IL-8 is a key chemokine regulating neutrophil recruitment in a new mouse model of Shigella-induced colitis

Outer membrane protein A (OmpA) of Shigella flexneri 2a, induces protective immune response in a mouse model

Background

In our earlier studies 34 kDa outer membrane protein (OMP) of Shigella flexneri 2a has been identified as an efficient immunostimulant.

Key Results

In the present study MALDI-TOF MS analysis of the purified 34 kDa OMP of Shigella flexneri 2a shows considerable sequence homology (Identity 65%) with the OmpA of S. flexneri 2a. By using the specific primers, the gene of interest has been amplified from S. flexneri 2a (N.Y-962/92) genomic DNA, cloned in pET100/D-TOPO® vector and expressed using induction with isopropyl thiogalactoside (IPTG) for the first time. Immunogenicity and protective efficacy of the recombinant OmpA has been evaluated in an intranasally immunized murine pulmonary model. The recombinant protein induces significantly enhanced protein specific IgG and IgA Abs in both mucosal and systemic compartments and IgA secreting cells in the systemic compartment (spleen). The mice immunized with OmpA have been protected completely from systemic challenge with a lethal dose of virulent S. flexneri 2a. Immunization with the protein causes mild polymorphonuclear neutrophil infiltration in the lung, without inducing the release of large amounts of proinflammatory cytokines.

Conclusion

These results suggest that the OmpA of S. flexneri 2a can be an efficacious mucosal immunogen inducing protective immune responses. Our findings also demonstrate that antibodies and Th1 immune response may be associated with the marked protective efficacy of immunized mice after intranasal shigellae infection.

Shigella enterotoxin-2 is a type III effector that participates in Shigella-induced interleukin 8 secretion by epithelial cells

We have previously described a protein termed Shigella enterotoxin 2 (ShET-2), which induces rises in short-circuit current in rabbit ileum mounted in the Ussing chamber. Published reports have postulated that ShET-2 may be secreted by the Shigella type III secretion system (T3SS). In this study, we show that ShET-2 secretion into the extracellular space requires the T3SS in Shigella flexneri 2a strain 2457T and a ShET-2-TEM fusion was translocated into epithelial cells in a T3SS-dependent manner. The ShET-2 gene, sen, is encoded downstream of the ospC1 gene of S. flexneri, and we show that sen is cotranscribed with this T3SS-secreted product. Considering that T3SS effectors have diverse roles in Shigella infection and that vaccine constructs lacking ShET-2 are attenuated in volunteers, we asked whether ShET-2 has a function other than its enterotoxic activity. We constructed a ShET-2 mutant in 2457T and tested its effect on epithelial cell invasion, plaque formation, guinea pig keratoconjunctivitis and interleukin 8 (IL-8) secretion from infected monolayers. Although other phenotypes were not different compared with the wild-type parent, we found that HEp-2 and T84 cells infected with the ShET-2 mutant exhibited significantly reduced IL-8 secretion into the basolateral compartment, suggesting that ShET-2 might participate in the Shigella-induced inflammation of epithelial cells.

Arsenic trioxide reduces 2,4,6-trinitrobenzene sulfonic acid-induced murine colitis via nuclear factor-κB down-regulation and caspase-3 activation

Arsenic trioxide, As 2O3, already used in human anti-cancer therapy, is also an efficient agent against the autoimmune and inflammatory diseases developed in MRL/lpr mice. Inflammatory bowel diseases (IBDs), notably Crohn’s disease, which remain without efficient treatment, display autoimmune and inflammatory components. We, therefore, hypothesized that As2O 3 may be active on IBDs. Using the 2,4,6-trinitrobenzene sulfonic acid-induced murine model of colitis, we demonstrate that As2O3 used either in a preventive or a curative mode markedly reduced the induced colitis as assessed by macroscopic and microscopic scores, leading to prolonged mice survival. In addition, As2O3 was able to inhibit NF-κB expression and DNA-binding in colon extracts leading to decreased cytokine gene expression (i.e. tumor necrosis factor-α, interleukin(IL)-1β, IL-12, IL-17, IL-18, and IL-23). Interestingly, As2O3 also reduced keratinocyte-derived chemokine (KC), inducible nitric oxide synthase (iNOS) mRNA levels, and myeloperoxidase (MPO) protein expression suggesting an impairment of neutrophils. This was associated with a marked increase of procaspase-3 and induced caspase-3 activation. This caspase-3 co-localized with MPO in the remaining neutrophils suggesting that As2O 3 might have eliminated inflamed cells probably by inducing their apoptosis. These results assessed the potent anti-inflammatory effect of As2O 3, that targets both NF-κB and caspase-3 pathways, and suggests a therapeutic potential for Crohn’s disease and other severe IBDs.

Enteropathogenic Escherichia coli, Samonella, Shigella and Yersinia: cellular aspects of host-bacteria interactions in enteric diseases

A successful infection of the human intestine by enteropathogenic bacteria depends on the ability of bacteria to attach and colonize the intestinal epithelium and, in some cases, to invade the host cell, survive intracellularly and disseminate from cell to cell. To accomplish these processes bacteria have evolved an arsenal of molecules that are mostly secreted by dedicated type III secretion systems, and that interact with the host, subverting normal cellular functions. Here we overview the most important molecular strategies developed by enteropathogenic Escherichia coli, Salmonella enterica, Shigella flexneri, and Yersinia enterocolitica to cause enteric infections. Despite having evolved different effectors, these four microorganisms share common host cellular targets.

Review article: anti-inflammatory mechanisms of action of Saccharomyces boulardii

BACKGROUND

Saccharomyces boulardii, a well-studied probiotic, can be effective in inflammatory gastrointestinal diseases with diverse pathophysiology, such as inflammatory bowel disease (IBD), and bacterially mediated or enterotoxin-mediated diarrhoea and inflammation.

AIM

To discuss the mechanisms of action involved in the intestinal anti-inflammatory action of S. boulardii.

METHODS

Review of the literature related to the anti-inflammatory effects of this probiotic.

