Defense mechanisms in Peyer's patches and mesenteric lymph nodes against Yersinia enterocolitica involve integrins and cytokines

Environmental health hazards of untreated livestock wastewater: potential risks and future perspectives

Due to technological and economic limitations, waste products such as sewage and manure generated in livestock farming lack comprehensive scientific and centralized treatment. This leads to the exposure of various contaminants in livestock wastewater, posing potential risks to both the ecological environment and human health. This review evaluates the environmental and physical health risks posed by common pollutants in livestock wastewater and outlines future treatment methods to mitigate these risks. Residual wastes in livestock wastewater, including pathogenic bacteria and parasites surviving after epidemics or diseases on various farms, along with antibiotics, organic wastes, and heavy metals from farming activities, contribute to environmental damage and pose risks to human health. As the livestock industry's development increasingly impacts society's future negatively, addressing the issue of residual wastes in livestock wastewater discharge becomes imperative. Ongoing advancements in wastewater treatment systems are consistently updating and refining practices to effectively minimize waste exposure at the discharge source, mitigating risks to environmental ecology and human health. This review not only summarizes the "potential risks of livestock wastewater" but also explores "the prospects for the development of wastewater treatment technologies" based on current reports. It offers valuable insights to support the long-term and healthy development of the livestock industry and contribute to the sustainable development of the ecological environment.

γδ T cell IFNγ production is directly subverted by Yersinia pseudotuberculosis outer protein YopJ in mice and humans

Yersinia pseudotuberculosis is a foodborne pathogen that subverts immune function by translocation of Yersinia outer protein (Yop) effectors into host cells. As adaptive γδ T cells protect the intestinal mucosa from pathogen invasion, we assessed whether Y. pseudotuberculosis subverts these cells in mice and humans. Tracking Yop translocation revealed that the preferential delivery of Yop effectors directly into murine Vγ4 and human Vδ2⁺ T cells inhibited anti-microbial IFNγ production. Subversion was mediated by the adhesin YadA, injectisome component YopB, and translocated YopJ effector. A broad anti-pathogen gene signature and STAT4 phosphorylation levels were inhibited by translocated YopJ. Thus, Y. pseudotuberculosis attachment and translocation of YopJ directly into adaptive γδ T cells is a major mechanism of immune subversion in mice and humans. This study uncovered a conserved Y. pseudotuberculosis pathway that subverts adaptive γδ T cell function to promote pathogenicity.

Unconventional γδ T cells are a dynamic immune population important for mucosal protection of the intestine against invading pathogens. We determined that the foodborne pathogen Y. pseudotuberculosis preferentially targets an adaptive subset of these cells to subvert immune function. We found that direct injection of Yersinia outer proteins (Yop) into adaptive γδ T cells inhibited their anti-pathogen functions. We screened all Yop effectors and identified YopJ as the sole effector to inhibit adaptive γδ T cell production of IFNγ. We determined that adaptive γδ T cell subversion occurred by limiting activation of the transcription factor STAT4. When we infected mice with Y. pseudotuberculosis expressing an inactive YopJ, this enhanced the adaptive γδ T cell response and led to greater cytokine production from this subset of cells to aid mouse recovery. This mechanism of immune evasion appears conserved in humans as direct injection of Y. pseudotuberculosis YopJ into human γδ T cells inhibited cytokine production. This suggested to us that Y. pseudotuberculosis actively inhibits the adaptive γδ T cell response through YopJ as a mechanism to evade immune surveillance at the site of pathogen invasion.

The role of innate lymphoid cells in response to microbes at mucosal surfaces

Innate lymphoid cells (ILCs) are a lymphocyte population that is mostly resident at mucosal surfaces. They help to induce an appropriate immune response to the microbiome at homeostasis. In healthy people, the mucosal immune system works symbiotically with organisms that make up the microbiota. ILCs play a critical role in orchestrating this balance, as they can both influence and in turn be influenced by the microbiome. ILCs also are important regulators of the early response to infections by diverse types of pathogenic microbes at mucosal barriers. Their rapid responses initiate inflammatory programs, production of antimicrobial products and repair processes. This review will focus on the role of ILCs in response to the microbiota and to microbial infections of the lung and intestine.

Mouse Models of Yersiniosis

Yersiniosis is common foodborne gastrointestinal disease caused by the enteric pathogens Yersinia enterocolitica and Yersinia pseudotuberculosis. The mouse model of oral infection serves as a useful tool to study enteropathogenic Yersinia infection in mammals. The following protocol describes two distinct oral infection methods: the commonly used oral gavage method in which the bacterial inoculum is instilled directly into the mouse stomach using a feeding needle, and an alternative method in which mice are fed bread soaked with Yersinia culture.

LIGHT-HVEM Signaling in Innate Lymphoid Cell Subsets Protects Against Enteric Bacterial Infection

Innate lymphoid cells (ILCs) are important regulators of early infection at mucosal barriers. ILCs are divided into three groups based on expression profiles, and are activated by cytokines and neuropeptides. Yet, it remains unknown if ILCs integrate other signals in providing protection. We show that signaling through herpes virus entry mediator (HVEM), a member of the tumor necrosis factor (TNF) receptor superfamily, in ILC3 is important for host defense against oral infection with the bacterial pathogen Yersinia enterocolitica. HVEM stimulates protective interferon-γ (IFN-γ) secretion from ILCs, and mice with HVEM-deficient ILC3 exhibit reduced IFN-γ production, higher bacterial burdens and increased mortality. In addition, IFN-γ production is critical as adoptive transfer of wild-type but not IFN-γ-deficient ILC3 can restore protection to mice lacking ILCs. We identify the TNF superfamily member, LIGHT, as the ligand inducing HVEM signals in ILCs. Thus HVEM signaling mediated by LIGHT plays a critical role in regulating ILC3-derived IFN-γ production for protection following infection. VIDEO ABSTRACT.

IL-12/23p40 overproduction by dendritic cells leads to an increased Th1 and Th17 polarization in a model of Yersinia enterocolitica-induced reactive arthritis in TNFRp55-/- mice

Dendritic cells (DCs) play critical functions in the initiation of immune responses. Understanding their role in reactive arthritis (ReA) will help delineate the pathogenesis of this arthropathy. In early studies, we detected IL-12/23p40 deregulation in Yersinia entercolitica (Ye)-induced ReA in TNFRp55-deficient (TNFRp55^-/-) mice. In this study, we assessed the contribution of DCs in this overproduction. First, greater levels of IL-12/23p40, IFN-γand IL-17A were confirmed in supernatants of lipopolysaccharide (LPS)-stimulated TNFRp55^-/-splenocytes obtained on arthritis onset (day 14 after Ye infection). Later, DCs were identified as a precise source of IL-12/23p40 since increased frequency of splenic IL-12/23p40⁺DCs was detected in TNFRp55^-/- mice. After robust in vivo amplification of DCs by injection of Fms-like tyrosine kinase 3-Ligand (Flt3L)-transfected BL16 melanoma, DCs were purified. These cells recapitulated the higher production of IL-12/23p40 under TNFRp55deficiency. In agreement with these results, TNFRp55^-/- DCs promoted Th1 and Th17 programs by co-culture with WT CD4⁺lymphocytes. A mechanistic study demonstrated that JNK and p38 MAPK pathways are involved in IL-12/23p40 overproduction in purified TNFRp55^-/- DCs as well as in the JAWS II cell line. This deregulation was once again attributed to TNFRp55 deficiency since CAY10500, a specific inhibitor of this pathway, compromised TNF-mediated IL-12/23p40 control in LPS-stimulated WT DCs. Simultaneously, this inhibition reduced IL-10 production, suggesting its role mediating IL-12/23p40 regulation by TNFRp55 pathway. These results provide experimental data on the existence of a TNFRp55-mediated anti-inflammatory circuit in DCs. Moreover, these cells may be considered as a novel target in the treatment of ReA.

