Histamine signaling through the H(2) receptor in the Peyer's patch is important for controlling Yersinia enterocolitica infection

Peyer's Patch: Possible target for modulating the Gut-Brain-Axis through microbiota

The gastrointestinal (GI) tract and the brain form bidirectional nervous, immune, and endocrine communications known as the gut-brain axis. Several factors can affect this axis; among them, various studies have focused on the microbiota and imply that alterations in microbiota combinations can influence both the brain and GI. Also, many studies have shown that the immune system has a vital role in varying gut microbiota combinations. In the current paper, we will review the multidirectional effects of gut microbiota, immune system, and nervous system on each other. Specifically, this review mainly focuses on the impact of Peyer's patches as a critical component of the gut immune system on the gut-brain axis through affecting the gut's microbial composition. In this way, some factors were discussed as proposed elements of missing gaps in this field.

Microbiota-Gut-Brain Axis: Pathophysiological Mechanism in Neuropsychiatric Disorders

Gut microbiota influence human behavior. The immunological, metabolic, and endocrine systems are involved in bidirectional communication between the gut and the brain, which is regulated by microbes through the microbiota-derived neurochemicals and metabolites. Gut microbiota have certain effects on neurodevelopment and maturation of immunity. However, gut dysbiosis can lead to neuropsychiatric disorders. Animal research and clinical case-control studies have demonstrated that gut dysbiosis has an adverse effect on human behavior through a variety of mechanisms. Recent meta-analysis on clinical studies confirmed gut dysbiosis in several major neuropsychiatric disorders. Microbiota-targeted intervention has recently been in the spotlight and meta-analyses have confirmed its effectiveness. In this chapter, we summarize the evidence for the interactions between microbiota and brain-gut network, as well as the potential pathophysiological mechanisms involved.

Deficiency of Lactoferrin aggravates lipopolysaccharide-induced acute inflammation via recruitment macrophage in mice

Lactoferrin (Lf), a multiple functional natural immune protein, is widely distributed in mammalian milk and glandular secretions (bile, saliva, tears and nasal mucosal secretions, etc.). In the previous study, we found that Lf plays an anti-inflammatory and anti-tumorigenesis role in AOM/DSS (azoxymethane/dextran sulfate sodium) induced mouse colitis-associated colon cancer model. Although we found that Lf has anti-inflammatory effects in chronic inflammation, its specific role and mechanisms in acute inflammation have not been clarified. Here, we reported that the expression levels of Lf were significantly increased when the organism was infected by Gram-negative bacteria. We then explored the role and potential mechanism of Lf in lipopolysaccharide (LPS)-induced acute inflammation. In the LPS-induced acute abdominal inflammation model, Lf deficiency aggravated inflammatory response and promoted macrophage chemotaxis to the inflammation site. Lf inhibited macrophage chemotaxis by suppressing the expression of macrophage-associated chemokines Ccl2 and Ccl5. Highly activated NF-κB signaling in Lf^−/− mice was responsible for the high expression of Ccl2 and Ccl5. Our results suggested that the anti-inflammatory effect of Lf offers a new potential treatment for acute inflammatory diseases.

Shedding light on biological sex differences and microbiota-gut-brain axis: a comprehensive review of its roles in neuropsychiatric disorders

Women and men are suggested to have differences in vulnerability to neuropsychiatric disorders, including major depressive disorder (MDD), generalized anxiety disorder (GAD), schizophrenia, eating disorders, including anorexia nervosa, and bulimia nervosa, neurodevelopmental disorders, such as autism spectrum disorder (ASD), and neurodegenerative disorders including Alzheimer’s disease, Parkinson’s disease. Genetic factors and sex hormones are apparently the main mediators of these differences. Recent evidence uncovers that reciprocal interactions between sex-related features (e.g., sex hormones and sex differences in the brain) and gut microbiota could play a role in the development of neuropsychiatric disorders via influencing the gut–brain axis. It is increasingly evident that sex–microbiota–brain interactions take part in the occurrence of neurologic and psychiatric disorders. Accordingly, integrating the existing evidence might help to enlighten the fundamental roles of these interactions in the pathogenesis of neuropsychiatric disorders. In addition, an increased understanding of the biological sex differences on the microbiota–brain may lead to advances in the treatment of neuropsychiatric disorders and increase the potential for precision medicine. This review discusses the effects of sex differences on the brain and gut microbiota and the putative underlying mechanisms of action. Additionally, we discuss the consequences of interactions between sex differences and gut microbiota on the emergence of particular neuropsychiatric disorders.

The human microbiome is a unique set of organisms affecting health via the gut–brain axis.

Neuropsychiatric disorders, eating disorders, neurodevelopmental disorders, and neurodegenerative disorders are regulated by the microbiota–gut–brain axis in a sex-specific manner.

Understanding the role of the microbiota–gut–brain axis and its sex differences in various diseases can lead to better therapeutic methods.

Yersiniabactin contributes to overcoming zinc restriction during Yersinia pestis infection of mammalian and insect hosts

Yersinia pestis causes human plague and colonizes both a mammalian host and a flea vector during its transmission cycle. A key barrier to bacterial infection is the host's ability to actively sequester key biometals (e.g., iron, zinc, and manganese) required for bacterial growth. This is referred to as nutritional immunity. Mechanisms to overcome nutritional immunity are essential virulence factors for bacterial pathogens. Y. pestis produces an iron-scavenging siderophore called yersiniabactin (Ybt) that is required to overcome iron-mediated nutritional immunity and cause lethal infection. Recently, Ybt has been shown to bind to zinc, and in the absence of the zinc transporter ZnuABC, Ybt improves Y. pestis growth in zinc-limited medium. These data suggest that, in addition to iron acquisition, Ybt may also contribute to overcoming zinc-mediated nutritional immunity. To test this hypothesis, we used a mouse model defective in iron-mediated nutritional immunity to demonstrate that Ybt contributes to virulence in an iron-independent manner. Furthermore, using a combination of bacterial mutants and mice defective in zinc-mediated nutritional immunity, we identified calprotectin as the primary barrier for Y. pestis to acquire zinc during infection and that Y. pestis uses Ybt to compete with calprotectin for zinc. Finally, we discovered that Y. pestis encounters zinc limitation within the flea midgut, and Ybt contributes to overcoming this limitation. Together, these results demonstrate that Ybt is a bona fide zinc acquisition mechanism used by Y. pestis to surmount zinc limitation during the infection of both the mammalian and insect hosts.

