Role of Toll-like receptors in health and diseases of gastrointestinal tract

Vortioxetine attenuates rotenone-induced enteric neuroinflammation via modulation of the TLR2/S100B/RAGE signaling pathway in a rat model of Parkinson's disease

Emerging evidence suggests that gastrointestinal dysfunction and enteric nervous system pathology play a critical role in the early stages of Parkinson's disease. Considering the bidirectional relationship between gastrointestinal symptoms and mood disorders, this study aimed to elucidate the effects and possible mechanisms of action of vortioxetine, a serotonergic antidepressant, on the pathophysiological changes induced by rotenone in the enteroglial cells. α-synuclein, phosphorylated α-synuclein, TLR2, S100B and RAGE expression were detected in duodenal tissues of rats administered rotenone (2 mg/kg/day, s.c.) and/or vortioxetine (10 mg/kg/day, s.c.) for 28 days. For the mechanism of action studies, rat-derived enteroglial cells were treated with rotenone (10 μM) and/or vortioxetine (5 μM or 1 μM) for 24 h. The effects of vortioxetine were evaluated in the presence of the TLR2 antagonist C29, RAGE antagonist FPS-ZM1 and the S100B inhibitor pentamidine. TLR2, S100B, RAGE, and NFκB mRNA levels and proinflammatory cytokines via RT-qPCR and ELISA. Our results demonstrate that rotenone treatment significantly increased α-synuclein, pS129-α-synuclein, TLR2, and S100B expression while reducing RAGE levels, indicating marked enteric pathology. Vortioxetine administration attenuated these effects, reducing α-synuclein accumulation and proinflammatory markers. In vitro, rotenone impaired glial responses, decreasing S100B, RAGE, and NFκB markers, while vortioxetine improved these responses, promoting resynthesis of inflammatory molecules. Notably, S100B, NFκB, and cytokine levels (TNF-α, IL-1β, IL-6) were affected by C29, FPS-ZM1, and pentamidine pretreatments. Thus, vortioxetine is thought to have beneficial effects on rotenone-induced pathological changes in EGCs, and some of these effects are thought to be mediated by the TLR2/S100B/RAGE pathway.

Potential role of gut microbiota in major depressive disorder: A review

Interactions between the gut microbiota and host immunity are sophisticated, dynamic, and host-dependent. Scientists have recently conducted research showing that disturbances in the gut bacterial community can lead to a decrease in some metabolites and, consequently, to behaviors such as depression. Exposure to stressors dropped the relative abundance of bacteria in the genus Bacteroides while soaring the relative abundance of bacteria in the genus Clostridium, Coprococcus, Dialister, and Oscillibacter, which were also reduced in people with depression. Microbiota and innate immunity are in a bilateral relationship. The gut microbiota has been shown to induce the synthesis of antimicrobial proteins such as catalysidins, type C lectins, and defensins. Probiotic bacteria can modulate depressive behavior through GABA signaling. The gut microbiome produces essential metabolites such as neurotransmitters, tryptophan metabolites, and short-chain fatty acids (SCFAs) that can act on the CNS. In the case of dysbiosis, due to mucin changes, the ratio of intestinal-derived molecules may change and contribute to depression. Psychotropics, including Bifidobacterium longum NCC3001, Clostridium butyricum CBM588, and Lactobacillus acidophilus, have mental health benefits, and can have a positive effect on the host-brain relationship, and have antidepressant effects. This article reviews current studies on the association between gut microbiota dysbiosis and depression. Comprehensively, these findings could potentially lead to novel approaches to improving depressive symptoms via gut microbiota alterations, including probiotics, prebiotics, and fecal microbiota transplantation.

Sustained exposure to Helicobacter pylori induces immune tolerance by desensitizing TLR6

Helicobacter pylori (H. pylori, Hp) has been designated a class I carcinogen and is closely associated with severe gastric diseases. During colonization in the gastric mucosa, H. pylori develops immune escape by inducing host immune tolerance. The gastric epithelium acts as the first line of defense against H. pylori, with Toll-like receptors (TLRs) in gastric epithelial cells being sensitive to H. pylori components and subsequently activating the innate immune system. However, the mechanism of immune tolerance induced by H. pylori through the TLR signalling pathway has not been fully elucidated. In this research, we detected the expression of TLRs and inflammatory cytokines in GES-1 cells upon sustained exposure to H. pylori or H. pylori lysate from 1 to 30 generations and in Mongolian gerbils infected with H. pylori for 5 to 90 weeks. We found that the levels of TLR6 and inflammatory cytokines first increased and then dropped during the course of H. pylori treatment in vitro and in vivo. The restoration of TLR6 potentiated the expression of IL-1β and IL-8 in GES-1 cells, which recruited neutrophils and reduced the colonization of H. pylori in the gastric mucosa of gerbils. Mechanistically, we found that persistent infection with H. pylori reduces the sensitivity of TLR6 to bacterial components and regulates the expression of inflammatory cytokines in GES-1 cells through TLR6/JNK signaling. The TLR6 agonist obviously alleviated inflammation in vitro and in vivo. Promising results suggest that TLR6 may be a potential candidate immunotherapy drug for H. pylori infection.

The role of toll-like receptors in immune tolerance induced by Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a gram-negative, microaerobic bacterium that colonizes the gastric mucosa in about half of the world's population. H. pylori infection can lead to various diseases. Chronic infection by H. pylori exposes the gastric mucosa to bacterial components such as lipopolysaccharide (LPS), outer membrane vesicles (OMVs), and several toxic proteins. Infected with H. pylori activates the release of pro-inflammatory factors and triggers inflammatory responses that damage the gastric mucosa. As the only microorganism that permanently colonizes the human stomach, H. pylori can suppress host immunity to achieve long-term colonization. Toll-like receptors (TLRs) play a crucial role in T-cell activation, promoting innate immune responses and immune tolerance during H. pylori infection. Among the 10 TLRs found in humans, TLR2, TLR4, TLR5, and TLR9 have been thoroughly investigated in relation to H. pylori-linked immune regulation. In the present review, we provide a comprehensive analysis of the various mechanisms employed by different TLRs in the induction of immune tolerance upon H. pylori infection, which will contribute to the research of pathogenic mechanism of H. pylori.

A review of heat stress in chickens. Part I: Insights into physiology and gut health

Heat stress (HS) compromises the yield and quality of poultry products and endangers the sustainability of the poultry industry. Despite being homeothermic, chickens, especially fast-growing broiler lines, are particularly sensitive to HS due to the phylogenetic absence of sweat glands, along with the artificial selection-caused increase in metabolic rates and limited development of cardiovascular and respiratory systems. Clinical signs and consequences of HS are multifaceted and include alterations in behavior (e.g., lethargy, decreased feed intake, and panting), metabolism (e.g., catabolic state, fat accumulation, and reduced skeletal muscle accretion), general homeostasis (e.g., alkalosis, hormonal imbalance, immunodeficiency, inflammation, and oxidative stress), and gastrointestinal tract function (e.g., digestive and absorptive disorders, enteritis, paracellular barrier failure, and dysbiosis). Poultry scientists and companies have made great efforts to develop effective solutions to counteract the detrimental effects of HS on health and performance of chickens. Feeding and nutrition have been shown to play a key role in combating HS in chicken husbandry. Nutritional strategies that enhance protein and energy utilization as well as dietary interventions intended to restore intestinal eubiosis are of increasing interest because of the marked effects of HS on feed intake, nutrient metabolism, and gut health. Hence, the present review series, divided into Part I and Part II, seeks to synthesize information on the effects of HS on physiology, gut health, and performance of chickens, with emphasis on potential solutions adopted in broiler chicken nutrition to alleviate these effects. Part I provides introductory knowledge on HS physiology to make good use of the nutritional themes covered by Part II.

