Immunologic regulation of toll-like receptors in gut epithelium

A study integrated metabolomics and network pharmacology to investigate the effects of Shicao in alleviating acute liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Shicao is the aerial part of Achillea alpina L., a common herb found mainly in Europe, Asia, and North America. Traditional Chinese medicine has a history of thousands of years and is widely used to treat various diseases.

AIM OF STUDY

To explore the hepatoprotective effects of Shicao on CCl4-induced acute liver injury.

METHODS

A rat model of acute liver injury was established and liver function indices were assessed to evaluate the protective effect of Shicao on the liver. Untargeted metabolomics of the serum and liver tissues was conducted using UPLC-Q-TOF/MS to identify differential metabolites related to acute liver injury. A network of metabolite-reaction-enzyme-gene constituents was constructed using network pharmacology. Hub targets and key components of the effect of Shicao on acute liver injury were screened from the network.

RESULTS

Compared to the model group, Shicao improved the degree of liver damage through the assessment of the liver index, ALT and AST levels, and hepatic pathology slices, demonstrating its hepatoprotective effect against acute liver injury in rats. 10 and 38 differential metabolites involved in acute liver injury were identified in serum and liver tissues, respectively. Most of these were regulated or restored following treatment with Shicao, which mainly consisted of bile acids, lipids, and nucleotides such as taurocholic acid, LysoPC (17:0), and adenosine diphosphate ribose. Through the network of metabolite-reaction-enzyme-gene-constituents, 10 key components and 5 hub genes, along with 7 crucial differential metabolites, were mainly involved in glycerophospholipid metabolism, purine metabolism, biosynthesis of unsaturated fatty acids, and primary bile acid biosynthesis, which may play important roles in the prevention of acute liver injury by Shicao.

CONCLUSION

This study revealed that Shicao had protective effects against CCl4-induced liver injury in rats. It was speculated that the ingredients of Shicao might be closely related to the hub targets, thereby regulating the levels of key metabolites, affecting inflammatory response and oxidative stress and attenuate the liver injury consequently. This study provides a basis for further investigation of its therapeutic potential and the mechanism of action.

Low n-6/n-3 PUFA ratio improves inflammation and myocardial ischemic reperfusion injury

This study investigated the potential effect of n-6/n-3 polyunsaturated fatty acids (PUFA) on inflammation and myocardial ischemic reperfusion injury (MIRI) in rats, together with the underlying protective mechanisms, and screen out most effective ratio of n-6/n-3 within limits. The rats with pre-infarct treatment were distributed among 5 groups according to the n-6/n-3 ratio (36:1; 1:1, 5:1, 10:1, 50:1); for the post-infarct treatment, the rats were distributed among 6 groups, including the control group (36:1) which was subjected to a sham procedure; the model group (36:1); and 4 test groups (n-6/n-3 ratio: 1:1, 5:1, 10:1, 50:1). All of the rats were fed a purple perilla seed oil and safflower oil-based fatty emulsion. The serum levels of monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α were determined using enzyme-linked immunosorbent assay. Staining with triphenyl tetrazolium chloride, hematoxylin and eosin, or Masson's trichrome was performed for histological examination. Cardiomyocyte apoptosis was examined by TUNEL assay. Western blotting was performed to examine the expression levels of apoptosis-related proteins and signaling pathway proteins. Our data indicate that in both the pre-infarct treatment and post-infarct treatment, low ratios of n-6/n-3 PUFAs significantly inhibited the levels of serum inflammatory factors, the infarct size of MIRI rats, number of cardiomyocytes undergoing apoptosis, and the expression levels of caspase-3, Bcl-2, and Bax in the MIRI group. Thus a low ratio of n-6/n-3 PUFAs ameliorates inflammation and myocardial ischemic reperfusion injury.

