Toll-like receptors and innate immunity in gut homeostasis and pathology

Toll-like receptors in health and disease

Toll-like receptors (TLRs) are inflammatory triggers and belong to a family of pattern recognition receptors (PRRs) that are central to the regulation of host protective adaptive immune responses. Activation of TLRs in innate immune myeloid cells directs lymphocytes to produce the most appropriate effector responses to eliminate infection and maintain homeostasis of the body's internal environment. Inappropriate TLR stimulation can lead to the development of general autoimmune diseases as well as chronic and acute inflammation, and even cancer. Therefore, TLRs are expected to be targets for therapeutic treatment of inflammation-related diseases, autoimmune diseases, microbial infections, and human cancers. This review summarizes the recent discoveries in the molecular and structural biology of TLRs. The role of different TLR signaling pathways in inflammatory diseases, autoimmune diseases such as diabetes, cardiovascular diseases, respiratory diseases, digestive diseases, and even cancers (oral, gastric, breast, colorectal) is highlighted and summarizes new drugs and related clinical treatments in clinical trials, providing an overview of the potential and prospects of TLRs for the treatment of TLR-related diseases.

Humoral and cellular immune responses induced by serogroup W135 meningococcal conjugate and polysaccharide vaccines

Investigating the mechanisms by which W135 meningococcal conjugate (PSW135-TT) activates adaptive immune responses in mice can provide a comprehensive understanding of the immune mechanisms of bacterial polysaccharide conjugate vaccines. We compared B-cell and T-cell immune responses immunized with W135 meningococcal capsular polysaccharides (PSW135), tetanus toxoid (TT) and PSW135-TT in mice. The results showed that PSW135-TT could induce higher PSW135-specific and TT-specific IgG antibodies with a significant enhancement after two doses. All serum antibodies immunized with PSW135- TT had strong bactericidal activity, whereas none of the serum antibodies immunized with PSW135 had bactericidal activity. Besides, IgM and IgG antibodies immunized with PSW135-TT after two doses were positively correlated with the titer of bactericidal antibodies. We also found Th cells favored Th2 humoral immune responses in PSW135-TT, PSW135, and TT-immunized mice, especially peripheral blood lymphocytes. Furthermore, PSW135-TT and TT could effectively activate bone marrow derived dendritic cells (BMDCs) and promote BMDCs to highly express major histocompatibility complex Ⅱ (MHCⅡ), CD86 and CD40 molecules in mice, whereas PSW135 couldn't. These data verified the typical characteristics of PSW135-TT and TT as T cell dependent antigen (TD-Ag) and PSW135 as T cell independent antigen (TI-Ag), which will be very helpful for further exploration of the immune mechanism of polysaccharide-protein conjugate vaccines and improvement of the quality of bacterial polysaccharide conjugate vaccines in future.

Somatostatin attenuates intestinal epithelial barrier injury during acute intestinal ischemia-reperfusion through Tollip/Myeloiddifferentiationfactor 88/Nuclear factor kappa-B signaling

In the process of ischemia-reperfusion injury, intestinal ischemia and inflammation interweave, leading to tissue damage or necrosis. However, oxygen radicals and inflammatory mediators produced after reperfusion cause tissue damage again, resulting in severe intestinal epithelial barrier dysfunction. The aim of this study was to determine the protective effect of somatostatin on intestinal epithelial barrier function during intestinal ischemia-reperfusion injury and explore its mechanism. By establishing a rat intestinal ischemia-reperfusion model, pretreating the rats with somatostatin, and then detecting the histopathological changes, intestinal permeability and expression of tight junction proteins in intestinal tissues, the protective effect of somatostatin on the intestinal epithelial barrier was measured in vivo. The mechanism was determined in interferon γ (IFN-γ)-treated Caco-2 cells in vitro. The results showed that somatostatin could ameliorate ischemia-reperfusion-induced intestinal epithelial barrier dysfunction and protect Caco-2 cells against IFN-γ-induced decreases in tight junction protein expression and increases in monolayer cell permeability. The expression of Tollip was upregulated by somatostatin both in ischemia-reperfusion rats and IFN-γ-treated Caco-2 cells, while the activation of TLR2/MyD88/NF-κB signaling was inhibited by somatostatin. Tollip inhibition reversed the protective effect of somatostatin on the intestinal epithelial barrier. In conclusion, somatostatin could attenuate ischemia-reperfusion-induced intestinal epithelial barrier injury by inhibiting the activation of TLR2/MyD88/NF-κB signaling through upregulation of Tollip.

Canine primary jejunal and colonic epithelial cells predominantly express TLR5 and TLR9 but do not change TLR expression pattern after stimulation with certain Toll-like receptor ligands

The intestinal mucosa is in contact with abundant luminal antigens and coordinates immune responses to differentiate commensals from pathogens. Intestinal epithelial cells (IECs) not only represent a physical barrier but also an immunologically important cell type that recognizes microbe-associated molecular patterns via Toll-like receptors (TLR). The importance of TLR expression has been elucidated for intestinal disorders in humans, mice and dogs. However, as knowledge about canine intestinal TLRs is mainly limited to the transcriptional level, the present study analyzed the protein expression of TLR2, TLR3, TLR4, TLR5 and TLR9 by primary canine IECs in the steady state and after stimulation with TLR ligands. This exhibited TLR5 and TLR9 to be predominantly expressed in canine IECs. TLR stimulation did not result in changes of the TLR expression pattern. Further studies are needed to elucidate whether this implicates hyporesponsiveness of canine IECs towards TLR stimulation under steady state conditions.

Cellular Differentiation of Non-Transformed Intestinal Epithelial Cells Is Regulated by Lactobacillus rhamnosus and L. casei Strains

The aim of this study was to characterize an in vitro modulating effect of three commensal Lactobacillus strains on cellular differentiation of non-transformed crypt-like rat small intestinal cell line IEC-18. IEC-18 was grown on extracellular matrix, with or without presence of Lactobacillus strains. Gene expression of IEC-18 bacterial detection system – such as Toll-like receptors TLR-2, TLR-4, signal adapter MyD88, cytoplasmic NOD2 receptor, inflammatory cytokines IL-18, IL-1β, chemokine IL-8 and enzyme caspase-1 – was evaluated using real-time PCR. Expression and localization of TLR-2, TLR-4, IL-18 and caspase-1 proteins was demonstrated by Western blotting and immunofluorescent staining. Secretion of IL-18 to apical and basolateral surfaces was assayed by ELISA. Our results suggested that L. casei LOCK0919 accelerated differentiation of IEC-18 by stimulating TLR-2, TLR-4, MyD88, IL-18, caspase-1 mRNAs and proteins. L. casei LOCK0919 increased expression and transfer of villin and β-catenin from cytoplasm to cell membrane. Presence of L. rhamnosus LOCK0900 resulted in detachment of IEC-18 layer from extracellular matrix leading to induction of IL-1β, of TLR-2 and IL-8 mRNAs and stimulation of MyD88, caspase-1 and cytosolic receptor NOD2 mRNAs. L. rhamnosus LOCK0908 was not recognized by TLR-2 or TLR-4 receptors. Lactobacilli-IEC-18 crosstalk enhanced immune and barrier mucosal functions.