Alpha-Lipoic Acid Promotes Intestinal Epithelial Injury Repair by Regulating MAPK Signaling Pathways

Intestinal epithelial cells are an essential barrier in human gastrointestinal tract, and healing of epithelial wound is a key process in many intestinal diseases. α-Lipoic acid (ALA) was shown to have antioxidative and anti-inflammatory effects, which could be helpful in intestinal epithelial injury repair. The effects of ALA in human colonic epithelial cells NCM460 and human colorectal adenocarcinoma cells Caco-2 were studied. ALA significantly promoted NCM460 and Caco-2 migration, increased mucosal tight junction factors ZO-1 and OCLN expression, and ALA accelerated cell injury repair of both cells in wound healing assay. Western blot analysis indicated that ALA inhibited a variety of mitogen-activated protein kinase (MAPK) signaling pathways in the epithelial cells. In conclusion, ALA was beneficial to repair of intestinal epithelial injury by regulating MAPK signaling pathways.

Involvement of CCN1 Protein and TLR2/4 Signaling Pathways in Intestinal Epithelial Cells Response to Listeria monocytogenes

CCN1 is well studied in terms of its functions in injury repair, cell adhesion survival and apoptosis, bacterial clearance and mediation of inflammation-related pathways, such as the TLR2/4 pathways. However, the role of CCN1 protein and its interaction with TLR2/4 pathways in intestinal epithelial cells was not elucidated after Listeria monocytogenes infection. The results of this study confirm that L. monocytogenes infection induced intestinal inflammation and increased the protein expression of CCN1, TLR2, TLR4 and p38, which followed a similar tendency in the expression of genes related to the TLR2/4 pathways. In addition, organoids infected by L. monocytogenes showed a significant increase in the expression of CCN1 and the activation of TLR2/4 pathways. Furthermore, pre-treatment with CCN1 protein to organoids infected by L. monocytogenes could increase the related genes of TLR2/4 pathways and up-regulate the expression of TNF, and increase the count of pathogens in organoids, which indicates that the interaction between the CCN1 protein and TLR2/4 signaling pathways in intestinal epithelial cells occurred after L. monocytogenes infection. This study will provide a novel insight of the role of CCN1 protein after L. monocytogenes infection in the intestine.

Recombinant soluble thrombomodulin accelerates epithelial stem cell proliferation in mouse intestinal organoids and promotes the mucosal healing in colitis

BACKGROUND AND AIM

Epithelial regeneration, a critical step for the mucosal healing in inflammatory bowel disease, is tightly regulated by stem cells. Therefore, identification of the specific factors that induce stem cell proliferation could contribute to the development of effective strategies for treating inflammatory bowel disease. Recombinant soluble thrombomodulin (rsTM) has previously been shown to promote cell proliferation in skin and corneal wound healing in murine models, but its effects on intestinal epithelial cell proliferation remains unclear.

METHODS

Mouse intestinal organoids and dextran sulfate sodium (DSS)-induced colitis mouse model were used to assess the effects of rsTM on proliferation of intestinal epithelial cells. The size and budding morphologies of organoids were studied by confocal microscopy. The gene expression levels were analyzed by quantitative real-time polymerase chain reaction and immunofluorescence analysis. The effects of rsTM on DSS-induced colitis were investigated by evaluating body weight changes, colon length, histological score, and survival rate.

RESULTS

The rsTM markedly stimulated the growth of intestinal organoids, thereby increasing the surface areas and budding phenotypes of the organoids. rsTM also significantly upregulated the gene expression of intestinal stem cell-specific and epithelial cell-specific markers in a dose-dependent manner. Furthermore, the treatment with high concentrations of rsTM significantly improved the recovery of body weight, histological outcomes, colon length shortening, and prolonged the survival of mice with colitis.

CONCLUSIONS

The rsTM promotes intestinal stem cell proliferation in intestinal organoids and enhances the mucosal healing during recovery phase in DSS-induced colitis.

Macrophage cytokine responses to commensal Gram-positive Lactobacillus salivarius strains are TLR2-independent and Myd88-dependent

The mechanisms through which cells of the host innate immune system distinguish commensal bacteria from pathogens are currently unclear. Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) expressed by host cells which recognize microbe-associated molecular patterns (MAMPs) common to both commensal and pathogenic bacteria. Of the different TLRs, TLR2/6 recognize bacterial lipopeptides and trigger cytokines responses, especially to Gram-positive and Gram-negative pathogens. We report here that TLR2 is dispensable for triggering macrophage cytokine responses to different strains of the Gram-positive commensal bacterial species Lactobacillus salivarius. The L. salivarius UCC118 strain strongly upregulated expression of the PRRs, Mincle (Clec4e), TLR1 and TLR2 in macrophages while downregulating other TLR pathways. Cytokine responses triggered by L. salivarius UCC118 were predominantly TLR2-independent but MyD88-dependent. However, macrophage cytokine responses triggered by another Gram-positive commensal bacteria, Bifidobacterium breve UCC2003 were predominantly TLR2-dependent. Thus, we report a differential requirement for TLR2-dependency in triggering macrophage cytokine responses to different commensal Gram-positive bacteria. Furthermore, TNF-α responses to the TLR2 ligand FSL-1 and L. salivarius UCC118 were partially Mincle-dependent suggesting that PRR pathways such as Mincle contribute to the recognition of MAMPs on distinct Gram-positive commensal bacteria. Ultimately, integration of signals from these different PRR pathways and other MyD88-dependent pathways may determine immune responses to commensal bacteria at the host-microbe interface.

Effects of TLR agonists on immune responses in Trichinella spiralis infected mice

Human trichinellosis is acquired by eating raw or undercooked meats carrying muscle larvae of Trichinella spp. Toll-like receptors (TLRs) are essential components of the innate immune system. However, little is known about the potential application of TLR agonists for immunotherapy against Trichinella spiralis (T. spiralis) infection. Here, we evaluated the effects of four TLR agonists (i.e., TLR3, TLR4, TLR8, and TLR9 agonists) on T. spiralis infection in mice. The reduction rate of worm burden showed that TLR3 agonist poly(I:C) significantly reduced T. spiralis infection rather than TLR4, TLR8, and TLR9 agonists (p < 0.05). Moreover, TLR3 showed a continuous high-level of expression during 6–35 days post infection (dpi). The levels of interferon-gamma (IFN-γ), interleukin (IL)-2, and IL-6 increased significantly in mice serum compared with control group after treatment with TLR3 agonist at 0, 3, 6, 9, 12, 15, 18, 21, 28, and 35 dpi (p < 0.05). A significant decreasing trend was also detected in levels of IL-10 and IL-4 after treatment with TLR3 agonist compared with control group at 0, 3, 6, 9, 12, 15, 18, 21, 28, and 35 dpi (p < 0.05). Overall, this study suggested that TLR3-targeted therapies might be effective on worm burden reduction by regulation of the cytokine levels in the mice infected with T. spiralis.

