Modulation of immune responses toward Helicobacter pylori infection by NLRs (INM6P.339)

Helicobacter pylori (HP) colonizes 50% of the world’s population resulting in a decades-long gastric infection. Bacterial interaction with host intracellular environment occurs via injection of bacterial components through a TIVSS or intracellular replication. HP has been recognized for its ability to modulate intracellular NOD-like receptors (NLR). Host responses toward the bacterium can result in asymptomatic, pathogenic or even favorable immunity. Mechanisms underlying the dual role of HP as a commensal versus pathogen are not completely understood. We combined computational modeling, bioinformatics and experimental validation to investigate intracellular host-HP interactions. Global transcriptomic analysis on bone marrow-derived macrophages (BMDM) in a gentamycin protection assay unveiled that intracellular colonization of HP upregulated NOD1, NOD2, NLRP3, NLRC5 and inflammasome components (Caspase-1 and -11) but suppressed regulatory NLRX1 which was inversely correlated to TRAF6, NF-B, proinflammatory cytokines and reactive oxygen species. Loss of NLRX1 facilitates bacterial clearance in BMDM and infected mice. Lastly, we constructed a computational model to shed light on complex immune responses and pathway crosstalk regulated by NLRX1 during infection. In conclusion, NLRX1 is associated with chronic bacterial persistence during H. pylori infection and it may represent an immune evasion mechanism employed by the bacterium to facilitate long-term host colonization.

Pharmacophore modeling improves virtual screening for novel peroxisome proliferator-activated receptor-gamma ligands

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear hormone receptor involved in regulating various metabolic and immune processes. The PPAR family of receptors possesses a large binding cavity that imparts promiscuity of ligand binding not common to other nuclear receptors. This feature increases the challenge of using computational methods to identify PPAR ligands that will dock favorably into a structural model. Utilizing both ligand- and structure-based pharmacophore methods, we sought to improve agonist prediction by grouping ligands according to pharmacophore features, and pairing models derived from these features with receptor structures for docking. For 22 of the 33 receptor structures evaluated we observed an increase in true positive rate (TPR) when screening was restricted to compounds sharing molecular features found in rosiglitazone. A combination of structure models used for docking resulted in a higher TPR (40 %) when compared to docking with a single structure model (<20 %). Prediction was also improved when specific protein-ligand interactions between the docked ligands and structure models were given greater weight than the calculated free energy of binding. A large-scale screen of compounds using a marketed drug database verified the predictive ability of the selected structure models. This study highlights the steps necessary to improve screening for PPARγ ligands using multiple structure models, ligand-based pharmacophore data, evaluation of protein-ligand interactions, and comparison of docking datasets. The unique combination of methods presented here holds potential for more efficient screening of compounds with unknown affinity for PPARγ that could serve as candidates for therapeutic development.

Loss of NLRX1 results in increased intestinal pathology and T cell responses in mice with inflammatory bowel disease (HUM1P.312)

NLRX1 is a mitochondrial-associated NOD-like receptor that modulates antiviral immunity, cellular stress, autophagy, and reactive oxygen species (ROS). The role of NLRX1 in inflammatory bowel disease remains unknown. This study aimed to characterize NLRX1-mediated mechanisms of protection from IBD. We investigated the ability of NLRX1 to modulate gut pathology, inflammation and immunity by using DSS and CD4+CD45RBhigh transfer colitis models. Colons, spleens, and mesenteric lymph nodes were excised for characterizing immune cell subsets, histological analyses, cytokine and autophagy expression, NF-κB activity, and ROS production. The loss of NLRX1 increased severity of disease and colonic histopathology in both models of IBD. Colons of NLRX1-/- mice had significantly increased epithelial ulceration and leukocyte infiltration in the DSS model, while recipients of NLRX1-/- CD4+ T cells had increased leukocytic infiltration, proliferation, fibrosis, and crypt abscessation in both colon and ileum. The loss of NLRX1 increased numbers of Th1, Th17, and Treg in the spleen, increased colonic NF-κB activity, upregulation of IL-17, IFNγ and TNF-α production, and increased ROS production. NLRX1 ameliorates intestinal pathology during IBD by acting as an internal thermostat that modulates the balance of effector versus regulatory CD4+ T cell responses, and suppressing colonic NF-κB activity, inflammatory cytokine expression, ROS production, and autophagy.