Gut Biofactory-Neurocompetent Metabolites within the Gastrointestinal Tract. A Scoping Review

The gut microbiota have gained much scientific attention recently. Apart from unravelling the taxonomic data, we should understand how the altered microbiota structure corresponds to functions of this complex ecosystem. The metabolites of intestinal microorganisms, especially bacteria, exert pleiotropic effects on the human organism and contribute to the host systemic balance. These molecules play key roles in regulating immune and metabolic processes. A subset of them affect the gut brain axis signaling and balance the mental wellbeing. Neurotransmitters, short chain fatty acids, tryptophan catabolites, bile acids and phosphatidylcholine, choline, serotonin, and L-carnitine metabolites possess high neuroactive potential. A scoping literature search in PubMed/Embase was conducted up until 20 June 2020, using three major search terms "microbiota metabolites" AND "gut brain axis" AND "mental health". This review aimed to enhance our knowledge regarding the gut microbiota functional capacity, and support current and future attempts to create new compounds for future clinical interventions.

Yersinia pseudotuberculosis YopH targets SKAP2-dependent and independent signaling pathways to block neutrophil antimicrobial mechanisms during infection

Yersinia suppress neutrophil responses by using a type 3 secretion system (T3SS) to inject 6–7 Yersinia effector proteins (Yops) effectors into their cytoplasm. YopH is a tyrosine phosphatase that causes dephosphorylation of the adaptor protein SKAP2, among other targets in neutrophils. SKAP2 functions in reactive oxygen species (ROS) production, phagocytosis, and integrin-mediated migration by neutrophils. Here we identify essential neutrophil functions targeted by YopH, and investigate how the interaction between YopH and SKAP2 influence Yersinia pseudotuberculosis (Yptb) survival in tissues. The growth defect of a ΔyopH mutant was restored in mice defective in the NADPH oxidase complex, demonstrating that YopH is critical for protecting Yptb from ROS during infection. The growth of a ΔyopH mutant was partially restored in Skap2-deficient (Skap2KO) mice compared to wild-type (WT) mice, while induction of neutropenia further enhanced the growth of the ΔyopH mutant in both WT and Skap2KO mice. YopH inhibited both ROS production and degranulation triggered via integrin receptor, G-protein coupled receptor (GPCR), and Fcγ receptor (FcγR) stimulation. SKAP2 was required for integrin receptor and GPCR-mediated ROS production, but dispensable for degranulation under all conditions tested. YopH blocked SKAP2-independent FcγR-stimulated phosphorylation of the proximal signaling proteins Syk, SLP-76, and PLCγ2, and the more distal signaling protein ERK1/2, while only ERK1/2 phosphorylation was dependent on SKAP2 following integrin receptor activation. These findings reveal that YopH prevents activation of both SKAP2-dependent and -independent neutrophilic defenses, uncouple integrin- and GPCR-dependent ROS production from FcγR responses based on their SKAP2 dependency, and show that SKAP2 is not required for degranulation.

Pathogenic Yersinia species carry a virulence plasmid encoding a type 3 secretion system that translocates 6–7 effector Yops into host cells. We demonstrate that YopH protects Yersinia pseudotuberculosis from neutrophil-produced reactive oxygen species (ROS) and degranulation by interfering with signaling pathways downstream of three major receptor classes in neutrophils. We show that a previously identified target of YopH, SKAP2, controls some of the pathways essential for YopH to inactivate during infection. SKAP2 is essential in mediating ROS production downstream of two major receptors; however, it is dispensable for degranulation from the three major receptors tested. Our study illustrates that YopH protects Y. pseudotuberculosis by blocking both SKAP2-dependent and independent signaling pathways that regulate several neutrophil functions.

Review: Microbial endocrinology: intersection of microbiology and neurobiology matters to swine health from infection to behavior

From birth to slaughter, pigs are in constant interaction with microorganisms. Exposure of the skin, gastrointestinal and respiratory tracts, and other systems allows microorganisms to affect the developmental trajectory and function of porcine physiology as well as impact behavior. These routes of communication are bi-directional, allowing the swine host to likewise influence microbial survival, function and community composition. Microbial endocrinology is the study of the bi-directional dialogue between host and microbe. Indeed, the landmark discovery of host neuroendocrine systems as hubs of host-microbe communication revealed neurochemicals act as an inter-kingdom evolutionary-based language between microorganism and host. Several such neurochemicals are stress catecholamines, which have been shown to drastically increase host susceptibility to infection and augment virulence of important swine pathogens, including Clostridium perfringens. Catecholamines, the production of which increase in response to stress, reach the epithelium of multiple tissues, including the gastrointestinal tract and lung, where they initiate diverse responses by members of the microbiome as well as transient microorganisms, including pathogens and opportunistic pathogens. Multiple laboratories have confirmed the evolutionary role of microbial endocrinology in infectious disease pathogenesis extending from animals to even plants. More recent investigations have now shown that microbial endocrinology also plays a role in animal behavior through the microbiota-gut-brain axis. As stress and disease are ever-present, intersecting concerns during each stage of swine production, novel strategies utilizing a microbial endocrinology-based approach will likely prove invaluable to the swine industry.