TLR4 Participates in the Inflammatory Response Induced by the AAF/II Fimbriae From Enteroaggregative Escherichia coli on Intestinal Epithelial Cells

Enteroaggregative Escherichia coli (EAEC) infections are one of the most frequent causes of persistent diarrhea in children, immunocompromised patients and travelers worldwide. The most prominent colonization factors of EAEC are aggregative adherence fimbriae (AAF). EAEC prototypical strain 042 harbors the AAF/II fimbriae variant, which mediates adhesion to intestinal epithelial cells and participates in the induction of an inflammatory response against this pathogen. However, the mechanism and the cell receptors implicated in eliciting this response have not been fully characterized. Since previous reports have shown that TLR4 recognize fimbriae from different pathogens, we evaluated the role of this receptor in the response elicited against EAEC by intestinal cells. Using a mutual antagonist against TLR2 and TLR4 (OxPAPC), we observed that blocking of these receptors significantly reduces the secretion of the inflammatory marker IL-8 in response to EAEC and AAF/II fimbrial extract in HT-29 cells. Using a TLR4-specific antagonist (TAK-242), we observed that the secretion of this cytokine was significantly reduced in HT-29 cells infected with EAEC or incubated with AAF/II fimbrial extract. We evaluated the participation of AAF/II fimbriae in the TLR4-mediated secretion of 38 cytokines, chemokines, and growth factors involved in inflammation. A reduction in the secretion of IL-8, GRO, and IL-4 was observed. Our results suggest that TLR4 participates in the secretion of several inflammation biomarkers in response to AAF/II fimbriae.

Molecular characterization and analysis of TLR-1 in rabbit tissues

The rabbit has great commercial importance as a source of meat and fur, as well as its uses as a laboratory animal for the production of antibodies, used to detect the presence or absence of disease and for research in infectious diseases and immunology. One of the most critical problems in immunology is to understand how the immune system detects the presence of infectious agents and disposes the invader without destroying the self-tissues. Genetic characterization of Toll-like receptors has established that innate immunity is a skillful system that detects invasion of microbial pathogens. Our work aimed to identify, clone and express the Oryctolagus cuniculus (rabbit) TLR-1 mRNA and its encoding protein. We cloned the complete mRNA sequence of Oryctolagus cuniculus TLR-1 and deposit it in the GenBank under accession number (KC349941), which has 2388 base pair and it encodes encode an open reading frame (ORF) translated into 796 amino acids mRNA and consist of 20 types of amino acids. The analysis of amino acid sequence revealed that the rabbit TLR-1 has a typical protein components belonging to the TLR family. Rabbit TLR-1 was expressed in a wide variety of rabbit tissues, which indicate an important role in immune system in different organs.

The effect of n-3/n-6 polyunsaturated fatty acids on acute reflux esophagitis in rats

BACKGROUND

Polyunsaturated fatty acids (PUFAs) play various roles in inflammation. However, the effect of PUFAs in the development of reflux esophagitis (RE) is unclear. This study is to investigate the potential effect of n-3/n-6 PUFAs on acute RE in rats along with the underlying protective mechanisms.

METHODS

Forty Sprague Dawley rats were randomly divided into four groups (n = 10 in each group). RE model was established by pyloric clip and section ligation. Fish oil- and soybean oil-based fatty emulsion (n-3 and n-6 groups), or normal saline (control and sham operation groups) was injected intraperitoneally 2 h prior to surgery and 24 h postoperatively (2 mL/kg, respectively). The expressions of interleukin (IL)-1β, IL-8, IL-6 and myeloid differentiation primary response gene 88 (MyD88) in esophageal tissues were evaluated by Western blot and immunohistochemistry after 72 h. The malondialdehyde (MDA) and superoxide dismutase (SOD) expression in the esophageal tissues were determined to assess the oxidative stress.

RESULTS

The mildest macroscopic/microscopic esophagitis was found in the n-3 group (P < 0.05). The expression of IL-1β, IL-8, IL-6 and MyD88 were increased in all RE groups, while the lowest and highest expression were found in n-3 and n-6 group, respectively (P < 0.05). The MDA levels were increased in all groups (P < 0.05), in an ascending trend from n-3, n-6 groups to control group. The lowest and highest SOD levels were found in the control and n-3 group, respectively (P < 0.05).

CONCLUSION

n-3 PUFAs may reduce acute RE in rats, which may be due to inhibition of the MyD88-NF-kB pathway and limit oxidative damage.