ENISI SDE: A New Web-Based Tool for Modeling Stochastic Processes

Modeling and simulations approaches have been widely used in computational biology, mathematics, bioinformatics and engineering to represent complex existing knowledge and to effectively generate novel hypotheses. While deterministic modeling strategies are widely used in computational biology, stochastic modeling techniques are not as popular due to a lack of user-friendly tools. This paper presents ENISI SDE, a novel web-based modeling tool with stochastic differential equations. ENISI SDE provides user-friendly web user interfaces to facilitate adoption by immunologists and computational biologists. This work provides three major contributions: (1) discussion of SDE as a generic approach for stochastic modeling in computational biology; (2) development of ENISI SDE, a web-based user-friendly SDE modeling tool that highly resembles regular ODE-based modeling; (3) applying ENISI SDE modeling tool through a use case for studying stochastic sources of cell heterogeneity in the context of CD4+ T cell differentiation. The CD4+ T cell differential ODE model has been published [8] and can be downloaded from biomodels.net. The case study reproduces a biological phenomenon that is not captured by the previously published ODE model and shows the effectiveness of SDE as a stochastic modeling approach in biology in general and immunology in particular and the power of ENISI SDE.

Lanthionine synthetase component C-like protein 2: a new drug target for inflammatory diseases and diabetes

Lanthionine synthetase component C-like protein 2 (LANCL2) is a member of the LANCL protein family, which is broadly expressed throughout the body. LANCL2 is the molecular target of abscisic acid (ABA), a compound with insulin-sensitizing and immune modulatory actions. LANCL2 is required for membrane binding and signaling of ABA in immune cells. Direct binding of ABA to LANCL2 was predicted in silico using molecular modeling approaches and validated experimentally using ligand-binding assays and kinetic surface plasmon resonance studies. The therapeutic potential of the LANCL2 pathway ranges from increasing cellular sensitivity to anticancer drugs, insulin-sensitizing effects and modulating immune and inflammatory responses in the context of immune-mediated and infectious diseases. A case for LANCL2-based drug discovery and development is also illustrated by the anti-inflammatory activity of novel LANCL2 ligands such as NSC61610 against inflammatory bowel disease and influenza-driven inflammation in mice. This review discusses the value of LANCL2 as a novel therapeutic target for the discovery and development of new classes of orally active drugs against chronic metabolic, immune-mediated and infectious diseases.

Zinc deficiency alters host response and pathogen virulence in a mouse model of enteroaggregative Escherichia coli-induced diarrhea

Enteroaggregative Escherichia coli (EAEC) is increasingly recognized as a major cause of diarrheal disease globally. In the current study, we investigated the impact of zinc deficiency on the host and pathogenesis of EAEC. Several outcomes of EAEC infection were investigated including weight loss, EAEC shedding and tissue burden, leukocyte recruitment, intestinal cytokine expression, and virulence expression of the pathogen in vivo. Mice fed a protein source defined zinc deficient diet (dZD) had an 80% reduction of serum zinc and a 50% reduction of zinc in luminal contents of the bowel compared to mice fed a protein source defined control diet (dC). When challenged with EAEC, dZD mice had significantly greater weight loss, stool shedding, mucus production, and, most notably, diarrhea compared to dC mice. Zinc deficient mice had reduced infiltration of leukocytes into the ileum in response to infection suggesting an impaired immune response. Interestingly, expression of several EAEC virulence factors were increased in luminal contents of dZD mice. These data show a dual effect of dietary zinc in benefitting the host while impairing virulence of the pathogen. The study demonstrates the critical importance of zinc and may help elucidate the benefits of zinc supplementation in cases of childhood diarrhea and malnutrition.

Computational modeling of heterogeneity and function of CD4+ T cells

The immune system is composed of many different cell types and hundreds of intersecting molecular pathways and signals. This large biological complexity requires coordination between distinct pro-inflammatory and regulatory cell subsets to respond to infection while maintaining tissue homeostasis. CD4+ T cells play a central role in orchestrating immune responses and in maintaining a balance between pro- and anti- inflammatory responses. This tight balance between regulatory and effector reactions depends on the ability of CD4+ T cells to modulate distinct pathways within large molecular networks, since dysregulated CD4+ T cell responses may result in chronic inflammatory and autoimmune diseases. The CD4+ T cell differentiation process comprises an intricate interplay between cytokines, their receptors, adaptor molecules, signaling cascades and transcription factors that help delineate cell fate and function. Computational modeling can help to describe, simulate, analyze, and predict some of the behaviors in this complicated differentiation network. This review provides a comprehensive overview of existing computational immunology methods as well as novel strategies used to model immune responses with a particular focus on CD4+ T cell differentiation.

