Emergence of Anthrax Edema Toxin as a Master Manipulator of Macrophage and B Cell Functions

Anthrax edema toxin (ET), a powerful adenylyl cyclase, is an important virulence factor of Bacillus anthracis. Until recently, only a modest amount of research was performed to understand the role this toxin plays in the organism’s immune evasion strategy. A new wave of studies have begun to elucidate the effects this toxin has on a variety of host cells. While efforts have been made to illuminate the effect ET has on cells of the adaptive immune system, such as T cells, the greatest focus has been on cells of the innate immune system, particularly the macrophage. Here we discuss the immunoevasive activities that ET exerts on macrophages, as well as new research on the effects of this toxin on B cells

Yersinia pestis targets neutrophils via complement receptor 3

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111208/1/cmi12391.pd

AB Toxins: A Paradigm Switch from Deadly to Desirable

To ensure their survival, a number of bacterial and plant species have evolved a common strategy to capture energy from other biological systems. Being imperfect pathogens, organisms synthesizing multi-subunit AB toxins are responsible for the mortality of millions of people and animals annually. Vaccination against these organisms and their toxins has proved rather ineffective in providing long-term protection from disease. In response to the debilitating effects of AB toxins on epithelial cells of the digestive mucosa, mechanisms underlying toxin immunomodulation of immune responses have become the focus of increasing experimentation. The results of these studies reveal that AB toxins may have a beneficial application as adjuvants for the enhancement of immune protection against infection and autoimmunity. Here, we examine similarities and differences in the structure and function of bacterial and plant AB toxins that underlie their toxicity and their exceptional properties as immunomodulators for stimulating immune responses against infectious disease and for immune suppression of organ-specific autoimmunity

Anthrax Edema Toxin Modulates PKA- and CREB-Dependent Signaling in Two Phases

Background: Anthrax edema toxin (EdTx) is an adenylate cyclase which operates in the perinuclear region of host cells. However, the action of EdTx is poorly understood, especially at molecular level. The ability of EdTx to modulate cAMPdependent signaling was studied in Jurkat T cells and was compared with that of other cAMP-rising agents: Bordetella pertussis adenylate cyclase toxin, cholera toxin and forskolin. Methodology/Principal Findings: EdTx caused a prolonged increase of the intracellular cAMP concentration. This led to nuclear translocation of the cAMP-dependent protein kinase (PKA) catalytic subunit, phosphorylation of cAMP response element binding protein (CREB) and expression of a reporter gene under control of the cAMP response element. Neither p90 ribosomal S6 kinase nor mitogen- and stress-activated kinase, which mediate CREB phosphorylation during T cell activation, were involved. The duration of phospho-CREB binding to chromatin correlated with the spatio-temporal rise of cAMP levels. Strikingly, EdTx pre-treated T cells were unresponsive to other stimuli involving CREB phosphorylation such as addition of forskolin or T cell receptor cross-linking. Conclusions/Significance: We concluded that, in a first intoxication phase, EdTx induces PKA-dependent signaling, which culminates in CREB phosphorylation and activation of gene transcription. Subsequently CREB phosphorylation is impaired and therefore T cells are not able to respond to cues involving CREB. The present data functionally link the perinuclea

Yersinia adhesins: an arsenal for infection

The Yersiniae are a group of Gram-negative coccobacilli inhabiting a wide range of habitats. The genus harbours three recognised human pathogens: Y. enterocolitica and Y. pseudotuberculosis, which both cause gastrointestinal disease, and Y. pestis, the causative agent of plague. These three organisms have served as models for a number of aspects of infection biology, including adhesion, immune evasion, evolution of pathogenic traits, and retracing the course of ancient pandemics. The virulence of the pathogenic Yersiniae is heavily dependent on a number of adhesin molecules. Some of these, such as the Yersinia adhesin A and invasin of the enteropathogenic species, and the pH 6 antigen of Y. pestis, have been extensively studied. However, genomic sequencing has uncovered a host of other adhesins present in these organisms, the functions of which are only starting to be investigated. Here, we review the current state of knowledge on the adhesin molecules present in the Yersiniae, their functions and putative roles in the infection process

Anthrax Edema Toxin Induces Maturation of Dendritic Cells and Enhances Chemotaxis towards Macrophage Inflammatory Protein 3β▿

Bacillus anthracis secretes two bipartite toxins, edema toxin (ET) and lethal toxin (LT), which impair immune responses and contribute directly to the pathology associated with the disease anthrax. Edema factor, the catalytic subunit of ET, is an adenylate cyclase that impairs host defenses by raising cellular cyclic AMP (cAMP) levels. Synthetic cAMP analogues and compounds that raise intracellular cAMP levels lead to phenotypic and functional changes in dendritic cells (DCs). Here, we demonstrate that ET induces a maturation state in human monocyte-derived DCs (MDDCs) similar to that induced by lipopolysaccharide (LPS). ET treatment results in downregulation of DC-SIGN, a marker of immature DCs, and upregulation of DC maturation markers CD83 and CD86. Maturation of DCs by ET is accompanied by an increased ability to migrate toward the lymph node-homing chemokine macrophage inflammatory protein 3β, like LPS-matured DCs. Interestingly, cotreating with LT differentially affects the ET-induced maturation of MDDCs while not inhibiting ET-induced migration. These findings reveal a mechanism by which ET impairs normal innate immune function and may explain the reported adjuvant effect of ET

Adhesins and Host Serum Factors Drive Yop Translocation by <i>Yersinia</i> into Professional Phagocytes during Animal Infection

