IL-17 receptor A functions to help maintain barrier integrity and limit activation of immunopathogenic response to H. pylori infection.

Activation of Th17 cell responses, including the production of IL-17A and IL-21, contributes to host defense and inflammatory responses by coordinating adaptive and innate immune responses. IL-17A and IL-17F signal through a multimeric receptor, which includes the IL-17 receptor A (IL-17RA) subunit and the IL-17RC subunit. IL-17RA is expressed by many cell types, and data from previous studies suggest that loss of IL-17 receptor is required to limit immunopathology in the Helicobacter pylori model of infection. Here, an Il17ra-/- mouse was generated on the FVB/n background, and the role of IL-17 signaling in the maintenance of barrier responses to H. pylori was investigated. Generating the Il17ra-/- on the FVB/n background allowed for the examination of responses in the paragastric lymph node and will allow for future investigation into carcinogenesis. While uninfected Il17ra-/- mice do not develop spontaneous gastritis following H. pylori infection, Il17ra-/- mice develop severe gastric inflammation accompanied by lymphoid follicle production and exacerbated production of Th17 cytokines. Increased inflammation in the tissue, increased IgA levels in the lumen, and reduced production of Muc5ac in the corpus correlate with increased H. pylori-induced paragastric lymph node activation. These data suggest that the cross talk between immune cells and epithelial cells regulates mucin production, IgA production, and translocation, impacting the integrity of the gastric mucosa and therefore activating of the adaptive immune response.

Interleukin-21 (IL-21) Downregulates Dendritic Cell Cytokine Responses to Helicobacter pylori and Modulates T Lymphocyte IL-17A Expression in Peyer's Patches during Infection.

Interleukin-21 (IL-21), a cytokine produced by many subsets of activated immune cells, is critical for driving inflammation in several models. Using Helicobacter pylori infection as a model for chronic mucosal infection, we previously published that IL-21 is required for the development of gastritis in response to infection. Concomitant with protection from chronic inflammation, H. pylori-infected IL-21-/- mice exhibited limited Th1 and Th17 responses in their gastric mucosa. Here we report that H. pylori-infected IL-21-/- mice express significantly higher levels of IL-17A than H. pylori-infected wild-type (WT) mice in the Peyer's patches and mesenteric lymph nodes. This led us to hypothesize that IL-21 may indirectly regulate H. pylori-specific T cell responses by controlling dendritic cell (DC) functions in mucosa-associated lymphoid tissue. It was found that IL-21 treatment reduced the ability of dendritic cells to produce proinflammatory cytokines in response to H. pylori While H. pylori increased the expression of costimulatory proteins on DCs, IL-21 reduced the expression of CD40 in the presence of H. pylori Also, Th17 recall responses were intact when DCs were used as antigen-presenting cells in the presence of IL-21, but IL-21 did impact the ability of DCs to induce antigen-specific proliferation. These data suggest that IL-21, while proinflammatory in most settings, downregulates the proinflammatory cytokine microenvironment through modulating the cytokine expression of DCs, indirectly modifying IL-17A expression. Understanding how these proinflammatory cytokines are regulated will advance our understanding of how and why H. pylori infection may be tolerated in some individuals while it causes gastritis, ulcers, or cancer in others.

Th17 Cells in Helicobacter pylori Infection: a Dichotomy of Help and Harm.

Helicobacter pylori is a Gram-negative bacterium that infects the gastric epithelia of its human host. Everyone who is colonized with these pathogenic bacteria can develop gastric inflammation, termed gastritis. Additionally, a small proportion of colonized people develop more adverse outcomes, including gastric ulcer disease, gastric adenocarcinoma, or gastric mucosa-associated lymphoid tissue lymphoma. The development of these adverse outcomes is dependent on the establishment of a chronic inflammatory response. The development and control of this chronic inflammatory response are significantly impacted by CD4+ T helper cell activity. Noteworthy, T helper 17 (Th17) cells, a proinflammatory subset of CD4+ T cells, produce several proinflammatory cytokines that activate innate immune cell antimicrobial activity, drive a pathogenic immune response, regulate B cell responses, and participate in wound healing. Therefore, this review was written to take an intricate look at the involvement of Th17 cells and their affiliated cytokines (interleukin-17A [IL-17A], IL-17F, IL-21, IL-22, and IL-26) in regulating the immune response to H. pylori colonization and carcinogenesis.