RESULTS

Several mechanisms of action have been identified directed against the host and pathogenic microorganisms. S. boulardii and S. boulardii secreted-protein(s) inhibit production of proinflammatory cytokines by interfering with the global mediator of inflammation nuclear factor kappaB, and modulating the activity of the mitogen-activated protein kinases ERK1/2 and p38. S. boulardii activates expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) that protects from gut inflammation and IBD. S. boulardii also suppresses 'bacteria overgrowth' and host cell adherence, releases a protease that cleaves C. difficile toxin A and its intestinal receptor and stimulates antibody production against toxin A. Recent results indicate that S. boulardii may interfere with IBD pathogenesis by trapping T cells in mesenteric lymph nodes.

CONCLUSIONS

The multiple anti-inflammatory mechanisms exerted by S. boulardii provide molecular explanations supporting its effectiveness in intestinal inflammatory states.

Which is better to preserve pulmonary function: short-term or prolonged leukocyte depletion during cardiopulmonary bypass?

OBJECTIVES

Neutrophils are crucial in the development of acute lung injuries during cardiopulmonary bypass. However, the efficacy of leukocyte depletion on pulmonary protection remains controversial, possibly owing to different filtration strategies used in the literature. In this study, we investigated whether short-term leukocyte depletion strategy is more efficacious than prolonged leukocyte depletion in preserving pulmonary function.

METHODS

Eighteen adult dogs were randomized equally into 3 groups. Leukocyte-depleting filters were used for 10 minutes in the LD-S group, throughout cardiopulmonary bypass in the LD-T group, and not used in the control group. Neutrophil counts, elastase, and interleukin-8 concentrations in plasma, myeloperoxidase and interleukin-8 concentrations in pulmonary tissue, and pulmonary vascular resistance and oxygen index were determined to evaluate the inflammatory response and damage to pulmonary function.

RESULTS

Although the neutrophil count and pulmonary parenchymal myeloperoxidase contents were significantly lower in both LD-S and LD-T groups than that in the control group, lower pulmonary parenchymal interleukin-8 level, lower pulmonary vascular resistance (113 +/- 33 dyne x s/cm(5)), higher oxygen index (366 +/- 82.3 mm Hg), and thinner alveolus wall thickness were seen only in the LD-S group, and the pulmonary parenchymal interleukin-8 levels were also lower in the LD-S group after cardiopulmonary bypass. The plasma elastase and interleukin-8 levels were significantly lower in the LD-S group, but they were significantly higher in the LD-T group compared with the control group after cardiopulmonary bypass.

CONCLUSIONS

Short-term rather than prolonged leukocyte depletion during cardiopulmonary bypass appears to be more efficacious in protecting pulmonary function via attenuation of the extracorporeal circulation-induced inflammatory response.

Commensal bacteria can enter colonic epithelial cells and induce proinflammatory cytokine secretion: a possible pathogenic mechanism of ulcerative colitis

Interleukin 2 (IL-2)- and IL-10-knockout mice develop spontaneous colitis under conventional but not germ-free conditions, suggesting that commensal bacteria play an important role in the pathogenesis of colitis. However, interactions between commensal bacteria and colonic epithelial cells have not been fully investigated. We therefore assessed the ability of various commensal bacteria and probiotics to adhere to and invade colonic epithelial cells. Effects of the bacteria on production of proinflammatory cytokines were also measured. Commensal bacteria, including mucosal organisms isolated from ulcerative colitis (UC) patients, such as Fusobacterium varium, reported as a possible pathogen in UC, Bacteroides vulgatus, Escherichia coli and Clostridium clostridioforme, as well as their type strains and probiotics, were assessed for their ability to adhere to and invade colonic epithelial cells using two cell lines, SW-480 and HT-29. Our experiments employed co-incubation, a combination of scanning and transmission electron microscopy and recovery of bacteria from infected-cell lysates. F. varium and several other commensal bacteria, but not probiotics, adhered to colonic epithelial cells and invaded their cytoplasm. ELISA and real-time PCR revealed that the host cells, particularly those invaded by F. varium, showed significant increases in IL-8 and TNF-alpha concentrations in supernatants, with elevation of IL-8, TNF-alpha, MCP-1 and IL-6 mRNAs. Furthermore, IL-8 and TNF-alpha expression and nuclear phosphorylated NF-kappaB p65 expression could be immunohistochemically confirmed in inflamed epithelium with cryptitis or crypt abscess in UC patients. Certain commensal bacteria can invade colonic epithelial cells, activating early intracellular signalling systems to trigger host inflammatory reactions.

Decreased expression of colonic Slc26a3 and carbonic anhydrase iv as a cause of fatal infectious diarrhea in mice

Citrobacter rodentium causes epithelial hyperplasia and colitis and is used as a model for enteropathogenic and enterohemorrhagic Escherichia coli infections. Little or no mortality develops in most inbred strains of mice, but C3H and FVB/N mice exhibit fatal outcomes of infection. Here we test the hypothesis that decreased intestinal transport activity during C. rodentium infection results in fatality in C3H/HeOu and FVB/N mice. Susceptible strains were compared to resistant C57BL/6 mice and to inbred strains SWR and SJL of Swiss origin, which have not been previously characterized for outcomes of C. rodentium infection. Mortality in susceptible strains C3H/HeOu and FVB/N was associated with significant fluid loss in feces, a remarkable downregulation of Slc26a3 and carbonic anhydrase IV (CAIV) message and protein expression, retention of chloride in stool, and hypochloremia, suggesting defects in intestinal chloride absorption. SWR, SJL, and C57BL/6 mice were resistant and survived the infection. Fluid therapy fully prevented mortality in C3H/HeOu and FVB/N mice without affecting clinical disease. Common pathogenic mechanisms, such as decreased levels of expression of Slc26a3 and CAIV, affect intestinal ion transport in C. rodentium-infected FVB and C3H mice, resulting in profound electrolyte loss, dehydration, and mortality. Intestinal chloride absorption pathways are likely a potential target for the treatment of infectious diarrhea.