Distinct roles of histamine H1- and H2-receptor signaling pathways in inflammation-associated colonic tumorigenesis

Inflammatory bowel disease (IBD) is a well-known risk factor for the development of colorectal cancer. Prior studies have demonstrated that microbial histamine can ameliorate intestinal inflammation in mice. We tested the hypothesis whether microbe-derived luminal histamine suppresses inflammation-associated colon cancer in Apc^min/+ mice. Mice were colonized with the human-derived Lactobacillus reuteri. Chronic inflammation was induced by repeated cycles of low-dose dextran sulfate sodium (DSS). Mice that were given histamine-producing L. reuteri via oral gavage developed fewer colonic tumors, despite the presence of a complex mouse gut microbiome. We further demonstrated that administration of a histamine H1-receptor (H1R) antagonist suppressed tumorigenesis, while administration of histamine H2-receptor (H2R) antagonist significantly increased both tumor number and size. The bimodal functions of histamine include protumorigenic effects through H1R and antitumorigenic effects via H2R, and these results were supported by gene expression profiling studies on tumor specimens of patients with colorectal cancer. Greater ratios of gene expression of H2R ( HRH2) vs. H1R ( HRH1) were correlated with improved overall survival outcomes in patients with colorectal cancer. Additionally, activation of H2R suppressed phosphorylation of mitogen-activated protein kinases (MAPKs) and inhibited chemokine gene expression induced by H1R activation in colorectal cancer cells. Moreover, the combination of a H1R antagonist and a H2R agonist yielded potent suppression of lipopolysaccharide-induced MAPK signaling in macrophages. Given the impact on intestinal epithelial and immune cells, simultaneous modulation of H1R and H2R signaling pathways may be a promising therapeutic target for the prevention and treatment of inflammation-associated colorectal cancer. NEW & NOTEWORTHY Histamine-producing Lactobacillus reuteri can suppress development of inflammation-associated colon cancer in an established mouse model. The net effects of histamine may depend on the relative activity of H1R and H2R signaling pathways in the intestinal mucosa. Our findings suggest that treatment with H1R or H2R antagonists could yield opposite effects. However, by harnessing the ability to block H1R signaling while stimulating H2R signaling, novel strategies for suppression of intestinal inflammation and colorectal neoplasia could be developed.

The Microbiota-Gut-Brain Axis in Neuropsychiatric Disorders: Pathophysiological Mechanisms and Novel Treatments

Background

The human gut microbiome comprise a huge number of microorganisms with co-evolutionary associations with humans. It has been repeatedly revealed that bidirectional communication exists between the brain and the gut and involves neural, hormonal, and immunological pathways. Evidences from neuroscience researches over the past few years suggest that microbiota is essential for the development and maturation of brain systems that are associated to stress responses.

Method

This review provides that the summarization of the communication among microbiota, gut and brain and the results of preclinical and clinical studies on gut microbiota used in treatments for neuropsychiatric disorders.

Result

Recent studies have reported that diverse forms of neuropsychiatric disorders (such as autism, depression, anxiety, and schizophrenia) are associated with or modulated by variations in the microbiome, by microbial substrates, and by exogenous prebiotics, antibiotics, and probiotics.

Conclusion

The microbiota–gut–brain axis might provide novel targets for prevention and treatment of neuropsychiatric disorders. However, further studies are required to substantiate the clinical use of probiotics, prebiotics and FMT.

Real-Time Detection of Melatonin Using Fast-Scan Cyclic Voltammetry

Melatonin is an important hormone whose functions span from regulating circadian rhythm in the brain to providing anti-inflammatory properties in the immune system. Melatonin secretion from the pineal gland is known; however, the mechanism of melatonin signaling in the immune system is not well understood. The lymph node is the hub of the immune system, and melatonin secretion from lymphocytes was proposed to be an important source specifically for regulating cytokine secretion. Methods exist to quantify the concentration of melatonin within biological samples; however, they often suffer from either a lack of selectivity for melatonin over common biological interferences or temporal resolution, which is not amenable to measuring real-time signaling dynamics. Here, we have characterized an electrochemical method for optimal melatonin detection with subsecond resolution using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. The oxidation peaks detected for melatonin were at 1.0, 1.1, and 0.6 V. Evidence for electrode fouling of the tertiary peak was present; therefore, an optimized waveform was developed scanning from 0.2 to 1.3 V at 600 V/s. The optimized waveform eliminated the detection of fouling products on the electrode with a 24 ± 10 nM limit of detection. Melatonin was distinguished between biological interferences, and codetection with the major synthetic precursor, serotonin, was possible. This method was used to detect melatonin in live lymph node slices and provides the first real-time measurements within the lymph node using FSCV. Real-time detection of melatonin dynamics could provide useful information on the mechanism of immunomodulation during inflammatory disease.

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.

May the Force Be With You: The Light and Dark Sides of the Microbiota-Gut-Brain Axis in Neuropsychiatry

The role of the gut microbiota in health and disease is becoming increasingly recognized. The microbiota-gut-brain axis is a bi-directional pathway between the brain and the gastrointestinal system. The bacterial commensals in our gut can signal to the brain through a variety of mechanisms, which are slowly being resolved. These include the vagus nerve, immune mediators and microbial metabolites, which influence central processes such as neurotransmission and behaviour. Dysregulation in the composition of the gut microbiota has been identified in several neuropsychiatric disorders, such as autism, schizophrenia and depression. Moreover, preclinical studies suggest that they may be the driving force behind the behavioural abnormalities observed in these conditions. Understanding how bacterial commensals are involved in regulating brain function may lead to novel strategies for development of microbiota-based therapies for these neuropsychiatric disorders.