Antibiotic-Induced Depletion of Murine Microbiota Induces Mild Inflammation and Changes in Toll-Like Receptor Patterns and Intestinal Motility

We examine the impact of changes in microbiota induced by antibiotics on intestinal motility, gut inflammatory response, and the function and expression of toll-like receptors (TLRs). Alterations in mice intestinal microbiota were induced by antibiotics and evaluated by q-PCR and DGGE analysis. Macroscopic and microscopic assessments of the intestine were performed in control and antibiotic-treated mice. TLR expression was determined in the intestine by q-RT-PCR. Fecal parameter measurements, intestinal transit, and muscle contractility studies were performed to evaluate alterations in intestinal motility. Antibiotics reduced the total bacterial quantity 1000-fold, and diversity was highly affected by treatment. Mice with microbiota depletion had less Peyer's patches, enlarged ceca, and mild gut inflammation. Treatment with antibiotics increased the expression of TLR4, TLR5, and TLR9 in the ileum and TLR3, TLR4, TLR6, TLR7, and TLR8 in the colon, and it reduced the expression of TLR2, TLR3, and TLR6 in the ileum and TLR2 and TLR9 in the colon. Antibiotics decreased fecal output, delayed the whole gut and colonic transit, and reduced the spontaneous contractions and the response to acetylcholine (ACh) in the ileum and colon. Activation of TLR4 by lipopolysaccharide (LPS) reverted the reduction of the spontaneous contractions induced by antibiotics in the ileum. Activation of TLR4 by LPS and TLR5 by flagellin reduced the response to ACh in the ileum in control mice. Our results confirm the role of the microbiota in the regulation of TLRs expression and shed light on the microbiota connection to motor intestinal alterations.

Prebiotics and the health benefits of fiber: current regulatory status, future research, and goals

First defined in the mid-1990s, prebiotics, which alter the composition and activity of gastrointestinal (GI) microbiota to improve health and well-being, have generated scientific and consumer interest and regulatory debate. The Life Sciences Research Organization, Inc. (LSRO) held a workshop, Prebiotics and the Health Benefits of Fiber: Future Research and Goals, in February 2011 to assess the current state of the science and the international regulatory environment for prebiotics, identify research gaps, and create a strategy for future research. A developing body of evidence supports a role for prebiotics in reducing the risk and severity of GI infection and inflammation, including diarrhea, inflammatory bowel disease, and ulcerative colitis as well as bowel function disorders, including irritable bowel syndrome. Prebiotics also increase the bioavailability and uptake of minerals and data suggest that they reduce the risk of obesity by promoting satiety and weight loss. Additional research is needed to define the relationship between the consumption of different prebiotics and improvement of human health. New information derived from the characterization of the composition and function of different prebiotics as well as the interactions among and between gut microbiota and the human host would improve our understanding of the effects of prebiotics on health and disease and could assist in surmounting regulatory issues related to prebiotic use.

Global analysis of the eukaryotic pathways and networks regulated by Salmonella typhimurium in mouse intestinal infection in vivo

BACKGROUND

Acute enteritis caused by Salmonella is a public health concern. Salmonella infection is also known to increase the risk of inflammatory bowel diseases and cancer. Therefore, it is important to understand how Salmonella works in targeting eukaryotic pathways in intestinal infection. However, the global physiological function of Salmonella typhimurium in intestinal mucosa in vivo is unclear. In this study, a whole genome approach combined with bioinformatics assays was used to investigate the in vivo genetic responses of the mouse colon to Salmonella. We focused on the intestinal responses in the early stage (8 hours) and late stage (4 days) after Salmonella infection.

RESULTS

Of the 28,000 genes represented on the array, our analysis of mRNA expression in mouse colon mucosa showed that a total of 856 genes were expressed differentially at 8 hours post-infection. At 4 days post-infection, a total of 7558 genes were expressed differentially. 23 differentially expressed genes from the microarray data was further examined by real-time PCR. Ingenuity Pathways Analysis identified that the most significant pathway associated with the differentially expressed genes in 8 hours post-infection is oxidative phosphorylation, which targets the mitochondria. At the late stage of infection, a series of pathways associated with immune and inflammatory response, proliferation, and apoptosis were identified, whereas the oxidative phosphorylation was shut off. Histology analysis confirmed the biological role of Salmonella, which induced a physiological state of inflammation and proliferation in the colon mucosa through the regulation of multiple signaling pathways. Most of the metabolism-related pathways were targeted by down-regulated genes, and a general repression process of metabolic pathways was observed. Network analysis supported IFN-γ and TNF-α function as mediators of the immune/inflammatory response for host defense against pathogen.

