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

Attenuated Yersinia enterocolitica mutant strains exhibit differential virulence in cytokine-deficient mice: implications for the development of novel live carrier vaccines

Yersinia enterocolitica mutant strains, including mutants deficient in the chaperone SycH resulting in a functional deficiency in tyrosine phosphatase (YopH), Mn-cofactored superoxide dismutase (SodA), iron-repressive protein 1 (IRP-1), and Yersinia adhesin A (YadA), were demonstrated to be highly attenuated in wild-type C57BL/6 mice. TNFRp55(-/-), IL-12p40(-/-), and IL-18(-/-) mutant mice, in which the Yersinia wild-type strain causes severe systemic infections, were used to investigate whether these Yersinia mutant strains would be attenuated in immunodeficient hosts. A plasmid-cured Yersinia mutant strain was unable to colonize any of the mutant mice tested. A SycH-deficient mutant strain colonized intestinal tissues of these mice but was attenuated for systemic infection in all of the mutant mice. Both YadA- and Irp-1-deficient Yersinia mutants were still attenuated in IL-12(-/-) and IL-18(-/-) mice but were pathogenic in TNFRp55(-/-) mice. By contrast, a Yersinia sodA mutant was highly pathogenic for TNFRp55(-/-) and IL-12p40(-/-) mice while interleukin-18 (IL-18) was dispensable. This finding demonstrates that certain virulence factors enable yersiniae to compete with distinct cytokine-dependent host defense mechanisms. Moreover, while gamma interferon mRNA expression did not reflect protective host responses in cytokine-deficient mice, IL-10 expression coincided with a heavy splenic bacterial load and was associated with progressive infection courses. We can thus segregate minor (SodA), intermediate (YadA and IRP-1), and major (YopH) virulence factors of Y. enterocolitica. Finally, we demonstrate that, even in immunocompromised hosts, Yersinia sycH and, with some restrictions, irp-1 mutants may be suitable for use as live carrier vaccines.

From farm to table to brain: foodborne pathogen infection and the potential role of the neuro-immune-endocrine system in neurotoxic sequelae

The American diet is among the safest in the world; however, diseases transmitted by foodborne pathogens (FBPs) still pose a public health hazard. FBPs are the second most frequent cause of all infectious illnesses in the United States. Numerous anecdotal and clinical reports have demonstrated that central nervous system inflammation, infection, and adverse neurological effects occur as complications of foodborne gastroenteritis. Only a few well-controlled clinical or experimental studies, however, have investigated the neuropathogenesis. The full nature and extent of neurological involvement in foodborne illness is therefore unclear. To our knowledge, this review and commentary is the first effort to comprehensively discuss the issue of FBP induced neurotoxicity. We suggest that much of this information supports the role of a theoretical model, the neuro-immune-endocrine system, in organizing and helping to explain the complex pathogenesis of FBP neurotoxicity.

Interleukin-12 and interleukin-18 are indispensable for protective immunity against enteropathogenic Yersinia

Previous results have demonstrated an essential role of gamma interferon (IFN-gamma) in resistance against Yersinia enterocolitica. Hence, we investigated the course of Yersinia infection in mice deficient for the IFN-gamma-inducing cytokines interleukin-12 (IL-12 p40(-/-)) or interleukin-18 (IL-18(-/-)). The experiments described herein argue for a critical role of both cytokines in protective immune responses against this pathogen.

Subversion of integrins by enteropathogenic Yersinia

Enteropathogenic Yersinia are gram-negative bacterial species that translocate from the lumen of the intestine and are able to grow within deep tissue sites. During the earliest stages of disease, the organism is able to bind integrin receptors that are presented on the apical surface of M cells in the intestine, which allows its internalization and subsequent translocation into regional lymph nodes. The primary integrin substrate is the outer-membrane protein invasin, which binds with extraordinarily high affinity to at least five different integrins that have the (beta)(1) chain. Bacterial uptake into host cells is modulated by the affinity of receptor-substrate interaction, receptor concentration and the ability of the substrate to aggregate target receptors.

Bacterial translocation and tumor necrosis factor-alpha gene expression in experimental hemorrhagic shock

OBJECTIVE

To investigate whether bacterial translocation is the causative mechanism underlying cytokine production during hemorrhagic shock.

DESIGN

Prospective, randomized, unblinded animal study.

