Special Issue "Enterotoxins"

Guest Editor
Dr. C. Chris Yun
Emory University, School of Medicine, Division of Digestive Diseases, Whitehead Bldg., Suite 201, 615 Michael St. Atlanta, GA 30322, USA
Website: http://medicine.emory.edu/gi/profile_highlights.cfm?id=4021#top
E-Mail:
Interests: effects of lysophosphoipids in colon cancer and colitis; sodium and fluid absorption in the intestine and kidney; protein-protein interaction; chemokine sin colon cancer; cancer therapeutics; GPCR signaling

Dear Colleagues,

Enterotoxins elicit their primary effects in the intestinal tract, initiating a metabolic cascade that results in excessive fluid and electrolyte secretion. Enterotoxins are frequently cytotoxic and kill cells by altering the apical membrane permeability of the mucosal epithelial cells of the intestinal wall. The uniform host response is the development of diarrhea. However, at a cellular level and subcellular level, certain enterotoxins induce sophisticated and fascinating metabolic alterations, which can affect the local immune system in a characteristic fashion. In some cases, enterotoxins induce disease outside the gastrointestinal tract, affecting other organ systems. Enterotoxins can exert diverse effects at the same time, either inducing or suppressing the immune cascade. This special issue of Toxins deals with major achievement and recent advances in enterotoxin secretion, toxin trafficking, toxin recognition, host interaction, and disease progression.

C. Chris Yun, Ph. D.
Guest Editor

Submission

All manuscripts should be submitted to toxins@mdpi.org with a copy to the Guest Editor. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Toxins is an international peer-reviewed Open Access monthly journal published by MDPI.

• enterotoxin
• immune response
• diarrhea
• ion channel
• epithelial cells
• membrane permeability

Type of Paper: Article
Title: Staphylococcal Enterotoxin B Binds and Regulates CD1d in Human Renal Proximal Tubule Epithelial Cells
Authors: Jeffrey W. Shupp and Rasha Hammamieh
Affiliation: The Burn Center, Washington Hospital Center, Room 3B-55, 110 Irving Street NW, Washington, DC 20010, USA; E-Mail: jeffrey.w.shupp@medstar.net (J.W.S.); rasha.hammamieh1@us.army.mil (R.H.)
Abstract: Staphylococcal eneterotoxin B (SEB) a monovalent T cell mitogen and inducer of T suppressor cells. It is known to form complexes with the major histocompatibility complex class II and T-cell receptor (TCR) in a manner that is quite different from the way the natural ligands bind to the same receptors. It was hypothesized that SEB binds to renal proximal tubule epithelial cells (RPTEC) using a mechanism that does not involve MHC-II. CD1d is an MHC class I homologous protein that is present in the plasma membrane lipid rafts and is proposed to be involved in presenting the antigen to the NK cells. SEBs ability to bind RPTECs was confirmed by fluorescent microscopy. Next, CD1d mRNA expression was showed to increase as early as one hour in cells exposed to SEB. Co-localization studies first completed qualitatively and visualized by fluorescent microscopy showed that the two molecular were interacting. Subsequent quantitative immunoprecipitation assays confirmed this co-localization. The kinetics of this interaction was further defined using diffraction-based dotReadyTM immunoassays which again confirmed binding. This work provides strong evidence that enterotoxin is binding a surface molecule not associated with MHC-II on kidney cells. This could explain additional toxin-mediate lesions not entirely attributed to superantigen response alone.

Type of Paper: Article
Title: Shiga Toxin 1 Is Transported Into the Nucleoli of Intestinal Epithelial Cells via a Carrier-Dependent Process
Authors: Boris Baibakov, Rakhilya Murtazina, Christian Elowsky, Francis M. Giardiello and Olga Kovbasnjuk
Affiliation: GI Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA; E-Mails: BorisB@intra.niddk.nih.gov (B.B.); rakhilya@hotmail.com (R.M.); celowsky21@yahoo.com (C.E.); fgiardi@jhmi.edu (F.M.G.); okovbas1@jhmi.edu (O.K.)
Abstract: Shiga toxin 1 (Stx1) produced by the invasive Shigella dysenteriae serotype1 (S. dysenteriae1) causes gastrointestinal and kidney complications. It has been assumed that Stx1 is released intracellularly after enterocyte invasion by S. dysenteriae1. There is little information about Stx1 distribution inside the S. dysenteriae1-infected enterocytes. Here, using intestinal epithelial T84 cell line we characterized the trafficking of Stx1 delivered into the cytosol, as in case of S. dysenteriae1 infection. We found that cytoplasmic Stx1 is transported into the nucleoli. Stx1 nucleolar movement is a carrier- and energy-dependent. Stx1 binding to the nucleoli of normal human colonocytes in vitro supports the role of nucleolar trafficking in toxin-induced intestinal pathology.