Microbiome as an Immunological Modifier

Humans are living ecosystems composed of human cells and microbes. The microbiome is the collection of microbes (microbiota) and their genes. Recent breakthroughs in the high-throughput sequencing technologies have made it possible for us to understand the composition of the human microbiome. Launched by the National Institutes of Health in USA, the human microbiome project indicated that our bodies harbor a wide array of microbes, specific to each body site with interpersonal and intrapersonal variabilities. Numerous studies have indicated that several factors influence the development of the microbiome including genetics, diet, use of antibiotics, and lifestyle, among others. The microbiome and its mediators are in a continuous cross talk with the host immune system; hence, any imbalance on one side is reflected on the other. Dysbiosis (microbiota imbalance) was shown in many diseases and pathological conditions such as inflammatory bowel disease, celiac disease, multiple sclerosis, rheumatoid arthritis, asthma, diabetes, and cancer. The microbial composition mirrors inflammation variations in certain disease conditions, within various stages of the same disease; hence, it has the potential to be used as a biomarker.

The modulatory effect of Artemisia annua L. on toll-like receptor expression in Acanthamoeba infected mouse lungs

The genus Acanthamoeba, which may cause different infections in humans, occurs widely in the environment. Lung inflammation caused by these parasites induces pulmonary pathological changes such as pulmonary necrosis, peribronchial plasma cell infiltration, moderate desquamation of alveolar cells and partial destruction of bronchial epithelial cells, and presence of numerous trophozoites and cysts among inflammatory cells. The aim of this study was to assess the influence of plant extracts from Artemisia annua L. on expression of the toll-like receptors TLR2 and TLR4 in lungs of mice with acanthamoebiasis. A. annua, which belongs to the family Asteraceae, is an annual plant that grows wild in Asia. In this study, statistically significant changes of expression of TLR2 and TLR4 were demonstrated. In the lungs of infected mice after application of extract from A. annua the expression of TLRs was observed mainly in bronchial epithelial cells, pneumocytes (to a lesser extent during the outbreak of infection), and in the course of high general TLR expression. TLR4 in particular was also visible in stromal cells of lung parenchyma. In conclusion, we confirmed that a plant extract of A. annua has a modulatory effect on components of the immune system such as TLR2 and TLR4.

Role of gut microbiota in intestinal wound healing and barrier function

The mammalian intestine harbors a highly complex and abundant ensemble of bacteria that flourish in a nutrient-rich environment while profoundly influencing many aspects of host biology. The intestine coevolved with its resident microbes in a manner where the mucosa developed a barrier function to segregate the resident microbes from the rest of the body, and yet paradoxically, allowing integration of microbial signals for the host benefit. In this review, we provided a comprehensive overview of why the gut microbiota is key to the efficient development and maintenance of the intestinal barrier. We also highlighted how a destabilized equilibrium between gut microbiota and the host may eventuate in a wide range of intestinal diseases characterized by the disrupted intestinal barrier. Finally, the review delineated how microenvironmental changes in the injured mucosa result in an enrichment of a pro-regenerating consortium of bacteria, which augments mucosal wound repair and restoration of barrier functions.

Effect of supplemental yeast cell walls on growth performance, gut mucosal glutathione pathway, proteolytic enzymes and transporters in growing broiler chickens

This study aimed to investigate the effect of supplemental yeast cell walls (YCW) on growth performance, gut mucosal glutathione pathway, proteolytic enzymes, and transporters in broiler chickens from 1 to 21 d of age. One-day-old broiler chickens (n = 480) were randomly allocated to 4 treatments with 6 replicates of 20 chicks each for diets containing YCW at 0, 0.5, 1.0, and 1.5 g/kg. The results showed that YCW supplementation increased (P < 0.05) ADFI and ADG by 15.3% and 16.0%, respectively, and the 2 higher doses of YCW had greater effects (P < 0.05) than the lower dose. For the glutathione pathway in the duodenal mucosa, the levels of reduced glutathione and glutathione reductase in the YCW treatments were increased (P < 0.05) by 15.6% and 17.4%, respectively, but glutathione S-transferases was not affected. Similarly, the YCW increased (P < 0.05) the mucosal activities of trypsin, dipeptidyl, and leucine aminopeptidase by 12.4%, 5.5%, and 17.3%, respectively, and the mRNA profiles of neutral, cationic, and oligopeptide transporters by 62.5%, 69.1%, and 11.5%, respectively. The YCW also increased (P < 0.05) the concentrations of Thr, Met, Ile, Leu, Lys, Arg, and Tyr in the blood by 8.8% to 39.2%. Additionally, the ADFI, ADG, reduced glutathione, trypsin, dipeptidyl aminopeptidase, leucine aminopeptidase, and cationic amino acid transporter increased linearly and quadratically (P < 0.05) with YCW supplementation. The results suggest that YCW supplementation can beneficially modulate intestinal glutathione pathway, proteolytic enzyme activity, and nutrient transport in growing animals.

Role of toll-like receptors in inflammatory bowel disease

Inflammatory bowel disease (IBD) is the chronic inflammation of the gastrointestinal tract. Recently, studies of the interplay between the adaptive and innate immune responses have provided a better understanding of the immunopathogenesis of inflammatory disorders such as IBD, as well as identification of novel targets for more potent interventions. Toll-like receptors (TLRs) are a class of proteins that play a significant role in the innate immune system and are involved in inflammatory processes. Activation of TLR signal transduction pathways lead to the induction of numerous genes that function in host defense, including those for inflammatory cytokines, chemokines, and antigen presenting molecules. It was proposed that TLR mutations and dysregulation are major contributing factors to the predisposition and susceptibility to IBD. Thus, modulating TLRs represent an innovative immunotherapeutic approach in IBD therapy. This article outlines the role of TLRs in IBD, focusing on both animal and human studies; the role of TLR-targeted agonists or antagonists as potential therapeutic agents in the different stages of the disease is discussed.

Influence of Artemisia annua L. on toll-like receptor expression in brain of mice infected with Acanthamoeba sp

The treatment of acanthamoebiasis is a still a problem. Our previous studies showed that the application of extracts from Artemisia annua L. significantly prolonged the survival of mice infected by Acanthamoeba. This plant has medicinal properties in the treatment of human parasitic diseases. The aim of this study was to evaluate the effects of A. annua on expression of Toll-like receptors (TLRs) 2 and 4 in brain of mice with Acanthamoeba infection. Mice were infected with Acanthamoeba sp. strain Ac309 (KY203908) by intranasal inoculation without and after application of A. annua extract. The administration of extract from A. annua significantly reduced the level of expression of TLR2 and modified the level of expression of TLR4. A. annua extract is a natural substance that is well tolerated in animals and may be considered as a combination therapy in treatment of acanthamoebiasis. Our study suggested that A. annua extract may be used as an alternative therapeutic tool.