Myeloid differentiation primary response gene (MyD) 88 signalling is not essential for intestinal fibrosis development

Dysregulation of the immune response to microbiota is associated with inflammatory bowel disease (IBD), which can trigger intestinal fibrosis. MyD88 is a key component of microbiota signalling but its influence on intestinal fibrosis has not been clarified. Small bowel resections from donor-mice were transplanted subcutaneously into the neck of recipients C57BL/6 B6-MyD88tm1 Aki (MyD88^-/-) and C57BL/6-Tg(UBC-green fluorescence protein (GFP))30Scha/J (GFP-Tg). Grafts were explanted up to 21 days after transplantation. Collagen layer thickness was determined using Sirius Red stained slides. In the mouse model of fibrosis collagen deposition and transforming growth factor-beta 1 (TGF-β1) expression was equal in MyD88^+/+ and MyD88^-/-, indicating that MyD88 was not essential for fibrogenesis. Matrix metalloproteinase (Mmp)9 expression was significantly decreased in grafts transplanted into MyD88^-/- recipients compared to MyD88^+/+ recipients (0.2 ± 0.1 vs. 153.0 ± 23.1, respectively, p < 0.05), similarly recruitment of neutrophils was significantly reduced (16.3 ± 4.5 vs. 25.4 ± 3.1, respectively, p < 0.05). Development of intestinal fibrosis appears to be independent of MyD88 signalling indicating a minor role of bacterial wall compounds in the process which is in contrast to published concepts and theories. Development of fibrosis appears to be uncoupled from acute inflammation.

The epithelial barrier and immunoglobulin A system in allergy

Airway and intestinal epithelial layers represent first-line physical barriers, playing a key role in mucosal immunity. Barrier dysfunction, characterized by alterations such as disruption of cell-cell apical junctions and aberrant epithelial responses, probably constitutes early and key events for chronic immune responses to environmental antigens in the skin and in the gut. For instance, barrier dysfunction drives Th2 responses in atopic disorders or eosinophilic esophagitis. Such epithelial impairment is also a salient feature of allergic asthma and growing evidence indicates that barrier alterations probably play a driving role in this disease. IgA has been identified as the most abundant immunoglobulin in mucosa, where it acts as an active barrier through immune exclusion of inhaled or ingested antigens or pathogens. Historically, it has been thought to represent the serum factor underlying reaginic activity before IgE was discovered. Despite several studies about regulation and major functions of IgA at mucosal surfaces, its role in allergy remains largely unclear. This review aims at summarizing findings about epithelial functions and IgA biology that are relevant to allergy, and to integrate the emerging concepts and the recent developments in mucosal immunology, and how these could translate to clinical observations in allergy.

Genetic selection pressure in TLR9 gene may enforce risk for SLE in Indian Tamils

Objectives Lupus is a classical systemic autoimmune disease with genetics as one of the well known causative factors for the disease pathogenesis. Toll-like receptors are the major pattern recognition receptors associated with innate immunity and also act as an interface with the adaptive immunity. Genetic polymorphisms in genes encoding TLRs were implicated in the development of infections, malignancies and autoimmune diseases. TLR9 is a member of TLR family, and recognizes the CpG DNA motifs of pathogens. Though the incidence rate of lupus in Asians was reported to be low (30 - 50/100,000 population), poor disease prognosis due to higher incidence of renal complications and aggressive disease worsens the scenario. The ability of TLR9 to detect and elicit an immune response against double-stranded DNA makes TLR9 a relevant factor to be tested for its association with the clinical and serological phenotypes of lupus. However, lack of relevant genetic data on normative frequencies of the TLR9 (rs187084) polymorphism may serve as a constraint to derive the sample size to conduct case control association studies. Hence this study was conducted to establish the normative frequency of TLR9 (rs187084) polymorphism in Indian Tamils. Materials and methods The TLR9 (rs187084) polymorphism was screened in South Indian Tamils ( n = 208) by PCR-RFLP. Results and discussion We observed a higher occurrence of the mutant allele (65%) in South Indian Tamils. No gender disparity with respect to the mutant allele frequency was observed. The higher incidence of mutant allele in both genders suggests that this population had undergone a genetic selection pressure as an evolutionary genetic measure to withstand the prevailing endemic infections like TB and malaria. Though the enhanced expression of TLR9 was protective against infections, it may also influence the development of autoimmune diseases. Conclusion The higher incidence of theTLR9 (rs187084) over-expression mutation in Indian Tamils is suggestive of a genetic adaptation or selection pressure to withstand the prevailing endemic infectious and parasitic diseases. However, this genetic adaptation poses a greater risk to develop autoimmune diseases like SLE etc through complex gene environment interactions. The normative frequency of the TLR9 (rs187084) polymorphism established in our population could now be used to define the sample size for future case control studies.

Study of the diversity and short-chain fatty acids production by the bacterial community in overweight and obese Mexican children

Obesity and overweight are health problems of multifactorial etiology, which may include changes in the microbiome. In Mexico, more than 30 % of the child population between 5 and 11 years of age suffer from being overweight or are obese, which makes it a public health issue in progress. The purpose of this work was to measure the short-chain fatty acid concentration by high-performance liquid chromatography (HPLC), and to characterize the bacterial diversity by ion torrent semiconductor sequencing, of 16S rDNA libraries prepared from stools collected from a sample of well-characterized Mexican children for normal weight, overweight, and obese conditions by anthropometric and biochemical criteria. We found that triglyceride levels are increased in overweight and obese children, who presented altered propionic and butyric acid concentrations in feces. In addition, although the colon microbiota did not show a clear bacterial dysbiosis among the three conditions, the abundance of some particular bacteria was changed with respect to normal controls. We conclude from our results that the imbalance in the abundance of at least nine different bacteria as well as altered short-chain fatty acid concentration in feces is associated to the overweight and obese conditions of Mexican children.

The intestinal microbiota and microenvironment in liver

The intestinal microbiome plays a significant role in the development of autoimmune diseases, in particular, inflammatory bowel diseases. But the interplay between the intestinal tract and the liver may explain the increased association with autoimmune liver diseases and inflammatory bowel diseases. The gut-liver axis involves multiple inflammatory cell types and cytokines, chemokines and other molecules which lead to the destruction of normal liver architecture. Triggers for the initiation of these events are unclear, but appear to include multiple environmental factors, including pathogenic or even commensal microbial agents. The variation in the gut microbiome has been cited as a major factor in the pathogenesis of autoimmune liver disease and even other autoimmune diseases. The unique positioning of the liver at the juncture of the peripheral circulation and the portal circulation augments the interaction between naïve T cells and other hepatic cells and leads to the disruption in the development of tolerance to commensal bacteria and other environmental agents. Finally, the innate immune system and in particular toll-like receptors play a significant role in the pathogenesis of autoimmune liver disease.

Regenerative medicine: prospects for the treatment of inflammatory bowel disease

This article reviews the current understanding of the processes driving the development and progression of inflammatory bowel disease (IBD), discusses how the dynamic crosstalk between resident microorganisms, host cells and the immune system is required in order to maintain immune homeostasis, and considers innovative strategies that allow the modification or modulation of the intestinal microorganismal community as a potential approach for treating IBD. This article next rationalizes the use of cell-based regenerative medicine as treatment for IBD, discusses the obstacles hindering its success, summarizes some of the results of recent clinical trials employing these therapies, and discusses ongoing work to enhance mesenchymal stem/stromal cells, making them better suited to the task of repairing the damage within the IBD gut.