Altered esophageal histamine receptor expression in Eosinophilic Esophagitis (EoE): implications on disease pathogenesis

Eosinophilic Esophagitis (EoE) is a chronic allergic disorder, whose pathobiology is incompletely understood. Histamine-producing cells including mast cells and basophils have been implicated in EoE. However, very little is currently known about the role of histamine and histamine receptor (HR) expression and signaling in the esophageal epithelium. Herein, we characterized HR (H1R, H2R, H3R, and H4R) expression in human esophageal biopsies and investigate the role of histamine signaling in inducible cytokine expression in human esophageal epithelial cells in vitro. HR expression was quantified in esophageal biopsies from non-EoE control (N = 23), inactive EoE (<15 eos/hpf, N = 26) and active EoE (>15 eos/hpf, N = 22) subjects using qRT-PCR and immunofluorescent localization. HR expression and histamine-mediated cytokine secretion were evaluated in human primary and telomerase-immortalized esophageal epithelial cells. H1R, H2R, and H4R expression were increased in active EoE biopsies compared to inactive EoE and controls. H2R was the most abundantly expressed receptor, and H3R expression was negligible in all 3 cohorts. Infiltrating eosinophils expressed H1R, H2R, and H4R, which contributed to the observed increase in HR in active subjects. H1R and H2R, but not H3R or H4R, were constitutively expressed by primary and immortalized cells, and epithelial histamine stimulation induced GM-CSF, TNFα, and IL-8, but not TSLP or eotaxin-3 secretion. Epithelial priming with the TLR3 ligand poly (I:C) induced H1R and H2R expression, and enhanced histamine-induced GM-CSF, TNFα, and IL-8 secretion. These effects were primarily suppressed by H1R antagonists, but unaffected by H2R antagonism. Histamine directly activates esophageal epithelial cytokine secretion in vitro in an H1R dependent fashion. However, H1R, H2R and H4R are induced in active inflammation in EoE in vivo. While systemic antihistamine (anti-H1R) therapy may not induce clinical remission in EoE, our study suggests that further study of histamine receptor signaling in EoE is warranted and that targeting of additional histamine receptors may lead to novel treatment strategies for this important disease.

Role of innate immunity and altered intestinal motility in LPS- and MnCl2-induced intestinal intussusception in mice

Intestinal intussusception (ISS) commonly causes intestinal obstruction in children. One mechanism that has been proposed to cause ISS is inflammation-induced alteration of intestinal motility. We investigated whether innate inflammatory factors or altered motility is required for induction of ISS by LPS. We compared rates of ISS among BALB/c and C57BL/6 mice, mice lacking lymphocytes or depleted of phagocytes, or mice with defects in the Toll-like receptor 4 (TLR4) signaling pathway following administration of LPS or the Ca(2+) analog MnCl2. At 6 or 2 h after administration of LPS or MnCl2, respectively, mice underwent image analysis to assess intestinal contraction rate or laparotomy to identify ISS. LPS-induced ISS (LPS-ISS) was observed in BALB/c mice, but not in C57BL/6 mice or any BALB/c mice with disruptions of TLR4 signaling. LPS-induced serum TNF-α, IL-6, and nitric oxide (NO) and intestinal NO levels were similar in BALB/c and C57BL/6 mice. The rate of LPS-ISS was significantly reduced in phagocyte-depleted, but not lymphocyte-deficient, mice. Intestinal contraction rates were reduced in LPS-ISS-susceptible BALB/c mice, but not in LPS-ISS-resistant C57BL/6 or TLR4 mutant mice, suggesting a role for reduced intestinal contraction rate in LPS-ISS susceptibility. This was tested with MnCl2, a Ca(2+) antagonist that reduced intestinal contraction rates and induced ISS, irrespective of mouse strain. Therefore, LPS-ISS is initiated by innate immune signaling that requires TLR4 and phagocytes but may be independent of TNF-α, IL-6, and NO levels. Furthermore, alteration of intestinal motility, specifically, reduced intestinal contraction rate, is a key factor in the development of ISS.

YopP-expressing variant of Y. pestis activates a potent innate immune response affording cross-protection against yersiniosis and tularemia [corrected]

Plague, initiated by Yersinia pestis infection, is a rapidly progressing disease with a high mortality rate if not quickly treated. The existence of antibiotic-resistant Y. pestis strains emphasizes the need for the development of novel countermeasures against plague. We previously reported the generation of a recombinant Y. pestis strain (Kim53ΔJ+P) that over-expresses Y. enterocolitica YopP. When this strain was administered subcutaneously to mice, it elicited a fast and effective protective immune response in models of bubonic, pneumonic and septicemic plague. In the present study, we further characterized the immune response induced by the Kim53ΔJ+P recombinant strain. Using a panel of mouse strains defective in specific immune functions, we observed the induction of a prompt protective innate immune response that was interferon-γ dependent. Moreover, inoculation of mice with Y. pestis Kim53ΔJ+P elicited a rapid protective response against secondary infection by other bacterial pathogens, including the enteropathogen Y. enterocolitica and the respiratory pathogen Francisella tularensis. Thus, the development of new therapies to enhance the innate immune response may provide an initial critical delay in disease progression following the exposure to highly virulent bacterial pathogens, extending the time window for successful treatment.