Subcellular alterations that lead to diarrhea during bacterial pathogenesis

Pathogenic microorganisms routinely exploit host cellular functions for their benefit. These alterations often enhance the survival and/or dissemination of the pathogen. However, these effects on the host can be quite debilitating. Consequently, an in-depth understanding of the molecular mechanisms employed by pathogens to manipulate their hosts is crucial. One of the common host phenotypes elicited by enteric pathogens is the generation of diarrhea. Here, we overview the current advances in understanding strategies used by bacterial pathogens to cause diarrheal diseases and discuss how the coordination of various subcellular events can influence disease progression.

The interplay between Entamoeba and enteropathogenic bacteria modulates epithelial cell damage

Background

Mixed intestinal infections with Entamoeba histolytica, Entamoeba dispar and bacteria with exacerbated manifestations of disease are common in regions where amoebiasis is endemic. However, amoeba–bacteria interactions remain largely unexamined.

Methodology

Trophozoites of E. histolytica and E. dispar were co-cultured with enteropathogenic bacteria strains Escherichia coli (EPEC), Shigella dysenteriae and a commensal Escherichia coli. Amoebae that phagocytosed bacteria were tested for a cytopathic effect on epithelial cell monolayers. Cysteine proteinase activity, adhesion and cell surface concentration of Gal/GalNAc lectin were analyzed in amoebae showing increased virulence. Structural and functional changes and induction of IL-8 expression were determined in epithelial cells before and after exposure to bacteria. Chemotaxis of amoebae and neutrophils to human IL-8 and conditioned culture media from epithelial cells exposed to bacteria was quantified.

Principal Findings

E. histolytica digested phagocytosed bacteria, although S. dysenteriae retained 70% viability after ingestion. Phagocytosis of pathogenic bacteria augmented the cytopathic effect of E. histolytica and increased expression of Gal/GalNAc lectin on the amoebic surface and increased cysteine proteinase activity. E. dispar remained avirulent. Adhesion of amoebae and damage to cells exposed to bacteria were increased. Additional increases were observed if amoebae had phagocytosed bacteria. Co-culture of epithelial cells with enteropathogenic bacteria disrupted monolayer permeability and induced expression of IL-8. Media from these co-cultures and human recombinant IL-8 were similarly chemotactic for neutrophils and E. histolytica.

Conclusions

Epithelial monolayers exposed to enteropathogenic bacteria become more susceptible to E. histolytica damage. At the same time, phagocytosis of pathogenic bacteria by amoebae further increased epithelial cell damage.

Significance

The in vitro system presented here provides evidence that the Entamoeba/enteropathogenic bacteria interplay modulates epithelial cell responses to the pathogens. In mixed intestinal infections, where such interactions are possible, they could influence the outcome of disease. The results offer insights to continue research on this phenomenon.

In amoebiasis, a human disease that is a serious health problem in many developing countries, efforts have been made to identify responsible factors for the tissue damage inflicted by the parasite Entamoeba histolytica. This amoeba lives in the lumen of the colon without causing damage to the intestinal mucosa, but under unknown circumstances becomes invasive, destroying the intestinal tissue. Bacteria in the intestinal flora have been proposed as inducers of higher amoebic virulence, but the causes or mechanisms responsible for the induction are still undetermined. Mixed intestinal infections with Entamoeba histolytica and enteropathogenic bacteria, showing exacerbated manifestations of disease, are common in endemic countries. We implemented an experimental system to study amoebic virulence in the presence of pathogenic bacteria and its consequences on epithelial cells. Results showed that amoebae that ingested enteropathogenic bacteria became more virulent, causing more damage to epithelial cells. Bacteria induced release of inflammatory proteins by the epithelial cells that attracted amoebae, facilitating amoebic contact to the epithelial cells and higher damage. Our results, although a first approach to this complex problem, provide insights into amoebic infections, as interplay with other pathogens apparently influences the intestinal environment, the behavior of cells involved and the manifestations of the disease.

Delivery of biologically active anti-inflammatory cytokines IL-10 and IL-1ra in vivo by the Shigella type III secretion apparatus

Pathogenicity of many Gram-negative bacteria relies on a type III secretion (T3S) apparatus, which is used for delivery of bacterial effectors into the host cell cytoplasm allowing the bacteria to manipulate host cell cytoskeleton network as well as to interfere with intracellular signaling pathways. In this study, we investigated the potential of the Shigella flexneri T3SA as an in vivo delivery system for biologically active molecules such as cytokines. The anti-inflammatory cytokines IL-10 and IL-1 receptor antagonist (IL-1ra) were genetically fused to the first 30 or 60 residues of the Shigella T3S effector IpaH9.8 or to the first 50 residues of the Yersinia enterocolitica effector YopE and the recombinant fusion proteins were expressed in S. flexneri. YopE(50)-IL-10, IpaH(60)-IL-10, and IpaH(60)-IL-1ra were efficiently secreted via the T3S apparatus of Shigella. Moreover, these recombinant proteins did not impair the invasive ability of the bacteria in vitro. In a murine model, Shigella strains expressing YopE(50)-IL-10, IpaH(60)-IL-10, and IpaH(60)-IL-1ra induced a lower mortality in mice that was associated with reduced inflammation and a restricted localization of bacteria within the lung tissues as compared with wild-type Shigella. Moreover, the level of TNF-alpha and IL-1beta mRNA were reduced in the lungs following infection by IL-10- and IL-1ra-secreting Shigella, respectively. These findings demonstrate that the Shigella T3S apparatus can deliver biologically active cytokines in vivo, thus opening new avenues for the use of attenuated bacteria to deliver proteins for immunomodulation or gene therapy purposes.