Role of the intestinal microbiome in liver disease

The liver integrates metabolic outcomes with nutrient intake while preventing harmful signals derived from the gut to spread throughout the body. Direct blood influx from the gastrointestinal tract through the portal vein makes the liver a critical firewall equipped with a broad array of immune cells and innate immune receptors that recognize microbial-derived products, microorganisms, toxins and food antigens that have breached the intestinal barrier. An overwhelming amount of evidence obtained in the last decade indicates that the intestinal microbiota is a key component of a wide variety of physiological processes, and alterations in the delicate balance that represents the intestinal bacterial communities are now considered important determinants of metabolic syndrome and immunopathologies. Moreover, it is now evident that the interaction between the innate immune system and the intestinal microbiota during obesity or autoimmunity promotes chronic liver disease progression and therefore it might lead to novel and individualized therapeutic approaches. In this review, we discuss a growing body of evidence that highlights the central relationship between the immune system, the microbiome, and chronic liver disease initiation and progression.

Reciprocal effects of Guizhi decoction to the Guizhi decoction syndrome by toll-like receptor mRNA expression and cytokines secretion

OBJECTIVE

To explore the pathological mechanisms of Guizhi Decoction () syndrome and the therapeutic molecular mechanisms of the Guizhi Decoction, Mahuang Decoction (), Sangju Decoction ( ) and Yinqiao Powder (), as well as the potentially biological basis that Guizhi Decoction is most effective only for the patients with Guizhi Decoction syndrome in clinical practice.

METHODS

We first got serum samples from the patients suffering from both upper respiratory tract infection and Guizhi Decoction syndrome identified by the doctors of Chinese medicine (CM) in the clinic. Four formulas with therapeutic actions of pungent warmth or pungent coolness for superficial syndromes were chosen and four kinds of rat serum samples each containing one of the above-mentioned herbal formulas were collected, then the effects of Guizhi Decoction syndromes' patient serum as well as the effects of sera containing the formulas after being stimulated by the patient serum samples on both the mRNA expression of certain toll-like receptor (TLR) subtypes and the release of some inflammatory cytokines in RAW264.7 cells were tested and analyzed in vitro.

RESULTS

The expression of TLR-3, TLR-4 and TLR-9 mRNA among the 9 tested TLR subforms were up-regulated in the macrophages stimulated by the sera from untreated upper respiratory infection patients with the Guizhi Decoction syndrome (symptomcomplex). The products such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α and interferon (IFN)-β from stimulated macrophages through TLR signaling pathways were also increased correspondingly. Interestingly, the changes induced by the Guizhi Decoction syndrome patients' sera were masked significantly after the macrophages were incubated with the sera from donors treated with Guizhi Decoction. Similarly, the three other exterior-releasing formulas were all effective in reversing the up-regulated changes of certain TLR subforms to different degrees, but both the number of targeted TLRs and efficacy of them seemed to be inferior to that of Guizhi Decoction.

CONCLUSION

Evidence from these experiments might contribute to the scientific explanation of both the pharmacological mechanisms of Guizhi Decoction and also the CM theory that Guizhi Decoction is specifically prescribed for the treatment of Guizhi Decoction syndrome (The gearing formula to the symptom-complex).

Toll-like receptor 3 (TLR3) activation induces microRNA-dependent reexpression of functional RARβ and tumor regression

Toll-like receptor 3 (TLR3) is a key effector of the innate immune system against viruses. Activation of TLR3 exerts an antitumoral effect through a mechanism of action still poorly understood. Here we show that TLR3 activation by polyinosinic:polycytidylic acid induces up-regulation of microRNA-29b, -29c, -148b, and -152 in tumor-derived cell lines and primary tumors. In turn, these microRNAs induce reexpression of epigenetically silenced genes by targeting DNA methyltransferases. In DU145 and TRAMP-C1 prostate and MDA-MB-231 breast cancer cells, we demonstrated that polyinosinic:polycytidylic acid-mediated activation of TLR3 induces microRNAs targeting DNA methyltransferases, leading to demethylation and reexpression of the oncosuppressor retinoic acid receptor beta (RARβ). As a result, cancer cells become sensitive to retinoic acid and undergo apoptosis both in vitro and in vivo. This study provides evidence of an antitumoral mechanism of action upon TLR3 activation and the biological rationale for a combined TLR3 agonist/retinoic acid treatment of prostate and breast cancer.

Acute ethanol administration inhibits Toll-like receptor 4 signaling pathway in rat intestinal epithelia

Excess alcohol intake, as in binge drinking, increases susceptibility to microbial pathogens. Alcohol impairs macrophage function by suppression of the Toll-like receptor 4 (TLR4) pathway. This study investigated the effects of acute ethanol intake on the TLR4 pathway in rat intestinal epithelia, which usually encounters luminal antigens at first and participates in the development of intestinal immunity. Twenty Wistar rats were randomly assigned to an ethanol group given ethanol as a 25% (v/v) solution in water at 7.5 g/kg, or a control group given saline, by oral gavage daily for 3 days. The epithelial histology and ultrastructure, the intestinal microflora, peripheral and portal venous plasma lipopolysaccharide (LPS) levels, and somatostatin (SST) levels in the peripheral plasma and small intestine were evaluated. Somatostatin receptor 2 (SSTR2), TLR4, TANK binding kinase-1 (TBK1), activated nuclear factor-κB (NF-κB), interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) in the intestinal mucosa were assayed. LPS responsiveness with or without SST pretreatment was assayed in vitro by quantification of TLR4, TBK1, activated NF-κB, IFN-γ and TNF-α in isolated intestinal epithelia. Mucosal damage was observed in the ethanol group by light and electron microscopy. Escherichia coli cultures were unchanged in rat intestine of the ethanol group compared with controls, but lactobacilli cultures were reduced (p < 0.05). LPS levels increased in peripheral and portal venous plasma (p < 0.05), but mucosal TLR4, TBK1, nuclear NF-κB, IFN-γ and TNF-α were unchanged in the ethanol group. LPS treatment in vitro up-regulated the level of TLR4, TBK1 and nuclear NF-κB as well as the production of IFN-γ and TNF-α in isolated intestinal epithelia in the control (p < 0.05), but not the ethanol group. The stimulatory effects of LPS on intestinal epithelia isolated from the control group were significantly inhibited by SST pretreatment (p < 0.05). The peripheral plasma and intestinal levels of SST and the mucosal expression of SSTR2 in the ethanol group were significantly higher than in the control group (p < 0.05). These findings suggest the hyposensitivity of intestinal epithelial TLR4 to LPS induced by acute alcohol abuse probably through ethanol per se and ethanol-enhanced intestinal mucosal SST pathway may be a novel mechanism for increased susceptibility to intestinal pathogens.