Mesenchymal Cell-Specific MyD88 Signaling Promotes Systemic Dissemination of Salmonella Typhimurium via Inflammatory Monocytes

Enteric pathogens including Salmonella enteric serovar Typhimurium can breach the epithelial barrier of the host and spread to systemic tissues. In response to infection, the host activates innate immune receptors via the signaling molecule MyD88, which induces protective inflammatory and antimicrobial responses. Most of these innate immune responses have been studied in hematopoietic cells, but the role of MyD88 signaling in other cell types remains poorly understood. Surprisingly, we found that Dermo1-Cre;Myd88^fl/fl mice with mesenchymal cell-specific deficiency of MyD88 were less susceptible to orogastric and i.p. STyphimurium infection than their Myd88^fl/fl littermates. The reduced susceptibility of Dermo1-Cre;Myd88^fl/fl mice to infection was associated with lower loads of S. Typhimurium in the liver and spleen. Mutant analyses revealed that S. Typhimurium employs its virulence type III secretion system 2 to promote its growth through MyD88 signaling pathways in mesenchymal cells. Inflammatory monocytes function as a major cell population for systemic dissemination of S. Typhimurium Mechanistically, mesenchymal cell-specific MyD88 signaling promoted CCL2 production in the liver and spleen and recruitment of inflammatory monocytes to systemic organs in response to STyphimurium infection. Consistently, MyD88 signaling in mesenchymal cells enhanced the number of phagocytes including Ly6C^hiLy6G^- inflammatory monocytes harboring STyphimurium in the liver. These results suggest that S. Typhimurium promotes its systemic growth and dissemination through MyD88 signaling pathways in mesenchymal cells.

Tissue dual RNA-seq allows fast discovery of infection-specific functions and riboregulators shaping host-pathogen transcriptomes

Pathogenic bacteria need to rapidly adjust their virulence and fitness program to prevent eradication by the host. So far, underlying adaptation processes that drive pathogenesis have mostly been studied in vitro, neglecting the true complexity of host-induced stimuli acting on the invading pathogen. In this study, we developed an unbiased experimental approach that allows simultaneous monitoring of genome-wide infection-linked transcriptional alterations of the host and colonizing extracellular pathogens. Using this tool for Yersinia pseudotuberculosis-infected lymphatic tissues, we revealed numerous alterations of host transcripts associated with inflammatory and acute-phase responses, coagulative activities, and transition metal ion sequestration, highlighting that the immune response is dominated by infiltrating neutrophils and elicits a mixed T_H17/T_H1 response. In consequence, the pathogen's response is mainly directed to prevent phagocytic attacks. Yersinia up-regulates the gene and expression dose of the antiphagocytic type III secretion system (T3SS) and induces functions counteracting neutrophil-induced ion deprivation, radical stress, and nutritional restraints. Several conserved bacterial riboregulators were identified that impacted this response. The strongest influence on virulence was found for the loss of the carbon storage regulator (Csr) system, which is shown to be essential for the up-regulation of the T3SS on host cell contact. In summary, our established approach provides a powerful tool for the discovery of infection-specific stimuli, induced host and pathogen responses, and underlying regulatory processes.

Mononuclear phagocytes contribute to intestinal invasion and dissemination of Yersinia enterocolitica

Enteropathogenic Yersinia enterocolitica (Ye) enters the host via contaminated food. After colonisation of the small intestine Ye invades the Peyer's patches (PPs) via M cells and disseminates to the mesenteric lymph nodes (MLNs), spleen and liver. Whether Ye uses other invasion routes and which pathogenicity factors are required remains elusive. Oral infection of lymphotoxin-β-receptor deficient mice lacking PPs and MLNs with Ye revealed similar bacterial load in the spleen 1h post infection as wild-type mice, demonstrating a PP-independent dissemination route for Ye. Immunohistological analysis of the small intestine revealed Ye in close contact with mononuclear phagocytes (MPs), specifically CX3CR1(+) monocyte-derived cells (MCs) as well as CD103(+) dendritic cells (DCs). This finding was confirmed by flow cytometry and imaging flow cytometry analysis of lamina propria (LP) leukocytes showing CD103(+) DCs and MCs with intracellular Ye. Uptake of Ye by LP CD103(+) DCs and MCs was dependent on the pathogenicity factor invasin, whereas the adhesin YadA was dispensable as demonstrated by Ye deletion mutants. Furthermore, Ye were found exclusively associated with CD103(+) DCs in the MLNs from wild-type mice, but not from CCR7(-/-) mice, demonstrating a CCR7 dependent transport of Ye by CD103(+) DCs from LP to the MLNs. In contrast, dissemination of Ye to the spleen was dependent on MCs as significantly less Ye could be recovered from the spleen of CX3CR1(GFP/GFP) mice compared to wild-type mice. Altogether, MCs and CD103(+) DCs contribute to immediate invasion and dissemination of Ye. This together with data from other bacteria suggests MPs as general pathogenic entry site in the intestine.

Role of β1 integrins and bacterial adhesins for Yop injection into leukocytes in Yersinia enterocolitica systemic mouse infection

Injection of Yersinia outer proteins (Yops) into host cells by a type III secretion system is an important immune evasion mechanism of Yersinia enterocolitica (Ye). In this process Ye invasin (Inv) binds directly while Yersinia adhesin A (YadA) binds indirectly via extracellular matrix (ECM) proteins to β1 integrins on host cells. Although leukocytes turned out to be an important target of Yop injection by Ye, it was unclear which Ye adhesins and which leukocyte receptors are required for Yop injection. To explain this, we investigated the role of YadA, Inv and β1 integrins for Yop injection into leukocytes and their impact on the course of systemic Ye infection in mice. Ex vivo infection experiments revealed that adhesion of Ye via Inv or YadA is sufficient to promote Yop injection into leukocytes as revealed by a β-lactamase reporter assay. Serum factors inhibit YadA- but not Inv-mediated Yop injection into B and T cells, shifting YadA-mediated Yop injection in the direction of neutrophils and other myeloid cells. Systemic Ye mouse infection experiments demonstrated that YadA is essential for Ye virulence and Yop injection into leukocytes, while Inv is dispensable for virulence and plays only a transient and minor role for Yop injection in the early phase of infection. Ye infection of mice with β1 integrin-depleted leukocytes demonstrated that β1 integrins are dispensable for YadA-mediated Yop injection into leukocytes, but contribute to Inv-mediated Yop injection. Despite reduced Yop injection into leukocytes, β1 integrin-deficient mice exhibited an increased susceptibility for Ye infection, suggesting an important role of β1 integrins in immune defense against Ye. This study demonstrates that Yop injection into leukocytes by Ye is largely mediated by YadA exploiting, as yet unknown, leukocyte receptors.

A Lactobacillus plantarum strain isolated from kefir protects against intestinal infection with Yersinia enterocolitica O9 and modulates immunity in mice

Lactobacillus plantarum C4, previously isolated from kefir and characterized as a potential probiotic strain, was tested for its protective and immunomodulatory capacity in a murine model of yersiniosis. The inoculation of BALB/c mice with a low pathogenicity serotype O9 strain of Yersinia enterocolitica results in a prolonged intestinal infection with colonization of Peyer's patches. Pretreatment with C4 was without effect on fecal excretion of yersiniae, but shortened the colonization of Peyer's patches. This protective effect was associated with pro-inflammatory status in the intestinal mucosa (TNF-α production in infected mice was increased by C4) and an increase in total IgA secretion. At a systemic level, C4 did not promote a pro-inflammatory response, although production of the immunoregulatory cytokine IFN-γ was enhanced. These findings suggest that L. plantarum C4 can increase resistance to intestinal infections through its immunomodulatory activity.

The adhesive protein invasin of Yersinia pseudotuberculosis induces neutrophil extracellular traps via β1 integrins

Yersinia pseudotuberculosis adhesive protein invasin is crucial for the bacteria to cross the intestine epithelium by binding to β1 integrins on M-cells and gaining access to the underlying tissues. After the crossing invasin can bind to β1 integrins on other cell surfaces, however effector proteins delivered by the type III secretion system Y. pseudotuberculosis efficiently inhibit potential immune responses induced by this interaction. Here, we use mutant Y. pseudotuberculosis strains lacking the type III secretion system and additionally invasin-expressing Escherichia coli to analyze neutrophil responses towards invasin. Our data reveals that invasin induces production of reactive oxygen species and release of chromatin into the extracellular milieu, which we confirmed to be neutrophil extracellular traps by immunofluorescence microscopy. This was mediated through β1 integrins and was dependent on both the production of reactive oxygen species and signaling through phosphoinositide 3-kinase. We therefore have gained insight into a potential role of integrins in inflammation and infection clearance that has not previously been described, suggesting that targeting of β1 integrins could be utilized as an adjunctive therapy against yersiniosis.