Maturation of paneth cells induces the refractory state of newborn mice to Shigella infection

The intestinal tract of adult mice is naturally resistant to infection by Shigella, the causative agent of bacillary dysentery in humans. Conversely, newborn mice are highly susceptible to intragastric Shigella infection and develop inflammatory lesions of the jejunal mucosa, very similar to those observed in the colon of dysenteric patients. However, the susceptibility period is short and one week after birth, animals have acquired a status of resistance characteristic of adult animals. To identify the developmental changes controlling the switch from disease susceptibility to resistance, we performed global gene expression analysis on noninfected and infected intestinal tissues taken from 4-day- and 7-day-old animals. Transcriptomic analysis of 4-day-old mice infected with the invasive Shigella strain showed a profile reflecting a strong inflammatory response with no evidence for retro-control, suggesting that the invasive process had occurred, whereas inflammation had been controlled after infection with the noninvasive strain. Differences in gene expression profiles between noninfected 4-day- and 7-day-old mice corresponded mainly to genes encoding anti-microbial peptides and proteases, suggesting that these molecules could be candidates for host antimicrobial resistance in the course of shigellosis. Indeed, expression of genes specific of Paneth cells was higher in 7-day- than in 4-day-old mice, and histological analysis indicated that Paneth cells were present only at day 7. Finally, using Sox9(flox/flox)-vil-cre mice, we showed that depletion of Paneth cells restored the susceptibility to Shigella of 7-day-old mice, clearly indicating that Paneth cells development is crucial for the clearance of intestinal infection.

Distinct isoforms of phospholipase A2 mediate the ability of Salmonella enterica serotype typhimurium and Shigella flexneri to induce the transepithelial migration of neutrophils

Salmonella spp. and Shigella spp. are responsible for millions of cases of enteric disease each year worldwide. While these pathogens have evolved distinct strategies for interacting with the human intestinal epithelium, they both induce significant proinflammatory responses that result in massive transepithelial migration of neutrophils across the intestinal mucosa. It has previously been shown with Salmonella enterica serotype Typhimurium that the process of neutrophil transmigration is mediated in part by the secretion of hepoxilin A(3) (HXA(3); 8-hydroxy-11,12-epoxy-eicosatetraenoic acid), a potent neutrophil chemoattractant, from the apical surface of infected model intestinal epithelium. This study confirms that HXA(3) is also secreted in response to infection by Shigella flexneri, that it is produced by a pathway involving 12/15-lipoxygenase (12/15-LOX), and that S. enterica serovar Typhimurium and S. flexneri share certain elements in the mechanism(s) that underlies the otherwise separate signal transduction pathways that are engaged to induce polymorphonuclear leukocyte (PMN) transepithelial migration (protein kinase C and extracellular signal-regulated kinases 1 and 2, respectively). PMN transepithelial migration in response to infection with S. flexneri was dependent on 12/15-LOX activity, the enzyme responsible for the initial metabolism of arachidonic acid to HXA(3). Probing further into this pathway, we also found that S. enterica serovar Typhimurium and S. flexneri activate different subtypes of phospholipase A(2), a critical enzyme involved in the liberation of arachidonic acid from cellular membranes. Thus, although S. enterica serovar Typhimurium and S. flexneri utilize different mechanisms for triggering the induction of PMN transepithelial migration, we found that their reliance on 12/15-LOX is conserved, suggesting that enteric pathogens may ultimately stimulate similar pathways for the synthesis and release of HXA(3).

Gastrin-mediated interleukin-8 and cyclooxygenase-2 gene expression: differential transcriptional and posttranscriptional mechanisms

BACKGROUND & AIMS

Gastrin induces the expression of cyclooxygenase (COX)-2 and interleukin (IL)-8; however, the mechanism(s), especially in gastric epithelial cells, is not well understood. Here, we have determined the intracellular mechanisms mediating gastrin-dependent gene expression.

METHODS

AGS-E human gastric cancer cell line stably expressing cholecystokinin-2 receptor was treated with amidated gastrin-17. Real-time polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay were performed to determine COX-2 and IL-8 expression and Akt, Erk, and p38 phosphorylation. Gene promoter activity was determined by luciferase assay. Electrophoretic mobility shift assay analysis was performed for nuclear factor kappaB (NF-kappaB) and activator protein-1 activity. RNA stability was determined after actinomycin D treatment. HuR localization was determined by immunocytochemistry.

RESULTS

Gastrin induced COX-2 and IL-8 expression in AGS-E cells, which was inhibited by phosphatidylinositol 3' kinase (PI3K) and p38 inhibitors. Gastrin-mediated Akt activation was observed to be downstream of p38. IL-8 expression was dependent on COX-2-mediated prostaglandin E(2) synthesis. In the presence of an NF-kappaB inhibitor MG132, IL-8 transcription was inhibited, but not that of COX-2. This was confirmed after knockdown of the p65 RelA subunit of NF-kappaB. Further studies showed that COX-2 gene transcription is regulated by activator protein-1. Gastrin increased the stability of both COX-2 and IL-8 messenger RNA (mRNA) in a p38-dependent manner, the half-life increasing from 31 minutes to 8 hours and approximately 4 hours, respectively. Gastrin, through p38 activity, also enhanced HuR expression, nucleocytoplasmic translocation, and enhanced COX-2 mRNA binding.

CONCLUSIONS

Gastrin differentially induces COX-2 and IL-8 expression at the transcriptional and posttranscriptional levels by PI3K and p38 mitogen-activated protein kinase pathways, respectively.

Saccharomyces boulardii interferes with Shigella pathogenesis by postinvasion signaling events

Saccharomyces boulardii is gaining in popularity as a treatment for a variety of diarrheal diseases as well as inflammatory bowel disease. This study was designed to examine the effect of this yeast on infection by Shigella flexneri, a highly infectious and human host-adapted enteric pathogen. We investigated key interactions between the bacteria and host cells in the presence of the yeast in addition to a number of host responses including proinflammatory events and markers. Although the presence of the yeast during infection did not alter the number of bacteria that was able to attach or invade human colon cancer-derived T-84 cells, it did positively impact the tight junction protein zonula occluden-2 and significantly increase the barrier integrity of model epithelia. The yeast also decreased ERK, JNK, and NF-kappaB activation in response to S. flexneri, events likely responsible for the observed reductions in IL-8 secretion and the transepithelial migration of polymorphonuclear leukocytes across T-84 monolayers. These results, suggesting that the yeast allowed for a dampened inflammatory response, were confirmed in vivo utilizing a highly relevant model of human fetal colonic tissue transplanted into scid mice. Furthermore, a cell-free S. boulardii culture supernatant was also capable of reducing IL-8 secretion by infected T-84 cells. These data suggest that although the use of S. boulardii during infection with S. flexneri may alleviate symptoms associated with the inflammatory response of the host, it would not prevent infection.