Commensal microbiota drive proliferation of conventional and Foxp3(+) regulatory CD4(+) T cells in mesenteric lymph nodes and Peyer's patches

Compelling evidence demonstrates that intestinal commensal microbiota modulate conventional and regulatory T cell (Treg) responses that are required for effective host defence against pathogens and avoidance of autoimmunity and other immunopathologic conditions. Here, we investigated the contribution of the commensal microbiota and Toll-like receptor (TLR) signaling to homeostasis of Foxp3(-) conventional CD4(+) T cells and Foxp3(+) Tregs. Upon long-term antibiotics treatment, we observed a significant reduction of conventional CD4(+) T cell proliferation in a systemic manner, whereas Foxp3(+) Treg proliferation was locally impaired in gut-draining mesenteric lymph nodes and Peyer's patches. The proliferative response to microbial components was not mediated by TLRs as MyD88- and various TLR-deficient mice displayed normal or even increased conventional T cell and Foxp3(+) Treg proliferation. Thus, commensal microbiota-derived stimuli support cycling of both conventional CD4(+) T cells and Foxp3(+) Tregs with TLR-mediated recognition of bacterial components not being the major mechanism controlling microbiota-driven T cell homeostasis.

Toll-like receptor signaling activation by Entamoeba histolytica induces beta defensin 2 in human colonic epithelial cells: its possible role as an element of the innate immune response

Background

Entamoeba histolytica, a protozoan parasite of humans, produces dysenteric diarrhea, intestinal mucosa damage and extraintestinal infection. It has been proposed that the intestinal microbiota composition could be an important regulatory factor of amebic virulence and tissue invasion, particularly if pathogenic bacteria are present. Recent in vitro studies have shown that Entamoeba histolytica trophozoites induced human colonic CaCo2 cells to synthesize TLR-2 and TLR-4 and proinflammatory cytokines after binding to the amebic Gal/GalNac lectin carbohydrate recognition domain. The magnitude of the inflammatory response induced by trophozoites and the subsequent cell damage were synergized when cells had previously been exposed to pathogenic bacteria.

Methodology/Principal Findings

We show here that E. histolytica activation of the classic TLR pathway in CaCo2 cells is required to induce β defensin-2 (HBD2) mRNA expression and production of a 5-kDa cationic peptide with similar properties to the antimicrobial HBD2 expressed by CaCo2 cells exposed to enterotoxigenic Escherichia coli. The induced peptide showed capacity to permeabilize membranes of bacteria and live trophozoites. This activity was abrogated by inhibition of TLR2/4-NFκB pathway or by neutralization with an anti-HBD2 antibody.

Conclusions/Significance

Entamoeba histolytica trophozoites bind to human intestinal cells and induce expression of HBD2; an antimicrobial molecule with capacity to destroy pathogenic bacteria and trophozoites. HDB2's possible role as a modulator of the course of intestinal infections, particularly in mixed ameba/bacteria infections, is discussed.

Entamoeba histolytica ameba/bacteria mixed intestinal infections are common in endemic regions of Amebiasis. Recent investigations support the idea that pathogen interplay in these infections may have a role in invasive disease, activating signals that increase intestinal inflammation. We have studied interactions of amebic trophozoites with human colonic CaCo2 cells, using as positive control pathogenic intestinal bacteria E. coli (ETEC). Both pathogens activated a chain of chemical reactions in the cells that led to production of the antimicrobial peptide β defensin-2 (HBD2), an element of the innate immune response. Pathogen activation of CaCo2 cell response and production of HBD2 were analyzed employing biochemical, cell, molecular biology, and immunology methods. Amebas induced HBD2 via the same classic Toll-receptor signaling pathway activated by ETEC. Amebic-induced HBD2 showed capacity to permeabilize and cause severe damage to bacteria and ameba membranes. Although this study was done in vitro, due to lack of an adequate animal model in which to monitor ameba/bacteria interactions, it provides a new insight into intestinal infections, showing that presence of amebas induces synthesis of elements of an innate immune response that could affect the equilibrium of the intestinal microbiota and modify the course of intestinal infections by other pathogens.

The intestinal microbiota in chronic liver disease

Recent evidence indicates that the intestinal microflora plays a critical role in physiological and pathological processes; in particular, it is now considered a key determinant of immune pathologies and metabolic syndrome. Receiving the majority of its blood supply from the portal vein, the liver represents the first line of defense against food antigens, toxins, microbial-derived products, and microorganisms. Moreover, the liver is critically positioned to integrate metabolic outcomes with nutrient intake. To accomplish this function, the liver is equipped with a broad array of immune networks. It is now evident that, during pathological processes associated with obesity, alcohol-intake, or autoimmunity, the interaction between these immune cell populations and the intestinal microbiota promotes chronic liver disease progression and therefore they represent a novel therapeutic target. Herein, we highlight recent studies that have shed new light on the relationship between the microbiome, the innate immune system, and chronic liver disease progression.

Hypoxia-inducible factor-1 up-regulates the expression of Toll-like receptor 4 in pancreatic cancer cells under hypoxic conditions

BACKGROUND & AIMS

Hypoxia is a common characteristic of solid tumors. Recent studies confirmed that Toll-like receptor 4 (TLR4) plays a significant role in cancer invasion and progression. In this study, the correlation between the expression of TLR4 and the change of the protein level of Hypoxia-inducible factor-1 alpha (HIF-1α) was studied.

METHODS

We examined 84 human pancreatic cancer tissues for expression of HIF-1α and TLR4 proteins. Panc-1 cells were exposed to normoxia (20% O(2)) or hypoxia (<1% O(2)) or treated with CoCl(2). TLR4 protein was analyzed by flow cytometry and immunostaining. Growth studies were conducted on cells with the HIF-1α inhibition isolated from stable transfected cell lines. Finally, TLR4 protein was detected by immunohistochemistry in vivo tumors.

RESULTS

There was a positive correlation between TLR4 and HIF-1α protein in pancreatic cancer tissues. Hypoxic stress induced TLR4 mRNA and protein expression in Panc-1 cells. Cells transfected with HIF-1α siRNA showed attenuation of hypoxia stress-induced TLR4 expression. In vivo growth decreased in response to TLR4 and HIF-1α inhibiton. Transient HIF-1α siRNA treatment could effectively curb tumor growth in vivo.

CONCLUSION

These results suggest that TLR4 expression in pancreatic cancer cells is up-regulated via HIF-1α in response to hypoxic stress and underscore the crucial role of HIF-1α-induced TLR4 in tumor growth.

Microbes, intestinal inflammation and probiotics

Inflammatory bowel disease (IBD) is known for causing disturbed homeostatic balance among the intestinal immune compartment, epithelium and microbiota. Owing to the emergence of IBD as a major cause of morbidity and mortality, great efforts have been put into understanding the sequence of intestinal inflammatory events. Intestinal macrophages and dendritic cells act in a synergistic fashion with intestinal epithelial cells and microbiota to initiate the triad that governs the intestinal immune responses (whether inflammatory or regulatory). In this review, we will discuss the interplay of intestinal epithelial cells, bacteria and the innate immune component. Moreover, whether or not genetic intervention of probiotic bacteria is a valid approach for attenuating/mitigating exaggerated inflammation and IBD will also be discussed.