Systems modeling of the role of interleukin-21 in the maintenance of effector CD4+ T cell responses during chronic Helicobacter pylori infection

The development of gastritis during Helicobacter pylori infection is dependent on an activated adaptive immune response orchestrated by T helper (Th) cells. However, the relative contributions of the Th1 and Th17 subsets to gastritis and control of infection are still under investigation. To investigate the role of interleukin-21 (IL-21) in the gastric mucosa during H. pylori infection, we combined mathematical modeling of CD4(+) T cell differentiation with in vivo mechanistic studies. We infected IL-21-deficient and wild-type mice with H. pylori strain SS1 and assessed colonization, gastric inflammation, cellular infiltration, and cytokine profiles. Chronically H. pylori-infected IL-21-deficient mice had higher H. pylori colonization, significantly less gastritis, and reduced expression of proinflammatory cytokines and chemokines compared to these parameters in infected wild-type littermates. These in vivo data were used to calibrate an H. pylori infection-dependent, CD4(+) T cell-specific computational model, which then described the mechanism by which IL-21 activates the production of interferon gamma (IFN-γ) and IL-17 during chronic H. pylori infection. The model predicted activated expression of T-bet and RORγt and the phosphorylation of STAT3 and STAT1 and suggested a potential role of IL-21 in the modulation of IL-10. Driven by our modeling-derived predictions, we found reduced levels of CD4(+) splenocyte-specific tbx21 and rorc expression, reduced phosphorylation of STAT1 and STAT3, and an increase in CD4(+) T cell-specific IL-10 expression in H. pylori-infected IL-21-deficient mice. Our results indicate that IL-21 regulates Th1 and Th17 effector responses during chronic H. pylori infection in a STAT1- and STAT3-dependent manner, therefore playing a major role controlling H. pylori infection and gastritis. Importance: Helicobacter pylori is the dominant member of the gastric microbiota in more than 50% of the world's population. H. pylori colonization has been implicated in gastritis and gastric cancer, as infection with H. pylori is the single most common risk factor for gastric cancer. Current data suggest that, in addition to bacterial virulence factors, the magnitude and types of immune responses influence the outcome of colonization and chronic infection. This study uses a combined computational and experimental approach to investigate how IL-21, a proinflammatory T cell-derived cytokine, maintains the chronic proinflammatory T cell immune response driving chronic gastritis during H. pylori infection. This research will also provide insight into a myriad of other infectious and immune disorders in which IL-21 is increasingly recognized to play a central role. The use of IL-21-related therapies may provide treatment options for individuals chronically colonized with H. pylori as an alternative to aggressive antibiotics.

Novel orally active ligands of lanthionine synthetase C-like protein 2 ameliorate influenza-related inflammation and immunopathology (IRM7P.482)

The use of broad-based drugs that target the host inflammatory response and facilitate recovery has been proposed for treating influenza. We previously identified lanthionine synthetase C-like protein 2 (LANCL2) as a new therapeutic target for inflammatory diseases, predicted in silico that NSC61610 and abscisic acid (ABA) bind to LANCL2 and demonstrated their therapeutic efficacy in mouse models of colitis. Here, we use surface plasmon resonance to demonstrate for the first time that NSC61610 binds to LANCL2, promotes cAMP accumulation and protein kinase A (PKA) phosphorylation in RAW macrophages. To examine the therapeutic efficacy of NSC61610 in vivo, we infected mice with influenza A H1N1pdm virus and determined its impact on influenza-related morbidity, mortality, lung inflammatory profiles and histopathology. Our results demonstrate that oral administration of NSC61610 (20 mg/kg/day) ameliorates influenza by down-modulating pulmonary TNF-α and MCP-1 mRNA expression and reducing the infiltration of neutrophils and pro-inflammatory monocytes in the lungs. The therapeutic actions and signaling of NSC61610 were abrogated following gene silencing by LANCL2 siRNA administration further validating our findings. Thus, binding of NSC61610 to LANCL2 and signaling through cAMP and PKA represents a novel mechanism for modulating pulmonary host responses and improving disease resolution in influenza virus-infected mice.