Comparison of cytokine immune responses to Brucella abortus and Yersinia enterocolitica serotype O:9 infections in BALB/c mice

Brucella abortus and Yersinia enterocolitica serotype O:9 serologically cross-react in the immune response with the host; therefore, our aim was to compare the immune responses to these two pathogens. We selected typical B. abortus and Y. enterocolitica O:9 strains to study the cytokine immune response and the histopathological changes in livers and spleens of BALB/c mice. The data showed the cytokine responses to the two strains of pathogens were different, where the average levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), gamma interferon (IFN-γ), interleukin-12 (IL-12), and tumor necrosis factor alpha (TNF-α) were higher with B. abortus infections than with Y. enterocolitica O:9 infections, especially for IFN-γ, while the IL-10 level was lower and the levels of IL-1β, IL-4, IL-5, and IL-6 were similar. The histopathological effects in the livers and spleens of the BALB/c mice with B. abortus and Y. enterocolitica O:9 infections were similar; however, the pathological changes in the liver were greater with B. abortus infections, while damage in the spleen was greater with Y. enterocolitica O:9 infections. These observations show that different cytokine responses and histopathological changes occur with B. abortus and Y. enterocolitica O:9 infections.

Human and animal isolates of Yersinia enterocolitica show significant serotype-specific colonization and host-specific immune defense properties

Yersinia enterocolitica is a human pathogen that is ubiquitous in livestock, especially pigs. The bacteria are able to colonize the intestinal tract of a variety of mammalian hosts, but the severity of induced gut-associated diseases (yersiniosis) differs significantly between hosts. To gain more information about the individual virulence determinants that contribute to colonization and induction of immune responses in different hosts, we analyzed and compared the interactions of different human- and animal-derived isolates of serotypes O:3, O:5,27, O:8, and O:9 with murine, porcine, and human intestinal cells and macrophages. The examined strains exhibited significant serotype-specific cell binding and entry characteristics, but adhesion and uptake into different host cells were not host specific and were independent of the source of the isolate. In contrast, survival and replication within macrophages and the induced proinflammatory response differed between murine, porcine, and human macrophages, suggesting a host-specific immune response. In fact, similar levels of the proinflammatory cytokine macrophage inflammatory protein 2 (MIP-2) were secreted by murine bone marrow-derived macrophages with all tested isolates, but the equivalent interleukin-8 (IL-8) response of porcine bone marrow-derived macrophages was strongly serotype specific and considerably lower in O:3 than in O:8 strains. In addition, all tested Y. enterocolitica strains caused a considerably higher level of secretion of the anti-inflammatory cytokine IL-10 by porcine than by murine macrophages. This could contribute to limiting the severity of the infection (in particular of serotype O:3 strains) in pigs, which are the primary reservoir of Y. enterocolitica strains pathogenic to humans.

Host innate recognition of an intestinal bacterial pathogen induces TRIF-dependent protective immunity

TRIF signaling triggers the amplification of macrophage bactericidal activity sufficient to eliminate invading intestinal pathogens through the sequential induction of IFN-β and IFN-γ from macrophages and NK cells, respectively.

Toll-like receptor 4 (TLR4), which signals through the adapter molecules myeloid differentiation factor 88 (MyD88) and toll/interleukin 1 receptor domain-containing adapter inducing IFN-β (TRIF), is required for protection against Gram-negative bacteria. TRIF is known to be important in TLR3-mediated antiviral signaling, but the role of TRIF signaling against Gram-negative enteropathogens is currently unknown. We show that TRIF signaling is indispensable for establishing innate protective immunity against Gram-negative Yersinia enterocolitica. Infection of wild-type mice rapidly induced both IFN-β and IFN-γ in the mesenteric lymph nodes. In contrast, TRIF-deficient mice were defective in these IFN responses and showed impaired phagocytosis in regional macrophages, resulting in greater bacterial dissemination and mortality. TRIF signaling may be universally important for protection against Gram-negative pathogens, as TRIF-deficient macrophages were also impaired in killing both Salmonella and Escherichia coli in vitro. The mechanism of TRIF-mediated protective immunity appears to be orchestrated by macrophage-induced IFN-β and NK cell production of IFN-γ. Sequential induction of IFN-β and IFN-γ leads to amplification of macrophage bactericidal activity sufficient to eliminate the invading pathogens at the intestinal interface. Our results demonstrate a previously unknown role of TRIF in host resistance to Gram-negative enteropathogens, which may lead to effective strategies for combating enteric infections.

Alternative endogenous protein processing via an autophagy-dependent pathway compensates for Yersinia-mediated inhibition of endosomal major histocompatibility complex class II antigen presentation

Extracellular Yersinia pseudotuberculosis employs a type III secretion system (T3SS) for translocating virulence factors (Yersinia outer proteins [Yops]) directly into the cytosol of eukaryotic cells. Recently, we used YopE as a carrier molecule for T3SS-dependent secretion and translocation of listeriolysin O (LLO) from Listeria monocytogenes. We demonstrated that translocation of chimeric YopE/LLO into the cytosol of macrophages by Yersinia results in the induction of a codominant antigen-specific CD4 and CD8 T-cell response in orally immunized mice. In this study, we addressed the requirements for processing and major histocompatibility complex (MHC) class II presentation of chimeric YopE proteins translocated into the cytosol of macrophages by the Yersinia T3SS. Our data demonstrate the ability of Yersinia to counteract exogenous MHC class II antigen presentation of secreted hybrid YopE by the action of wild-type YopE and YopH. In the absence of exogenous MHC class II antigen presentation, an alternative pathway was identified for YopE fusion proteins originating in the cytosol. This endogenous antigen-processing pathway was sensitive to inhibitors of phagolysosomal acidification and macroautophagy, but it did not require the function either of the proteasome or of transporters associated with antigen processing. Thus, by an autophagy-dependent mechanism, macrophages are able to compensate for the YopE/YopH-mediated inhibition of the endosomal MHC class II antigen presentation pathway for exogenous antigens. This is the first report demonstrating that autophagy might enable the host to mount an MHC class II-restricted CD4 T-cell response against translocated bacterial virulence factors. We provide critical new insights into the interaction between the mammalian immune system and a human pathogen.

Lack of TNFR p55 results in heightened expression of IFN-γ and IL-17 during the development of reactive arthritis

Reactive arthritis (ReA) is a type of arthritis originating from certain gastrointestinal or genitourinary infections. In previous studies, we reported the development of progressive Yersinia enterocolitica-induced ReA in mice lacking TNFR p55; however, the mechanisms underlying this effect are still uncertain. In this study, we investigated the impact of TNFR p55 deficiency in modulating Ag-specific Th1 and Th17 responses during this arthritogenic process. We found more severe ReA in TNFRp55(-/-) mice compared with their wild-type (WT) counterparts. This effect was accompanied by increased levels of Yersinia LPS in the joints of knockout mice. Analysis of the local cytokine profile revealed greater amounts of IFN-γ and IL-17 in arthritic joints of TNFRp55(-/-) mice compared with WT mice at day 21 postinfection. Moreover, altered IL-17 and IFN-γ production was observed in mesenteric and inguinal lymph nodes of Yersinia-infected TNFRp55(-/-) mice, as well as in spleen cells obtained from infected mice and restimulated ex vivo with bacterial Ags. Increased levels of cytokine secretion were associated with a greater frequency of CD4(+)IL-17(+), CD4(+)IFN-γ(+), and IL-17(+)IFN-γ(+) cells in TNFRp55(-/-) mice compared with WT mice. Remarkably, Ab-mediated blockade of IL-17 and/or IFN-γ resulted in reduced joint histological scores in TNFRp55(-/-) mice. A mechanistic analysis revealed the involvement of p40, a common subunit of heterodimeric IL-12 and IL-23, in the generation of augmented IFN-γ and IL-17 production under TNFR p55 deficiency. Taken together, these data indicate that, in the absence of TNFR p55 signaling, Th1 and Th17 effector cells may act in concert to sustain the inflammatory response in bacterial-induced arthritogenic processes.