Mast cell-mediated inhibition of abdominal neutrophil inflammation by a PEGylated TLR7 ligand

Although the mechanisms for sustained chemokine gradients and recurring cell infiltration in sterile peritonitis have not been elucidated, toll-like receptors (TLRs) have been implicated. To abate the deleterious recruitment of neutrophils in sterile inflammation, we repeatedly administered a TLR7 ligand that hyposensitized to TLR7 and receptors that converged on the MyD88-signaling intermediary and reduced cellular infiltration in murine autoimmune models of multiple sclerosis and arthritis. To reduce potential adverse effects, a polyethylene glycol polymer was covalently attached to the parent compound (Tolerimod1). The proinflammatory potency of Tolerimod1 was 10-fold less than the unconjugated TLR7 ligand, and Tolerimod1 reduced neutrophil recruitment in chemically induced peritonitis and colitis. The effects of Tolerimod1 were mediated by the radioresistant cells in radiation chimeric mice and by mast cells in reconstituted mast cell-deficient mice (Kit(W-sh)). Although the Tolerimod1 had weak proinflammatory agonist activity, it effectively reduced neutrophil recruitment in sterile peritoneal inflammation.

Unraveling the ties between celiac disease and intestinal microbiota

Celiac disease is a multifactorial disorder that involves interactions between genetic and environmental factors. Gluten proteins are responsible for the symptoms of celiac disease, but other environmental factors that influence the intestinal ecosystem, including the milk-feeding type and gastrointestinal infections, may also play a role. Moreover, intestinal dysbiosis, characterized by increased Gram-negative bacteria and reduced bifidobacteria, has been detected in celiac disease patients. This review summarizes current knowledge of the associations between the intestinal microbiota and celiac disease and its possible modes of action in pathogenesis. Deeper understanding of these interactions can help redefine how this disorder is investigated.

Endogenous toll-like receptor ligands and their biological significance

Toll-like receptors (TLRs), a family of pattern recognition receptors, recognize and respond to conserved components of microbes and play a crucial role in both innate and adaptive immunity. In addition to binding exogenous ligands derived from pathogens, TLRs interact with endogenous molecules released from damaged tissues or dead cells and regulate many sterile inflammation processes. Putative endogenous TLR ligands include proteins and peptides, polysaccharides and proteoglycan, nucleic acids and phospholipids, which are cellular components, particularly extracellular matrix degradation products. Accumulating evidence demonstrates that endogenous ligand-mediated TLR signalling is involved in pathological conditions such as tissue injury, repair and regeneration; autoimmune diseases and tumorigenesis. The ability of TLRs to recognize endogenous stimulators appears to be essential to their function in regulating non-infectious inflammation. In this review, we summarize current knowledge of endogenous TLR ligands and discuss the biological significance of TLR signalling triggered by endogenous ligands in several sterile inflammation conditions.

Rebamipide suppresses TLR-TBK1 signaling pathway resulting in regulating IRF3/7 and IFN-α/β reduction

TANK-binding kinase 1 (TBK1) regulates the interferon regulatory factor (IRF) 3 and IRF7 activation pathways by double strand RNA (dsRNA) via Toll-like receptor (TLR) 3 and by lipopolysaccharide (LPS) via TLR4. Rebamipide is useful for treating inflammatory bowel disease (IBD). Although IBD is associated with nuclear factor-κB (NF-κB), any association with the TBK1-IRF pathway remains unknown. How rebamipide affects the TBK1-IRF pathway is also unclear. We analyzed the relationship between IBD (particularly ulcerative colitis; UC) and the TLR-TBK1-IRF3/7 pathway using human colon tissue, a murine model of colitis and human colonic epithelial cells. Inflamed colonic mucosa over-expressed TKB1, NAP1, IRF3, and IRF7 mRNA compared with normal mucosa. TBK1 was mainly expressed in inflammatory epithelial cells of UC patients. The expression of TBK1, IRF3, IRF7, IFN-α and IFN-β mRNA was suppressed in mice given oral dextran sulfate-sodium (DSS) and daily rectal rebamipide compared with mice given only DSS. Rebamipide reduced the expression of TBK1, IRF3 and IRF7 mRNA induced by LPS/dsRNA, but not of NF-κB mRNA in colonic epithelial cells. Rebamipide might suppress the TLR-TBK1 pathway, resulting in IRF3/7-induction of IFN-α/β and inflammatory factors. TBK1 is important in the induction of inflammation in patients with UC. If rebamipide represses the TLR-TBK1 pathway, then rectal administration should suppress inflammation of the colonic mucosa in patients with UC.

Role of negative regulators of TLR/IL-1 signaling in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is an autoimmune-like disorder characterized by chronic, idiopathic inflammation of the intestinal mucosa. Ulcerative colitis and Crohn's disease are known as the two forms of IBD. Although the etiology of IBD is still unclear, many experimental and clinical observations suggest the involvement of environmental, hereditary and immunological factors in the pathogenesis of IBD. Recent studies have showed that IBD is associated with immunologic dysfunction. Toll-like receptors (TLR) are pathogen pattern recognition receptors expressed by immune and nonimmune cells in the intestinal mucosa that play a central role in the initiation of innate immune responses and subsequent adaptive immune responses to microbial pathogens. In recent years there has been rapid progress in our understanding of the role of positive regulation of TLR signaling in the pathogenesis of IBD. However, the role of negative regulators of TLR signaling in this process remains unclear and will therefore be summarized in this paper.

Pathogenic and protective roles of MyD88 in leukocytes and epithelial cells in mouse models of inflammatory bowel disease

BACKGROUND & AIMS

Toll-like receptors (TLR) are innate immune receptors involved in recognition of the intestinal microflora; they are expressed by numerous cell types in the intestine, including epithelial cells, myeloid cells, and lymphocytes. Little is known about the relative contributions of TLR signaling in distinct cellular compartments to intestinal homeostasis. We aimed to define the roles of TLR signals in distinct cell types in the induction and regulation of chronic intestinal inflammation.

METHODS

We assessed the roles of the shared TLR signaling adaptor protein, MyD88, in several complementary mouse models of inflammatory bowel disease, mediated by either innate or adaptive immune activation. MyD88-deficient mice and bone marrow chimeras were used to disrupt TLR signals selectively in distinct cellular compartments in the intestine.

RESULTS

MyD88-dependent activation of myeloid cells was required for the development of chronic intestinal inflammation. By contrast, although epithelial cell MyD88 signals were required for host survival, they were insufficient to induce intestinal inflammation in the absence of an MyD88-competent myeloid compartment. MyD88 expression by T cells was not required for their pathogenic and regulatory functions in the intestine.

CONCLUSIONS

Cellular compartmentalization of MyD88 signals in the intestine allow the maintenance of host defense and prevent deleterious inflammatory responses.

Role of the gut microbiota in defining human health

The human superorganism is a conglomerate of mammalian and microbial cells, with the latter estimated to outnumber the former by ten to one and the microbial genetic repertoire (microbiome) to be approximately 100-times greater than that of the human host. Given the ability of the immune response to rapidly counter infectious agents, it is striking that such a large density of microbes can exist in a state of synergy within the human host. This is particularly true of the distal gastrointestinal (GI) tract, which houses up to 1000 distinct bacterial species and an estimated excess of 1 x 10(14) microorganisms. An ever-increasing body of evidence implicates the GI microbiota in defining states of health and disease. Here, we review the literature in adult and pediatric GI microbiome studies, the emerging links between microbial community structure, function, infection and disease, and the approaches to manipulate this crucial ecosystem to improve host health.