Novel insights on the role of CD8+ T cells and cytotoxic responses during Helicobacter pylori infection

Helicobacter pylori chronically persists in 50% of the human population and causes serious gastric and duodenal pathologies in 15% of infected people. Research on the immune response to the infection has mainly focused on the induction of CD4+ T cell responses. Human studies emphasize the potential clinical relevance of CD8+ cytotoxic T lymphocytes, however this cell type has barely been reported in studies employing mouse or gerbil models. Traditionally characterized as an extracellular bacterium, H. pylori has been identified inside epithelial and immune cells. Similarly to other intracellular bacteria, H. pylori infection of macrophages can alter autophagy and phagosome processing. A novel animal model of H. pylori infection demonstrates for the first time the induction of cytotoxic CD8+ T cell responses in pigs and localization of intracellular H. pylori within lymphoid aggregates. Here, we discuss novel mechanisms of host-H. pylori interactions that could lead to the induction of cytotoxic responses.

Mucosal antimicrobial protection toward enteroaggregative Escherichia coli infection is modulated by dietary tryptophan through an IL17-dependent mechanism (MUC4P.846)

Enteroaggregative E. coli (EAEC) is a predominant extracellular pathogen that causes inflammatory diarrhea in individuals worldwide, especially in persons suffering from malnutrition. We previously reported that protein-energy malnutrition abrogates protective Th17-dependent antimicrobial immunity in a murine model of EAEC infection. However, mechanisms whereby malnutrition enhances host-susceptibility to EAEC colonization remain unreported. This study presents evidence that tryptophan is crucial for antibacterial protection against EAEC infection. Mice fed tryptophan-free diet had reduced antimicrobial peptide production coinciding with significantly high pathogen levels. Likewise, bacterial burden occurred in a dose dependent manner when mice were supplemented with glycly-L-tryptophan dipeptide. Low serum tryptophan directly correlated with hampered gene expression levels of cytokines regulating effector IL-17A responses (e.g. IL-23 and IL-6). Mechanistically, orally administered tryptophan enhanced IL-17A and IL-17C production at the colonic and ileal mucosa facilitating antimicrobial defense and protection against EAEC colonization. IL17a-/- and IL17ra-/- mice receiving nourished diets or tryptophan supplements were unable to recover from disease due to impaired intestinal epithelial barrier function. Thus, our data suggests that tryptophan modulates IL17-dependent antimicrobial responses and is required for preventing EAEC colonization and pathogenic disease.

Immunoregulatory mechanisms of microRNAs during Clostridium difficult infection (MUC9P.819)

MicroRNAs are small non-coding RNA molecules that play pivotal roles in the development and functionality of innate and adaptive immune cells, making them essential during the regulation of bacterial, viral and other immune infections. The role of miRNAs during host-pathogen interactions has recently been highlighted. However, the mechanisms by which miRNAs exert immunoregulatory actions are poorly understood. Our aim is to investigate the impact of Clostidium difficile infection (CDI) on host regulatory and effector pathways by focusing on the disruption of mucosal homeostasis by miRNAs. Sequencing studies on colonic samples and mucosal CD4+ T cells revealed a consistent upregulation of miR146b during CDI in mice, which correlated with worsened disease severity and upregulated MCP-1, IL-1β, IL-6 and IL-17. Moreover, upregulation of miR146b correlated with increased levels of Th17 cells in the spleen, MLN and colonic lamina propria of CDI mice, while abrogating anti-inflammatory responses characterized by IL-10 production. In vivo miR146b inhibition by using locked nucleic acid resulted in accelerated recovery as well as a significant induction of IL-10 production by CD4+, CD8+ and NK T cells and reduced expression of IL-17 by CD4+RORγt+ T cells. C. difficile infection induces upregulation of miR146b at the gut mucosa that contributes to pathogenic Th17 responses and impared immunoregulation.

Elevated CD8 T cell responses in type 1 diabetes patients to a 13 amino acid coeliac-active peptide from α-gliadin

Some type 1 diabetes (T1D) patients have been reported to exhibit T cell reactivity to wheat gluten. We tested the hypothesis that this T cell reactivity could be abolished by using prolyl-endopeptidase (PEP), an enzyme that cleaves peptide bonds after proline. Peripheral blood mononuclear cells (PBMCs) were isolated from T1D patients and healthy controls. PBMCs were stimulated with a peptic-tryptic digest of wheat gluten; a peptic-tryptic-PEP digest of wheat gluten; and a 13 amino acid peptide from wheat gluten. Fluorescent-labelled antibodies to CD3, CD4 and CD8 cell marker proteins were utilized to determine proliferative responses of CD3, CD4 and CD8 T cells. There were no significant differences in proliferative responses of CD3 or CD4 T cells to the wheat gluten antigens. A significantly higher proportion of CD8(+) T cells from T1D patients proliferated in the presence of the 13 amino acid peptide than when challenged with the peptic-tryptic or the peptic-tryptic-PEP digests of wheat gluten. PEP treatment had no significant effect on CD8 T cell reactivity to the peptic-trytic digest of wheat gluten. Our results suggest that wheat gluten-derived peptides, containing ≤ 13 amino acids, may evoke T cell responses in T1D patients.