SETTING

Surgical research laboratories of Shiga University of Medical Science.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

The rats were randomly divided into three groups. Each animal was anesthetized with pentobarbital, given a continuous infusion of 0.9% saline, and monitored for blood pressure. The normoxic and sham shock groups breathed room air, whereas the hyperoxic shock group was administered 100% oxygen. Except in the sham shock group, blood was withdrawn to induce a hemorrhagic shock state, then the shed blood was reinfused. Sixty minutes after the induction of hemorrhagic shock, arterial blood cultures were performed in all three groups. The animals were then killed, and their mesenteric lymph nodes (MLNs) were harvested for bacterial culture. The terminal ileum, liver, spleen, kidney, lung, and MLNs were also collected for histologic study by in situ hybridization.

MEASUREMENTS AND MAIN RESULTS

In the bacteriologic study, the prevalence of bacterial translocation was 0% (0/11) in the hyperoxic shock group, 55% (6/11) in the normoxic shock group, and 0% (0/9) in the sham shock group. In the in situ hybridization study, tumor necrosis factor-alpha gene expression was detected only in the ileal tissue, MLNs, and spleens of the normoxic shock group. Blood cultures were sterile in all three groups.

CONCLUSIONS

Bacterial translocation occurred in MLNs within 1 hr of hemorrhage. Hemorrhagic shock causes tumor necrosis factor-alpha gene expression as well as bacterial translocation in MLNs, but not in the liver, in this model. Bacterial translocation was prevented by hyperoxia early in the course of hemorrhagic shock. Hyperoxia also prevented tumor necrosis factor-alpha gene expression along the bacterial invasion route.

Bacterial interplay at intestinal mucosal surfaces: implications for vaccine development

The discovery of 'molecular syringes' in several important gastrointestinal pathogens including Escherichia coli, Salmonella, Shigella and Yersinia, together with a better understanding of M cells and the mucosal immune system, has advanced our appreciation of multistage microorganism-host cell interactions. Recent studies suggest that these molecular strategies could be adapted for the development of modular mucosal vaccines.

Yersinia enterocolitica invasin protein triggers differential production of interleukin-1, interleukin-8, monocyte chemoattractant protein 1, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha in epithelial cells: implications for understanding the early cytokine network in Yersinia infections

Yersinia enterocolitica infection of epithelial cells results in interleukin-8 (IL-8) mRNA expression. Herein we demonstrate that besides IL-8, increased mRNA levels of five other cytokines, IL-1alpha, IL-1beta, monocyte chemoattractant protein 1 (MCP-1), granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-alpha), can be detected upon infection of HeLa cells with Yersinia. Yersinia-triggered cytokine production was not affected by blocking phosphatidylinositol-3-phosphate kinase with wortmannin, which inhibited bacterial invasion. Comparable cytokine mRNA responses were triggered by Escherichia coli expressing Yersinia inv, while no response was triggered by an inv-deficient Yersinia mutant. Moreover, cytokine responses were independent from metabolic activity of the bacteria, as killed bacterial cells were sufficient for triggering cytokine responses in HeLa cells. Semiquantitative reverse transcription-PCR analysis was used to assess the kinetics of cytokine mRNA expression in infected HeLa cells. IL-8, IL-1alpha, IL-1beta, MCP-1, GM-CSF, and TNF-alpha mRNA expression increased within 1 h postinfection, reached a maximum after 3 to 4 h, and then declined to preinfection levels within 3 h. IL-8, MCP-1, and GM-CSF were secreted by HeLa cells, whereas IL-1alpha and IL-1beta were not secreted and thus were found exclusively intracellularly. TNF-alpha protein could not be detected in cell lysates or supernatants. Stimulation of HeLa cells with IL-1alpha was followed by increased IL-8 mRNA expression, whereas stimulation with IL-8 did not induce cytokine production. Likewise, MCP-1 and GM-CSF did not induce significant cytokine responses in HeLa cells. Our results implicate that the initial host response to Yersinia infection might be sustained by IL-8, MCP-1, and GM-CSF produced by epithelial cells.