Incidence of staphylococcal colonization and of the 753Q Toll-like receptor 2 variant in nasal polyposis

BACKGROUND

The impact of Staphylococcus aureus on the development of chronic sinusitis with nasal polyps (nasal polyposis [NP]) is a controversial discussion because different S. aureus colonization rates have been reported. Aside from the presence of a microbial stimulus, elements of innate immunity such as Toll-like receptors (TLRs) and/or impaired TLR function could be relevant for the development of this disease. Because the 753Q TLR2 variant may predispose to staphylococcal infection, we simultaneously analyzed staphylococcal colonization and the R753Q TLR2 single nucleotide polymorphism (SNP) in NP.

METHODS

Sixty-eight patients with NP (47 men and 21 women; mean age [+/-SD], 51.8 years [16.3]) and 51 controls (32 men and 19 women; mean age [+/-SD], 36.3 years [12.2]) were included. Patient characteristics studied included status of allergy, asthma, aspirin intolerance, and endoscopic and CT polyp score. For detection of bacteria, standard procedures of bacteriology and 16S rRNA gene sequencing were used. The R753Q TLR2 polymorphism was studied by allelic discrimination assay.

RESULTS

Overall, 128 isolates were cultured from 68 NP specimens, with Staphylococcus epidermidis and S. aureus being the most frequent bacterial isolates. Other bacterial species were infrequently detected. Fifty-nine isolates were cultured from 51 controls. Similarly, S. epidermidis and S. aureus were the most frequent bacterial isolates. S. aureus colonization was significantly increased in NP (p < 0.05). However, SNP genotyping results showed no association of the 753Q TLR2 variant with NP.

CONCLUSION

Although S. aureus detection was increased in NP, nasal polyp pathology is not related to the 753Q TLR2 variant.

ERK activation drives intestinal tumorigenesis in Apc(min/+) mice

Toll-like receptor (TLR) signaling is essential for intestinal tumorigenesis in Apc(min/+) mice, but the mechanisms by which Apc enhances tumor growth are unknown. Here we show that microflora-MyD88-ERK signaling in intestinal epithelial cells (IECs) promotes tumorigenesis by increasing the stability of the c-Myc oncoprotein. Activation of ERK (extracellular signal-related kinase) phosphorylates c-Myc, preventing its ubiquitination and subsequent proteasomal degradation. Accordingly, Apc(min/+)/Myd88(-/-) mice have lower phospho-ERK (p-ERK) levels and fewer and smaller IEC tumors than Apc(min/+) mice. MyD88 (myeloid differentiation primary response gene 88)-independent activation of ERK by epidermal growth factor (EGF) increased p-ERK and c-Myc and restored the multiple intestinal neoplasia (Min) phenotype in Apc(min/+)/Myd88(-/-) mice. Administration of an ERK inhibitor suppressed intestinal tumorigenesis in EGF-treated Apc(min/+)/Myd88(-/-) and Apc(min/+) mice and increased their survival. Our data reveal a new facet of oncogene-environment interaction, in which microflora-induced TLR activation regulates oncogene expression and related IEC tumor growth in a susceptible host.

Syk-coupled C-type lectin receptors that mediate cellular activation via single tyrosine based activation motifs

Different dendritic cell (DC) subsets have distinct specialized functions contributed in part by their differential expression of pattern recognition receptors (PRRs). C-type lectin receptors (CLRs) are a group of PRRs expressed by DCs and other myeloid cells that can recognize endogenous ligands as well as a wide range of exogenous structures present on pathogens. Dual roles in homeostasis and immunity have been demonstrated for some members of this receptor family. Largely due to their endocytic ability and subset specific expression, DC-expressed CLRs have been the focus of significant antigen-targeting studies. A number of CLRs function on the basis of signaling via association with immunoreceptor tyrosine-based activation motif (ITAM)-containing adapter proteins. Others contain ITAM-related motifs or immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in their cytoplasmic tails. Here we review CLRs that induce intracellular signaling via a single tyrosine-based ITAM-like motif and highlight their relevance in terms of DC function.

Gut microbiota and probiotics in modulation of epithelium and gut-associated lymphoid tissue function

The intestinal tract mucosa is exposed to a vast number of environmental antigens and a large community of commensal bacteria. The mucosal immune system has to provide both protection against pathogens and tolerance to harmless bacteria. Immune homeostasis depends on the interaction of indigenous commensal and transient bacteria (probiotics) with various components of the epithelium and the gut-associated lymphoid tissue. Herein, an update is given of the mechanisms by which the gut microbiota and probiotics are translocated through the epithelium, sensed via pattern-recognition receptors, and activate innate and adaptive immune responses.

Flagellin-induced corneal antimicrobial peptide production and wound repair involve a novel NF-kappaB-independent and EGFR-dependent pathway

Background

The bacterial protein flagellin plays a major role in stimulating mucosal surface innate immune response to bacterial infection and uniquely induces profound cytoprotection against pathogens, chemicals, and radiation. This study sought to determine signaling pathways responsible for the flagellin-induced inflammatory and cytoprotective effects on human corneal epithelial cells (HCECs).

Methodology/Principal Findings

Flagellin purified from Pseudomonas aeruginosa (strain PAK) or live bacteria were used to challenge cultured HCECs. The activation of signaling pathways was assessed with Western blot, and the secretion of cytokine/chemokine and production of antimicrobial peptides (AMPs) were measured with ELISA and dot blot, respectively. Effects of flagellin on wound healing were assessed in cultured porcine corneas. L94A (a site mutation in TLR5 binding region) flagellin and PAK expressing L94A flagellin were unable to stimulate NF-κB activation, but were potent in eliciting EGFR signaling in a TGF-α–related pathway in HCECs. Concomitant with the lack of NF-κB activation, L94A flagellin was ineffective in inducing IL-6 and IL-8 production in HCECs. Surprisingly, the secretion of two inducible AMPs, LL-37 and hBD2, was not affected by L94A mutation. Similar to wild-type flagellin, L94A induced epithelial wound closure in cultured porcine cornea through maintaining EGFR-mediated signaling.

Conclusions/Significance

Our data suggest that inflammatory response mediated by NF-κB can be uncoupled from epithelial innate defense machinery (i.e., AMP expression) and major epithelial proliferation/repair pathways mediated by EGFR, and that flagellin and its derivatives may have broad therapeutic applications in cytoprotection and in controlling infection in the cornea and other mucosal tissues.

Translational Mini-Review Series on Vaccines for HIV: T lymphocyte trafficking and vaccine-elicited mucosal immunity

Many pathogens use mucosal surfaces to enter and propagate within the host, making particularly desirable vaccines that target immune responses specifically to mucosal compartments. The majority of mucosal vaccine design strategies to date have been empirical in nature. However, an emerging body of basic immunological knowledge is providing new insights into the regulation of tissue-specific lymphocyte trafficking and differentiation. These insights afford the opportunity for the rational design of vaccines that focus immune responses at mucosal surfaces. Mucosal cellular immunity may prove critical for protection in the context of HIV infection, and thus there has been considerable interest in developing vaccines that target HIV-specific cellular immune responses to the gastrointestinal and vaginal mucosa. However, the optimal strategies for eliciting mucosal cellular immune responses through vaccination remain to be determined. Here, we review both recent vaccine studies and emerging paradigms from the basic immunological literature that are relevant to the elicitation of potent and protective mucosal cellular immune memory. Increasing the synergy between these avenues of research may afford new opportunities for mucosal vaccine design.