Predictive computational modeling of the mucosal immune responses during Helicobacter pylori infection

T helper (Th) cells play a major role in the immune response and pathology at the gastric mucosa during Helicobacter pylori infection. There is a limited mechanistic understanding regarding the contributions of CD4+ T cell subsets to gastritis development during H. pylori colonization. We used two computational approaches: ordinary differential equation (ODE)-based and agent-based modeling (ABM) to study the mechanisms underlying cellular immune responses to H. pylori and how CD4+ T cell subsets influenced initiation, progression and outcome of disease. To calibrate the model, in vivo experimentation was performed by infecting C57BL/6 mice intragastrically with H. pylori and assaying immune cell subsets in the stomach and gastric lymph nodes (GLN) on days 0, 7, 14, 30 and 60 post-infection. Our computational model reproduced the dynamics of effector and regulatory pathways in the gastric lamina propria (LP) in silico. Simulation results show the induction of a Th17 response and a dominant Th1 response, together with a regulatory response characterized by high levels of mucosal Treg) cells. We also investigated the potential role of peroxisome proliferator-activated receptor γ (PPARγ) activation on the modulation of host responses to H. pylori by using loss-of-function approaches. Specifically, in silico results showed a predominance of Th1 and Th17 cells in the stomach of the cell-specific PPARγ knockout system when compared to the wild-type simulation. Spatio-temporal, object-oriented ABM approaches suggested similar dynamics in induction of host responses showing analogous T cell distributions to ODE modeling and facilitated tracking lesion formation. In addition, sensitivity analysis predicted a crucial contribution of Th1 and Th17 effector responses as mediators of histopathological changes in the gastric mucosa during chronic stages of infection, which were experimentally validated in mice. These integrated immunoinformatics approaches characterized the induction of mucosal effector and regulatory pathways controlled by PPARγ during H. pylori infection affecting disease outcomes.

Animal models of enteroaggregative Escherichia coli infection

Enteroaggregative Escherichia coli (EAEC) has been acknowledged as an emerging cause of gastroenteritis worldwide for over two decades. Epidemiologists are revealing the role of EAEC in diarrheal outbreaks as a more common occurrence than ever suggested before. EAEC induced diarrhea is most commonly associated with travelers, children and immunocompromised individuals however its afflictions are not limited to any particular demographic. Many attributes have been discovered and characterized surrounding the capability of EAEC to provoke a potent pro-inflammatory immune response, however cellular and molecular mechanisms underlying initiation, progression and outcomes are largely unknown. This limited understanding can be attributed to heterogeneity in strains and the lack of adequate animal models. This review aims to summarize current knowledge about EAEC etiology, pathogenesis and clinical manifestation. Additionally, current animal models and their limitations will be discussed along with the value of applying systems-wide approaches such as computational modeling to study host-EAEC interactions.

IL-21 is required for maintaining mucosal Th1 and Th17 responses during Helicobacter pylori infection (P3184)

CD4+ T cells play a major role in the modulation of immune responses at the gastric mucosa during Helicobacter pylori infection. The relative contributions of CD4+ T cell subsets to gastritis and control of H. pylori colonization and clearance are not completely understood. Expression of IL-21, which is produced by a number of T cell subsets, increases during H. pylori infection. To elucidate the mechanisms of action of IL-21 in effector and regulatory CD4+ T cells during H. pylori infection, we combined computational modeling of CD4+ T cell differentiation and in vivo challenge studies in mice. Our computational modeling predicted activated production of IFNγ and IL-17 by IL-21, and the expression of T-bet, RORγt and phosphorylation of STAT3. To investigate the role of IL-21 in vivo, we infected IL-21-/- and wild-type mice with H. pylori SS1, and assessed colonization, gastric inflammation, cellular infiltration and cytokine profiles in the gastric mucosa. During chronic infection, IL-21-/- mice had higher H. pylori colonization, less gastritis and reduced expression of inflammatory cytokines and chemokines. Moreover, H. pylori infected IL-21-/- mice had reduced levels of CD4+ T cell specific RORγt and T-bet when compared to infected wild-type mice. Our results indicate that IL-21 contributes to the control of infection and severity of gastritis, suggesting a role for induction of gastritis in response to H. pylori through activation of both Th17 and Th1 effector responses.