Probiotic bacteria prevent Salmonella - induced suppression of lymphoproliferation in mice by an immunomodulatory mechanism

Background

Salmonella enterica infections often exhibit a form of immune evasion. We previously observed that probiotic bacteria could prevent inhibition of lymphoproliferation and apoptosis responses of T cells associated with S. enterica infections in orally challenged mice.

Results

In this study, changes in expression of genes related to lymphocyte activation in mucosa-associated lymphoid tissues (MALT) of mice orally infected with S. enterica with and without treatment with probiotic bacteria were evaluated. Probiotic bacteria increased expression of mRNA for clusters of differentiation antigen 2 (Cd2), protein tyrosine phosphatase receptor type C (Ptprc), and Toll-like receptor 6 (Tlr6) genes related to T and B cell activation in mouse intestinal tissue. The probiotic bacteria were also associated with reduced mRNA expression of a group of genes (RelB, Myd88, Iκκa, Jun, Irak2) related to nuclear factor of kappa light chains enhancer in B cells (NF-κB) signal transduction pathway-regulated cytokine responses. Probiotic bacteria were also associated with reduced mRNA expression of apoptotic genes (Casp2, Casp12, Dad1, Akt1, Bad) that suggest high avidity lymphocyte sparing. Reduced CD2 immunostaining in mesenteric lymph nodes (MLN) was suggestive of reduced lymphocyte activation in probiotic-treated mice. Reduced immunostaining of TLR6 in MALT of probiotic-treated, S. enterica-infected mice suggests that diminished innate immune sensitivity to S. enterica antigens is associated with preventing lymphocyte deletion.

Conclusions

The results of this study are consistent with prevention of S. enterica-induced deletion of lymphocytes by the influence of probiotic bacteria in mucosal lymphoid tissues of mice.

Localization of Toll-like Receptor (TLR) 2 and TLR4 mRNA in the Colorectal Mucosa of Miniature Dachshunds with Inflammatory Colorectal Polyps

Inflammatory colorectal polyps (ICRPs) are characterized by the formation of multiple or solitary polyps with marked neutrophil infiltration in the colorectal area, and are speculated to be a novel form of breed-specific canine idiopathic inflammatory bowel disease (IBD). In human IBD, toll-like receptor (TLR) 2 and TLR4 have been reported to be involved in the pathogenesis of the disease. The aim of this study was to evaluate the expression of TLR2 and TLR4 mRNA in the colorectal mucosa of dogs with ICRPs by in-situ hybridization using an RNAscope assay. Samples of inflamed colorectal mucosa (n = 5) and non-inflamed mucosa (n = 5) from miniature dachshunds (MDs) with ICRPs and colonic mucosa from healthy beagles (n = 5) were examined. TLR2 and TLR4 hybridization signals were localized to the colorectal epithelium, inflammatory cells and fibroblasts in the inflamed colorectal mucosa of affected dogs. The signals were significantly greater in inflamed colorectal epithelium compared with non-inflamed epithelium of MDs with ICRPs and healthy beagles (P <0.05). These results suggest that increased expression of TLR2 and TLR4 mRNA in the inflamed colorectal mucosa results from not only inflammatory cell infiltration, but also the upregulation of TLR2 and TLR4 mRNA in the colonic epithelium.

Acanthamoeba infection in lungs of mice expressed by toll-like receptors (TLR2 and TLR4)

Toll-like receptors (TLRs) play a key role in the innate immune responses to a variety of pathogens including parasites. TLRs are among the most highly conserved in the evolution of the receptor family, localized mainly on cells of the immune system and on other cells such as lung cells. The aim of this study was to determine for the first time the expression of TLR2 and TLR4 in the lung of Acanthamoeba spp. infected mice using quantitative real-time polymerase chain reaction (Q-PCR) and immunohistochemical (IHC) staining. The Acanthamoeba spp. were isolated from a patient with Acanthamoeba keratitis (AK) (strain Ac 55) and from environmental samples of water from Malta Lake (Poznań, Poland - strain Ac 43). We observed a significantly increased level of expression of TLR2 as well as TLR4 mRNA from 2 to 30 days post Acanthamoeba infection (dpi) in the lungs of mice infected with Ac55 (KP120880) and Ac43 (KP120879) strains. According to our observations, increased TLR2 and TLR4 expression in the pneumocytes, interstitial cells and epithelial cells of the bronchial tree may suggest an important role of these receptors in protective immunity against Acanthamoeba infection in the lung. Moreover, increased levels of TLR2 and TLR4 mRNA expression in infected Acanthamoeba mice may suggest the involvement of these TLRs in the recognition of this amoeba pathogen-associated molecular pattern (PAMP).

The Colonic Tissue Levels of TLR2, TLR4 and Nitric Oxide in Patients with Irritable Bowel Syndrome

Objective Irritable bowel syndrome (IBS) is a highly prevalent and debilitating functional disorder. The toll-like receptors (TLRs) are a family of pathogen-recognition receptors in the innate immune system. In the present study we aimed to investigate the TLR2, TLR4 and nitric oxide (NO) levels in patients with IBS. Methods Fifty-one IBS patients and 15 healthy controls were included in the present study. Colonic tissue levels of TLR2, TLR4 and NO were detected using an enzyme-linked immunosorbent assays (ELISA) and through biochemical methods. Results The colonic tissue levels of TLR4 and NO were significantly higher in IBS patients than in healthy controls. A subgroup analysis, which was based on the presence of diarrhea and constipation, showed that TLR2 levels were significantly higher among individuals with diarrhea-predominant IBS than among constipation-predominant IBS patients and healthy controls. The TLR4 levels were significantly higher in the diarrhea-predominant IBS patients and constipation-predominant IBS patients than in comparison healthy controls. The colonic tissue levels of NO were higher in the constipation-predominant IBS patients than in the diarrhea-predominant IBS patients and healthy controls. Conclusion In the present study we found that the colonic tissue levels of TLR and NO were elevated in IBS patients. Our results support the presence of a degree of immune dysregulation and oxidative stress in patients with IBS.

The Interaction among Microbiota, Immunity, and Genetic and Dietary Factors Is the Condicio Sine Qua Non Celiac Disease Can Develop

Celiac disease (CD) is an immune-mediated enteropathy, triggered by dietary wheat gluten and similar proteins of barley and rye in genetically susceptible individuals. This is a complex disorder involving both environmental and immune-genetic factors. The major genetic risk factor for CD is determined by HLA-DQ genes. Dysfunction of the innate and adaptive immune systems can conceivably cause impairment of mucosal barrier function and development of localized or systemic inflammatory and autoimmune processes. Exposure to gluten is the main environmental trigger responsible for the signs and symptoms of the disease, but exposure to gluten does not fully explain the manifestation of CD. Thus, both genetic determination and environmental exposure to gluten are necessary for the full manifestation of CD; neither of them is sufficient alone. Epidemiological and clinical data suggest that other environmental factors, including infections, alterations in the intestinal microbiota composition, and early feeding practices, might also play a role in disease development. Thus, this interaction is the condicio sine qua non celiac disease can develop. The breakdown of the interaction among microbiota, innate immunity, and genetic and dietary factors leads to disruption of homeostasis and inflammation; and tissue damage occurs. Focusing attention on this interaction and its breakdown may allow a better understanding of the CD pathogenesis and lead to novel translational avenues for preventing and treating this widespread disease.