Transforming growth factor beta and CD25 are important for controlling systemic dissemination following Yersinia enterocolitica infection of the gut

Infection of the gut by invasive bacterial pathogens leads to robust inflammatory responses that if left unchecked can lead to autoimmune disease and other sequelae. How the immune system controls inflammation and limits collateral damage to the host during acute bacterial infection is poorly understood. Here, we report that antibody-mediated neutralization of transforming growth factor beta (TGF-beta) prior to infection with the model enteric pathogen Yersinia enterocolitica reduces the mean time to death by 1 day (P=0.001), leads to rapid colonization of the liver and lung, and is associated with exacerbation of inflammatory histopathology. During Yersinia enterocolitica infection CD4+ cells are the source of de novo TGF-beta transcription in the Peyer's patches, mesenteric lymph nodes, and spleen. Correspondingly there is both antigen-specific and -independent expansion of CD4+ CD25+ Foxp3+ and TGF-beta+ T-regulatory cells (T-regs) after Yersinia infection that is reduced in ovalbumin T-cell receptor-restricted OT-II mice. Functional inactivation of CD25 by anti-CD25 treatment results in more rapid death, dissemination of the bacteria to the liver and lungs, and exacerbated inflammatory histopathology, similar to what is seen during TGF-beta neutralization. Altogether, these data suggest that TGF-beta produced by T-regs is important in restricting bacteria during the acute phase of invasive bacterial infection of the gut. These data expand the roles of T-regs to include tempering inflammation during acute infection in addition to the well-established roles of T-regs in chronic infection, control of immune homeostasis, and autoimmune disease.

Yersinia enterocolitica promotes robust mucosal inflammatory T-cell immunity in murine neonates

Mucosal immunity to gastrointestinal pathogens in early life has been studied only slightly. Recently, we developed an infection model in murine neonates using the gastroenteric pathogen Yersinia enterocolitica. Here, we report that oral infection of neonatal mice with low doses of virulent Y. enterocolitica leads to vigorous intestinal and systemic adaptive immunity. Y. enterocolitica infection promoted the development of anti-LcrV memory serum IgG1 and IgG2a responses of comparable affinity and magnitude to adult responses. Strikingly, neonatal mesenteric lymph node CD4(+) T cells produced Yersinia-specific gamma interferon (IFN-gamma) and interleukin-17A (IL-17A), exceeding adult levels. The robust T- and B-cell responses elicited in neonates exposed to Y. enterocolitica were associated with long-term protection against mucosal challenge with this pathogen. Using genetically deficient mice, we found that IFN-gamma and CD4(+) cells, but not B cells, are critical for protection of neonates during primary Y. enterocolitica infection. In contrast, adults infected with low bacterial doses did not require either cell population for protection. CD4-deficient neonatal mice adoptively transferred with CD4(+) cells from wild-type, IFN-gamma-deficient, or IL-17AF-deficient mice were equally protected from infection. These data demonstrate that inflammatory CD4(+) T cells are required for protection of neonatal mice and that this protection may not require CD4-derived IFN-gamma, IL-17A, or IL-17F. Overall, these studies support the idea that Y. enterocolitica promotes the development of highly inflammatory mucosal responses in neonates and that intestinal T-cell function may be a key immune component in protection from gastrointestinal pathogens in early life.

Interaction of Yersinia with the gut: mechanisms of pathogenesis and immune evasion

Yersinia entercolitica and Yersinia pseudotuberculosis are human foodborne pathogens that interact extensively with tissues of the gut and the host's immune system to cause disease. As part of their pathogenic strategies, the Yersinia have evolved numerous ways to invade host tissues, gain essential nutrients, and evade host immunity. Technological advances over the last 10 years have revolutionized our understanding of host-pathogen interactions. The application of these new technologies has also shown that even well-understood pathogens such as the Yersinia have many surprises waiting to be revealed. The complex interaction with the host has made Yersinia a paradigm for understanding bacterial pathogenesis and the host response to invasive bacterial infections. This review examines the mechanisms of immune evasion employed by the Yersinia and highlights recent advances in understanding the host-pathogen interaction.

Yersinia pseudotuberculosis virulence determinants invasin, YopE, and YopT modulate RhoG activity and localization

The Yersinia pseudotuberculosis surface protein invasin binds to multiple beta1 integrins with high affinity, leading to misregulation of Rac1 activity. Upon host cell binding, alteration of Rho GTPase activity results from the action of several Yersinia outer proteins (Yops) that are translocated into the cytoplasm. We report here that three virulence determinants encoded by Y. pseudotuberculosis manipulate the Rho GTPase RhoG. Y. pseudotuberculosis binding to cells caused robust recruitment of RhoG to the site of attachment, which required high-affinity invasin-beta1 integrin association. Furthermore, inactivation of RhoG significantly reduced the efficiency of invasin-mediated bacterial internalization. To investigate the activation state of RhoG, a fluorescence resonance energy transfer-based activation biosensor was developed and used to show distinct spatial activation of RhoG at the site of bacterial attachment. The biosensor was also used to show efficient RhoG inactivation by Y. pseudotuberculosis YopE, a potent Rho GTPase activating protein. Additionally, RhoG mislocalization by the prenylcysteine endoprotease YopT was demonstrated by two independent assays. Functional bacterial uptake experiments demonstrated that RhoG activation can bypass a deficit in Rac1 activity. Interestingly, increasing the size of the particle gave results more consistent with a linear pathway, in which RhoG acts as an upstream activator of Rac1, indicating that increased surface area introduces constraints on the signaling pathways required for efficient internalization. Taken together, these data demonstrate the misregulation of RhoG by multiple Y. pseudotuberculosis virulence determinants. Since RhoG is imperative for proper neutrophil function, this misregulation may represent a unique mechanism by which Yersinia species dampen the immune response.

Helicobacter hepaticus HHGI1 is a pathogenicity island associated with typhlocolitis in B6.129-IL10 tm1Cgn mice

Helicobacter hepaticus strain 3B1 (H. hepaticus) contains a genomic island of approximately 71 kb, HHGI1, with some of the common features shared among known bacterial pathogenicity islands. In this study, we characterized the pathogenic potential of HHGI1 by infecting B6.129-IL10 tm1Cgn (IL10-/-) mice with an isogenic mutant (namely HhPAId1) lacking 19 predicted genes within HHGI1. In contrast to H. hepaticus (P<0.001), HhPAId1 did not cause typhlocolitis and hyperplasia in IL10-/- mice. Colonization levels of HhPAId1 were significantly higher in the cecum (P<0.007) and similar in the colon (P=0.27) when compared to H. hepaticus by 13 or 16 weeks post inoculation (WPI). The magnitude of the Th1-associated IgG2c response against HhPAId1 was less than that against H. hepaticus (P<0.004). There was no significant difference in Th2-associated IgG1 responses against these two strains. Cecal and colonic mRNA levels of proinflammatory cytokines IFN-gamma, TNF-alpha and IL-17a in the HhPAId1-infected mice were significantly lower than those in the H. hepaticus-infected mice (P<0.05) at 13 WPI. These results demonstrate that genes in the HHGI1 contribute to the pathogenicity of H. hepaticus, at least in part via up-regulation of proinflammatory mediators IFN-gamma, TNF-alpha and IL-17a.

Yersinia as oral live carrier vaccine: influence of Yersinia outer proteins (Yops) on the T-cell response

Attenuated enteropathogenic Yersinia strains are attractive candidates for the development of oral live carrier vaccines. Yersiniae colonize the small intestine and invade lymphoid tissue of the terminal ileum where they replicate extracellularly. Yersiniae can be engineered to secrete or translocate heterologous antigens into the cytosol of antigen-presenting cells by their type 3 secretion system (T3SS). This results in the induction of both cellular and humoral immune responses to heterologous antigens of viral, bacterial and parasitic origin. In this review, we summarize the progress in developing Yersinia-based vaccine carrier strains by mutating the T3SS effector proteins of Yersinia called Yops (Yersinia outer proteins) to both attenuate the strains and to modulate the T-cell response.