Modulation of mucosal immune responses to Clostridium difficile by probiotic bacteria (P3073)

Commensal bacteria play a critical role in maintaining intestinal epithelium and mucosal immune homeostasis. Alterations in intestinal microflora predispose mammalian hosts to infection with pathogens such as Clostridium difficile, which has recently re-emerged as a pathogen causing nosocomial diarrhea, colitis and death. We investigated the mechanisms by which the probiotic VSL#3 ameliorates C. difficile-associated disease (CDAD) in mice. Oral VSL#3 administration reduced disease activity, body weight loss, and colonic inflammatory lesions after infection. Probiotic treatment also decreased Th17 and IL-17-producing TCRγδ cell populations at the colonic lamina propria as well as production of IL-17 and IL-1β in the colonic mucosa. Increased numbers of regulatory T cells (Treg) were seen in spleens of VSL#3-treated mice, which correlated to increased peroxisome proliferator-activated receptor γ (PPARγ) activity. PPARγ is a transcription factor and nuclear receptor that modulates immune responses and whose activation is essential for the maintenance of innate antimicrobial immunity in the colon. Mice treated with VSL#3 had an upregulation of calprotectin antimicrobial peptides S100A8 and S100A9 in the colon correlating to decreased fecal clostrial burden at day 4 post-infection. VSL#3 probiotic bacteria regulate colitis by increasing PPARγ activity and decreasing IL-17 responses and increase clostridial clearance by upregulating antimicrobial peptides in mice with CDAD.

IL-17 mediates the protective actions of PPAR γ blockade during enteroaggregative Escherichia coli infection (P3238)

Enteroaggregative Escherichia coli (EAEC) is an etiologic agent of enterocolitis and persistent diarrhea worldwide, especially in malnourished children and immunosuppressed individuals. Expression of IL-17, which is produced by a number of immune and epithelial cells, increases during EAEC infection. We previously demonstrated that blocking peroxisome proliferator-activated receptor gamma (PPARγ) enhances mucosal Th17 responses that contribute to bacterial clearance in EAEC-infected mice. Here we investigate whether IL-17 mediates the effects of PPARγ blockade in the gut. We show that increasing doses of PPARγ antagonist GW9662 (0.5, 1, or 2µM) directly correlated to increased IL-17 expression in the colon. C57BL/6 wild type mice were challenged with EAEC strain JM221 on day 0 and administered anti IL-17 neutralizing antibody (50μg) i.p. on days 0, 2, and 4 of the study. Anti (α)-IL17 antibody-mediated neutralization of IL-17 abrogated the beneficial effects of PPARγ blockade on weight loss and fecal EAEC burden. In addition, infiltration of CD11c+ dendritic cells and CD4+ T cells into the colonic lamina propria, as well as colonic antimicrobial peptide expression were significantly reduced in mice treated with αIL-17 and GW9662 when compared to mice receiving GW9662 alone. These findings suggest that the beneficial effects from PPARγ blockade in disease activity and bacterial burden during EAEC infection are largely mediated through an IL-17-dependent mechanism.

Vitamin D receptor regulates mucosal immune responses to Clostridium difficile infection (P3076)

Clostridium difficile is an anaerobic bacterium that has re-emerged as a facultative pathogen and can cause diarrhea, colitis or even death. Vitamin D deficiency contributes to a 5-fold increase in healthcare costs during C. difficile infection (CDI). We investigated the role of vitamin D signaling during CDI by using vitamin D receptor (VDR) -/- and wild-type (WT) mice. The loss of VDR increased disease activity, weight loss, and the severity of colonic inflammatory lesions following CDI. RNAseq analyses showed upregulation of sentrin/SUMO-specific proteases (SENPs), downregulation of phosphatidylinositol 3-kinase regulatory subunit and cAMP-specific 3’5’-cyclic phophodiesterase in colons of VDR-/- mice. SENPs mediate deSUMOylation reactions that can affect both the transcriptional activity of nuclear receptors such as VDR and peroxisome proliferator-activated receptor (PPAR) γ as well as their ability to antagonize NF-kB activity. These results provide a mechanistic basis for the upregulation of IFNγ, IL-6, IL-17 and IL-1β in colons of VDR-/- mice infected with C. difficile. In addition, miR-760-5p was down-regulated in VDR-/- mice and upregulated in WT mice after CDI. Of note, miR-760 has 128 mRNA targets, including lanthionine synthetase component C-like 2 (LANCL2), which is upstream of PPARγ. We provide novel molecular evidence in vivo suggesting novel mechanisms involving LANCL2 and PPARγ by which vitamin D regulates C. difficile-associated disease and immunopathology.