Translocation of Yersinia entrocolitica across reconstituted intestinal epithelial monolayers is triggered by Yersinia invasin binding to beta1 integrins apically expressed on M-like cells

Yersinia enterocolitica cross the intestinal epithelium via translocation through M cells, which are located in the follicle-associated epithelium (FAE) of Peyer's patches (PP). To investigate the molecular basis of this process, studies were performed using a recently developed in vitro model, in which the enterocyte-like cell line Caco-2 and PP lymphocytes are co-cultured in order to establish FAE-like structures including M cells. Here, we demonstrate that Y. enterocolitica does not adhere significantly to the apical membrane of differentiated enterocyte-like Caco-2 cells that express binding sites for Ulex europaeus agglutinin (UEA)-1. In contrast, Y. enterocolitica adhered to, and was internalized by, cells that lacked UEA-1 binding sites and displayed a disorganized brush border. These cells were considered to be converted to M-like cells. Further analysis revealed that part of these cells expressed beta1 integrins at their apical surface and, as revealed by comparison of wild-type and mutant strains, interacted with invasin of Y. enterocolitica. Consistently, anti-beta1 integrin antibodies significantly inhibited internalization of inv-expressing yersiniae. Experiments with Yersinia mutant strains deficient in YadA or Yop secretion revealed that these virulence factors play a minor role in this process. After internalization, yersiniae were transported within LAMP-1-negative vacuoles to, and released at, the basal surface. Internalization and transport of yersiniae was inhibited by cytochalasin D, suggesting that F-actin assembly is required for this process. These results provide direct evidence that expression of beta1 integrins at the apical surface of M cells enables interaction with the invasin of Y. enterocolitica, and thereby initiates internalization and translocation of bacteria.

Interferon consensus sequence binding protein confers resistance against Yersinia enterocolitica

Interferon consensus sequence binding protein (ICSBP)-deficient mice display enhanced susceptibility to intracellular pathogens. At least two distinct immunoregulatory defects are responsible for this phenotype. First, diminished production of reactive oxygen intermediates in macrophages results in impaired intracellular killing of microorganisms. Second, defective early interleukin-12 (IL-12) production upon microbial challenge leads to a failure in gamma interferon (IFN-gamma) induction and subsequently in T helper 1 immune responses. Here, we investigated the role of ICSBP in resistance against the extracellular bacterium Yersinia enterocolitica. ICSBP(-/-) mice failed to produce IL-12 and IFN-gamma, but also IL-4, after Yersinia challenge. In addition, granuloma formation was highly disturbed in infected ICSBP(-/-) mice, leading to multiple necrotic abscesses in affected organs. Consequently, ICSBP(-/-) mice rapidly succumbed to acute Yersinia infection. In vitro treatment of spleen cells from ICSBP(-/-) mice with recombinant IL-12 (rIL-12) or rIL-18 in combination with a second stimulus resulted in IFN-gamma induction. In experimental therapy of infected ICSBP(-/-) mice, we observed that administration of rIL-12 induced IFN-gamma production which was associated with improved resistance to Yersinia. In contrast, treatment with rIL-18 failed to enhance endogenous IFN-gamma production but nevertheless reduced bacterial burden in ICSBP(-/-) mice. Although cytokine therapy with rIL-12 or rIL-18 ameliorated the course of Yersinia infection in ICSBP(-/-) mice, both cytokines failed to completely restore impaired immunity. Taken together, the results indicate that the transcription factor ICSBP is essential for efficient host immune defense against Yersinia. These results are important for understanding the complex host immune responses in bacterial infections.

Studies on the interactions of immunostimulated macrophages andYersinia enterocoliticaO:8

Immunological and electron microscopy investigations of the phagocytic and killing activities of peritoneal macrophages from rats and mice against Yersinia enterocolitica serotype O:8 cells were performed. The effect of in vivo application of cytoplasmic membranes (CM) from the stable Escherichia coli WF+ L-form on macrophage activity was also studied. It was established that rat macrophages more actively phagocytosed the plasmidless pYV(-) Y. enterocolitica cells, compared to the plasmid-bearing pYV(+) Y. enterocolitica cells. The killing ability against both variants of the Y. enterocolitica strain was significantly enhanced in macrophages from CM-treated rats after 2 h, 4 h, and 24 h incubation. The CM treatment enhanced the phagocytic activity of the macrophages. The in vitro interaction of normal and immunostimulated rat macrophages with both pYV(+) and pYV(-) variants of Y. enterocolitica did not lead to any additional apoptotic and necrotic changes in macrophages compared to control macrophages, which were cultivated without Y. enterocolitica. Electron-microscopic investigation showed that mouse macrophages eliminated Y. enterocolitica pYV(+) cells in vivo after 24 h. No engulfed or digested bacterial cells were observed. Activation of cell surfaces and vacuolization of macrophage cytoplasm, both of CM-treated non-infected and infected mice, were observed. The experimental results showed that Y. enterocolitica pYV(+) cells could be eliminated by peritoneal macrophages.Key words: Yersinia enterocolitica, immunostimulation, electron microscopy, bacterial L-forms, macrophages.