Purine Biosynthesis Metabolically Constrains Intracellular Survival of Uropathogenic Escherichia coli.

The ability to de novo synthesize purines has been associated with the intracellular survival of multiple bacterial pathogens. Uropathogenic Escherichia coli (UPEC), the predominant cause of urinary tract infections, undergoes a transient intracellular lifestyle during which bacteria clonally expand into multicellular bacterial communities within the cytoplasm of bladder epithelial cells. Here, we characterized the contribution of the conserved de novo purine biosynthesis-associated locus cvpA-purF to UPEC pathogenesis. Deletion of cvpA-purF, or of purF alone, abolished de novo purine biosynthesis but did not impact bacterial adherence properties in vitro or in the bladder lumen. However, upon internalization by bladder epithelial cells, UPEC deficient in de novo purine biosynthesis was unable to expand into intracytoplasmic bacterial communities over time, unless it was extrachromosomally complemented. These findings indicate that UPEC is deprived of purine nucleotides within the intracellular niche and relies on de novo purine synthesis to meet this metabolic requirement.

IL-17 Receptor Signaling through IL-17A or IL-17F Is Sufficient to Maintain Innate Response and Control of Helicobacter pylori Immunopathogenesis.

IL-17R signaling is required for control of extracellular pathogens and is also implicated in development of chronic inflammatory processes. The response to the human pathogen Helicobacter pylori results in Th1 and Th17 cell activation and a chronic inflammatory process that can lead to adverse outcomes, such as gastric cancer. Previously, we identified IL-17RA as a requirement for the recruitment of neutrophils and control of H. pylori colonization in the gastric mucosa. Unexpectedly, H. pylori-infected Il17ra -/- mice had significantly more chronic inflammation than H. pylori-infected wild-type mice. In this study, human epithelial cell lines and murine models were used to investigate differential roles for IL-17A, IL-17F, and IL-17A/F during H. pylori infection. Moreover, the hypothesis that IL-17RA signaling, specifically in lymphocytes, provides an autocrine feedback loop that downregulates Th17 cytokine production was investigated. The data indicate that epithelial cells exhibit a stronger response to IL-17A and IL-17A/F than IL-17F, and that IL-17A and IL-17A/F can synergize with TNF and IL-22 to induce antimicrobial genes of gastric epithelial cells. In vivo deficiencies of IL-17A or IL-17F alone did not significantly change the immunopathological response to H. pylori, but if both cytokines were absent, a hyperinflammatory lymphocytic response developed. Using a cre/flox targeting approach for IL-17RA combined with infection, our findings demonstrate that increased chronic inflammation in Il17ra -/- mice was not attributed to a T cell-intrinsic defect. These data imply that IL-17A and IL-17F may have overlapping roles in maintenance of the gastric mucosal response to infection.

Loss of Corpus-Specific Lipids in Helicobacter pylori-Induced Atrophic Gastritis.

