srep23346

Abstract

Lethal and edema toxins are critical virulence factors of Bacillus anthracis. However, little is known about their in vivo dynamics of production during anthrax. In this study, we unraveled for the first time the in vivo kinetics of production of the toxin components EF (edema factor) and LF (lethal factor) during cutaneous infection with a wild-type toxinogenic encapsulated strain in immuno-competent mice. We stratified the asynchronous infection process into defined stages through bioluminescence imaging (BLI), while exploiting sensitive quantitative methods by measuring the enzymatic activity of LF and EF. LF was produced in high amounts, while EF amounts steadily increased during the infectious process. This led to high LF/EF ratios throughout the infection, with variations between 50 to a few thousands. In the bloodstream, the early detection of active LF and EF despite the absence of bacteria suggests that they may exert long distance effects. Infection with a strain deficient in the protective antigen toxin component enabled to address its role in the diffusion of LF and EF within the host. Our data provide a picture of the in vivo complexity of the infectious process.

Highlights

Lethal and edema toxins are critical virulence factors of Bacillus anthracis
The vegetative form of B. anthracis produces a capsule as protection from the host immune defenses, and three, individually non-toxic, proteins that associate to form toxin complexes: lethal toxin (LeTx) which consists of the association of lethal factor (LF) and protective antigen (PA), and edema toxin (EdTx) formed by the association of edema factor (EF) and PA
To understand in depth how B. anthracis subverts the host defenses through its toxins, we used highly sensitive assays to quantify the amount of active edema and lethal factors at specific time points of infection, either at the initial site of a cutaneous infection or at distance in plasma

Summary

Introduction

Lethal and edema toxins are critical virulence factors of Bacillus anthracis. little is known about their in vivo dynamics of production during anthrax. The vegetative form of B. anthracis produces a capsule as protection from the host immune defenses, and three, individually non-toxic, proteins that associate to form toxin complexes: lethal toxin (LeTx) which consists of the association of lethal factor (LF) and protective antigen (PA), and edema toxin (EdTx) formed by the association of edema factor (EF) and PA. Consistent with this, in vivo studies showed that both toxins critically impair myeloid cells in order to evade the scavenging functions of neutrophils and successfully establish infection[19]. These data suggest that B. anthracis relies on the toxins to invade its host. At the organ and animal levels, EdTx and LeTx critically target two distinct vital systems; EdTx induces mortality through hepatocytes, while LeTx kills by acting on cardiomyocytes and vascular smooth cells[20]

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Conclusion