Extraintestinal dissemination of Salmonella by CD18-expressing phagocytes

Specialized epithelia known as M cells overlying the lymphoid follicles of Peyer's patches are important in the mucosal immune system, but also provide a portal of entry for pathogens such as Salmonella typhimurium, Mycobacterium bovis, Shigella flexneri, Yersinia enterocolitica and reoviruses. Penetration of intestinal M cells and epithelial cells by Salmonella typhimurium requires the invasion genes of Salmonella Pathogenicity Island 1 (SPI1). SPI1-deficient S. typhimurium strains gain access to the spleen following oral administration and cause lethal infection in mice without invading M cells or localizing in Peyer's patches, which indicates that Salmonella uses an alternative strategy to disseminate from the gastrointestinal tract. Here we report that Salmonella is transported from the gastrointestinal tract to the bloodstream by CD18-expressing phagocytes, and that CD18-deficient mice are resistant to dissemination of Salmonella to the liver and spleen after oral administration. This CD18-dependent pathway of extraintestinal dissemination may be important for the development of systemic immunity to gastrointestinal pathogens, because oral challenge with SPI1-deficient S. typhimurium elicits a specific systemic IgG humoral immune response, despite an inability to stimulate production of specific mucosal IgA.

The lipopolysaccharide outer core of Yersinia enterocolitica serotype O:3 is required for virulence and plays a role in outer membrane integrity

Lipopolysaccharide (LPS) of Yersinia enterocolitica O:3 has an inner core linked to both the O-antigen and to an outer core hexasaccharide that forms a branch. The biological role of the outer core was studied using polar and non-polar mutants of the outer core biosynthetic operon. Analysis of O-antigen- and outer core-deficient strains suggested a critical role for the outer core in outer membrane properties relevant in resistance to antimicrobial peptides and permeability to hydrophobic agents, and indirectly relevant in resistance to killing by normal serum. Wild-type bacteria but not outer core mutants killed intragastrically infected mice, and the intravenous lethal dose was approximately 10(4)-fold higher for outer core mutants. After intragastric infection, outer core mutants colonized Peyer's patches and invaded mesenteric lymph nodes, spleen and liver, and induced protective immunity against wild-type bacteria. In mice co-infected intragastrically with an outer core mutant-wild type mixture, both strains colonized Peyer's patches similarly during the first 2 days, but the mutant was much less efficient in colonizing deeper organs and was cleared faster from Peyer's patches. The results demonstrate that outer core is required for Y. enterocolitica O:3 full virulence, and strongly suggest that it provides resistance against defence mechanisms (most probably those involving bactericidal peptides).

DNA immunization confers systemic, but not mucosal, protection against enteroinvasive bacteria

Naked plasmid DNA (pRc/Y-hsp60) with a cytomegalovirus promoter and a sequence encoding Yersinia enterocolitica 60-kDa heat shock protein (Y-HSP60) was used for vaccination. After intramuscular injection of pRc/Y-hsp60, Y-hsp60 mRNA could be detected by reverse transcription-PCR in muscle, liver and spleen. A single immunization with pRc/Y-hsp60 induced significant Y-HSP60-specific T cell responses after 1 week. IFN-gamma production by spleen cells upon stimulation with Y-HSP60 was strictly dependent on the presence of CD4+ T cells, indicating the generation of a Th1 response upon DNA immunization. DNA immunization in addition induced strong Y-HSP60-specific IgG2a, weak IgG1, but not IgA antibodies. Immunization of BALB/c and C57BL/6 mice with pRc/Y-hsp60 conferred protection against disseminated Y. enterocolitica infection in spleen, but not at the site of mucosal entry, the Peyer's patches. Furthermore, pRc/Y-hsp60 vaccination did not induce cross-protection against related pathogens. Vaccination of beta2-microglobulin- and H2-I-Abeta-deficient mice was not protective, suggesting that both CD4+ and CD8+ T cells are required for protective immunity induced by DNA vaccination.