The role of microbiota in infectious disease

The intestine harbors an ecosystem composed of the intestinal mucosa and the commensal microbiota. The microbiota fosters development, aids digestion and protects host cells from pathogens - a function referred to as colonization resistance. Little is known about the molecular basis of colonization resistance and how it can be overcome by enteropathogenic bacteria. Recently, studies on inflammatory bowel diseases and on animal models for enteric infection have provided new insights into colonization resistance. Gut inflammation changes microbiota composition, disrupts colonization resistance and enhances pathogen growth. Thus, some pathogens can benefit from inflammatory defenses. This new paradigm will enable the study of host factors enhancing or inhibiting bacterial growth in health and disease.

Molecular pathogenesis of Shigella spp.: controlling host cell signaling, invasion, and death by type III secretion

Shigella spp. are gram-negative pathogenic bacteria that evolved from harmless enterobacterial relatives and may cause devastating diarrhea upon ingestion. Research performed over the last 25 years revealed that a type III secretion system (T3SS) encoded on a large plasmid is a key virulence factor of Shigella flexneri. The T3SS determines the interactions of S. flexneri with intestinal cells by consecutively translocating two sets of effector proteins into the target cells. Thus, S. flexneri controls invasion into EC, intra- and intercellular spread, macrophage cell death, as well as host inflammatory responses. Some of the translocated effector proteins show novel biochemical activities by which they intercept host cell signal transduction pathways. An understanding of the molecular mechanisms underlying Shigella pathogenesis will foster the development of a safe and efficient vaccine, which, in parallel with improved hygiene, should curb infections by this widespread pathogen.

Mycoplasma pneumoniae-derived lipopeptides induce acute inflammatory responses in the lungs of mice

The pathogenesis of Mycoplasma pneumoniae infection is considered to be in part attributable to excessive immune responses. In this study, we investigated whether synthetic lipopeptides of subunit b of F0F1-type ATPase (F0F1-ATPase), NF-kappaB-activating lipoprotein 1 (N-ALP1), and N-ALP2 (named FAM20, sN-ALP1, and sN-ALP2, respectively) derived from M. pneumoniae induce cytokine and chemokine production and leukocyte infiltration in vivo. Intranasal administration of FAM20 and sN-ALP2 induced infiltration of leukocyte cells and production of chemokines and cytokines in bronchoalveolar lavage fluid, but sN-ALP1 failed to do so. The activity of FAM20 was notably higher than that of sN-ALP2. FAM20 and sN-ALP2 induced tumor necrosis factor alpha (TNF-alpha) through Toll-like receptor 2 in mouse peritoneal macrophages. Moreover, in the range of low concentrations of lipopeptides, FAM20 showed relatively high activity of inducing TNF-alpha in mouse peritoneal macrophages compared to synthetic lipopeptides such as MALP-2 and FSL-1, derived from Mycoplasma fermentans and Mycoplasma salivarium, respectively. These findings indicate that the F0F1-ATPase might be a key molecule in inducing cytokines and chemokines contributing to inflammatory responses during M. pneumoniae infection in vivo.

Comparison of tissue-selective proinflammatory gene induction in mice infected with wild-type, DNA adenine methylase-deficient, and flagellin-deficient Salmonella enterica

Mutants of Salmonella enterica serovar Typhimurium deficient in DNA adenine methylase (Dam) are attenuated for virulence in mice and confer heightened immunity in vaccinated animals. In contrast, infection of mice with wild-type (WT) strains or flagellin-deficient mutants of Salmonella causes typhoid fever. Here we examined the bacterial load and spatiotemporal kinetics of expression of several classes of host genes in Peyer's patches, the liver, and the spleen following oral infection of mice with WT, dam mutant, or flagellin-deficient (flhC) Salmonella. The genes evaluated included inflammatory (interleukin-1beta [IL-1beta], tumor necrosis factor alpha), chemokine (macrophage inflammatory protein 2), Th1/Th2 indicator (IL-12p40, IL-4), and interferon system (beta interferon [IFN-beta], IFN-gamma, protein Mx1 GTPase, RNA-dependent protein kinase, inducible nitric oxide synthase, suppressor of cytokine signaling 1) beacons. We showed that maximal interferon system and proinflammatory gene induction occurred by 5 days after infection and that the levels were comparable for the WT and flhC strains but were significantly lower for the dam mutant. Additionally, host gene expression in systemic tissues of individual animals was dependent on the bacterial load in the Peyer's patches for mice infected with WT, dam mutant, or flhC mutant Salmonella as early as 8 h after infection. Moreover, a bacterial load threshold in the Peyer's patches was necessary to stimulate the host gene induction in the liver and spleen. Taken together, these results suggest that bacterial load and the accompanying strain-specific cytokine signature are important determinants of the host innate immune response and associated disease manifestations observed in dam mutant Salmonella-infected animals compared to the immune response and disease manifestations observed in WT and flhC mutant Salmonella-infected animals.

Helicobacter pylori chemotaxis modulates inflammation and bacterium-gastric epithelium interactions in infected mice

The ulcer-causing pathogen Helicobacter pylori uses directed motility, or chemotaxis, to both colonize the stomach and promote disease development. Previous work showed that mutants lacking the TlpB chemoreceptor, one of the receptors predicted to drive chemotaxis, led to less inflammation in the gerbil stomach than did the wild type. Here we expanded these findings and examined the effects on inflammation of completely nonchemotactic mutants and mutants lacking each chemoreceptor. Of note, all mutants colonized mice to the same levels as did wild-type H. pylori. Infection by completely nonchemotactic mutants (cheW or cheY) resulted in significantly less inflammation after both 3 and 6 months of infection. Mutants lacking either the TlpA or TlpB H. pylori chemotaxis receptors also had alterations in inflammation severity, while mutants lacking either of the other two chemoreceptors (TlpC and HylB) behaved like the wild type. Fully nonchemotactic and chemoreceptor mutants adhered to cultured gastric epithelial cells and caused cellular release of the chemokine interleukin-8 in vitro similar to the release caused by the wild type. The situation appeared to be different in the stomach. Using silver-stained histological sections, we found that nonchemotactic cheY or cheW mutants were less likely than the wild type to be intimately associated with the cells of the gastric mucosa, although there was not a strict correlation between intimate association and inflammation. Because others have shown that in vivo adherence promotes inflammation, we propose a model in which H. pylori uses chemotaxis to guide it to a productive interaction with the stomach epithelium.