Low crude protein diets modulate intestinal responses in weaned pigs challenged with Escherichia coli K88

Opapeju, F. O., Rodriguez-Lecompte, J. C., Rademacher, M., Krause, D. O. and Nyachoti, C. M. 2015. Low crude protein diets modulate intestinal responses in weaned pigs challenged with Escherichia coli K88. Can. J. Anim. Sci. 95: 71–78. Effects of dietary crude protein (CP) content on intestinal indicators of infection and diarrhea in pigs challenged with enterotoxigenic Escherichia coli (ETEC) K88 were investigated. Forty piglets [body weight (BW)=6.96±0.45, mean±SD], housed four per pen, were randomly allotted to two diets (five pens per diet): a 22.2% CP or a 17.3% CP supplemented with amino acids. Diets contained the same amount of standardized ileal digestible Lys, Met+Cys, Thr, Trp based on the ideal amino acid ratio. Isoleucine and Val were added to the 17.3% CP diet up to the level in the 22.2% CP diet. All other nutrients were as per National Research Council (1998) specification. Three piglets per pen were serially slaughtered on days 3, 5, and 7 after weaning for evaluation of intestinal hydrolases (data reported elsewhere). On day 8 post-weaning, the remaining pigs were inoculated with 6 mL of ETEC suspension (1010 CFU mL−1) and slaughtered 20 h later. Mucosal-associated ETEC was detected in higher counts (3.17±0.63 log10 CFU g−1 digesta) in 80% of pigs fed the 22.2% CP diet compared with 20% of those fed the 17.3% CP diet in which the counts were also lower (2.00±log10 CFU g−1 digesta). Pigs fed the 22.2% CP diet tended (P=0.09) to have fewer goblet cells with sialomucins in jejunal villi compared with those fed the 17.3% CP diet. The expression of toll-like receptors 4 and 5 was unaffected by diet but the expression of sodium-coupled glucose transporter 1 was higher (P=0.04) in the jejunum of pigs fed the 22.2% CP diet compared with those fed the 17.3% CP diet. The results suggest that feeding a low-CP diet decreases ETEC proliferation and attachment in the intestinal mucosa and this is accompanied by a reduced expression of sodium-coupled glucose transporter 1.

The blood-epididymis barrier and inflammation

The blood-epididymis barrier (BEB) is a critical structure for male fertility. It enables the development of a specific luminal environment that allows spermatozoa to acquire both the ability to swim and fertilize an ovum. The presence of tight junctions and specific cellular transporters can regulate the composition of the epididymal lumen to favor proper sperm maturation. The BEB is also at the interface between the immune system and sperm. Not only does the BEB protect maturing spermatozoa from the immune system, it is also influenced by cytokines released during inflammation, which can result in the loss of barrier function. Such a loss is associated with an immune response, decreased sperm functions, and appears to be a contributing factor to post-testicular male infertility. Alterations in the BEB may be responsible for the formation of inflammatory conditions such as sperm granulomas. The present review summarizes current knowledge on the morphological, physiological and pathological components associated with the BEB, the role of immune function on the regulation of the BEB, and how disturbance of these factors can result in inflammatory lesions of the epididymis.

Activation of Toll-like receptors by intestinal microflora reduces radiation-induced DNA damage in mice

Activation of Toll-like receptors (TLRs) signaling by intestinal microflora-derived bacterial products plays a key role in injury defence for the host. We investigated the role of TLRs activated by intestinal microflora in radiation-induced DNA damage in mice. We analyzed DNA damage induced by 2Gy γ-ray radiation in an intestinal commensal bacteria-depleted mouse model (CD group), in which TLRs (TLR2/6, TLR4 and TLR5) ligand levels in serum were reduced. Chromosomal aberrations were measured in bone marrow cells and peripheral blood leukocyte comet assays were performed. DNA damage was increased in the CD group compared with the control group. Treatment of mice with TLR agonists (CBLB502, LPS and lipopeptide) 1h before radiation resulted in a significant decrease in DNA damage. Genes induced by TLR5 activation were analyzed; activation of TLRs regulated the expression of Gadd45b, Sod2, and Rad21, which are involved in DNA damage repair. In summary, our data indicate that TLRs activation by intestinal microflora reduces DNA damage induced by radiation and regulates expression of several DNA repair genes.

Multivariate inference of pathway activity in host immunity and response to therapeutics

Developing a quantitative view of how biological pathways are regulated in response to environmental factors is central for understanding of disease phenotypes. We present a computational framework, named Multivariate Inference of Pathway Activity (MIPA), which quantifies degree of activity induced in a biological pathway by computing five distinct measures from transcriptomic profiles of its member genes. Statistical significance of inferred activity is examined using multiple independent self-contained tests followed by a competitive analysis. The method incorporates a new algorithm to identify a subset of genes that may regulate the extent of activity induced in a pathway. We present an in-depth evaluation of specificity, robustness, and reproducibility of our method. We benchmarked MIPA's false positive rate at less than 1%. Using transcriptomic profiles representing distinct physiological and disease states, we illustrate applicability of our method in (i) identifying gene–gene interactions in autophagy-dependent response to Salmonella infection, (ii) uncovering gene–environment interactions in host response to bacterial and viral pathogens and (iii) identifying driver genes and processes that contribute to wound healing and response to anti-TNFα therapy. We provide relevant experimental validation that corroborates the accuracy and advantage of our method.

The effect of Biolex-MB40 on the phagocytic activity and oxidative metabolism of peripheral blood granulocytes and monocytes in lambs

The objective of this study was to determine the effect of Biolex-MB40 on the phagocytic activity and oxidative metabolism of peripheral blood granulocytes and monocytes in lambs. The experimental material comprised 32 lambs aged 30 +/- 3 days, divided into two equal groups: control and experimental. Experimental group animals were fed a diet supplemented with the Biolex-MB40 (Saccharomyces cerevisiae) in the amount of 3 g/kg of the concentrate. At the beginning of the experiment (day 0) and on experimental days 15, 30 and 60, blood was sampled from the jugular vein to determine and compare the phagocytic activity (PHAGOTEST) and oxidative metabolism (BURSTTEST) of peripheral blood granulocytes and monocytes by flow cytometry. Based on the results of an analysis of granulocyte and monocyte phagocytic activity, statistically higher levels of phagocytic activity were observed in the group of lambs administered Biolex-MB40 than in the control animals, expressed in terms of the percentage of phagocytic cells as well as mean fluorescence intensity. Biolex-MB40 also had a positive effect on the oxidative metabolism of both granulocytes and monocytes after stimulation with Escherichia coli bacteria and with PMA (4-phorbol-12-beta-myristate-13-acetate), expressed in terms of the percentage of oxidative metabolism as well as mean fluorescence intensity.