Yersinia-induced apoptosis in vivo aids in the establishment of a systemic infection of mice

Pathogenic Yersinia cause a systemic infection in mice that is dependent on the presence of a large plasmid encoding a number of secreted virulence proteins called Yops. We previously demonstrated that a plasmid-encoded Yop, YopJ, was essential for inducing apoptosis in cultured macrophages. Here we report that YopJ is a virulence factor in mice and is important for the establishment of a systemic infection. The oral LD50 for a yopJ mutant Yersinia pseudotuberculosis increases 64-fold compared with wild-type. Although the yopJ mutant strain is able to reach the spleen of infected mice, the mutant strain seldom reaches the same high bacterial load that is seen with wild-type Yersinia strain and begins to be cleared from infected spleens on day 4 after infection. Furthermore, when in competition with wild-type Yersinia in a mixed infection, the yopJ mutant strain is deficient for spread from the Peyer's patches to other lymphoid tissue. We also show that wild-type Yersinia induces apoptosis in vivo of Mac-1(+) cells from infected mesenteric lymph nodes or spleens, as measured by quantitative flow cytometry of TUNEL (Tdt-mediated dUTP-biotin nick-end labeling)-positive cells. The levels of Mac-1(+), TUNEL+ cells from tissue infected with the yopJ mutant strain were equivalent to the levels detected in cells from uninfected tissue. YopJ is necessary for the suppression of TNF-alpha production seen in macrophages infected with wild-type Yersinia, based on previous in vitro studies (Palmer, L.E., S. Hobbie, J.E. Galan, and J.B. Bliska. 1998. Mol. Microbiol. 27:953-965). We conclude here that YopJ plays a role in the establishment of a systemic infection by inducing apoptosis and that this is consistent with the ability to suppress the production of the proinflammatory cytokine tumor necrosis factor alpha.

The virulence plasmid of Yersinia, an antihost genome

The 70-kb virulence plasmid enables Yersinia spp. (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) to survive and multiply in the lymphoid tissues of their host. It encodes the Yop virulon, an integrated system allowing extracellular bacteria to disarm the cells involved in the immune response, to disrupt their communications, or even to induce their apoptosis by the injection of bacterial effector proteins. This system consists of the Yop proteins and their dedicated type III secretion apparatus, called Ysc. The Ysc apparatus is composed of some 25 proteins including a secretin. Most of the Yops fall into two groups. Some of them are the intracellular effectors (YopE, YopH, YpkA/YopO, YopP/YopJ, YopM, and YopT), while the others (YopB, YopD, and LcrV) form the translocation apparatus that is deployed at the bacterial surface to deliver the effectors into the eukaryotic cells, across their plasma membrane. Yop secretion is triggered by contact with eukaryotic cells and controlled by proteins of the virulon including YopN, TyeA, and LcrG, which are thought to form a plug complex closing the bacterial secretion channel. The proper operation of the system also requires small individual chaperones, called the Syc proteins, in the bacterial cytosol. Transcription of the genes is controlled both by temperature and by the activity of the secretion apparatus. The virulence plasmid of Y. enterocolitica and Y. pseudotuberculosis also encodes the adhesin YadA. The virulence plasmid contains some evolutionary remnants including, in Y. enterocolitica, an operon encoding resistance to arsenic compounds.

Pathogenesis of human leukocyte antigen B27-positive arthritis. Information from clinical materials

In the spondyloarthropathies human leukocyte antigen (HLA) B27 confers a strong genetic predisposition to the development and to the chronicity of disease after extra-articular infection with certain gram-negative bacteria. The close relationships between infection, HLA-B27, other genetic factors, and the host immune system, however, still are unexplained. HLA-B27-positive arthritis continues to be an area of intensive investigation in basic and clinical research. New animal models with HLA-B27 transgenic mice and rats, as well as recent developments in understanding the processes involved in signal transduction, cytokine production, and human T-lymphocyte activation, contribute to the development of new pathogenic models of the spondyloarthropathies. This article summarizes the current concepts of the cause and pathogenesis of the spondyloarthropathies resulting from studies of clinical materials. The host-microbial interplay in human disease, namely in bacteria-induced reactive arthritis, may eludicate principle disease mechanisms in acute disease and in the development of chronic autoimmune arthritis or ankylosing spondylitis.