Immunogenicity and protective efficacy offered by a ribosomal-based vaccine from Shigella flexneri 2a

Shigellosis is a major form of bacillary dysentery caused by Shigella infection. Shigella ribosome-based vaccines (SRV), considered among the potent vaccine candidates, are composed of O-antigen and ribosome isolated from S. flexneri 2a. To investigate the immunogenicity and protective efficacy of SRV, mice were vaccinated with SRV via the intranasal (i.n.) route. Interestingly, robust levels of Shigella-derived LPS-specific IgG and IgA Abs and antibody-forming cells were elicited in systemic and mucosal compartments following two i.n. administrations of SRV. Groups of mice receiving i.n. SRV developed milder pulmonary pneumonia upon challenge with virulent S. flexneri 2a than did those receiving parenteral SRV. We further found that the MyD88-dependent TLR2 signal partially mediates SRV-induced mucosal immunity, with the exception of TLR4- and TLR5-governed innate immunity. Most importantly, polymeric immunoglobulin receptor knockout (pIgR-/-) mice, which lack secretory IgA Ab, were afforded less protective efficacy than were wild-type mice. It can be concluded then that SRV is immunogenic and provides protective efficacy in mice. It can also be surmised that a mucosal SRV vaccine would be particularly relevant in targeting shigellosis, which provokes inflammation in the human colon.

New Animal Model of Shigellosis in the Guinea Pig: Its Usefulness for Protective Efficacy Studies

It has been difficult to evaluate the protective efficacy of vaccine candidates against shigellosis, a major form of bacillary dysentery caused by Shigella spp. infection, because of the lack of suitable animal models. To develop a proper animal model representing human bacillary dysentery, guinea pigs were challenged with virulent Shigella flexneri serotype 2a (strains 2457T or YSH6000) or S. flexneri 5a (strain M90T) by the intrarectal (i.r.) route. Interestingly, all guinea pigs administered these Shigella strains developed severe and acute rectocolitis. They lost approximately 20% of their body weight and developed tenesmus by 24 h after Shigella infection. Shigella invasion and colonization of the distal colon were seen at 24 h but disappeared by 48 h following i.r. infection. Histopathological approaches demonstrated significant damage and destruction of mucosal and submucosal layers, thickened intestinal wall, edema, erosion, infiltration of neutrophils, and depletion of goblet cells in the distal colon. Furthermore, robust expression of IL-8, IL-1beta, and inducible NO synthase mRNA was detected in the colon from 6 to 24 h following Shigella infection. Most importantly, in our new shigellosis model, guinea pigs vaccinated with an attenuated S. flexneri 2a SC602 strain possessing high levels of mucosal IgA Abs showed milder symptoms of bacillary dysentery than did animals receiving PBS alone after Shigella infection. In the guinea pig, administration of Shigella by i.r. route induces acute inflammation, making this animal model useful for assessing the protective efficacy of Shigella vaccine candidates.

Shigella’ s ways of manipulating the host intestinal innate and adaptive immune system: a tool box for survival?

Shigella, a Gram-negative invasive enteropathogenic bacterium, causes the rupture, invasion and inflammatory destruction of the human colonic epithelium. This complex and aggressive process accounts for the symptoms of bacillary dysentery. The so-called invasive phenotype of Shigella is linked to expression of a type III secretory system (TTSS) injecting effector proteins into the epithelial cell membrane and cytoplasm, thereby inducing local but massive changes in the cell cytoskeleton that lead to bacterial internalization into non-phagocytic intestinal epithelial cells. The invasive phenotype also accounts for the potent pro-inflammatory capacity of the microorganism. Recent evidence indicates that a large part of the mucosal inflammation is initiated by intracellular sensing of bacterial peptidoglycan by cytosolic leucine-rich receptors of the NOD family, particularly NOD1, in epithelial cells. This causes activation of the nuclear factor kappa B and c-JunNH(2)-terminal-kinase pathways, with interleukin-8 appearing as a major chemokine mediating the inflammatory burst that is dominated by massive infiltration of the mucosa by polymorphonuclear leukocytes. Not unexpectedly, this inflammatory response, which is likely to be very harmful for the invading microbe, is regulated by the bacterium itself. A group of proteins encoded by Shigella, which are injected into target cells by the TTSS, has been recently recognized as a family of potent regulators of the innate immune response. These enzymes target key cellular functions that are essential in triggering the inflammatory response, and more generally defense responses of the intestinal mucosa. This review focuses on the mechanisms employed by Shigella to manipulate the host innate response in order to escape early bacterial killing, thus ensuring establishment of its infectious process. The escape strategies, the possible direct effect of Shigella on B and T lymphocytes, their impact on the development of adaptive immunity, and how they may help explain the limited protection induced by natural infection are discussed.

Shigella chromosomal IpaH proteins are secreted via the type III secretion system and act as effectors

Shigella possess 220 kb plasmid, and the major virulence determinants, called effectors, and the type III secretion system (TTSS) are exclusively encoded by the plasmid. The genome sequences of S. flexneri strains indicate that several ipaH family genes are located on both the plasmid and the chromosome, but whether their chromosomal IpaH cognates can be secreted from Shigella remains unknown. Here we report that S. flexneri strain, YSH6000 encodes seven ipaH cognate genes on the chromosome and that the IpaH proteins are secreted via the TTSS. The secretion kinetics of IpaH proteins by bacteria, however, showed delay compared with those of IpaB, IpaC and IpaD. Expression of the each mRNA of ipaH in Shigella was increased after bacterial entry into epithelial cells, and the IpaH proteins were secreted by intracellular bacteria. Although individual chromosomal ipaH deletion mutants showed no appreciable changes in the pathogenesis in a mouse pulmonary infection model, the DeltaipaH-null mutant, whose chromosome lacks all ipaH genes, was attenuated to mice lethality. Indeed, the histological examination for mouse lungs infected with the DeltaipaH-null showed a greater inflammatory response than induced by wild-type Shigella, suggesting that the chromosomal IpaH proteins act synergistically as effectors to modulate the host inflammatory responses.