Yersinia enterocolitica: subversion of adaptive immunity and implications for vaccine development

Enteric Yersinia spp. invade Peyer's patches, disseminate to lymphoid tissues, and induce mucosal and systemic immune responses. Many virulence factors of Yersinia enterocolitica have been investigated in detail and were found to act on host cells involved in innate and adaptive immunity. Recent work explored as to whether attenuated Y. enterocolitica or recombinant components of Y. enterocolitica can be used as tools for vaccination. We and others have tested whether by means of the type three secretion system in attenuated Y. enterocolitica strains antigens might be delivered to antigen-presenting cells in order to induce CD8 and CD4 T cell responses. Alternatively, recombinant components of Y. enterocolitica such as invasin protein which binds to beta1 integrins of host cells have been tested for their ability to target antigen along with microparticles (fused to invasin) to antigen-presenting cells and to act as adjuvant. The work summarized in this article demonstrates that Y. enterocolitica and its components might be useful tools for novel vaccination strategies; in fact, invasin when fused to antigen and coated to microparticles might induce both CD4 and CD8 T cell responses. Likewise, attenuated Y. enterocolitica live carrier strains were reported to induce both CD8 and some CD4 T cell responses. However, we need to know more about how Y. enterocolitica subverts functions of antigen-presenting cells in order to design mutants with optimized antigen delivery features and deletion in those virulence factor that contribute to subversion of innate or adaptive immune responses.

General and specific host responses to bacterial infection in Peyer's patches: a role for stromelysin-1 (matrix metalloproteinase-3) during Salmonella enterica infection

Salmonella enterica serovar Typhimurium (S. typhimurium) and Yersinia enterocolitica are enteric pathogens capable of colonizing and inducing inflammatory responses in Peyer's patches (PPs) and mesenteric lymph nodes (MLNs). Although the tissue colonization pattern is similar between these two pathogens, their pathogenic lifestyles are quite different. For example, while S. typhimurium is primarily an intracellular pathogen, Y. enterocolitica survives primarily extracellularly. We determined and compared the transcriptional changes occurring in response to S. typhimurium and Y. enterocolitica colonization of PP using Affymetrix GeneChip technology. Both pathogens elicited a general inflammatory response indicated by the upregulation of cytokines and chemokines. However, specific differences were also observed, most notably in the transcriptional regulation of gamma interferon (IFN-gamma) and IFN-gamma-regulated genes in response to S. typhimurium but not Y. enterocolitica. Of particular note, a group of genes encoding matrix metalloproteinases (MMPs) had increased transcript numbers in the PPs following infection with both pathogens. The experiments described here compare oral S. typhimurium or Y. enterocolitica infection in stromelysin-1 (MMP-3)-deficient mice (mmp-3(-/-)) with mice possessing functional MMP-3 (mmp-3(+/+)). There was little difference in the survival of MMP-3-deficient mice infected with Y. enterocolitica when compared with littermate controls. Surprisingly though, mmp-3(-/-) mice were markedly more resistant to S. typhimurium infection than the control mice. S. typhimurium was able to colonize mmp-3(-/-) mice, albeit in a delayed fashion, to equivalent levels as mmp-3(+/+) mice. Nevertheless, significantly lower levels of inflammatory cytokines were detected in tissues and serum in the mmp-3(-/-) mice in comparison with mmp-3(+/+) mice. We hypothesize that MMP-3 is involved in initiating an early and lethal cytokine response to S. typhimurium colonization.

Yersinia-triggered arthritis in IL-12p40-deficient mice: relevant antigens and local expression of Toll-like receptor mRNA

OBJECTIVES

To study the role of IL-12p40 at the onset of reactive arthritis (ReA) after Yersinia enterocolitica O:3 infection, and analyse relevant microbial antigens and articular expression of Toll-like receptor (TLR) mRNA.

METHODS

Wild-type C57BL/6 and IL-12p40-deficient (IL-12p40-/-) mice were orogastrically infected with Y. enterocolitica O:3. Early (day 3) and late (day 21) after infection, the number of bacteria were determined in Peyer's patches (PP), mesenteric lymph nodes (MLN), the spleen, and joints. Histological studies of joints were performed. Collagen-specific and anti-Yersinia antibodies were measured by enzyme-linked immunosorbent assay (ELISA). The presence of Yersinia antigens was studied by dot blot. Induction of articular mRNA of TLR2, TLR4, and tumour necrosis factor (TNF)-alpha was analysed by reverse transcription-polymerase chain reaction (RT-PCR). TNFalpha protein levels were measured by ELISA.

RESULTS

At day 3, bacterial recovery in PP, MLN, and spleen was significantly increased in IL-12p40-/- mice. Histopathological changes were observed in IL-12p40-/- mice at day 21 after infection, and correlated with higher antibody response against type II collagen. Although live bacteria could not be isolated at day 21 after infection, articular microbial components, especially from the outer membrane (OM), were detected. Moreover, intra-articular immunoglobulins to Yersinia antigens were significantly higher in IL-12p40-/- mice. Furthermore, mRNA levels for TLR2, TLR4 and TNFalpha, and TNFalpha protein were increased in joints from IL-12p40-/- mice.

CONCLUSIONS

We concluded that IL-12p40 influences the resistance against Yersinia-triggered ReA. Bacterial products such as Yersinia OM could contribute to the ReA by induction of articular TLR expression, which results in an inflammatory response in the joint.

Murine neonates are highly resistant to Yersinia enterocolitica following orogastric exposure

Neonates are considered highly susceptible to gastrointestinal infections. This susceptibility has been attributed partially to immaturity in immune cell function. To study this phenomenon, we have developed a model system with murine neonates, using the natural orogastric route of transmission for the enteropathogen Yersinia enterocolitica. The susceptibilities of 7-day-old and adult mice to orogastric Y. enterocolitica infection were assessed in 50% lethal dose experiments. Remarkably, neonatal mice of either the BALB/c or C57BL/6 mouse strain showed markedly enhanced survival after infection compared to adult mice. The resistance of neonates was not due to failure of the bacteria to colonize neonatal tissues; Y. enterocolitica was readily detectable in the intestine and mesenteric lymph nodes (MLN) for at least 1 week after infection. In adult mice, Y. enterocolitica rapidly disseminated to the spleen and liver. In striking contrast, bacterial invasion of the spleen and liver in neonates was limited. Using flow cytometry and histology, we found substantial increases in the percentages of neutrophils and macrophages in the neonatal MLN, while influx of these cells into the adult MLN was limited. Similar results were obtained using two different high-virulence Y. enterocolitica strains. Importantly, depletion of neutrophils with a specific antibody led to increased translocation of the bacteria to the spleens and livers of neonates. Together, these experiments support the hypothesis that the neonatal intestinal immune system can rapidly mobilize innate phagocytes and thereby confine the bacterial infection to the gut, resulting in a high level of resistance.

Salmonella typhimurium disseminates within its host by manipulating the motility of infected cells

The mammalian host has a number of innate immune mechanisms designed to limit the spread of infection, yet many bacteria, including Salmonella, can cause systemic disease. Salmonella typhimurium-infected phagocytes traverse the gastrointestinal (GI) epithelium and enter the bloodstream within minutes after ingestion, thereby spreading throughout its host. Here, we provide a cellular and molecular basis for this phenomenon. We demonstrate that S. typhimurium manipulates the migratory properties of infected GI phagocytes with a type III secretion system. We show that one secreted effector, SrfH, interacts with the host protein TRIP6, a member of the zyxin family of adaptor proteins that regulate motility. SrfH promotes phagocyte motility in vitro and accelerates the systemic spread of infection away from the lumen of the intestine in the mouse. This is a previously uncharacterized mechanism by which an intracellular pathogen overcomes host defenses designed to immobilize infected cells.