Type of Paper: Review
Title: The Pulmonary Response to Staphylococcal Enterotoxins Provide New Ground for Understanding T Cell Mediated Toxicity
Author: Anthony T. Vella
Affiliation: Department of Immunology-MC1319, University of Connecticut Heath Center, 263 Farmington Avenue, Farmington, CT 06030, USA; E-Mail: vella@uchc.edu
Abstract: In response to environmental cues the human pathogen Staphylococcus aureus synthesizes and releases proteinaceous enterotoxins. These enterotoxins are etiologic entities of severe food poisoning and toxic shock syndrome, and are currently listed as Category B Bioterrorism Agents by the Center for Disease Control and Prevention. Nevertheless, they are associated with human respiratory illnesses. Their role in respiratory disease is only beginning to be understood, but likely stems from the ability of enterotoxins to elicit powerful episodes of T cell stimulation resulting in release of pro-inflammatory cytokines. Here, we discuss the role of the immune system and potential therapies.

Type of Paper: Review
Title: Multiple Roles of Staphylococcus Aureus Enterotoxins: Pathogenicity, Superantigenic Activity, and Correlation to Antibiotic Resistance
Authors: Elena Ortega, Hikmate Abriouel, Rosario Lucas and Antonio Gálvez
Affiliation: Area de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071-Jaén, Spain; E-Mail: agalvez@ujaen.es
Abstract: Heat-stable enterotoxins are the most notable virulence factors associated with Staphylococcus aureus, a common pathogen associated with serious community and hospital acquired diseases. Staphylococcal enterotoxins (SEs) belong to a large family of pyrogenic exotoxins that cause toxic shock-like syndromes and have been implicated in food poisoning. But SEs also act as superantigens that stimulate non-specific T-cell proliferation, and a high correlation between these activities has been detected, so in most cases a loss of superantigen activity results in loss of enterotoxic activity as well. Most of the nosocomial S. aureus infections are caused by methicillin-resistant S. aureus (MRSA) strains, widely recognized as a major cause of morbidity and mortality throughout the world. MRSA strains resistant to quinolones or multiresistant to other antibiotics are emerging, leaving a limited choice for their control. This review focuses on these diverse roles of SE, their possible correlations and the influence in disease progression and therapy.