Murine neonates infected with Yersinia enterocolitica develop rapid and robust proinflammatory responses in intestinal lymphoid tissues

Neonatal animals are generally very susceptible to infection with bacterial pathogens. However, we recently reported that neonatal mice are highly resistant to orogastric infection with Yersinia enterocolitica. Here, we show that proinflammatory responses greatly exceeding those in adults arise very rapidly in the mesenteric lymph nodes (MLN) of neonates. High-level induction of proinflammatory gene expression occurred in the neonatal MLN as early as 18 h postinfection. Marked innate phagocyte recruitment was subsequently detected at 24 h postinfection. Enzyme-linked immunosorbent spot assay (ELISPOT) analyses indicated that enhanced inflammation in neonatal MLN is contributed to, in part, by an increased frequency of proinflammatory cytokine-secreting cells. Moreover, both CD11b(+) and CD11b(-) cell populations appeared to play a role in proinflammatory gene expression. The level of inflammation in neonatal MLN was also dependent on key bacterial components. Y. enterocolitica lacking the virulence plasmid failed to induce innate phagocyte recruitment. In contrast, tumor necrosis factor alpha (TNF-α) protein expression and neutrophil recruitment were strikingly higher in neonatal MLN after infection with a yopP-deficient strain than with wild-type Y. enterocolitica, whereas only modest increases occurred in adults. This hyperinflammatory response was associated with greater colonization of the spleen and higher mortality in neonates, while there was no difference in mortality among adults. This model highlights the dynamic levels of inflammation in the intestinal lymphoid tissues and reveals the protective (wild-type strain) versus harmful (yopP-deficient strain) consequences of inflammation in neonates. Moreover, these results reveal that the neonatal intestinal lymphoid tissues have great potential to rapidly mobilize innate components in response to infection with bacterial enteropathogens.

Inhibitors of gastric acid secretion drugs increase neonatal morbidity and mortality

AIMS

To analyze all evidence on the possible increase in morbidity and mortality determined by the use of inhibitors of gastric acid secretion (IGAS) drugs.

MATERIALS AND METHODS

We review all evidence exploring the adverse events associated with IGAS use in neonates.

RESULTS

Despite being prescribed in an off-label manner because of the perceived safety and potential benefit demonstrated for older populations, IGAS are being increasingly used in the neonatal period with much evidence derived from adults and children. Few data are available for neonates and indicate an association between IGAS use with infections and necrotizing enterocolitis (NEC), and with an increased mortality. Delayed gastric emptying, increased gastric mucus viscosity, modification in microbiota, and impairment of neutrophils functions are possible mechanisms of adverse events associated with IGAS use.

CONCLUSIONS

A careful prescription of IGAS is crucial in order to reduce iatrogenic damage in neonates.

Transcriptional signatures as a disease-specific and predictive inflammatory biomarker for type 1 diabetes

The complex milieu of inflammatory mediators associated with many diseases is often too dilute to directly measure in the periphery, necessitating development of more sensitive measurements suitable for mechanistic studies, earlier diagnosis, guiding therapeutic decisions and monitoring interventions. We previously demonstrated that plasma samples from recent-onset type 1 diabetes (RO T1D) patients induce a proinflammatory transcriptional signature in freshly drawn peripheral blood mononuclear cells (PBMCs) relative to that of unrelated healthy controls (HC). Here, using cryopreserved PBMC, we analyzed larger RO T1D and HC cohorts, examined T1D progression in pre-onset samples, and compared the RO T1D signature to those associated with three disorders characterized by airway infection and inflammation. The RO T1D signature, consisting of interleukin-1 cytokine family members, chemokines involved in immunocyte chemotaxis, immune receptors and signaling molecules, was detected during early pre-diabetes and found to resolve post-onset. The signatures associated with cystic fibrosis patients chronically infected with Pseudomonas aeruginosa, patients with confirmed bacterial pneumonia, and subjects with H1N1 influenza all reflected immunological activation, yet each were distinct from one another and negatively correlated with that of T1D. This study highlights the remarkable capacity of cells to serve as biosensors capable of sensitively and comprehensively differentiating immunological states.

Histamine derived from probiotic Lactobacillus reuteri suppresses TNF via modulation of PKA and ERK signaling

Beneficial microbes and probiotic species, such as Lactobacillus reuteri, produce biologically active compounds that can modulate host mucosal immunity. Previously, immunomodulatory factors secreted by L. reuteri ATCC PTA 6475 were unknown. A combined metabolomics and bacterial genetics strategy was utilized to identify small compound(s) produced by L. reuteri that were TNF-inhibitory. Hydrophilic interaction liquid chromatography-high performance liquid chromatography (HILIC-HPLC) separation isolated TNF-inhibitory compounds, and HILIC-HPLC fraction composition was determined by NMR and mass spectrometry analyses. Histamine was identified and quantified in TNF-inhibitory HILIC-HPLC fractions. Histamine is produced from L-histidine via histidine decarboxylase by some fermentative bacteria including lactobacilli. Targeted mutagenesis of each gene present in the histidine decarboxylase gene cluster in L. reuteri 6475 demonstrated the involvement of histidine decarboxylase pyruvoyl type A (hdcA), histidine/histamine antiporter (hdcP), and hdcB in production of the TNF-inhibitory factor. The mechanism of TNF inhibition by L. reuteri-derived histamine was investigated using Toll-like receptor 2 (TLR2)-activated human monocytoid cells. Bacterial histamine suppressed TNF production via activation of the H₂ receptor. Histamine from L. reuteri 6475 stimulated increased levels of cAMP, which inhibited downstream MEK/ERK MAPK signaling via protein kinase A (PKA) and resulted in suppression of TNF production by transcriptional regulation. In summary, a component of the gut microbiome, L. reuteri, is able to convert a dietary component, L-histidine, into an immunoregulatory signal, histamine, which suppresses pro-inflammatory TNF production. The identification of bacterial bioactive metabolites and their corresponding mechanisms of action with respect to immunomodulation may lead to improved anti-inflammatory strategies for chronic immune-mediated diseases.