Toll-like receptors -4 and -5 in oral and cutaneous squamous cell carcinomas

BACKGROUND

Oral squamous cell carcinoma (OSCC) has a worse prognosis than cutaneous squamous cell carcinoma (CSCC). Toll-like receptor- 4 (TLR-4) and TLR-5 are transmembrane proteins that recognize endogenous and microbial agents. Their activation has been connected to cancer invasion.

OBJECTIVE

The aim was to study the expression of TLR-4 and TLR-5 in OSCC and CSCC samples, and the effects of TLR-5 ligand flagellin on the proliferation, migration, and invasion of different mucocutaneous cell lines in vitro.

METHODS

Samples of early-stage tumors (T1-T2N0M0) from 63 patients with OSCC and CSCC were obtained, in addition to eight normal mucosa and skin tissues from healthy subjects. Oral-cavity-derived highly aggressive HSC-3, less invasive SAS, and HPV-transformed benign IHGK as well as C-ha-ras-transformed (HaCat) skin carcinoma II-4 and non-invasive A5 cell lines were used. Flagellin-induced mucocutaneous cell lines were compared by using BrdU-proliferation, scratch migration, and myoma organotypic invasion assays.

RESULTS

TLR-4 expression was similar in OSCC and CSCC tumors. TLR-5 was more abundant in OSCC than in CSCC samples. Flagellin induced the proliferation of SAS, II-4 and A5, migration of IHGK, II-4 and A5, and the invasion of II-4 cells. It had no effect on HSC-3 cells.

CONCLUSIONS

Flagellin, a TLR-5 agonist, induced the migration and invasion of less aggressive mucocutaneous cell lines, but it had no effect on the most invasive oral carcinoma cells. The more aggressive clinical behavior of OSCC compared to CSCC may partially be related to the differences in the expression of TLR-5 in these malignancies.

Associations of a TLR4 single-nucleotide polymorphism with H. pylori associated gastric diseases in Iranian patients

OBJECTIVE

Helicobacter pylori (H. pylori) is associated with gastric ulcer and gastric adenocarcinoma. Polymorphisms in the host genes coding for toll-like receptors (TLRs) may influence the innate and adaptive immune response to the infection, affecting the susceptibility to H. pylori or the disease outcomes. But the details and association to different polymorphisms and different clinical expressions in patients infected with H. pylori (different clinical expression of H. pylori infection) remain unclear.

METHODS

A case-control study consisting of 195 patients with H. pylori infection and 241 H. pylori uninfection was conducted. Genomic DNA was extracted and genotypes of TLR4Asp299Gly polymorphism were assessed through polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Presence of cagA was evaluated using PCR.

RESULTS

TLR4 (Asp299Gly) G and DG alleles frequency in H. pylori infected population was significantly higher in the chronic gastritis group than in the chronic active gastritis group (P=0.021; OR, 2.409; 95% CI, 1.124-5.162). Grade mononuclear (MN) infiltration in H. pylori infected patients with DG genotype of TLR-4 Asp299Gly increased significantly. CagA positivity was more frequently associated with chronic active gastritis (P=0.017, OR=2.26, 95% CI=1.144-4.462) and grade polymorphonucler (PMN) infiltration.

CONCLUSION

TLR-4 Asp299Gly G allele substitution may be modified pattern of immune response in the gastric mucosa of H. pylori infected patients and may be H. pylori infected patients with gastritis have increased risk for the development of chronic gastritis. CagA positivity may be a risk factor for development of gastritis.

NOD-like receptors in intestinal homeostasis and epithelial tissue repair

The intestinal epithelium constitutes a dynamic physical barrier segregating the luminal content from the underlying mucosal tissue. Following injury, the epithelial integrity is restored by rapid migration of intestinal epithelial cells (IECs) across the denuded area in a process known as wound healing. Hence, through a sequence of events involving restitution, proliferation and differentiation of IECs the gap is resealed and homeostasis reestablished. Relapsing damage followed by healing of the inflamed mucosa is a hallmark of several intestinal disorders including inflammatory bowel diseases (IBD). While several regulatory peptides, growth factors and cytokines stimulate restitution of the epithelial layer after injury, recent evidence in the field underscores the contribution of innate immunity in controlling this process. In particular, nucleotide-binding and oligomerization domain-like receptors (NLRs) play critical roles in sensing the commensal microbiota, maintaining homeostasis, and regulating intestinal inflammation. Here, we review the process of intestinal epithelial tissue repair and we specifically focus on the impact of NLR-mediated signaling mechanisms involved in governing epithelial wound healing during disease.

Activation of innate immunity by bacterial ligands of toll-like receptors

Tγδ and B1 lymphocytes are essential components of the mucosal immune system, activated directly by different bacterial and viral ligands without additional costimulatory signals and preprocessing of other immune effectors. This ability enables the immune system to provide rapid protection against pathogens and contributes to the decoding mechanism of the sensitizing activity of mucosal antigens. The early interaction of these cells results in the production of antibodies of immunoglobulin M (IgM) and IgA isotypes, but not immunoglobulin E (IgE). We studied the subcutaneous, intranasal, and oral delivery as three major routes of potential entry for antigens of opportunistic microorganisms, using the immunomodulator Immunovac-VP-4, which is able to activate Tγδ and B1 lymphocytes. The subcutaneous and intranasal routes produced a significant increase of these cells in lymph nodes associated with the nasal cavity (NALT) and in those associated with bronchial tissue (BALT). The oral route significantly increased levels of these cells in the spleen, in NALT, BALT, and in nodes associated with the gut (GALT). We found that mucosal application of Immunovac-VP-4, which contains antigens of conditionally pathogenic microorganisms, in conjunction with the activation of Tγδ and B1, induces adaptive immune mechanisms not only in the lymphoid formations associated with the respiratory system and with GALT, but also in the spleen [increased expression of cluster of differentiation 3 (CD3), CD4, CD8, CD19, and CD25]. This indicates that there is migration of lymphoid cells from the regional lymph nodes and mucosal lymphoid tissues via the lymph and blood to distant organs, resulting in lymphoid development, and both local and systemic immunity. Mucosal application of Immunovac-VP-4 in mice potentiates the cytotoxic activity of NK cells in the NALT, BALT, and GALT. The highest cytotoxicity was observed in cells, derived from lymphoid tissue of the intestine after oral immunization. Although we found that cytokine production was increased by all three immunization routes, it was most intensive after subcutaneous injection. Our findings confirm that there is an intensive exchange of lymphocytes not only between lymphoid formations in the mucous membranes of the respiratory tract and of GALT, but also with the spleen, which means that if effective mucosal vaccines are developed, they can induce both local and systemic immunity.