The Yersinia enterocolitica invasin protein promotes major histocompatibility complex class I- and class II-restricted T-cell responses

Yersinia enterocolitica invasin (Inv) protein confers internalization into and expression of proinflammatory cytokines by host cells. Both events require binding of Inv to beta1 integrins, which initiates signaling cascades including activation of focal adhesion complexes, Rac1, mitogen-activated protein kinase, and NF-kappaB. Here we tested whether Inv might be suitable as a delivery molecule and adjuvant if used as a component of a vaccine. For this purpose, hybrid proteins composed of Inv and ovalbumin (OVA) were prepared, applied as a coating to microparticles, and used for vaccination. Fusion of OVA to Inv did not significantly disturb the ability of Inv to promote host cell binding, internalization, and interleukin-8 (IL-8) secretion when applied as a coating to microparticles. The microparticles were used for vaccination of mice adoptively transferred with OVA-specific T cells from OT-1 or DO11.10 mice. Administration of OVA-Inv-coated microparticles induced OVA-specific T-cell responses. OVA-specific CD4 T cells produced both gamma interferon (IFN-gamma) and IL-4 as determined by enzyme-linked immunosorbent assay. Likewise, pronounced OVA-specific CD8 T-cell responses associated with IFN-gamma production were observed. Together, these results suggest that Inv might be an attractive tool in vaccination as it confers both host cell uptake and adjuvant activity by engagement of beta1 integrins of host cells, which leads to CD4 as well as CD8 T-cell responses.

A small molecule alpha 4 beta 1 antagonist prevents development of murine Lyme arthritis without affecting protective immunity

After infection with Borrelia burgdorferi, humans and mice under certain conditions develop arthritis. Initiation of inflammation is dependent on the migration of innate immune cells to the site of infection, controlled by interactions of a variety of adhesion molecules. In this study, we used the newly synthesized compound S18407, which is a prodrug of the active drug S16197, to analyze the functional importance of alpha4beta1-dependent cell adhesion for the development of arthritis and for the antibacterial immune response. S16197 is shown to interfere specifically with the binding of alpha4beta(1 integrin to its ligands VCAM-1 and fibronectin in vitro. Treatment of B. burgdorferi-infected C3H/HeJ mice with the alpha4beta1 antagonist significantly ameliorated the outcome of clinical arthritis and the influx of neutrophilic granulocytes into ankle joints. Furthermore, local mRNA up-regulation of the proinflammatory mediators IL-1, IL-6, and cyclooxygenase-2 was largely abolished. Neither the synthesis of spirochete-specific Igs nor the development of a Th1-dominated immune response was altered by the treatment. Importantly, the drug also did not interfere with Ab-mediated control of spirochete load in the tissues. These findings demonstrate that the pathogenesis, but not the protective immune response, in Lyme arthritis is dependent on the alpha4beta1-mediated influx of inflammatory cells. The onset of inflammation can be successfully targeted by treatment with S18407.

Induction of CD8+ T cell responses by Yersinia vaccine carrier strains

Yersinia enterocolitica employs a type III secretion system (TTSS) to target virulence factors (e.g. YopE) into the cytosol of the host cells. We utilized the TTSS to introduce a recombinant antigen directly into the cytosol of host cells and to investigate the potential of Y. enterocolitica and Y. pseudotuberculosis as live carrier for vaccines. The model antigen ovalbumin (Ova) was fused to defined secretion or translocation domains of the Yersinia effector protein YopE and introduced into attenuated mutant strains of Y. enterocolitica and Y. pseudotuberculosis. In vitro experiments showed secretion and translocation of YopE-Ova hybrid proteins into host cells. To investigate the resulting immune responses, mice expressing transgenic Ova-specific T cell receptors were used. Both Y. enterocolitica and Y. pseudotuberculosis mutants induced efficaciously Ova-specific CD8+ T cell responses. The translocation domain of YopE was required for induction of CD8+ T cell responses in vivo, but not for T cell responses induced in vitro. The in vivo frequency of Ova-specific splenic T cells was up to six-fold higher in mice immunized with YopE-Ova-translocating Y. enterocolitica/Y. pseudotuberculosis mutants than in control mice. The Ova-specific T cells were shown to produce high amounts of IFN-gamma. We did not observe significant Ova-specific CD4+ T cell or antibody responses upon vaccination with either of the strains. In conclusion, Yersinia live carrier vaccine strains are suitable to target antigens into the MHC class I pathway and stimulate CD8+ T cell responses and thus, might be useful in vaccine approaches against intracellular pathogens.

Role of macrophage apoptosis in the pathogenesis of Yersinia

Yersinia species that are pathogenic for humans (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica) induce apoptosis in macrophages. Yersinia-induced apoptosis utilizes the mitochondrial pathway and is executed by activation of caspase cascades. The mechanism of Yersinia-induced apoptosis in macrophages has two essential components. One component is the innate immune response of macrophages to the pathogen, which leads to the activation of a survival response and a death response. Recognition of the bacterial cell envelope component lipopolysaccharide by Toll-like receptor 4 (TLR4) constitutes an important part of the innate immune response to the pathogen. The second essential component is YopJ, a protein secreted into Yersinia-infected macrophages via a bacterial type III secretion system, which selectively shuts down the survival pathway. In the absence of the survival pathway, the death pathway is executed, and Yersinia-infected macrophages undergo apoptosis. In this review, we introduce the basic features of Yersinia pathogenesis, summarize our current understanding of Yersinia-induced apoptosis, and discuss the role of apoptosis during Yersinia infection.

Involvement of the virulence gene products of Yersinia enterocolitica in the immune response of infected mice

The virulence of Yersinia enterocolitica is known to be highly dependent on its virulence plasmid. However, it remains unclear whether the virulence plasmid is engaged also in the induction of cell-mediated immunity that is essential for protective immunity in the host. In this study, we have compared the induction of type 1 helper T cell immunity against Y. enterocolitica using a virulent strain (P+) harboring the pYV plasmid and an avirulent strain (P-) harboring no pYV. Spleen cells from both groups of mice immunized with 1/10 LD50 of P+ strain and those with 1/10 LD50 of P- strain produced a high level of gamma interferon (IFN-gamma) upon stimulation with heat-killed bacteria, and CD4+ T cells were exclusively responsible for IFN-gamma production. When crude Yersinia outer proteins (Yops) were used for antigenic stimulation, IFN-gamma response of immune spleen cells against crude Yops was observed only in mice immunized with P+ strain. Flowcytometric analysis revealed a significant level of increase in IFN-gamma-producing CD8+ T cells as well as the increase in IFN-gamma-producing CD4+ T cells against crude Yops. These results suggest that the virulence plasmid of Y. enterocolitica is involved in the induction of Th1-type of possibly protective T cells in infected mice.

Cell invasion and IL-8 production pathways initiated by YadA of Yersinia pseudotuberculosis require common signalling molecules (FAK, c-Src, Ras) and distinct cell factors

The YadA protein of Yersinia pseudotuberculosis promotes tight adhesion and invasion into mammalian cells through beta(1)-integrins. In this work, we demonstrate that YadA also triggers the production of interleukin-8 (IL-8) in host cells and we identify intracellular signal transduction mechanisms involved in YadA-initiated cell invasion and/or IL-8 synthesis. Tyrosine protein kinases, including the focal adhesion kinase (FAK) and c-Src, as well as the small GTPase Ras, were shown to play a significant role in both YadA-promoted cell processes. YadA-mediated cell contact led to autophosphorylation of FAK at position Tyr397 and induced GTP-loading of Ras. Furthermore, IL-8 production and invasion induced by YadA were strongly reduced in FAK- and c-Src-deficient cells and in cells overexpressing dominant interfering forms of FAK, c-Src or Ras. We also demonstrate that YadA activates the Ras-dependent Raf-MEK1/2-ERK1/2 pathway and mitogen-activated protein kinases (MAPKs) p38 and JNK. Moreover, inhibition of ERK1/2 by pharmacological agents or overexpression of dominant negative FAK, c-Src or Ras abrogated IL-8 release, whereas invasion remained unaffected. In contrast, actin polymerization and phosphatidylinositol 3-kinase (PI3K) activity is essential for YadA-promoted cell entry, but not for cytokine secretion. We conclude that YadA triggers FAK-Src complex formation and subsequent Ras activation, which leads to the stimulation of MAPKs-dependent IL-8 production or to PI3K-dependent invasion.