Helicobacter pylori colonization of the stomach is a strong risk factor for the development of stomach cancer and peptic ulcer disease. In this study, we tested the hypothesis that H. pylori infection triggers alterations in gastric lipid composition. Mongolian gerbils were experimentally infected with H. pylori for 3 months. Conventional histologic staining revealed mucosal inflammation in stomachs from the H. pylori-infected animals but not in stomachs from uninfected control animals. Atrophic gastritis (a premalignant condition characterized by loss of corpus-specific parietal and chief cells), gastric mucosal hyperplasia, dysplasia, and/or gastric cancer were detected in stomachs from several infected animals. We then used imaging mass spectrometry to analyze the relative abundance and spatial distribution of gastric lipids. We detected ions corresponding to 36 distinct lipids that were differentially abundant when comparing gastric tissues from H. pylori-infected animals with tissues from uninfected animals. Liquid chromatography-tandem mass spectrometry analysis of lipid extracts from homogenized gastric tissues provided additional supportive evidence for the identification of several differentially abundant lipids. Sixteen of the differentially abundant lipids were localized mainly to the gastric corpus in stomachs from uninfected animals and were markedly reduced in abundance in stomachs from H. pylori-infected animals with severe disease (atrophic gastritis and dysplasia or gastric cancer). These findings indicate that H. pylori infection can lead to alterations in gastric lipid composition and constitute a new approach for identifying biomarkers of gastric atrophy and premalignant changes. IMPORTANCE H. pylori colonization of the stomach triggers a cascade of gastric alterations that can potentially culminate in stomach cancer. The molecular alterations that occur in gastric tissue prior to development of stomach cancer are not well understood. We demonstrate here that H. pylori-induced premalignant changes in the stomach are accompanied by extensive alterations in gastric lipid composition. These alterations are predicted to have important functional consequences relevant to H. pylori-host interactions and the pathogenesis of gastric cancer.

Temporal Control of the Helicobacter pylori Cag Type IV Secretion System in a Mongolian Gerbil Model of Gastric Carcinogenesis.

The Helicobacter pylori Cag type IV secretion system (T4SS) translocates the effector protein CagA and nonprotein bacterial constituents into host cells. In this study, we infected Mongolian gerbils with an H. pylori strain in which expression of the cagUT operon (required for Cag T4SS activity) is controlled by a TetR/tetO system. Transcript levels of cagU were significantly higher in gastric tissue from H. pylori-infected animals receiving doxycycline-containing chow (to derepress Cag T4SS activity) than in tissue from infected control animals receiving drug-free chow. At 3 months postinfection, infected animals receiving doxycycline had significantly increased gastric inflammation compared to infected control animals. Dysplasia (a premalignant histologic lesion) and/or invasive gastric adenocarcinoma were detected only in infected gerbils receiving doxycycline, not in infected control animals. We then conducted experiments in which Cag T4SS activity was derepressed during defined stages of infection. Continuous Cag T4SS activity throughout a 3-month time period resulted in higher rates of dysplasia and/or gastric cancer than observed when Cag T4SS activity was limited to early or late stages of infection. Cag T4SS activity for the initial 6 weeks of infection was sufficient for the development of gastric inflammation at the 3-month time point, with gastric cancer detected in a small proportion of animals. These experimental results, together with previous studies of cag mutant strains, provide strong evidence that Cag T4SS activity contributes to gastric carcinogenesis and help to define the stages of H. pylori infection during which Cag T4SS activity causes gastric alterations relevant for cancer pathogenesis.IMPORTANCE The "hit-and-run model" of carcinogenesis proposes that an infectious agent triggers carcinogenesis during initial stages of infection and that the ongoing presence of the infectious agent is not required for development of cancer. H. pylori infection and actions of CagA (an effector protein designated a bacterial oncoprotein, secreted by the Cag T4SS) are proposed to constitute a paradigm for hit-and-run carcinogenesis. In this study, we report the development of methods for controlling H. pylori Cag T4SS activity in vivo and demonstrate that Cag T4SS activity contributes to gastric carcinogenesis. We also show that Cag T4SS activity during an early stage of infection is sufficient to initiate a cascade of cellular alterations leading to gastric inflammation and gastric cancer at later time points.

Protein kinase D mediates inflammatory responses of human placental macrophages to Group B Streptococcus.