Effect of dietary supplementation on the antimicrobial activity of blood leukocytes isolated from Holstein heifers

The purpose of this investigation was to evaluate the effect of an immunostimulating feed supplement (OmniGen-AF®) on the antimicrobial properties of blood leukocytes in dairy heifers in an attempt to prevent mastitis. Blood leukocytes from supplemented and unsupplemented controls were used. Phagocytic activity and reactive oxygen species (ROS) production were studied on d 0 (prior to feed supplementation) and on days 30 and 60 after supplementation. L-selectin and IL-8R mRNA expressions on blood leukocytes were evaluated on d 0 (prior to feed supplementation) and monthly thereafter for 15 mo. On d 30 after supplementation, neutrophils from treated heifers exhibited greater binding and internalization of Escherichia coli and greater ROS production compared with unsupplemented controls. L-selectin mRNA expression was increased in supplemented heifers vs. controls; however, IL-8R mRNA expression was not different. Results support the continued study of dietary supplementation as an additional management tool to enhance udder health in dairy heifers.

Hymenolepis diminuta: analysis of the expression of Toll-like receptor genes (TLR2 and TLR4) in the small and large intestines of rats. Part II

Toll-like receptors in the gastrointestinal tract can influence intestinal homeostasis and play a role in the repair and restitution of intestinal epithelium following tissue damage. In our previous study a statistically significant increase in the level of TLR4 and TLR2 gene expression was observed in rats in early stages of hymenolepidosis. Moreover, the immunopositive cell number and the intensity of immunohistochemical staining (indicating the presence of TLRs within intestinal epithelial cells) increased over the infection period. In this paper, we determined changes in the expression of TLR2 and TLR4 and the number of anaerobic intestinal commensal bacteria in Hymenolepis diminuta infected rats. In the isolated jejunum of infected rats at 16 days post infection (dpi), the expression of TLR4 and TLR2 was significantly higher than uninfected rats. In the colon, a statistically significantly increased expression of TLR2 was observed from 16 to 40 dpi, and TLR4 from 16 to 60 dpi. The jejunum and colon of infected rats contained Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Enterococcus, Streptococcus, Staphylococcus, Bacillus, Lactobacillus) and Candida. The total number of intestinal bacteria was higher in H. diminuta infected rats, but the observed microbiota had only minor effects on the expression of TLR2 and TLR4. Toll-like receptors play a role in maintaining epithelial barrier function in response to enteric pathogens and parasites. In our study, the alteration of TLR2 and TLR4 expression in the infected rats indicates the potential role of the innate immune system in the pathomechanism of this infection.

The role of IL-15 in gastrointestinal diseases: a bridge between innate and adaptive immune response

IL-15 is a member of the IL-2 family of cytokines whose signaling pathways are a bridge between innate and adaptive immune response. IL-15 is part of the intestinal mucosal barrier, and functions to modulate gut homeostasis. IL-15 has pivotal roles in the control of development, proliferation and survival of both innate and adaptive immune cells. IL-15 becomes up-regulated in the inflamed tissue of intestinal inflammatory disease, such as IBD, Celiac Disease and related complications. Indeed, several studies have reported that IL-15 may participate to the pathogenesis of these diseases. Furthermore, although IL-15 seems to be responsible for inflammation and autoimmunity, it also may increase the immune response against cancer. For these reasons, we decided to study the intestinal mucosa as an 'immunological niche', in which immune response, inflammation and local homeostasis are modulated. Understanding the role of the IL-15/IL-15R system will provide a scientific basis for the development of new approaches that use IL-15 for immunotherapy of autoimmune diseases and malignancies. Indeed, a better understanding of the complexity of the mucosal immune system will contribute to the general understanding of immuno-pathology, which could lead to new therapeutical tools for widespread immuno-mediated diseases.

Expression of Toll-like receptors 2 and 9 in cells of dog jejunum and colon naturally infected with Leishmania infantum

BACKGROUND

Infection with parasite protozoa is a long-term health issue in tropical and subtropical regions throughout the world. The Toll-like receptor (TLR) signaling pathway is one of the first-responding defense systems against Leishmania. The aim of this study was to investigate the expression of TLR2 and TLR9 in jejunum and colon and its correlation with CD11c, CD11b, and CD14 receptors used as markers for dendritic cells and macrophages.

METHODS

Twenty four dogs infected with Leishmania infantum were used in this study. Cytometry was carried out in lamina propria cells from jejunum and colon using markers for TLR2, TLR9, CD11b, CD11c and CD14.

RESULTS

Cellular inflammatory exudate was diffuse in the mucosa and submucosa, predominately comprising mononuclear cells: plasma cells, macrophages, and lymphocytes. Despite the parasite load, microscopy showed no erosion was evident in the epithelial mucosa layers. The colon harbored more parasites than the jejunum. Flow cytometry revealed higher frequency of TLR2+ and CD11c+ dendritic cells in the colon than in the jejunum. Conversely, TLR9-expressing cells were more frequent in jejunum. Moreover, frequency of macrophages (CD11b+ and CD14+) expressing simultaneity TLR9 were lower in the colon than in jejunum, while CD11c+ cells predominated in the colon. Despite of the negative ELISA serum results, IL-10 and TNF-α were higher in jejunum than colon of infected animals. However, IL-4 was higher in colon than jejunum of infected animals. A higher expression these cytokines were demonstrated in infected dogs compared to uninfected dogs.

CONCLUSIONS

There was no correlation between clinical signs and pathological changes and immunological and parasitological findings in the gastrointestinal tract in canine visceral leishmaniasis. However, jejunum showed a lower parasite load with increased frequency and expression of CD11b, TLR9, CD14/CD11b/TLR9 receptors and IL-10 and TNF-α cytokines. Conversely, the colon showed a higher parasite load along with increased frequency and expression of TLR2, CD11c receptors, and IL-4 cytokine. Thus, Leishmania infantum is able to interfere in jejunum increased expression of TLR2, TLR9, CD11b, CD14, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α; and in colon increased expression of CD11c, TLR2, TLR9, CD11b, CD14 e, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α.

Differential gene expression profiling of porcine epithelial cells infected with three enterotoxigenic Escherichia coli strains

Background

Enterotoxigenic Escherichia coli (ETEC) is one of the most important pathogenic bacteria causing severe diarrhoea in human and pigs. In ETEC strains, the fimbrial types F4 and F18 are commonly found differently colonized within the small intestine and cause huge economic losses in the swine industry annually worldwide. To address the underlying mechanism, we performed a transcriptome study of porcine intestinal epithelial cells (IPEC-J2) with and without infection of three representative ETEC strains.

Results

A total 2443, 3493 and 867 differentially expressed genes were found in IPEC-J2 cells infected with F4ab ETEC (C_F4ab), with F4ac ETEC (C_F4ac) and with F18ac ETEC (C_F18ac) compared to the cells without infection (control), respectively. The number of differentially expressed genes between C_F4ab and C_F4ac, C_F4ab and C_F18ac, and C_F4ac and C_F18ac were 77, 1446 and 1629, respectively. The gene ontology and pathway analysis showed that the differentially expressed genes in C_F4abvs control are significantly involved in cell-cycle progress and amino acid metabolism, while the clustered terms of the differentially expressed genes in C_F4acvs control comprise immune, inflammation and wounding response and apoptosis as well as cell cycle progress and proteolysis. Differentially expressed genes between C_F18acvs control are mainly involved in cell-cycle progression and immune response. Furthermore, fundamental differences were observed in expression levels of immune-related genes among the three ETEC treatments, especially for the important pro-inflammatory molecules, including IL-6, IL-8, TNF-α, CCL20, CXCL2 etc.