Title: Unexpected Modulation of Recall B and T Cell Responses After Immunization with Rotavirus-like Particles in the Presence of LT-R192G
Authors: Fatou Thiam ¹, Cyrille Di Martino ¹, Fabienne Bon ¹, Annie Charpilienne ², Didier Poncet ², John D. Clements ³, Christelle Basset ¹ and Evelyne Kohli ¹
Affiliations: ¹ Laboratoire des Interactions Muqueuses-Agents transmissibles (LIMA), UPR562, UFRs Médecine et Pharmacie, IFR Santé-STIC, Université de Bourgogne, Dijon, France; E-Mail: doyen.ufrpharmacie@u-bourgogne.fr (E.K.)
² Virologie Moléculaire et Structurale, UMR CNRS 2472 INRA 1157, Gif/Yvette, France
³ Department of Microbiology and Immunology, Tulane University Health Sciences Center, New Orleans, LA 70112, USA
Abstract: LT-R192G, a mutant of the thermolabile enterotoxin of E.coli (LT), is a potent adjuvant that enhances immune responses to coadministered antigens. Humoral and cellular immune responses are generally analyzed at the end of protocols including at least 2 administrations, but rarely after a prime. To investigate this point, we compared B and T cell responses in mice after one and two intrarectal immunizations with 2/6 rotavirus-like particles (2/6-VLP) in the presence of LT-R192G. Despite a secondary antibody response, we found, after a second immunization, an unexpected lower B cell expansion measured by flow cytometry in related lymphoid tissues. Of note, most of B cells were non conventional CD5+ B cells. We then analyzed CD4+CD25+Foxp3+ regulatory (Tregs) and CD4+CD25+Foxp3- helper T cells after in vitro (re)stimulation of cells from mice immunized with the antigen (VLP) and/or LT-R192G as well as control mice. VLP did not have any effects on cells from non-immunized and VLP immunized mice, whereas they activated CD4+CD25+Foxp3- helper T cells from mice immunized with VLP and LT-R192G, as seen with CD25 expression and IL-2 production. They also increased CD25 and Foxp3 expression on Tregs. LT-R192G decreased dramatically Tregs from non-immunized and VLP immunized mice but not from mice immunized in the presence of adjuvant. On the contrary, after a recall, LT-R192G increased Foxp3 expression on CD4+CD25+Foxp3+ cells. Finally, when both VLP and LT-R192G were used for restimulation, LT-R192G inhibited VLP-induced CD25 increase on both Tregs and helper T cells, whereas Foxp3 expression by Tregs was increased.
All together, these results suggest that LT-R192G exerts different effects, depending on a first or a second contact, an adjuvant effect during the prime and an immunomodulatory effect during the boost.

Title: Cholera-like Enterotoxins and Regulatory T Cells
Authors: Christelle Basset ¹, Fatou Thiam ¹, Cyrille Di Martino ¹, John Holton ² and Evelyne Kohli ¹
Affiliations: ¹ Laboratoire des Interactions Muqueuses-Agents transmissibles (LIMA), UPR562, UFRs Médecine et Pharmacie, IFR Santé-STIC, Université de Bourgogne, Dijon, France; E-Mail: doyen.ufrpharmacie@u-bourgogne.fr (E.K.)
² Windeyer Institute of Medical Sciences, University College London, London
Abstract: Cholera toxin (CT) and the heat-labile enterotoxin of E. coli (LT), as well as their non toxic mutants, are potent mucosal adjuvants of immunization eliciting mucosal and systemic responses against unrelated co-administered antigens in experimental models and in humans (non toxic mutants). These enterotoxins are composed of two subunits, the A subunit, responsible for an ADP-ribosyl transferase activity and the B subunit, responsible for cell binding. Paradoxically, whereas the whole toxins have adjuvant properties, the B subunits of CT (CTB) and of LT (LTB) have been shown to induce antigen specific tolerance when administered mucosally with antigens, in experimental models as well as, recently, in humans, making them an attractive strategy to prevent or treat autoimmune or allergic disorders. Immunomodulation is a complex process involving many cell types notably antigen presenting cells and regulatory T cells. In this review, we will focus on regulatory T cells and cholera-like enterotoxins and their non toxic derivates, with regard to subtype, in vivo/vitro effects and possible role in the modulation of immune responses to co-administered antigens.

Type of Paper: Review
Title: Production, Secretion and Biological Activity of Bacillus cereus Enterotoxins
Authors: Sonia Senesi and Emilia Ghelardi
Affiliation: Dipartimento di Patologia Sperimentale, Biotecnologie Mediche, Infettivologia ed Epidemiologia, and Dipartimento di Biologia, Università di Pisa, 56127 Pisa, Italy; E-Mail: ssenesi@biologia.unipi.it (S.S.)
Abstract: Bacillus cereus behaves as an opportunistic pathogen frequently causing gastrointestinal diseases, though it is increasingly recognised to be responsible for severe local or systemic infections. Pathogenicity of B. cereus mainly relies on the secretion of a wide array of toxins and enzymes and also on the ability to undergo swarming differentiation in response to surface-sensing. In this report, the pathogenicity exerted by B. cereus toxins is described with particular attention to the regulatory mechanisms of production and secretion of HBL, NhE and CytK enterotoxins.