Cadmium induces Interleukin-8 production via NF-κB activation in the human intestinal epithelial cell, Caco-2

In the present study, we investigated the effect of CdCl2 on the inflammatory cytokines in human intestinal Caco-2 cells. The secretion of IL-8 from Caco-2 cells was significantly increased in a dose- and time-dependent manner, whereas the secretion of such other inflammatory cytokines as TNF-alpha and IFN-gamma was not changed. And IL-8 mRNA level was significantly increased by exposing the cells to CdCl2. A reporter vector containing the IL-8 promoter region was then constructed to determine the IL-8 transcriptional activity. The results of this assay demonstrated that the transcriptional activity of IL-8 was increased by CdCl2. Treatment with PDTC, an NF-kappaB inhibitor, suppressed the IL-8 secretion in Caco-2 cells. Site-directed mutation of the NF-kappaB consensus element in the human IL-8 promoter abolished the increased transcriptional activity by CdCl2. The increased transcriptional activity caused by CdCl2 was also suppressed in an NF-kappaB knock-down Caco-2 cell line that had been stably established by the RNAi method. The increase in translocation of the NF-kappaB protein into the nucleus and I-kappaB alpha degradation resulting from CdCl2 stimulation was also confirmed by a Western analysis. Our results suggest that CdCl2 induced IL-8 secretion, its transcription, and its transcriptional activation regulated by NF-kappaB via I-kappaB alpha degradation.

An injected bacterial effector targets chromatin access for transcription factor NF-kappaB to alter transcription of host genes involved in immune responses

Phosphorylation of histone H3 at Ser10 increases chromatin accessibility to transcription factor NF-kappaB on a subset of genes involved in immune responses. Here we report that a bacterial pathogen abrogated phosphorylation of histone H3 to 'shape' the transcriptional responses of infected host cells. We identify the Shigella flexneri protein effector OspF as a dually specific phosphatase that dephosphorylated mitogen-activated protein kinases in the nucleus, thus preventing histone H3 phosphorylation at Ser10 in a gene-specific way. That activity of OspF enabled shigella to block the activation of a subset of NF-kappaB-responsive genes, leading to compromised recruitment of polymorphonuclear leukocytes to infected tissues. S. flexneri has thus evolved the capacity to precisely modulate host cell epigenetic 'information' as a strategy for repressing innate immunity.

Cigarette smoke-induced pulmonary inflammation and emphysema are attenuated in CCR6-deficient mice

Chronic obstructive pulmonary disease (COPD) is mainly caused by cigarette smoking, and is characterized by an increase in inflammatory cells in the airways and pulmonary tissue. The chemokine receptor CCR6 and its ligand MIP-3alpha/CCL20 may be involved in the recruitment of these inflammatory cells. To investigate the role of CCR6 in the pathogenesis of COPD, we analyzed the inflammatory responses of CCR6 knockout (KO) and wild-type mice upon cigarette smoke (CS) exposure. Both subacute and chronic exposure to CS induced an increase in cells of the innate and adaptive immune system in the bronchoalveolar lavage, both in CCR6 KO and wild-type mice. However, the accumulation of dendritic cells, neutrophils, and T lymphocytes, which express CCR6, was significantly attenuated in the CCR6 KO mice, compared with their wild-type littermates. In the lung tissue of CCR6 KO mice, there was an impaired increase in dendritic cells, activated CD8(+) T lymphocytes, and granulocytes. Moreover, this attenuated inflammatory response in CCR6 KO mice offered a partial protection against pulmonary emphysema, which correlated with an impaired production of MMP-12. Importantly, protein levels of MIP-3alpha/CCL20, the only chemokine ligand of the CCR6 receptor, and MCP-1/CCL2 were significantly increased upon CS exposure in wild-type, but not in CCR6 KO mice. In contrast, CCR6 deficiency had no effect on the development of airway wall remodeling upon chronic CS exposure. These results indicate that the interaction of CCR6 with its ligand MIP-3alpha contributes to the pathogenesis of CS-induced pulmonary inflammation and emphysema in this murine model of COPD.

The Caenorhabditis elegans ABL-1 tyrosine kinase is required for Shigella flexneri pathogenesis

Shigellosis is a diarrheal disease caused by the gram-negative bacterium Shigella flexneri. Following ingestion of the bacterium, S. flexneri interferes with innate immunity, establishes an infection within the human colon, and initiates an inflammatory response that results in destruction of the tissue lining the gut. Examination of host cell factors required for S. flexneri pathogenesis in vivo has proven difficult due to limited host susceptibility. Here we report the development of a pathogenesis system that involves the use of Caenorhabditis elegans as a model organism to study S. flexneri virulence determinants and host molecules required for pathogenesis. We show that S. flexneri-mediated killing of C. elegans correlates with bacterial accumulation in the intestinal tract of the animal. The S. flexneri virulence plasmid, which encodes a type III secretory system as well as various virulence determinants crucial for pathogenesis in mammalian systems, was found to be required for maximal C. elegans killing. Additionally, we demonstrate that ABL-1, the C. elegans homolog of the mammalian c-Abl nonreceptor tyrosine kinase ABL1, is required for S. flexneri pathogenesis in nematodes. These data demonstrate the feasibility of using C. elegans to study S. flexneri pathogenesis in vivo and provide insight into host factors that contribute to S. flexneri pathogenesis.