Porphyromonas gingivalis fimbriae use beta2 integrin (CD11/CD18) on mouse peritoneal macrophages as a cellular receptor, and the CD18 beta chain plays a functional role in fimbrial signaling

In this study, we demonstrate that Porphyromonas gingivalis fimbriae use molecules of beta2 integrin (CD11/CD18) on mouse peritoneal macrophages as cellular receptors and also show that the beta chain (CD18) may play a functional role in signalling for the fimbria-induced expression of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) genes in the cells. Using a binding assay with 125I-labeled fimbriae, we observed that fimbrial binding to the macrophages was inhibited by treatment with CD11a, CD11b, CD11c, or CD18 antibody but not by that with CD29 antibody. Western blot assays showed that the fimbriae bound to molecules of beta2 integrin (CD11/CD18) on the macrophages. Furthermore, Northern blot analyses showed that the fimbria-induced expression of IL-1beta and TNF-alpha genes in the cells was inhibited strongly by CD18 antibody treatment and slightly by CD11a, CD11b, or CD11c antibody treatment. Interestingly, intracellular adhesion molecule 1 (ICAM-1), a ligand of CD11/CD18, inhibited fimbrial binding to the cells in a dose-dependent manner. In addition, ICAM-1 clearly inhibited the fimbria-induced expression of IL-1beta and TNF-alpha genes in the cells. However, such inhibitory action was not observed with laminin treatment. These results suggest the importance of beta2 integrin (CD11/CD18) as a cellular receptor of P. gingivalis fimbriae in the initiation stage of the pathogenic mechanism of the organism in periodontal disease.

In vivo tracking and protective properties of Yersinia-specific intestinal T cells

After invasion via M cells enteropathogenic Yersinia enterocolitica subsequently establish an infection at three different sites: (i) Peyer's patches (PP), (ii) mesenteric lymph nodes (MLN), and after systemic dissemination in (iii) spleen, liver and lung. In order to characterize protective properties of intestinal T cells at the different sites of Y. enterocolitica infection, PP and MLN T cells were isolated from Y. enterocolitica-infected C57B1/6 mice and Yersinia-specific T cell lines were generated. These T cells exhibited the phenotype of CD4 Th1 cells. The adoptive transfer of Yersinia-specific Th1 cells from PP and MLN conferred protection against a lethal orogastric inoculum with Y. enterocolitica as revealed by survival post-infection. However, determination of bacterial counts in infected organs revealed that the transfer of PP T cells conferred protection in spleen but not in MLN and PP, whereas the transfer of T cells from MLN reduced bacterial counts in both spleen and MLN but not in PP. To elucidate the different protection pattern we wanted to track the transferred cells in vivo. For this purpose the cells were labelled with the stable green fluorescent cell linker PKH2-GL prior to the adoptive transfer. In vivo tracking of these cells revealed that the distribution pattern of transferred T cells in spleen, MLN and PP correlated closely with the protection pattern observed after Yersinia infection. Thus, most cells were recovered from the spleen, while only few cells were recovered from MLN and PP. In keeping with these results a rapid and significant increase in interferon-gamma (IFN-gamma) production in the spleen of mice after adoptive transfer of T cell lines was observed. Taken together, the present results demonstrate that intestinal CD4 Th1 cells from PP and MLN may be involved in the defence against Y. enterocolitica at different sites of the infection, and that PKH2-GL labelling is a suitable tool to characterize T cell functions in vivo.

Phospholipase A of Yersinia enterocolitica contributes to pathogenesis in a mouse model

Some isolates of Yersinia enterocolitica exhibit phospholipase activity, which has been linked to lecithin-dependent hemolysis (M. Tsubokura, K. Otsoki, I. Shimohira, and H. Yamamoto, Infect. Immun. 25:939-942, 1979). A gene encoding Y. enterocolitica phospholipase was identified, and analysis of the nucleotide sequence revealed two tandemly transcribed open reading frames. The first, yplA, has 74% identity and 85% similarity to the phospholipase A found in Serratia liquefaciens. Though the other, yplB, was less similar to the downstream accessory protein found in S. liquefaciens, the organization in both species is similar. Subsequently, a yplA-null Y. enterocolitica strain, YEDS10, was constructed and demonstrated to be phospholipase negative by plate and spectrophotometric assays. To ascertain whether the phospholipase has a role in pathogenesis, YEDS10 was tested in the mouse model. In experiments with perorally infected BALB/c mice, fewer YEDS10 organisms were recovered from the mesenteric lymph nodes and Peyer's patches (PP) than the parental strain at 3 or 5 days postinfection. Furthermore, bowel tissue and PP infected with YEDS10 appeared to be less inflamed than those infected with the parental strain. When extremely high doses of both the parental and YEDS10 strains were given, similar numbers of viable bacteria were recovered from the PP and mesenteric lymph nodes on day 3. However, the numbers of foci and the extent of inflammation and necrosis within them were noticeably less for YEDS10 compared to the parental strain. Together these findings suggest that Y. enterocolitica produces a phospholipase A which has a role in pathogenesis.