Toll-like receptors in ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injuries are implicated in a large array of pathological conditions such as myocardial infarction, cerebral stroke, and hepatic, renal, and intestinal ischemia, as well as following cardiovascular and transplant surgeries. The hallmark of these pathologies is excessive inflammation. Toll-like receptors (TLRs) are recognized as one of the main contributors to pathogen-induced inflammation and, more recently, injury-induced inflammation. Endogenous ligands such as low-molecular hyaluronic acid, fibronectin, heat shock protein 70, and heparin sulfate were all found to be cleaved in the inflamed tissue and to activate TLR2 and TLR4, initiating an inflammatory response even in the absence of pathogens and infiltrating immune cells. In this review, we discuss the contribution of TLR activation in hepatic, renal, cerebral, intestinal, and myocardial I/R injuries. A greater understanding of the role of TLRs in I/R injuries may aid in the development of specific TLR-targeted therapeutics to treat these conditions.

The significance of toll-like receptors in human diseases

Toll-like receptors (TLRs) are a family of transmembrane receptors that have been preserved throughout evolution and which selectively recognize a broad spectrum of microbial components and endogenous molecules released by injured tissue. Identification of these ligands by TLRs triggers signalling pathways which lead to the expression of numerous genes involved in a defensive response. In mammals, the products of these genes initiate inflammation, coordinate the effector functions of innate immunity, instruct and modulate adaptive immunity and initiate tissue repair and regeneration. Different mutations and experimental models which alter TLR function have revealed the significance of these receptors in susceptibility to infection and their involvement in the pathogenesis of a large number of non-infective inflammatory disorders such as cancer, allergy, autoimmunity, inflammatory bowel disease, or atherosclerosis. TLRs are currently viewed as important targets for the development of new vaccines and innovative therapies to prevent and treat human diseases.

Ubiquitin-editing enzyme A20 promotes tolerance to lipopolysaccharide in enterocytes

Although enterocytes are capable of innate immune responses, the intestinal epithelium is normally tolerant to commensal bacteria. To elucidate the mechanisms of tolerance, we examined the effect of preexposure to LPS on activation of p38, c-Jun, and NF-kappaB in enterocytes by several inflammatory and stress stimuli. Shortly after the initial LPS challenge, enterocytes become tolerant to restimulation with LPS or CpG DNA, but not with IL-17 or UV. The state of tolerance, which lasts 20-26 h, temporally coincides with LPS-induced expression of the anti-inflammatory ubiquitin-editing enzyme A20. Small interfering RNA silencing of A20 prevents tolerance, whereas ectopic expression of A20 blocks responses to LPS and CpG DNA, but not to IL-17 or UV. A20 levels in the epithelium of the small intestine are low at birth and following gut decontamination with antibiotics, but high under conditions of bacterial colonization. In the small intestine of adult rodents, A20 prominently localizes to the luminal interface of villus enterocytes. Lower parts of the crypts display relatively low levels of A20, but relatively high levels of phospho-p38. Gut decontamination with antibiotics reduces the levels of both A20 and phospho-p38. Along with the fact that A20-deficient mice develop severe intestinal inflammation, our results indicate that induction of A20 plays a key role in the tolerance of the intestinal epithelium to TLR ligands and bacteria.

Decreased somatostatin is related to the hypersensitivity of intestinal epithelia to LPS via upregulated TLR4-TBK1 pathway in rats chronically exposed to ethanol

Chronic alcoholics are predisposed to the development of a systemic inflammatory response syndrome, which is usually triggered in the gut. This study aimed to investigate in rats the role of intestinal epithelial inflammatory responsiveness in the susceptibility of alcoholics to excessive inflammation. Thirty Wistar rats were randomly divided into three groups: 10 rats killed immediately after acclimation (baseline control), 10 rats treated with 25% (vol/vol) ethanol for 6 months (ethanol group), and 10 rats given double-distilled water until killed simultaneously with the ethanol group (9-month control). The intestinal microflora, the epithelial histology and ultrastructure, the level of Toll-like receptor 4 (TLR4), TANK-binding kinase-1 (TBK1), and activated nuclear factor-kappaB (NF-kappaB) in the intestinal mucosa, and somatostatin (SST) levels in plasma and small intestine were evaluated in each group. Isolated intestinal epithelia from each rat were used to examine lipopolysaccharide (LPS) responsiveness with or without SST pretreatment by quantification of TLR4, TBK1, activated NF-kappaB, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha). Compared with both the control groups, the amount of mucosal Escherichia coli in the ethanol group was not changed, whereas the number of intestinal lactobacilli in the ethanol group was significantly reduced (P<.05). Mild inflammatory injury and upregulation of TLR4 and TBK1 were observed in the intestinal mucosa of the ethanol group. The LPS-enhanced in vitro expression of TLR4, TBK1, and production of IFN-gamma and TNF-alpha in isolated intestinal epithelia of the ethanol group were significantly higher than those in either control group (P<.05) and were dramatically inhibited by SST (P<.05), whereas NF-kappaB was activated by LPS only in the control groups. The plasma and intestinal levels of SST in the ethanol group were significantly lower than those in either control group (P<.05). These findings suggest that impairment of intestinal SST production by chronic ethanol administration leading to upregulation of the TLR4-TBK1 pathway may be one of the mechanisms underlying the LPS hypersensitivity of intestinal epithelia.

Transgenic zebrafish reporter lines reveal conserved Toll-like receptor signaling potential in embryonic myeloid leukocytes and adult immune cell lineages

The immune response of a host to an invading pathogen is dependent on the capacity of its immune cell compartment to recognize highly conserved pathogen components using an ancient class of pattern recognition receptors known as Toll-like receptors (TLRs). Initiation of TLR-mediated signaling results in the induction of proinflammatory cytokines that help govern the scale and duration of any ensuing response. Specificity for TLR signaling is, in part, a result of the differential recruitment of intracellular adaptor molecules. Of these, MyD88 is required for the majority of TLR signaling. Zebrafish have been shown to possess TLRs and adaptor molecules throughout early development, including MyD88, strongly suggesting conservation of this ancient defense mechanism. However, information about which embryonic cells/tissues possess this conserved signaling potential is lacking. To help define which embryonic cells, in particular, those of the innate immune system, have the potential for MyD88-dependent, TLR-mediated signaling, we generated transgenic reporter lines using regulatory elements of the myd88 gene to drive the fluorescent reporters enhanced GFP and Discosoma red fluorescent protein 2 within live zebrafish. These lines possess fluorescently marked cells/tissues consistent with endogenous myd88 expression, including a subset of myeloid leukocytes. These innate immune cells were confirmed to express other TLR adaptors including Mal, trif, and Sarm. Live wound-healing and infection assays validated the potential of these myd88-expressing leukocytes to participate in immune responses. These lines will provide a valuable resource for further resolving the contribution of MyD88 to early vertebrate immunity.