Cytolethal distending toxin is essential for Helicobacter hepaticus colonization in outbred Swiss Webster mice

Helicobacter hepaticus, which induces chronic hepatitis and typhlocolitis in susceptible mouse strains, produces a cytolethal distending toxin (CDT) consisting of CdtA, CdtB, and CdtC. A cdtB-deficient H. hepaticus isogenic mutant (HhcdtBm7) was generated and characterized for colonization parameters in four intestinal regions (jejunum, ileum, cecum, and colon) of outbred Swiss Webster (SW) mice. Inactivation of the cdtB gene abolished the ability of HhcdtBm7 to colonize female mice at both 8 and 16 weeks postinfection (wpi), whereas HhcdtBm7 colonized all of four intestinal regions of three of five males at 8 wpi and then was eliminated by 16 wpi. Wild-type (WT) H. hepaticus was detected in the corresponding intestinal regions of both male and female mice at 8 and 16 wpi; however, colonization levels of WT H. hepaticus in the cecum and colon of male mice were approximately 1,000-fold higher than in females (P < 0.0079) at 16 wpi. Infection with WT H. hepaticus, but not HhcdtBm7, at 8 wpi was associated with significantly increased mRNA level of ileal and cecal gamma interferon (IFN-gamma) in females (P < 0.016 and 0.031 between WT H. hepaticus-infected and sham-dosed females, respectively). In contrast, the mRNA levels of IFN-gamma were significantly higher in the colon (P < 0.0079) and trended to be higher in the cecum (P < 0.15) in the HhcdtBm7-colonized male mice versus the sham-dosed controls at 8 wpi. In addition, mRNA levels of ileal IFN-gamma were significantly higher in the control females than males at 8 wpi (P < 0.016). There were significantly higher Th1-associated immunoglobulin G2a (IgG2a), Th2-associated IgG1 and mucosal IgA (P < 0.002, 0.002, 0.002, respectively) responses in the mice infected with WT H. hepaticus when compared to HhcdtBm7 at 16 wpi. Colonic interleukin-10 (IL-10) expressions at 16 wpi were significantly lower in both female and male mice colonized by WT H. hepaticus or in males transiently colonized through 8 wpi by HhcdtBm7 versus control mice (P < 0.0159). These lines of evidence indicate that (i) H. hepaticus CDT plays a crucial role in the persistent colonization of H. hepaticus in SW mice; (ii) SW female mice are more resistant to H. hepaticus colonization than male mice; (iii) there was persistent colonization of WT H. hepaticus in cecum, colon, and jejunum but only transient colonization of H. hepaticus in the ileum of female mice; (iv) H. hepaticus colonization was associated with down-regulation of colonic IL-10 production.

Y. enterocolitica translocated Yops impair stimulation of T-cells by antigen presenting cells

As T helper cells play a crucial role in the defense of the mouse immune system against Yersinia enterocolitica, an effective subversion strategy for the pathogen would be the inhibition of T-cell activation. In this study, we investigated whether Y. enterocolitica impairs this process on the level of antigen presentation. For this purpose, we used T-cells to measure the antigen presentation capacity of dendritic cells after they had been incubated with different types of Yersinia mutants. We could show that Y. enterocolitica impairs the processing of antigens by dendritic cells, that this effect is dependent on factors translocated by the pathogenicity-plasmid-encoded type III secretion system and that the most important factor appears to be YopP. The YopP effect is partly mediated by the killing of APCs, but in addition to this there appears to be an alternative way of action that results in the inhibition of antigen processing. The YopP effect is not mediated by soluble factors. In contrast to antigen processing, antigen presentation was only weakly affected by pathogenicity plasmid encoded factors in dendritic cells, but obviously in A20.J B-cells.

Turning Yersinia pathogenesis outside in: subversion of macrophage function by intracellular yersiniae

Three bacterial species within the genus Yersinia are causative agents of human disease. Yersinia pestis is transmitted by fleas or in aerosols, infects regional lymph nodes or lungs, and causes the highly lethal disease known as plague. Yersinia enterocolitica and Yersinia pseudotuberculosis are enteric pathogens most commonly associated with self-limiting infections of the mesenteric lymph nodes. Although Y. pestis and the enteropathogenic Yersinia species utilize different modes of transmission and cause different diseases, they rely on a common set of "core" virulence determinants to successfully infect a mammalian host. These virulence factors are encoded on the bacterial chromosome and on an approximately 70-kb plasmid. Once established in lymphoid tissue, all three Yersinia species replicate as aggregates of extracellular bacteria within necrotic lesions or abscesses. At this stage of the infectious process, the bacteria resist phagocytosis by neutrophils, which are able to destroy the bacteria if they are internalized. A type III secretion system encoded on the 70-kb plasmid functions to export multiple proteins (the Yops and LcrV) that are delivered to the extracellular milieu, the plasma membrane, or the cytosol of a host target cell. The Yops and LcrV act in concert to inhibit phagocytosis and downregulate inflammation. Although it is clear that the bulk of bacterial multiplication occurs in an extracellular phase, there is also evidence that all three pathogenic Yersinia survive and multiply in macrophages. Survival and replication of Yersinia in macrophages may occur throughout the infection, but is likely to be of greatest importance at early stages of colonization. That macrophages can serve as permissive sites for bacterial replication in vivo is supported by in vitro experiments, which demonstrate that Y. pestis, Y. peudotuberculosis, and Y. enterocolitica share the ability to survive and multiply in macrophage phagosomes. There is also evidence that the bacteria can subvert the functions of macrophages from within, by inhibiting phagosome acidification (Y. pseudotuberculosis) and the production of nitric oxide (Y. pestis and Y. pseudotuberculosis). Although considerable attention has been focused on how Yersinia subverts the functions of phagocytes from the outside, the study of how these bacteria subvert macrophage functions from the inside will lead to a better overall understanding of Yersinia pathogenesis.

Yersinia enterocolitica adhesin A induces production of interleukin-8 in epithelial cells

The major invasive factor of Yersinia enterocolitica, the invasin (Inv) protein, induces proinflammatory host cell responses, including interleukin-8 (IL-8) secretion from human epithelial cells, by engagement of beta1 integrins. The Inv-triggered beta1 integrin signaling involves the small GTPase Rac; the activation of MAP kinases, such as p38, MEK1, and JNK; and the activation of the transcription factor NF-kappaB. In the present study, we demonstrate that Y. enterocolitica YadA, which is a major adhesin of Y. enterocolitica with pleiotropic virulence effects, induces IL-8 secretion in epithelial cells. The abilities of YadA and Inv to promote adhesion to and invasion of HeLa cells and to induce IL-8 production by the cells were investigated by expression of YadA and Inv in Escherichia coli. While YadA mediates efficacious adhesion to HeLa cells, it mediates marginal invasion compared with Inv. Both YadA and Inv trigger comparable levels of IL-8 production. Conformational changes of the YadA head domain by mutation of NSVAIG-S motifs, which abolish collagen binding, also abolish adhesion of Yersinia to HeLa cells and YadA-mediated IL-8 secretion. Furthermore, experiments in which blocking antibodies against beta1 integrins were used demonstrate that beta1 integrins are crucial for YadA-mediated IL-8 secretion. Inhibitor studies demonstrate the involvement of small GTPases and MAP kinases, such as p38, MEK1, and JNK, indicating that beta1 integrin-dependent signaling mediated by Inv or YadA involves similar signaling pathways. These data present YadA, in addition to Inv, YopB, and Yersinia lipopolysaccharide, as a further inducer of proinflammatory molecules by which Y. enterocolitica might promote inflammatory tissue reactions.