Role of YopP in suppression of tumor necrosis factor alpha release by macrophages during Yersinia infection

The Yersinia plasmid-encoded Yop virulon enables extracellular adhering bacteria to deliver toxic effector proteins inside their target cells. It includes a type III secretion system (Ysc), at least two translocator proteins (YopB, YopD), and a set of intracellular Yop effectors (YopE, YopH, YopO, YopM, and YopP). Infection of macrophages with a wild-type strain leads to low levels of tumor necrosis factor alpha (TNF-alpha) release compared to infection with plasmid-cured strains, suggesting that the virulence plasmid encodes a factor impairing the normal TNF-alpha response of infected macrophages. This effect is correlated with the inhibition of the macrophage mitogen-activated protein kinase (MAPK) activities. To identify the Yop protein responsible for the suppression of TNF-alpha release, we infected J774A.1 and PU5-1.8 macrophages with a battery of knockout Yersinia enterocolitica mutants and we quantified the TNF-alpha released. Mutants affected in secretion (yscN), in translocation (yopB and yopD), or in synthesis of all the known Yop effectors (yopH, yopO, yopP, yopE, and yopM polymutants) were unable to block the TNF-alpha response of the macrophages. In contrast, single yopE, yopH, yopO, and yopM mutants behaved like the wild-type strain. A yopP mutant elicited elevated TNF-alpha release, and complementation of the yopP mutant or the yop effector polymutant strain with yopP alone led to a drop in TNF-alpha release. In addition, YopP was also responsible for the inhibition of the extracellular signal-regulated kinase2 (ERK2) and p38 MAPK activities. These results show that YopP is the Yop effector responsible for the Yersinia-induced suppression of TNF-alpha release by infected macrophages.

Yersinia enterocolitica-induced interleukin-8 secretion by human intestinal epithelial cells depends on cell differentiation

In response to bacterial entry epithelial cells up-regulate expression and secretion of various proinflammatory cytokines, including interleukin-8 (IL-8). We studied Yersinia enterocolitica O:8-induced IL-8 secretion by intestinal epithelial cells as a function of cell differentiation. For this purpose, human T84 intestinal epithelial cells were grown on permeable supports, which led to the formation of tight monolayers of polarized intestinal epithelial cells. To analyze IL-8 secretion as a function of cell differentiation, T84 monolayers were infected from the apical or basolateral side at different stages of differentiation. Both virulent (plasmid-carrying) and nonvirulent (plasmid-cured) Y. enterocolitica strains invaded nondifferentiated T84 cells from the apical side. Yersinia invasion into T84 cells was followed by secretion of IL-8. After polarized differentiation of T84 cells Y. enterocolitica was no longer able to invade from the apical side or to induce IL-8 secretion by T84 cells. However, Y. enterocolitica invaded and induced IL-8 secretion by polarized T84 cells after infection from the basolateral side. Basolateral invasion required the presence of the Yersinia invasion locus, inv, suggesting beta1 integrin-mediated cell invasion. After basolateral infection, Yersinia-induced IL-8 secretion was not strictly dependent on cell invasion. Thus, although the plasmid-carrying Y. enterocolitica strain did not significantly invade T84 cells, it induced significant IL-8 secretion. Taken together, these data show that Yersinia-triggered IL-8 secretion by intestinal epithelial cells depends on cell differentiation and might be induced by invasion as well as by basolateral adhesion, suggesting that invasion is not essential for triggering IL-8 production. Whether IL-8 secretion is involved in the pathogenesis of Yersinia-induced abscess formation in Peyer's patch tissue remains to be shown.