<div><p><i>Yersinia</i> delivers Yops into numerous types of cultured cells, but predominantly into professional phagocytes and B cells during animal infection. The basis for this cellular tropism during animal infection is not understood. This work demonstrates that efficient and specific Yop translocation into phagocytes by <i>Yersinia pseudotuberculosis</i> (<i>Yptb</i>) is a multi-factorial process requiring several adhesins and host complement. When WT <i>Yptb</i> or a multiple adhesin mutant strain, <i>ΔailΔinvΔyadA</i>, colonized tissues to comparable levels, <i>ΔailΔinvΔyadA</i> translocated Yops into significantly fewer cells, demonstrating that these adhesins are critical for translocation into high numbers of cells. However, phagocytes were still selectively targeted for translocation, indicating that other bacterial and/or host factors contribute to this function. Complement depletion showed that complement-restricted infection by <i>ΔailΔinvΔyadA</i> but not WT, indicating that adhesins disarm complement in mice either by prevention of opsonophagocytosis or by suppressing production of pro-inflammatory cytokines. Furthermore, in the absence of the three adhesins and complement, the spectrum of cells targeted for translocation was significantly altered, indicating that <i>Yersinia</i> adhesins and complement direct Yop translocation into neutrophils during animal infection. In summary, these findings demonstrate that in infected tissues, <i>Yersinia</i> uses adhesins both to disarm complement-dependent killing and to efficiently translocate Yops into phagocytes.</p></div

Adhesin mutants have variable, strain dependent effects on translocation into professional phagocytes.

<p>Splenocytes were infected with the indicated ETEM-expressing strains at an MOI of 1∶1 for (<b>A</b>) 1 h with IP2666, (<b>B</b>) 45 min with IP32953 strains or (<b>C</b>) 45 min with YPIII strains. Professional phagocytes were distinguished by cell-type surface marker staining using flow cytometry. The left Y-axis represents the percentage of each cell type in the spleen (white bars) while the right Y-axis represents the percentage of each cell type present in the Blue⁺ population (grey bars). Experiment was repeated 3–8 times (ND, not determined; *P<0.05, **P<0.01 and ***P<0.001 compared to WT).</p

Complement depletion restores virulence and translocation of Yops by the <i>ΔailΔinvΔyadA</i> mutant.

<p>CVF-treated mice were infected IV with 800 CFU of IP2666 WT-ETEM (1X-WT), 800 CFU of <i>ΔailΔinvΔyadA-ETEM</i> (1X-<i>ΔailΔinvΔyadA</i>), or 30,000 CFU of <i>ΔailΔinvΔyadA-ETEM</i> (37.5X-<i>ΔailΔinvΔyadA</i>). (<b>A</b>) Animals were monitored for morbidity and mortality for a period of 15 days post infection and survival was plotted. (<b>B–D</b>) Four days post-infection, spleens were isolated to determine CFUs (<b>B</b>) and the percentage of Blue⁺ cells present in the organ compared to the log₁₀CFU (<b>C</b>). (<b>B–C</b>) Each symbol represents data from one mouse; the bar in (<b>B</b>) represents the geometric mean. (<b>C</b>) The black line represents values from mice infected with 800 CFU WT-ETEM as shown in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003415#ppat-1003415-g004" target="_blank">Fig. 4B</a>, open-grey squares with grey line represents CVF-treated mice infected with 800 CFU WT-ETEM and open-grey triangles with dashed grey dotted line represent values from 800 CFU <i>ΔailΔinvΔyadA</i>-ETEM. Linear regression analysis determined that the percentage of Blue⁺ cells is the same in both WT infections regardless of CVF. In contrast, the CVF+1X-<i>ΔailΔinvΔyadA</i> injected Yops into significantly more cells than 1X-WT and CVF+1X-WT (with P<0.0001 for both). (<b>D</b>) The distribution of cell types found in the organ (white bars, left y-axis) versus the distribution of cell types found in the Blue⁺ population (gray bars, right y-axis) for each infection condition was compared. (<b>B and D</b>) (**P<0.01 and ***P<0.001). Data from mice infected with 800 CFU of WT-ETEM and 30,000 CFU of <i>ΔailΔinvΔyadA</i> in panels <b>B–D</b> are from the same mice analyzed in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003415#ppat-1003415-g004" target="_blank">Fig. 4B–C</a>.</p

Serum directs Yop translocation into professional phagocytes.

<p>(<b>A–C</b>) Splenocytes in 5% HIS, Fn (40 µg/ml), BSA (5 mg/ml) or SFM were infected for 1 h with IP2666 WT-ETEM at an MOI of 0.2∶1, 0.5∶1 or 1∶1 and the percentage of Blue⁺ cells was determined by FACS. (<b>B–C</b>) Splenocytes infected for 1 h with IP2666 WT-ETEM at an MOI of 0.2∶1 or 1∶1 in SFM or an MOI of 1∶1 in HIS were analyzed for (<b>B</b>) the percentage of Blue⁺ cells in each cell type population or (<b>C</b>) the percentage of each cell type in the Blue⁺ population (gray bars) compared to the percentage of each cell type in the spleen (white bars). (<b>D</b>) Splenocytes were infected for 1 h at an MOI of 1∶1 with IP2666 WT-ETEM, <i>ΔailΔinvΔyadA-ETEM</i> or <i>ΔyopB-ETEM</i> and the percentage of Blue⁺ cells was determined. (<b>E–F</b>) Splenocytes were infected with the indicated IP2666 GFP⁺ strains at an MOI of 0.5∶1 and (<b>E</b>) the percentage of cells bound to GFP⁺ bacteria determined by fluorescence intensity in the FITC channel of the total splenocyte population, or (<b>F</b>) the percentage of specific cell types bound by GFP⁺<i>Yptb</i>. Experiment was repeated 5–8 times (*P<0.05, **P<0.01 and ***P<0.001).</p