PROBLEM: During pregnancy, Group B Streptococcus (GBS) can infect fetal membranes to cause chorioamnionitis, resulting in adverse pregnancy outcomes. Macrophages are the primary resident phagocyte in extraplacental membranes. Protein kinase D (PKD) was recently implicated in mediating pro-inflammatory macrophage responses to GBS outside of the reproductive system. This work aimed to characterize the human placental macrophage inflammatory response to GBS and address the extent to which PKD mediates such effects. METHOD: Primary human placental macrophages were infected with GBS in the presence or absence of a specific, small molecule PKD inhibitor, CRT 0066101. Macrophage phenotypes were characterized by evaluating gene expression, cytokine release, assembly of the NLRP3 inflammasome, and NFκB activation. RESULTS: GBS evoked a strong inflammatory phenotype characterized by the release of inflammatory cytokines (TNFα, IL-1ß, IL-6 (P ≤ 0.05), NLRP3 inflammasome assembly (P ≤ 0.0005), and NFκB activation (P ≤ 0.05). Pharmacological inhibition of PKD suppressed these responses, newly implicating a role for PKD in mediating immune responses of primary human placental macrophages to GBS. CONCLUSION: PKD plays a critical role in mediating placental macrophage inflammatory activation in response to GBS infection.

Helicobacter pylori genetic diversification in the Mongolian gerbil model.

Helicobacter pylori requires genetic agility to infect new hosts and establish long-term colonization of changing gastric environments. In this study, we analyzed H. pylori genetic adaptation in the Mongolian gerbil model. This model is of particular interest because H. pylori-infected gerbils develop a high level of gastric inflammation and often develop gastric adenocarcinoma or gastric ulceration. We analyzed the whole genome sequences of H. pylori strains cultured from experimentally infected gerbils, in comparison to the genome sequence of the input strain. The mean annualized single nucleotide polymorphism (SNP) rate per site was 1.5e-5, which is similar to the rates detected previously in H. pylori-infected humans. Many of the mutations occurred within or upstream of genes associated with iron-related functions (fur, tonB1, fecA2, fecA3, and frpB3) or encoding outer membrane proteins (alpA, oipA, fecA2, fecA3, frpB3 and cagY). Most of the SNPs within coding regions (86%) were non-synonymous mutations. Several deletion or insertion mutations led to disruption of open reading frames, suggesting that the corresponding gene products are not required or are deleterious during chronic H. pylori colonization of the gerbil stomach. Five variants (three SNPs and two deletions) were detected in isolates from multiple animals, which suggests that these mutations conferred a selective advantage. One of the mutations (FurR88H) detected in isolates from multiple animals was previously shown to confer increased resistance to oxidative stress, and we now show that this SNP also confers a survival advantage when H. pylori is co-cultured with neutrophils. Collectively, these analyses allow the identification of mutations that are positively selected during H. pylori colonization of the gerbil model.

IL-17a and IL-22 Induce Expression of Antimicrobials in Gastrointestinal Epithelial Cells and May Contribute to Epithelial Cell Defense against Helicobacter pylori.

Helicobacter pylori colonization of the human stomach can lead to adverse clinical outcomes including gastritis, peptic ulcers, or gastric cancer. Current data suggest that in addition to bacterial virulence factors, the magnitude and types of immune responses influence the outcome of colonization. Specifically, CD4+ T cell responses impact the pathology elicited in response to H. pylori. Because gastritis is believed to be the initiating host response to more detrimental pathological outcomes, there has been a significant interest in pro-inflammatory T cell cytokines, including the cytokines produced by T helper 17 cells. Th17 cells produce IL-17A, IL-17F, IL-21 and IL-22. While these cytokines have been linked to inflammation, IL-17A and IL-22 are also associated with anti-microbial responses and control of bacterial colonization. The goal of this research was to determine the role of IL-22 in activation of antimicrobial responses in models of H. pylori infection using human gastric epithelial cell lines and the mouse model of H. pylori infection. Our data indicate that IL-17A and IL-22 work synergistically to induce antimicrobials and chemokines such as IL-8, components of calprotectin (CP), lipocalin (LCN) and some ß-defensins in both human and primary mouse gastric epithelial cells (GEC) and gastroids. Moreover, IL-22 and IL-17A-activated GECs were capable of inhibiting growth of H. pylori in vitro. While antimicrobials were activated by IL-17A and IL-22 in vitro, using a mouse model of H. pylori infection, the data herein indicate that IL-22 deficiency alone does not render mice more susceptible to infection, change their antimicrobial gene transcription, or significantly change their inflammatory response.