Interaction of Yersinia enterocolitica with macrophages leads to macrophage cell death through apoptosis

Suppression of the host defense is one of the hallmarks of Yersinia enterocolitica infection. This enteric pathogen resists phagocytosis and interferes with macrophage functions from an extracellular localization (oxidative-burst generation and tumor necrosis factor alpha production). In this study, we investigated the fate of the Y. enterocolitica-infected macrophage. We found that murine J774A.1 macrophages and macrophages derived from human monocytes were killed by infection with Y. enterocolitica. Analysis of cellular morphology and DNA fragmentation revealed that macrophage cell death occurs through the induction of apoptosis. A total of 92% +/- 5% (mean +/- standard deviation) of murine J774A.1 macrophages and 74% +/- 6% of human monocyte-derived macrophages underwent apoptosis upon Yersinia infection after 4 and 20 h, respectively. The broad-spectrum caspase inhibitor Z-Val-Ala-DL-Asp-fluoromethylketone blocked completion of the Yersinia-induced apoptotic program but not the surface exposure of phosphatidylserine as an early-stage apoptotic event. Analysis of different Yersinia mutants showed that macrophage apoptosis depends on a functional Y. enterocolitica type III protein secretion system. Apoptotic cell death of macrophages was not related to the YopE-mediated cytotoxic effect of Yersinia, since disruption of actin microfilaments by a Y. enterocolitica strain expressing a restricted repertoire of yop genes, including YopE, did not result in macrophage apoptosis. Furthermore, Yersinia-induced cytotoxic alterations in epithelial HeLa cells, which are conferred by YopE, did not lead to apoptosis. Our data demonstrate for the first time that Y. enterocolitica promotes the apoptosis of macrophages, an effect which is clearly distinct from the morphological alterations mediated by Yersinia on epithelial HeLa cells.

Immunity against Yersinia enterocolitica by vaccination with Yersinia HSP60 immunostimulating complexes or Yersinia HSP60 plus interleukin-12

Microbial heat shock proteins (HSP) are dominant antigens for the host immune response. Because of the high sequence homology between mammalian and microbial HSP, their value as component of a subunit vaccine has been the subject of controversy. Previous work from this laboratory, however, demonstrated for the first time that the adoptive transfer of HSP60-reactive CD4+ alphabeta T-cell clones confers protection against bacterial infection in mice but does not induce autoimmunity. In the present study, we have therefore evaluated the potential role of Yersinia HSP60 (Y-HSP60) as a vaccine in the Yersinia enterocolitica mouse infection model. For this purpose, immunostimulating complexes (ISCOM) which included Y-HSP60 were constructed. Parenteral administration of this vaccine induced high Y-HSP60-specific serum antibody responses as well as T-cell responses. This reaction was parallelled by immunity against a lethal challenge with Y. enterocolitica. In contrast, mucosal application of Y-HSP60-ISCOM failed to induce systemic Y-HSP60-specific T-cell responses and thus failed to induce immunity against yersiniae. Likewise, vaccination with purified recombinant Y-HSP60 induced antibody responses but only weak T-cell responses. Therefore, this vaccination protocol was not protective. However, when interleukin-12 was used as an adjuvant, purified Y-HSP60 induced significant Y-HSP60-specific T-cell responses and thus induced protection against subsequent challenge with yersiniae. These studies suggest that (i) microbial HSP might be promising candidates for the design of subunit vaccines and (ii) interleukin-12 is an efficient alternative adjuvant to ISCOM particles for induction of protective CD4 Th1-cell-dependent immune responses against bacterial pathogens.

Cytokine gene expression in immune mice reinfected with Mycoplasma pneumoniae: the role of T cell subsets in aggravating the inflammatory response

Cytokine gene expression was examined by qualitative and semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) in the lungs of Mycoplasma pneumoniae infected immune C57BL/6 mice depleted of either CD4+, CD8+ or both CD4+ and CD8+ T cells. Immediately after M. pneumoniae reinfection of control immune mice, mRNAs for TNF-alpha, IFN-gamma, IL-1 beta, IL-6, IL-2 and IL-2 receptor were promptly detected in the lungs. In animals depleted of CD4+ T cells, mRNA expression for IL-2, IL-2 receptor and IFN-gamma were completely abrogated and mRNA expression for TNF-alpha, IL-1 beta and IL-6 were reduced by 10- to 100-fold. In mice depleted of CD8+ T cells, mRNA expression for IL-2 and the IL-2 receptor was also undetectable, while mRNA for TNF-alpha, IL-1 beta and IL-6 were only marginally decreased. Histological evaluation of the infected lungs performed in parallel revealed dense mononuclear infiltrations around small bronchi and small blood vessels in control reinfected mice. In contrast, in CD4+ T cell-depleted mice, these focal accumulation of lung tissue infiltrating cells were found to be greatly reduced. The data indicate that the inflammatory response in lung tissue thought to be mainly responsible for Mycoplasma pneumoniae disease is associated with an increased level and a prolonged expression of proinflammatory cytokines due to CD4+ lung infiltrating T cells.