Preventive and prophylactic mechanisms of action of pomegranate bioactive constituents

Pomegranate fruit presents strong anti-inflammatory, antioxidant, antiobesity, and antitumoral properties, thus leading to an increased popularity as a functional food and nutraceutical source since ancient times. It can be divided into three parts: seeds, peel, and juice, all of which seem to have medicinal benefits. Several studies investigate its bioactive components as a means to associate them with a specific beneficial effect and develop future products and therapeutic applications. Many beneficial effects are related to the presence of ellagic acid, ellagitannins (including punicalagins), punicic acid and other fatty acids, flavonoids, anthocyanidins, anthocyanins, estrogenic flavonols, and flavones, which seem to be its most therapeutically beneficial components. However, the synergistic action of the pomegranate constituents appears to be superior when compared to individual constituents. Promising results have been obtained for the treatment of certain diseases including obesity, insulin resistance, intestinal inflammation, and cancer. Although moderate consumption of pomegranate does not result in adverse effects, future studies are needed to assess safety and potential interactions with drugs that may alter the bioavailability of bioactive constituents of pomegranate as well as drugs. The aim of this review is to summarize the health effects and mechanisms of action of pomegranate extracts in chronic inflammatory diseases.

Systems modeling of molecular mechanisms controlling cytokine-driven CD4+ T cell differentiation and phenotype plasticity

Differentiation of CD4+ T cells into effector or regulatory phenotypes is tightly controlled by the cytokine milieu, complex intracellular signaling networks and numerous transcriptional regulators. We combined experimental approaches and computational modeling to investigate the mechanisms controlling differentiation and plasticity of CD4+ T cells in the gut of mice. Our computational model encompasses the major intracellular pathways involved in CD4+ T cell differentiation into T helper 1 (Th1), Th2, Th17 and induced regulatory T cells (iTreg). Our modeling efforts predicted a critical role for peroxisome proliferator-activated receptor gamma (PPARγ) in modulating plasticity between Th17 and iTreg cells. PPARγ regulates differentiation, activation and cytokine production, thereby controlling the induction of effector and regulatory responses, and is a promising therapeutic target for dysregulated immune responses and inflammation. Our modeling efforts predict that following PPARγ activation, Th17 cells undergo phenotype switch and become iTreg cells. This prediction was validated by results of adoptive transfer studies showing an increase of colonic iTreg and a decrease of Th17 cells in the gut mucosa of mice with colitis following pharmacological activation of PPARγ. Deletion of PPARγ in CD4+ T cells impaired mucosal iTreg and enhanced colitogenic Th17 responses in mice with CD4+ T cell-induced colitis. Thus, for the first time we provide novel molecular evidence in vivo demonstrating that PPARγ in addition to regulating CD4+ T cell differentiation also plays a major role controlling Th17 and iTreg plasticity in the gut mucosa.

CD4+ T cells can differentiate into different phenotypes depending on the cytokine milieu. Due to the complexity of this process, we have constructed a computational and mathematical model with sixty ordinary differential equations representing a CD4+ T cell differentiating into either Th1, Th2, Th17 or iTreg cells. The model includes cytokines, nuclear receptors and transcription factors that define fate and function of CD4+ T cells. Computational simulations illustrate how a proinflammatory Th17 cell can undergo reprogramming into an anti-inflammatory iTreg phenotype following PPARγ activation. This modeling-derived hypothesis has been validated with in vitro and in vivo experiments. Experimental data support the modeling-derived prediction and demonstrate that the loss of PPARγ enhances a proinflammatory response characterized by Th17 in colitis-induced mice. Moreover, pharmacological activation of PPARγ in vivo can affect the Th17/iTreg balance by upregulating FOXP3 and downregulating IL-17A and RORγt. In summary, we demonstrate that computational simulations using our CD4+ T cell model provide novel unforeseen hypotheses related to the molecular mechanisms controlling differentiation and function of CD4+ T cells. In vivo findings validated the modeling prediction that PPARγ modulates differentiation and plasticity of CD4+ T cells in mice.