A metabolic network approach for the identification and prioritization of antimicrobial drug targets

For many infectious diseases, novel treatment options are needed in order to address problems with cost, toxicity and resistance to current drugs. Systems biology tools can be used to gain valuable insight into pathogenic processes and aid in expediting drug discovery. In the past decade, constraint-based modeling of genome-scale metabolic networks has become widely used. Focusing on pathogen metabolic networks, we review in silico strategies used to identify effective drug targets and highlight recent successes as well as limitations associated with such computational analyses. We further discuss how accounting for the host environment and even targeting the host may offer new therapeutic options. These systems-level approaches are beginning to provide novel avenues for drug targeting against infectious agents.

Mycoplasma pneumoniae CARDS toxin induces pulmonary eosinophilic and lymphocytic inflammation

Mycoplasma pneumoniae causes acute and chronic lung infections in humans, leading to a variety of pulmonary and extrapulmonary sequelae. Of the airway complications of M. pneumoniae infection, M. pneumoniae-associated exacerbation of asthma and pediatric wheezing are emerging as significant sources of human morbidity. However, M. pneumoniae products capable of promoting allergic inflammation are unknown. Recently, we reported that M. pneumoniae produces an ADP-ribosylating and vacuolating toxin termed the community-acquired respiratory distress syndrome (CARDS) toxin. Here we report that naive mice exposed to a single dose of recombinant CARDS (rCARDS) toxin respond with a robust inflammatory response consistent with allergic disease. rCARDS toxin induced 30-fold increased expression of the Th-2 cytokines IL-4 and IL-13 and 70- to 80-fold increased expression of the Th-2 chemokines CCL17 and CCL22, corresponding to a mixed cellular inflammatory response comprised of a robust eosinophilia, accumulation of T cells and B cells, and mucus metaplasia. The inflammatory responses correlate temporally with toxin-dependent increases in airway hyperreactivity characterized by increases in airway restriction and decreases in lung compliance. Furthermore, CARDS toxin-mediated changes in lung function and histopathology are dependent on CD4(+) T cells. Altogether, the data suggest that rCARDS toxin is capable of inducing allergic-type inflammation in naive animals and may represent a causal factor in M. pneumoniae-associated asthma.

Mitogen-activated protein kinase-dependent interleukin-1α intracrine signaling is modulated by YopP during Yersinia enterocolitica infection

Yersinia enterocolitica is a food-borne pathogen that preferentially infects the Peyer's patches and mesenteric lymph nodes, causing an acute inflammatory reaction. Even though Y. enterocolitica induces a robust inflammatory response during infection, the bacterium has evolved a number of virulence factors to limit the extent of this response. We previously demonstrated that interleukin-1α (IL-1α) was critical for the induction of gut inflammation characteristic of Y. enterocolitica infection. More recently, the known actions of IL-1α are becoming more complex because IL-1α can function both as a proinflammatory cytokine and as a nuclear factor. In this study, we tested the ability of Y. enterocolitica to modulate intracellular IL-1α-dependent IL-8 production in epithelial cells. Nuclear translocation of pre-IL-1α protein and IL-1α-dependent secretion of IL-8 into the culture supernatant were increased during infection with a strain lacking the 70-kDa virulence plasmid compared to the case during infection with the wild type, suggesting that Yersinia outer proteins (Yops) might be involved in modulating intracellular IL-1α signaling. Infection of HeLa cells with a strain lacking the yopP gene resulted in increased nuclear translocation of pre-IL-1α and IL-1α-dependent secretion of IL-8 similar to what is observed with bacteria lacking the virulence plasmid. YopP is a protein acetylase that inhibits mitogen-activated protein kinase (MAP kinase)- and NF-κB-dependent signal transduction pathways. Nuclear translocation of pre-IL-1α and IL-1α-dependent secretion of IL-8 in response to Yersinia enterocolitica infection were dependent on extracellular signal-regulated kinase (ERK) and p38 MAP kinase signaling but independent of NF-κB. These data suggest that Y. enterocolitica inhibits intracellular pre-IL-1α signaling and subsequent proinflammatory responses through inhibition of MAP kinase pathways.

New developments in the use of histamine and histamine receptors

Histamine and the histamine receptors are important regulators of a plethora of biological processes, including immediate hypersensitivity reactions and acid secretion in the stomach. In these roles, antihistamines have found widespread therapeutic applications, while the last receptor to be discovered, the H4 histamine receptor, has become a major target of novel therapeutics. Recent studies involving human genetic variance and the development of mice lacking specific receptors or the ability to generate histamine have shown roles for the histamine pathway that extend well beyond the established roles. These include identification of previously unappreciated mechanisms through which histamine regulates inflammation in allergy, as well as roles in autoimmunity, infection, and pain. As a result, antihistamines may have wider applications in the future than previously predicted.

Histidine decarboxylase is identified as a potential biomarker of intestinal mucosal injury in patients with acute intestinal obstruction

Various biomarkers currently used for the diagnosis of intestinal mucosal injury (IMI) in patients with acute intestinal obstruction have low sensitivity and specificity. In the present study, IMI, as indicated by the impaired expression of tight junction proteins, including zonula occludens-1, occludin and claudin-1, and inflammation were determined in colonic tissues of patients with 45 strangulated intestinal obstruction (STR-IO) and the adjacent "normal" colonic tissues of 35 patients with colon cancers by quantitative real-time polymerase chain reaction (QRT-PCR), Western blotting, immunohistochemistry and histological examination, respectively. Then, two-dimensional fluorescent difference gel electrophoresis coupled with linear trap quadrupole mass spectrometry was used to screen for potential biomarkers of IMI in the serum samples of 10 STR-IO, 10 simple intestinal obstruction (SIM-IO) and 10 normal healthy controls. A total of 35 protein spots were differentially expressed among the serum samples, and six of the proteins were identified as potential biomarkers. Among the six proteins, histidine decarboxylase (HDC) and ceruloplasmin (CP) were elevated significantly in patients with STR-IO, compared with patients with SIM-IO and healthy controls. Thus, HDC and CP were further validated by QRT-PCR, Western blotting, immunohistochemistry and enzyme-linked immunosorbent assay, respectively, in colonic tissues, serum and urine samples. Finally, the receiver operating characteristic curves were used to show the area under the curves of HDC, CP and several established biomarkers, followed by the determination of the appropriate cutoff values and their sensitivities and specificities. It was shown that for serum and urine, HDC levels achieved sensitivities and specificities compatible to or even greater than those of established biomarkers for the diagnosis of IMI in patients with acute intestinal obstruction, although further validation in a larger cohort is required.