Involvement of TRAIL/TRAIL-receptors in human intestinal cell differentiation

Despite the fact that tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) and its receptors (TRAIL-Rs) are expressed in intestinal mucosa, little is known about the biological role of this system in intestinal cell physiology. The expression of surface TRAIL and TRAIL-R1, -R2, -R3, -R4 were examined by flow cytometry in the immortalized human cell line tsFHI under culture conditions promoting growth or growth arrest and expression of differentiated traits. A progressive increase of surface TRAIL expression paralleled tsFHI differentiation, consistently with immunohistochemistry analysis showing an increase of TRAIL immunostaining along the crypt-villus axis in normal jejuneal mucosa. In spite of the presence of TRAIL-R1 and TRAIL-R2 "death receptors," recombinant TRAIL was not cytotoxic for tsFHI cells. Exposure of tsFHI to recombinant TRAIL rather increased/anticipated the expression levels of the cyclin-dependent kinase inhibitors p21 and p27, which mediate the induction of growth arrest and the stabilization of differentiated traits, respectively, as well as of the canonical differentiation marker DPPIV. The differentiation inducing activity of TRAIL was abolished by pre-incubation with a Fc-TRAIL-R2 chimera. On the other hand, TRAIL did not significantly modulate the levels of osteoprotegerin (OPG), CXCL8/IL-8, CXCL9/MIG, and CXCL10/IP10 spontaneously released or induced by inflammatory cytokines. Taken together, these data suggest that TRAIL might act as a paracrine trophic cytokine on intestinal epithelium, promoting intestinal cell differentiation.

Importance of heat-labile enterotoxin in colonization of the adult mouse small intestine by human enterotoxigenic Escherichia coli strains

Enterotoxigenic Escherichia coli (ETEC) infections are a significant cause of diarrheal disease and infant mortality in developing countries. Studies of ETEC pathogenesis relevant to vaccine development have been greatly hampered by the lack of a suitable small-animal model of infection with human ETEC strains. Here, we demonstrate that adult immunocompetent outbred mice can be effectively colonized with the prototypical human ETEC H10407 strain (colonization factor antigen I; heat-labile and heat-stable enterotoxin positive) and that production of heat-labile holotoxin provides a significant advantage in colonization of the small intestine in this model.

The role of toll-like receptor 4 in airway inflammation induced by diesel exhaust particles

Although several studies have demonstrated that airway exposure to diesel exhaust particles (DEP) induces lung inflammation, the signaling pathways involved in the pathogenesis remain unclear. Toll-like receptors (TLRs) are generally accepted to be pathogen recognition receptors in mammalians. In the present study, we investigated the role of TLR-4 in DEP-induced lung inflammation and cytokine expression in the lung in TLR-4 point mutant (C3H/HeJ) mice and corresponding control (C3H/HeN) mice. Both the types of mice were randomized into four experimental groups that received vehicle or DEP (12 mg/kg body weight) by intratracheal instillation (n = 8-10 in each group). Cellular profile of bronchoalveolar lavage (BAL) fluid, expressions of cytokines and chemokines in the lung, and circulatory fibrinogen levels were evaluated 24 h after the instillation.DEP challenge revealed a significant increase in the numbers of total cells and neutrophils in the BAL fluid as compared to vehicle challenge, however, the numbers were less in C3H/HeJ mice than in C3H/HeN mice. DEP exposure significantly induced the lung expression of interleukin (IL)-1beta, keratinocyte chemoattractant (KC), and macrophage inflammatory protein (MIP)-1alpha when compared to vehicle challenge in both genotypes of mice. In the presence of DEP, the level of MIP-1alpha was significantly lower in C3H/HeJ mice than in C3H/HeN mice, however, the levels of IL-1beta, KC, and fibrinogen showed opposite findings. These results suggest that TLR-4 is one of recognition receptors against DEP in the airways.

Shigella effector IpaH9.8 binds to a splicing factor U2AF(35) to modulate host immune responses

Shigella effectors injected into the host cell via the type III secretion system are involved in various aspects of infection. Here, we show that one of the effectors, IpaH9.8, plays a role in modulating inflammatory responses to Shigella infection. In murine lung infection model, DeltaipaH9.8 mutant caused more severe inflammatory responses with increased pro-inflammatory cytokine production levels than did wild-type Shigella, which resulted in a 30-fold decrease in bacterial colonization. Binding assays revealed that IpaH9.8 has a specific affinity to U2AF(35), a mammalian splicing factor, which interferes with U2AF(35)-dependent splicing as assayed for IgM pre-mRNA. Reducing the U2AF(35) level in HeLa cells and infecting HeLa cells with wild-type caused a decrease in the expression of the il-8, RANTES, GM-CSF, and il-1beta genes as examined by RT-PCR. The results indicate that IpaH9.8 plays a role in Shigella infection to optimize the host inflammatory responses, thus facilitating bacterial colonization within the host epithelial cells.

Pulmonary exposure to diesel exhaust particles induces airway inflammation and cytokine expression in NC/Nga mice

Although several studies have reported that diesel exhaust particles (DEP) affect cardiorespiratory health in animals and humans, the effect of DEP on animal models with spontaneous allergic disorders has been far less intensively studied. The Nc/Nga mouse is known to be a typical animal model for human atopic dermatitis (AD). In the present study, we investigated the effects of repeated pulmonary exposure to DEP on airway inflammation and cytokine expression in NC/Nga mice. The animals were randomized into two experimental groups that received vehicle or DEP by intratracheal instillation weekly for six weeks. Cellular profiles of bronchoalveolar lavage (BAL) fluid and expressions of cytokines and chemokines in both the BAL fluid and lung tissues were evaluated 24 h after the last instillation. The DEP challenge produced an increase in the numbers of total cells, neutrophils, and mononuclear cells in BAL fluid as compared to the vehicle challenge (P<0.01). DEP exposure significantly induced the lung expressions of interleukin (IL)-4, keratinocyte chemoattractant (KC), and macrophage inflammatory protein (MIP)-1alpha when compared to the vehicle challenge. These results indicate that intratracheal exposure to DEP induces the recruitment of inflammatory cells, at least partially, through the local expression of IL-4 and chemokines in NC/Nga mice.

War and peace at mucosal surfaces

That we live with numerous bacteria in our gut without any adverse effects is a remarkable feat by the body's immune system, particularly considering the wealth of sensing and effector systems that are available to trigger inflammatory or innate immune responses to microbial intrusion. So, a fine line seems to exist between the homeostatic balance maintained in the presence of commensal gut flora and the necessarily destructive response to bacterial pathogens that invade the gut mucosa. This review discusses the mechanisms for establishing and controlling the 'dialogue' between unresponsiveness and initiation of active immune defences in the gut. Si vis pacem, para bellum. (If you wish for peace, prepare for war.).