Enteroaggregative Escherichia coli strain in a novel weaned mouse model: exacerbation by malnutrition, biofilm as a virulence factor and treatment by nitazoxanide

Enteroaggregative Escherichia coli (EAEC) is increasingly recognized as a common cause of diarrhoea in healthy, malnourished and immune-deficient adults and children. There is no reproducible non-neonatal animal model for longitudinal studies of disease mechanism or therapy. Using two strains of human-derived EAEC to challenge weaned C57BL/6 mice, we explored an in vivo model of EAEC infection in mice, in which disease was monitored quantitatively as the growth rate, stool shedding and tissue burden of organisms; nutritional status was varied, and a new class of therapeutics was assessed. A single oral challenge of EAEC strain 042 resulted in significant growth shortfalls (5-8 % of body weight in 12 days), persistent shedding of micro-organisms in stools [>10(3.2) c.f.u. (10 mg stool)(-1) for at least 14 days] and intestinal tissue burden [~10(3) c.f.u. (10 mg tissue)(-1) detectable up to 14 days post-challenge]. Moderate malnourishment of mice using a 'regional basic diet' containing 7 % protein and reduced fat and micronutrients heightened all parameters of infection. Nitazoxanide in subMIC doses, administered for 3 days at the time of EAEC challenge, lessened growth shortfalls (by >10 % of body weight), stool shedding [by 2-3 logs (10 mg stool)(-1)] and tissue burden of organisms (by >75 % in the jejunum and colon). Thus, weaned C57BL/6 mice challenged with EAEC is a convenient, readily inducible model of EAEC infection with three highly quantifiable outcomes in which disease severity is dependent on the nutritional status of the host, and which is modifiable in the presence of inhibitors of pyruvate ferredoxin oxidoreductase such as nitazoxanide.

The role of peroxisome proliferator-activated receptor γ in immune responses to enteroaggregative Escherichia coli infection

Background

Enteroaggregative Escherichia coli (EAEC) is recognized as an emerging cause of persistent diarrhea and enteric disease worldwide. Mucosal immunity towards EAEC infections is incompletely understood due in part to the lack of appropriate animal models. This study presents a new mouse model and investigates the role of peroxisome proliferator-activated receptor gamma (PPARγ) in the modulation of host responses to EAEC in nourished and malnourished mice.

Methods/Principal Findings

Wild-type and T cell-specific PPARγ null C57BL/6 mice were fed protein-deficient diets at weaning and challenged with 5×10⁹cfu EAEC strain JM221 to measure colonic gene expression and immune responses to EAEC. Antigen-specific responses to E. coli antigens were measured in nourished and malnourished mice following infection and demonstrated the immunosuppressive effects of malnutrition at the cellular level. At the molecular level, both pharmacological blockade and deletion of PPARγ in T cells resulted in upregulation of TGF-β, IL-6, IL-17 and anti-microbial peptides, enhanced Th17 responses, fewer colonic lesions, faster clearance of EAEC, and improved recovery. The beneficial effects of PPARγ blockade on weight loss and EAEC clearance were abrogated by neutralizing IL-17 in vivo.

Conclusions

Our studies provide in vivo evidence supporting the beneficial role of mucosal innate and effector T cell responses on EAEC burden and suggest pharmacological blockade of PPARγ as a novel therapeutic intervention for EAEC infection.

ENteric Immunity SImulator: a tool for in silico study of gastroenteric infections

Clinical symptoms of microbial infection of the gastrointestinal (GI) tract are often exacerbated by inflammation induced pathology. Identifying novel avenues for treating and preventing such pathologies is necessary and complicated by the complexity of interacting immune pathways in the gut, where effector and inflammatory immune cells are regulated by anti-inflammatory or regulatory cells. Here we present new advances in the development of the ENteric Immunity SImulator (ENISI), a simulator of GI immune mechanisms in response to resident commensal bacteria as well as invading pathogens and the effect on the development of intestinal lesions. ENISI is a tool for identifying potential treatment strategies that reduce inflammation-induced damage and, at the same time, ensure pathogen removal by allowing one to test plausibility of in vitro observed behavior as explanations for observations in vivo, propose behaviors not yet tested in vitro that could explain these tissue-level observations, and conduct low-cost, preliminary experiments of proposed interventions/treatments. An example of such application is shown in which we simulate dysentery resulting from Brachyispira hyodysenteriae infection and identify aspects of the host immune pathways that lead to continued inflammation-induced tissue damage even after pathogen elimination.