Type of Paper: Review
Title: Heat-Labile Enterotoxin: Beyond GM1 Binding
Authors: Benjamin Mudrak ¹ and Meta J. Kuehn ²
Affiliations: ¹ Department of Molecular Genetics and Microbiology, Duke University, Durham, NC 27710, USA; E-Mail: bm36@duke.edu
² Department of Biochemistry (M.J.K.), Duke University, Durham, NC 27710, USA; E-Mail: mkuehn@biochem.duke.edu
Abstract: Enterotoxigenic Escherichia coli (ETEC) is a significant source of morbidity and mortality worldwide. One major virulence factor released by ETEC is the heat-labile enterotoxin LT, which is structurally and functionally similar to cholera toxin. LT consists of five B subunits carrying a single catalytically active A subunit. LTB binds the monosialoganglioside GM1, the toxin's host receptor, but interactions with A-type blood sugars and E. coli lipopolysaccharide have also been identified within the past decade. Here, we review the regulation, assembly, and binding properties of the LT B-subunit pentamer and discuss the possible roles of its numerous molecular interactions.

Type of Paper: Article
Title: The Cytokine Storm Induced by TSST-1 LPS Treatment in Human MNC in Vitro and in Rabbits and Mice in Vivo Is Completely Dependent on TSST-1-TCR Interaction
Authors: Norbert Stich ¹, Martina Waclavicek ¹, Nina Model ¹ and Martha M. Eibl ^1,2
Affiliations: ¹ Biomedizinische ForschungsgmbH, Vianna, Austria; E-Mail: martha.eibl@meduniwien.ac.at (M.M.E.)
² Immunology Outpatient Clinic, Vianna, Austria
Abstract: LPS toxicity paralleled by cytokine gene expression can be upregulated by pre-treatment with staph. superantigens. We assessed cytokine gene induction by staph. toxin TSST-1 and LPS in human MNC and detected the amplified expression of inflammatory cytokine genes. Cytokine gene expression in vivo after this double challenge in rabbits and mice was also greatly amplified in the organs - liver, spleen and lungs, but not in cells in the circulation. Two TSST-1 mutants – an MHC and a TCR binding site mutant – revealed that the MHC binding site mutant behaved like the toxin, while the cytokine storm was abrogated by the TCR binding site mutant. This is the first demonstration in vivo that the induction of inflammatory cytokines (cytokine storm) by staph. superantigens and LPS is completely dependent on superantigen TCR interaction.

Type of Paper: Article
Title: Expression of Functional Heat-labile Enterotoxin and Mutants in Plant Systems
Author: Hugh Mason
Affiliation: Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, AZ 85287-5401, USA; E-Mail: Hugh.Mason@asu.edu
Abstract: Plants and plant cell expression systems represent robust alternatives for recombinant protein production. We produced functional E. coli heat-labile enterotoxin (LT) in whole plants and plant cells by co-expressing plant-optimized genes encoding native or mutant A (enzymatic component) and B (binding) subunits. A1:B5 complexes, assayed by ganglioside-dependent ELISA, accumulated in stably transgenic tobacco cell lines and in leaves of Nicotiana benthamiana that were transfected with plant viral vectors. Native or mutant LT’s displayed functionality and equivalence to bacterial LT’s in the cell-rounding assay. We conclude that plant systems will be useful for expression of LT’s, especially for use as mucosal adjuvants.

Type of Paper: Review
Title: The Enterotoxicity of Clostridium Difficile Toxins
Author: Hanping Feng
Affiliation: Cummings School of Veterinary Medicine, Tufts University 200 Westboro Rd, Bldg 20, Rm103 North Grafton, MA 01536, USA; E-Mail: hanping.feng@tufts.edu
Abstract: It is well established that the major virulence factors of Clostridium difficile infection (CDI) are two large exotoxins A (TcdA) and B (TcdB). However, our understanding of the specific roles of these toxins in CDI is still evolving. It is now accepted that both toxins are enterotoxic and proinflammatory in human intestine. Both purified TcdA and TcdB are capable of mimicking the pathophysiological events evident during CDI, although most studies have focused on TcdA. C. difficile toxins exert a wide array of biological activities, either by directly acting on intestinal epithelial cells, or indirectly by stimulating neurons and immune cells to elicit proinflammatory cytokines, neuropeptides, and other neuroimmune mediators. This review covers the mechanisms of TcdA- and TcdB-induced enterotoxicity and the recent developments in this field.