Conclusions

The discovery in this study provides insights into the interaction of porcine intestinal epithelial cells with F4 ETECs and F18 ETEC, respectively. The genes induced by ETECs with F4 versus F18 fimbriae suggest why ETEC with F4 may be more virulent compared to F18 which seems to elicit milder effects.

Interactions between microbes and the gut epithelium

Gut microbes interact with the epithelium through cell surface components, fermentation products, and extracellular secreted proteins. Host-microbial interactions primarily involve TLRs (toll-like receptors) and NLR (nucleotide-binding oligomerization domain and leucine-rich repeat containing proteins). In a strain and dose-dependent manner, several probiotic strains directly alter tight junction protein expression and/or localization in gut epithelial cells through the release of secreted compounds. Interactions between gut microbes and intestinal epithelial and immune cells are necessary for the development and maintenance of intestinal homeostasis.

Luminal-applied flagellin is internalized by polarized intestinal epithelial cells and elicits immune responses via the TLR5 dependent mechanism

Bacteria release flagellin that elicits innate responses via Toll-like receptor 5 (TLR5). Here, we investigated the fate of apically administrated full length flagellin from virulent and avirulent bacteria, along with truncated recombinant flagellin proteins in intestinal epithelial cells and cellular responses. Flagellin was internalized by intestinal epithelial cell (IEC) monolayers of IEC-18. Additionally, apically applied flagellin was internalized by polarized human Caco-2BBe and T-84 cells in a TLR5 dependent mechanism. More, flagellin exposure did not affect the integrity of intestinal monolayers. With immunofluorescent staining, internalized flagellin was detected in both early endosomes as well as lysosomes. We found that apical exposure of polarized Caco-2BBe and T-84 to flagellin from purified Salmonella, Escherichia coli O83:H1 (isolate from Crohn's lesion) or avirulent E. coli K12 induced comparable levels of basolateral IL-8 secretion. A recombinant protein representing the conserved amino (N) and carboxyl (C) domains (D) of the flagellin protein (ND1/2ECHCD2/1) induced IL-8 secretion from IEC similar to levels elicited by full-length flagellins. However, a recombinant flagellin protein containing only the D3 hypervariable region elicited no IL-8 secretion in both cell lines compared to un-stimulated controls. Silencing or blocking TLR5 in Caco-2BBe cells resulted in a lack of flagellin internalization and decreased IL-8 secretion. Furthermore, apical exposure to flagellin stimulated transepithelial migration of neutrophils and dendritic cells. The novel findings in this study show that luminal-applied flagellin is internalized by normal IEC via TLR5 and co-localizes to endosomal and lysosomal compartments where it is likely degraded as flagellin was not detected on the basolateral side of IEC cultures.

A role for TLR4 in Clostridium difficile infection and the recognition of surface layer proteins

Clostridium difficile is the etiological agent of antibiotic-associated diarrhoea (AAD) and pseudomembranous colitis in humans. The role of the surface layer proteins (SLPs) in this disease has not yet been fully explored. The aim of this study was to investigate a role for SLPs in the recognition of C. difficile and the subsequent activation of the immune system. Bone marrow derived dendritic cells (DCs) exposed to SLPs were assessed for production of inflammatory cytokines, expression of cell surface markers and their ability to generate T helper (Th) cell responses. DCs isolated from C3H/HeN and C3H/HeJ mice were used in order to examine whether SLPs are recognised by TLR4. The role of TLR4 in infection was examined in TLR4-deficient mice. SLPs induced maturation of DCs characterised by production of IL-12, TNFα and IL-10 and expression of MHC class II, CD40, CD80 and CD86. Furthermore, SLP-activated DCs generated Th cells producing IFNγ and IL-17. SLPs were unable to activate DCs isolated from TLR4-mutant C3H/HeJ mice and failed to induce a subsequent Th cell response. TLR4⁻/⁻ and Myd88⁻/⁻, but not TRIF⁻/⁻ mice were more susceptible than wild-type mice to C. difficile infection. Furthermore, SLPs activated NFκB, but not IRF3, downstream of TLR4. Our results indicate that SLPs isolated from C. difficile can activate innate and adaptive immunity and that these effects are mediated by TLR4, with TLR4 having a functional role in experimental C. difficile infection. This suggests an important role for SLPs in the recognition of C. difficile by the immune system.

Wound healing of intestinal epithelial cells

The intestinal epithelial cells (IECs) form a selective permeability barrier separating luminal content from underlying tissues. Upon injury, the intestinal epithelium undergoes a wound healing process. Intestinal wound healing is dependent on the balance of three cellular events; restitution, proliferation, and differentiation of epithelial cells adjacent to the wounded area. Previous studies have shown that various regulatory peptides, including growth factors and cytokines, modulate intestinal epithelial wound healing. Recent studies have revealed that novel factors, which include toll-like receptors (TLRs), regulatory peptides, particular dietary factors, and some gastroprotective agents, also modulate intestinal epithelial wound repair. Among these factors, the activation of TLRs by commensal bacteria is suggested to play an essential role in the maintenance of gut homeostasis. Recent studies suggest that mutations and dysregulation of TLRs could be major contributing factors in the predisposition and perpetuation of inflammatory bowel disease. Additionally, studies have shown that specific signaling pathways are involved in IEC wound repair. In this review, we summarize the function of IECs, the process of intestinal epithelial wound healing, and the functions and mechanisms of the various factors that contribute to gut homeostasis and intestinal epithelial wound healing.

All-trans retinoic acid induces TLR-5 expression and cell differentiation and promotes flagellin-mediated cell functions in human THP-1 cells

Toll-like receptor 5 (TLR-5), which is expressed on macrophages and dendritic cells (DCs), is a crucial cell surface molecule that senses microbial-associated molecular patterns and initiates host innate immune responses upon infection with invaders that express flagellin. Little information is known about the induction factors and mechanisms of TLR-5 expression. In this study, we demonstrate that all-trans retinoic acid (ATRA) significantly up-regulated TLR-5 expression in human macrophage THP-1 cells by co-activating NF-κB and the RARα receptor and inducing the differentiation of CD11b(-)CD11c(-) THP-1 cells to CD11b(+)CD11c(low) cells. Furthermore, when stimulated with flagellin, ATRA-induced THP-1 cells expressed multiple cytokines, including TNF-α, IL-1beta, and IL-12p40, and several co-stimulatory molecules, such as CD40, CD80, CD86, and MHC class I and II. We also showed that when ATRA-induced THP-1 cells were stimulated with flagellin, the cells displayed an allostimulatory capacity rather than phagocytic activity. Taken together, our findings suggest that ATRA is a crucial immunostimulatory cofactor that induces the activation of macrophages and their subsequent differentiation into dendritic-like cells.