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.

Gastric acidity inhibitors and the risk of intestinal infections

PURPOSE OF REVIEW

We reviewed recent clinical studies performed in adults, children, and neonates exploring the possible association of gastric acidity inhibitors use with intestinal infections. Possible mechanisms have also been reported.

RECENT FINDINGS

Many studies and systematic reviews demonstrate an increased risk of bacterial infection in adults taking acid suppressors. Little evidence is derived from the pediatric population. The use of gastric acidity inhibitors has been associated with systemic infections and necrotizing enterocolitis in preterm infants. Reduced gastric acidity, delayed gastric emptying, increased gastric mucus viscosity, modification in microbiota, and impairment of neutrophils functions, are all conditions determined by gastric acidity blockers that potentially lead to an increased risk of gastrointestinal infections.

SUMMARY

A proper utilization of these drugs, particularly for patients at high risk, is imperative in order to reduce deleterious effects on infection risk and to optimize cost-effectiveness ratio.

Differential expression of enteric neuroimmune-network in invasive and acute watery diarrhoea

We aimed to evaluate the changes of nerve morphology and distribution of neurotransmitters and neuropeptides in the rectum of Shigella flexneri-infected patients and in the duodenum of Vibrio cholerae O1-infected patients. Nerve morphology was observed by transmission electron microscopy. Immunoreactivity of nerve growth factor (NGF), neurotransmitters and neuropeptides in tissues were studied by immunohistochemistry. Ultrastructural analysis of intestinal biopsy revealed persisting axons degeneration throughout the study period in all patients. Regeneration was already evident at the acute stage with marked increase at late convalescence. Both acute shigellosis and cholera were accompanied by increased expression of NGF and histamine and decreased expression of serotonin that was restored at convalescence. Immunoreactivity of vasoactive intestinal peptide (VIP) was increased during acute cholera, whereas in shigellosis VIP- and substance P-immunoreactive nerves appeared at early convalescence. Both shigellosis and cholera induced long-lasting degeneration of enteric neuronal axons, despite the presence of ongoing proliferation and regeneration processes. Neurotransmitters and neuropeptides may play differential roles in invasive and watery diarrhoea.

Histamine plays an essential regulatory role in lung inflammation and protective immunity in the acute phase of Mycobacterium tuberculosis infection

The course and outcome of infection with mycobacteria are determined by a complex interplay between the immune system of the host and the survival mechanisms developed by the bacilli. Recent data suggest a regulatory role of histamine not only in the innate but also in the adaptive immune response. We used a model of pulmonary Mycobacterium tuberculosis infection in histamine-deficient mice lacking histidine decarboxylase (HDC(-/-)), the histamine-synthesizing enzyme. To confirm that mycobacterial infection induced histamine production, we exposed mice to M. tuberculosis and compared responses in C57BL/6 (wild-type) and HDC(-/-) mice. Histamine levels increased around fivefold above baseline in infected C57BL/6 mice at day 28 of infection, whereas only small amounts were detected in the lungs of infected HDC(-/-) mice. Blocking histamine production decreased both neutrophil influx into lung tissue and the release of proinflammatory mediators, such as interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), in the acute phase of infection. However, the accumulation and activation of CD4(+) T cells were augmented in the lungs of infected HDC(-/-) mice and correlated with a distinct granuloma formation that contained abundant lymphocytic infiltration and reduced numbers of mycobacteria 28 days after infection. Furthermore, the production of IL-12, gamma interferon, and nitric oxide, as well as CD11c(+) cell influx into the lungs of infected HDC(-/-) mice, was increased. These findings indicate that histamine produced after M. tuberculosis infection may play a regulatory role not only by enhancing the pulmonary neutrophilia and production of IL-6 and TNF-alpha but also by impairing the protective Th1 response, which ultimately restricts mycobacterial growth.

Forced IFIT-2 expression represses LPS induced TNF-alpha expression at posttranscriptional levels

Background

Interferon induced tetratricopeptide repeat protein 2 (IFIT-2, P54) belongs to the type I interferon response genes and is highly induced after stimulation with LPS. The biological function of this protein is so far unclear. Previous studies indicated that IFIT-2 binds to the initiation factor subunit eIF-3c, affects translation initiation and inhibits protein synthesis. The aim of the study was to further characterize the function of IFIT-2.

Results

Stimulation of RAW264.7 macrophages with LPS or IFN-γ leads to the expression of IFIT-2 in a type I interferon dependent manner. By using stably transfected RAW264.7 macrophages overexpressing IFIT-2 we found that IFIT-2 inhibits selectively LPS induced expression of TNF-α, IL-6, and MIP-2 but not of IFIT-1 or EGR-1. In IFIT-2 overexpressing cells TNF-α mRNA expression was lower after LPS stimulation due to reduced mRNA stability. Further experiments suggest that characteristics of the 3'UTR of transcripts discriminate whether IFIT-2 has a strong impact on protein expression or not.

Conclusion

Our data suggest that IFIT-2 may affect selectively LPS induced protein expression probably by regulation at different posttranscriptional levels.

Role of IFN-gamma and IL-6 in a protective immune response to Yersinia enterocolitica in mice

Background

Yersinia outer protein (Yop) H is a secreted virulence factor of Yersinia enterocolitica (Ye), which inhibits phagocytosis of Ye and contributes to the virulence of Ye in mice. The aim of this study was to address whether and how YopH affects the innate immune response to Ye in mice.