Deletion of the mouse meprin beta metalloprotease gene diminishes the ability of leukocytes to disseminate through extracellular matrix

Meprins are metalloendopeptidases expressed by leukocytes in the lamina propria of the human inflamed bowel, that degrade extracellular matrix proteins in vitro implicating them in leukocyte transmigration events. The aims of these studies were to 1) examine the expression of meprins in the mouse mesenteric lymph node, 2) determine whether macrophages express meprins, and 3) determine whether deletion of the meprin beta gene (Mep-1beta) mitigated the ability of leukocytes to disseminate through extracellular matrix in vitro. These studies show that meprin alpha and beta are expressed in leukocytes of the mouse mesenteric lymph node, and meprin alpha, but not beta, decreased during intestinal inflammation. Deletion of Mep-1beta gene decreased the ability of leukocytes to migrate through matrigel compared with wild-type leukocytes. Meprin beta, but not alpha, was detected in cortical and medullary macrophages of the lymph node. Thus overall, meprin beta is expressed by leukocytes in the draining lymph node of the intestine, regardless of the inflammatory status of the animal, and is likely to contribute to leukocyte transmigration events important to intestinal immune responses. Thus, the expression of meprins by leukocytes of the intestinal immune system may have important implications for diseases such as inflammatory bowel diseases, which are aggravated by leukocyte infiltration.

Protective role of interleukin-6 during Yersinia enterocolitica infection is mediated through the modulation of inflammatory cytokines

Yersinia enterocolitica is a gram-negative enteric pathogen responsible for a number of gastrointestinal disorders. A striking feature of the pathology of a Y. enterocolitica infection is inflammation. Recently, we demonstrated a role for interleukin-1alpha (IL-1alpha) in the establishment of intestinal inflammation in response to a Y. enterocolitica infection. A cytokine directly affected by IL-1 levels is IL-6. A previous report suggested that IL-6 plays an anti-inflammatory role during Y. enterocolitica infection, and in other systems IL-6 has been shown to be proinflammatory. Therefore, a closer examination of the roles of IL-6 and inflammatory cytokines in the control of Y. enterocolitica infection in IL-6(-/-) mice was undertaken. Y. enterocolitica organisms were more virulent in the IL-6(-/-) mice (60-fold decreased 50% lethal dose) and colonized systemic tissues more rapidly and to a higher level than in the wild-type mice. One role of IL-6 during a Y. enterocolitica infection may be the downmodulation of the inflammatory response. The IL-6(-/-) mice have a more robust T(H)1 T-cell response, as well as hyperinflammatory pathologies. These phenotypes appear to be due to the misregulation of tumor necrosis factor alpha, monocyte chemotactic protein 1, IL-10, transforming growth factor beta1, and gamma interferon in the IL-6(-/-) mouse. These data provide further insight into the intricate cytokine signaling pathways involved in the regulation of inflammatory responses and the control of bacterial infections.

Characterization of oral Yersinia enterocolitica infection in three different strains of inbred mice

Several studies have highlighted differences in the resistances of various mouse strains to intravenous (i.v.) infection with Yersinia enterocolitica. In particular, differences in resistance and immunological response between BALB/c and C57BL/6 mouse strains have been determined. Following i.v infection, C57BL/6 mice are more resistant to Y. enterocolitica than are BALB/c mice. However, because Y. enterocolitica is typically a food-borne pathogen, the oral route of infection more accurately reflects the natural route of infection. Therefore, it was of interest to ascertain if the differences in resistance between mouse strains observed for an i.v. infection can be recapitulated following an oral infection. C57BL/6j, BALB/cj, and 129X1/Svj mouse strains presented no differences in 50% lethal dose (LD(50)) following oral infection with Y. enterocolitica. Subsequent analysis of cytokine levels, bacterial colonization and immune cell populations following oral infection confirmed characteristics previously described following i.v. Y. enterocolitica infection. All tissues analyzed from each mouse strain demonstrated a polarized Th1 cytokine profile and inflammatory cell influx throughout a 7-day course of infection. This immune response was present in all tissues and increased as bacterial colonization progressed. The lack of a differing LD(50) phenotype and common trends in immunological response among the three mouse strains tested suggests that oral infection is a useful model for studying the host response to Y. enterocolitica infection.

Gene expression patterns of epithelial cells modulated by pathogenicity factors of Yersinia enterocolitica

Epithelial cells express genes whose products signal the presence of pathogenic microorganisms to the immune system. Pathogenicity factors of enteric bacteria modulate host cell gene expression. Using microarray technology we have profiled epithelial cell gene expression upon interaction with Yersinia enterocolitica. Yersinia enterocolitica wild-type and isogenic mutant strains were used to identify host genes modulated by invasin protein (Inv), which is involved in enteroinvasion, and Yersinia outer protein P (YopP) which inhibits innate immune responses. Among 22 283 probesets (14,239 unique genes), we found 193 probesets (165 genes) to be regulated by Yersinia infection. The majority of these genes were induced by Inv, whose recognition leads to expression of NF-kappa B-regulated factors such as cytokines and adhesion molecules. Yersinia virulence plasmid (pYV)-encoded factors counter regulated Inv-induced gene expression. Thus, YopP repressed Inv-induced NF-kappa B regulated genes at 2 h post infection whereas other pYV-encoded factors repressed host cell genes at 4 and 8 h post infection. Chromosomally encoded factors of Yersinia, other than Inv, induced expression of genes known to be induced by TGF-beta receptor signalling. These genes were also repressed by pYV-encoded factors. Only a few host genes were exclusively induced by pYV-encoded factors. We hypothesize that some of these genes may contribute to pYV-mediated silencing of host cells. In conclusion, the data demonstrates that epithelial cells express a limited number of genes upon interaction with enteric Yersinia. Both Inv and YopP appear to modulate gene expression in order to subvert epithelial cell functions involved in innate immunity.

Activation of NF-kappaB and IL-8 by Yersinia enterocolitica invasin protein is conferred by engagement of Rac1 and MAP kinase cascades

Yersinia enterocolitica triggers activation of the nuclear factor (NF)-kappaB and production of the proinflammatory chemokine interleukin (IL)-8 in intestinal epithelial cells. This activation is due to adhesion of the bacteria via their outer membrane protein invasin to the host cells. Using Clostridium difficile toxins that specifically inactivate small GTPases, and transfection of inhibitory proteins of the Rho-GTPases, we demonstrate that Rac1, but not Cdc42 or Rho, is required for activation of NF-kappaB by invasin. Invasin activated the mitogen activated protein kinases (MAPK) p38 and c-Jun N-terminal protein kinase (JNK) but not extracellular signal regulated kinase (ERK). The functional relevance of these pathways for invasin-mediated IL-8 expression was assessed by protein kinase inhibitors and dominant-negative kinase mutants. While NF-kappaB and JNK contribute to IL-8 transcription, p38 MAPK also acts through stabilization of IL-8 mRNA, as confirmed by quantitative RT-PCR and electrophoretic mobility shift assays. Transfection experiments with I-kappaB kinase (IKK)1 and IKK2 mutants indicate that the release of NF-kappaB from its cytoplasmic inhibitor I-kappaB and its translocation into the nucleus is mediated by these kinases. Our data identify Rac1 as a key intermediate in invasin-triggered IL-8 synthesis and demonstrate that maximum IL-8 induction involves several MAP kinase cascades.

Interaction of Yersinia enterocolitica with epithelial cells: invasin beyond invasion

The chromosomally encoded inv gene product is an outer membrane protein that is functionally expressed in the enteropathogenic Yersinia species Yersinia enterocolitica and Yersinia pseudotuberculosis. Invasin protein is a high-affinity ligand for beta1 integrins and especially important in the early phase of intestinal infection for efficient translocation through the M cells located in the follicle-associated epithelium overlying the Peyer's patches. In addition to bacterial internalization, Yersinia invasin mediates proinflammatory epithelial cell reactions. Epithelial cells exhibit immunological functions including production of cytokines thereby signaling to the immune system the presence of invasive or pathogenic bacteria. Several other enteropathogenic bacteria also induce cytokine production in epithelial cells. However, the signaling pathways by which this reaction is accomplished differ for various pathogens. Binding of invasin-expressing Yersinia to beta1 integrin receptors of epithelial cells induces activation of a signal cascade involving Rac1, MAP kinases, activation of the transcription factor NF-kappaB, and the subsequent production of chemotactic cytokines. The Yersinia invasin-triggered inflammatory epithelial cell reaction may lead to the recruitment of phagocytes followed by tissue disruption which may be part of the strategy of the pathogen to promote its dissemination in the host tissue.