The gut microbiota of toll-like receptor 2-deficient mice exhibits lineage-specific modifications

Mutations in toll-like receptors that mediate bacterial recognition by the mammalian innate immune system have the potential to substantially alter the composition of an individual's microbiota. Here we tested this hypothesis by comparing the intestinal microbiota of toll-like receptor 2-deficient mice, both young and middle aged, with that of wild-type mice of the same genetic background, housed together under specific pathogen-free conditions. Bacterial DNA was extracted from mouse caecal tissue samples, amplified using universal bacterial 16S ribosomal RNA gene primers, and cloned into a plasmid vector. Insert-containing colonies were picked for high-throughput sequencing, and sequence data were analysed yielding species-level phylogenetic data. Clone libraries were compared by phylogenetic composition analysis using UniFrac. While pairwise differences in phylogenetic population structure between mutant and wild-type mice were not statistically significant, anosim analysis did demonstrate a significant difference between toll-like receptor 2-deficient mice and their wild-type counterparts. The difference observed was probably due to a high level of colonization of the toll-like receptor 2-deficient mice by two distinct Helicobacter phylotypes that were totally absent from wild-type mice. Principal coordinate analysis clustering indicated that age is a weaker determinate than genotype and maternal heritage in the mouse caecal microbiota. The findings suggest that although mutations in toll-like receptors may cause increased susceptibility to specific opportunistic bacteria, they do not dramatically alter the phylogenetic structure of microbiota.

Toll-like receptors and cancer

Toll-like receptors (TLRs) are a family of pattern recognition receptors that are best-known for their role in host defence from infection. Emerging evidence also suggests that TLRs have an important role in maintaining tissue homeostasis by regulating the inflammatory and tissue repair responses to injury. The development of cancer has been associated with microbial infection, injury, inflammation and tissue repair. Here we discuss how the function of TLRs may relate to these processes in the context of carcinogenesis.

Role of toll-like receptors in tissue repair and tumorigenesis

Toll-like receptors (TLRs) play a critical role in host defense from microbial infection. TLRs recognize conserved molecular structures produced by microorganisms and induce activation of innate and adaptive immune responses. The inflammatory responses induced by TLRs play an important role TLRs not only in host defense from infection, but also in tissue repair and regeneration. This latter function of TLRs can also contribute to tumorigenesis. Here we review recent progress in understanding the role of TLRs in cancer development.

Mucosal cytokine network in inflammatory bowel disease

Inflammatory bowel disease (IBD), ulcerative colitis (UC) and Crohn’s disease (CD) are characterized by ongoing mucosal inflammation in which dysfunction of the host immunologic response against dietary factors and commensal bacteria is involved. The chronic inflammatory process leads to disruption of the epithelial barrier, and the formation of epithelial ulceration. This permits easy access for the luminal microbiota and dietary antigens to cells resident in the lamina propria, and stimulates further pathological immune cell responses. Cytokines are essential mediators of the interactions between activated immune cells and non-immune cells, including epithelial and mesenchymal cells. The clinical efficacy of targeting TNF-α clearly indicates that cytokines are the therapeutic targets in IBD patients. In this manuscript, we focus on the biological activities of recently-reported cytokines [Interleukin (IL)-17 cytokine family, IL-31 and IL-32], which might play a role through interaction with TNF-α in the pathophysiology of IBD.

Neuro-immune interactions in inflammatory bowel disease and irritable bowel syndrome: future therapeutic targets

The gastro-intestinal tract is well known for its largest neural network outside the central nervous system and for the most extensive immune system in the body. Research in neurogastroenterology implicates the involvement of both enteric nervous system and immune system in symptoms of inflammatory bowel disease and irritable bowel syndrome. Since both disorders are associated with increased immune cell numbers, nerve growth and activation of both immune cells and nerves, we focus in this review on the involvement of immune cell-nerve interactions in inflammatory bowel disease and irritable bowel syndrome. Firstly, the possible effects of enteric nerves, especially of the nonadrenergic and noncholinergic nerves, on the intestinal immune system and their possible role in the pathogenesis of chronic intestinal inflammatory diseases are described. Secondly, the possible effects of immunological factors, from the innate (chemokines and Toll-like receptors) as well as the adaptive (cytokines and immunoglobulins) immune system, on gastro-intestinal nerves and its potential role in the development of inflammatory bowel disease and irritable bowel syndrome are reviewed. Investigations of receptor-mediated and intracellular signal pathways in neuro-immune interactions might help to develop more effective therapeutic approaches for chronic inflammatory intestinal diseases.

Cutting edge: natural DNA repetitive extragenic sequences from gram-negative pathogens strongly stimulate TLR9

Bacterial DNA exerts immunostimulatory effects on mammalian cells via the intracellular TLR9. Although broad analysis of TLR9-mediated immunostimulatory potential of synthetic oligonucleotides has been developed, which kinds of natural bacterial DNA sequences are responsible for immunostimulation are not known. This work provides evidence that the natural DNA sequences named repetitive extragenic palindromic (REPs) sequences present in Gram-negative bacteria are able to produce innate immune system stimulation via TLR9. A strong induction of IFN-alpha production by REPs from Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, and Neisseria meningitidis was detected in splenocytes from 129 mice. In addition, the involvement of TLR9 in immune stimulation by REPs was confirmed using B6.129P2-Tlr9(tm1Aki) knockout mice. Considering the involvement of TLRs in Gram-negative septic shock, it is conceivable that REPs play a role in its pathogenesis. This study highlights REPs as a potential novel target in septic shock treatment.

Epithelial overexpression of interleukin-32alpha in inflammatory bowel disease

Interleukin (IL)-32 is a recently described proinflammatory cytokine, characterized by induction of nuclear factor (NF)-kappaB activation. We studied IL-32alpha expression in the inflamed mucosa of inflammatory bowel disease (IBD). We also investigated mechanisms regulating IL-32alpha expression. Tissue samples were obtained endoscopically or surgically from patients with ulcerative colitis (UC) (n = 10), Crohn's disease (CD) (n = 10), ischaemic colitis (n = 4) and normal colorectal tissues (n = 10). IL-32alpha expression was evaluated by standard immunohistochemical procedure. IL-32 mRNA expression was analysed by Northern blot. IL-32alpha was expressed weakly by colonic epithelial cells from normal individuals and subjects with ischaemic colitis. In the inflamed mucosa of IBD patients, epithelial IL-32alpha expression was increased markedly. In UC and CD patients, IL-32alpha expression was enhanced in affected mucosa compared to non-affected mucosa. In intestinal epithelial cell lines, expression of IL-32alpha mRNA and protein was enhanced by IL-1beta, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha. A combination of TNF-alpha plus IFN-gamma exerted synergistic effects. IL-32alpha induction by IL-1beta and/or TNF-alpha was mediated by NF-kappaB activation. Epithelial IL-32alpha expression was increased in IBD patients, and in CD patients in particular. IL-32alpha might be involved in the pathophysiology of IBD as a proinflammatory cytokine and a mediator of innate immune response.