Results

For this purpose, mice were infected with wild type Ye (pYV⁺) or a YopH-deficient Ye mutant strain (ΔyopH). CD11b⁺ cells were isolated from the infected spleen and subjected to gene expression analysis using microarrays. Despite the attenuation of ΔyopH in vivo, by variation of infection doses we were able to achieve conditions that allow comparison of gene expression in pYV⁺ and ΔyopH infection, using either comparable infection courses or splenic bacterial burden. Gene expression analysis provided evidence that expression levels of several immune response genes, including IFN-γ and IL-6, are high after pYV⁺ infection but low after sublethal ΔyopH infection. In line with these findings, infection of IFN-γR^-/- and IL-6^-/- mice with pYV⁺ or ΔyopH revealed that these cytokines are not necessarily required for control of ΔyopH, but are essential for defense against infection with the more virulent pYV⁺. Consistently, IFN-γ pretreatment of bone marrow derived macrophages (BMDM) strongly enhanced their ability in killing intracellular Ye bacteria.

Conclusion

In conclusion, this data suggests that IFN-γ-mediated effector mechanisms can partially compensate virulence exerted by YopH. These results shed new light on the protective role of IFN-γ in Ye wild type infections.

Effects of colonization, luminescence, and autoinducer on host transcription during development of the squid-vibrio association

The light-organ symbiosis between the squid Euprymna scolopes and the luminous bacterium Vibrio fischeri offers the opportunity to decipher the hour-by-hour events that occur during the natural colonization of an animal's epithelial surface by its microbial partners. To determine the genetic basis of these events, a glass-slide microarray was used to characterize the light-organ transcriptome of juvenile squid in response to the initiation of symbiosis. Patterns of gene expression were compared between animals not exposed to the symbiont, exposed to the wild-type symbiont, or exposed to a mutant symbiont defective in either of two key characters of this association: bacterial luminescence or autoinducer (AI) production. Hundreds of genes were differentially regulated as a result of symbiosis initiation, and a hierarchy existed in the magnitude of the host's response to three symbiont features: bacterial presence > luminescence > AI production. Putative host receptors for bacterial surface molecules known to induce squid development are up-regulated by symbiont light production, suggesting that bioluminescence plays a key role in preparing the host for bacteria-induced development. Further, because the transcriptional response of tissues exposed to AI in the natural context (i.e., with the symbionts) differed from that to AI alone, the presence of the bacteria potentiates the role of quorum signals in symbiosis. Comparison of these microarray data with those from other symbioses, such as germ-free/conventionalized mice and zebrafish, revealed a set of shared genes that may represent a core set of ancient host responses conserved throughout animal evolution.

Bacteria induce CTGF and CYR61 expression in epithelial cells in a lysophosphatidic acid receptor-dependent manner

Cysteine-rich protein 61 (Cyr61/CCN1) and connective tissue growth factor (CTGF/CCN2) are members of the CCN (CYR61, CTGF, nephroblastoma overexpressed gene) family and exert pleiotropic functions such as regulation of adhesion, migration, extracellular matrix deposition, or cell differentiation, and play an important role in wound healing. This study focused on the nature of the so far unknown CTGF and CYR61 mRNA expression of epithelial cells after infection with bacteria. We demonstrate that infection of epithelial cells with attenuated Yersinia enterocolitica lacking the virulence plasmid pYV leads to the expression of CYR61 and CTGF. Virulent Y. enterocolitica bearing the pYV virulence plasmid suppressed the mRNA expression of these genes. Yersinia-mediated inhibition of CTGF and CYR61 mRNA expression is partially mediated by the cysteine protease YopT. Further characterization of the Yersinia factors, which trigger CTGF and CYR61 mRNA expression, demonstrated that these factors were secreted and could be enriched in lipid extracts. Beside Yersinia, several other bacteria such as Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, or Staphylococcus aureus, as well as supernatants of these bacteria induced CTGF and CYR61 expression. Blocking experiments with the lysophosphatidic acid (LPA) receptor-specific inhibitor Ki16425 suggest a general involvement of LPA receptors in bacteria-triggered CTGF and CYR61 expression. These data suggest that LPA receptor-dependent expression of CTGF and CYR61 represents a common host response after interaction with bacteria.

Identification of a molecular target for the Yersinia protein kinase A

Pathogenic bacteria of the genus Yersinia employ a type III secretion system to inject bacterial effector proteins directly into the host cytosol. One of these effectors, the Yersinia serine/threonine protein kinase YpkA, is an essential virulence determinant involved in host actin cytoskeletal rearrangements and in inhibition of phagocytosis. Here we report that YpkA inhibits multiple Galphaq signaling pathways. The kinase activity of YpkA is required for Galphaq inhibition. YpkA phosphorylates Ser47, a key residue located in the highly conserved diphosphate binding loop of the GTPase fold of Galphaq. YpkA-mediated phosphorylation of Ser47 impairs guanine nucleotide binding by Galphaq. Y. pseudotuberculosis expressing wild-type YpkA, but not a catalytically inactive YpkA mutant, interferes with Galphaq-mediated signaling pathways. Identification of a YpkA-mediated phosphorylation site in Galphaq sheds light on the contribution of the kinase activity of YpkA to Yersinia pathogenesis.

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.

Comparison of the host responses to wild-type and cpsB mutant Klebsiella pneumoniae infections

Previously, we established an intranasal mouse model of Klebsiella pneumoniae infection and validated its utility using a highly virulent wild-type strain and an avirulent capsular polysaccharide mutant. In the present study we compare the host responses to both infections by examining cytokine production, cellular infiltration, pulmonary histology, and intranasal immunization.