CONCLUSION

Our study provides novel genome-wide transcriptional profiling data on the mouse colon mucosa's response to the Salmonella typhimurium infection. Building the pathways and networks of interactions between these genes help us to understand the complex interplay in the mice colon during Salmonella infection, and further provide new insights into the molecular cascade, which is mobilized to combat Salmonella-associated colon infection in vivo.

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.

Toll-like receptor 4 is protective against neonatal murine ischemia-reperfusion intestinal injury

PURPOSE

Premature infants receiving probiotics have a decreased incidence of necrotizing enterocolitis. This may be mediated by intestinal bacterial signaling via toll-like receptors (TLRs) 2 and 4 maintaining intestinal homeostasis. We hypothesized that TLRs 2 and 4 are protective against ischemia-reperfusion (I/R) intestinal injury.

METHODS

Two-week-old C57BL/6 wild-type (WT), B6.TLR2(-/-), B6.TLR4(-/-), B6.TLR2(-/-)4(-/-), and microbially reduced (antibiotic-treated) mice (MR) underwent 60 minutes of superior mesenteric artery occlusion (I) followed by 90 minutes of reperfusion (R). Small intestine was harvested for analysis of microscopic injury, apoptosis, and inflammatory gene expression using quantitative polymerase chain reaction.

RESULTS

After I/R, the median histologic injury scores of the B6.TLR4(-/-), B6.TLR2(-/-)4(-/-), and MR pups were higher than the WT or B6.TLR2(-/-) pups that corresponded with greater apoptosis based on terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick-end labeling and activated caspase-3 immunostaining. B6.TLR4(-/-), B6.TLR2(-/-)4(-/-), and MR also had elevated tissue innate immunity-associated chemokine and cytokine expression.

CONCLUSIONS

Neonatal mice deficient in TLR4, either alone or also deficient in TLR2, as well as those lacking a normal commensal intestinal microbiome are more susceptible to an I/R model of intestinal injury. These results may provide a mechanism for commensal bacterial-mediated protection, which may help to direct further studies to elucidate the mechanism of probiotic protection.

Immunomodulatory effects of Lactobacillus plantarum on human colon cancer cells

Probiotics, defined as live microbial food supplements which improve the health of the host, have obtained increasing medical importance. In the intestine they may prevent the overgrowth of pathogenic bacteria, increase the resistance of the gut to invasion by pathogens and ameliorate disease processes by inducting the secretion of soluble factors such as cytokines and antimicrobial beta-peptides. One important class of human antimicrobial peptides is the family of defensins. Human beta-defensin 2 (HBD-2) is a major inducible peptide which plays an important role in host defense and represents a link between innate and adaptive immune responses. This linkage is in part mediated through the recognition of conserved bacterial products or bacteria by Toll-like receptors (TLRs). The aim of this study was to investigate the effects of Lactobacillus plantarum on intestinal epithelial cells. We found that Caco-2 cells exposed to L. plantarum bacteria significantly induced HBD-2 mRNA expression and HBD-2 secretion in a dose- (16+/-1.4 pg/ml and 31.5+/-2.3 pg/ml at MOI 10 and 50, respectively) and time-dependent manner, but not HBD-3, compared to controls; in addition, when LPS was added to cells for 48 h, the interleukin (IL)-23 secretion (850+/-5.4 pg/ml) and IL-23 mRNA expression increased; while it was reduced when LPS was cocultured with L. plantarum (330+/-4.2 pg/ml). The L. plantarum-induced increase in HBD-2 expression is inhibited by anti-TLR-2 neutralizing antibodies, in the same way the pre-treatment with the anti-TLR-2 antibody inhibited the production of IL-23 induced by LPS in Caco-2 cells. The results of our study help to achieve a better understanding of how the intestinal epithelium participates in the innate immune response to commensal bacteria and pathogens in the gut.

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.

Toll-like receptors, transduction-effector pathways, and disease diversity: evidence of an immunobiological paradigm explaining all human illness?

Membrane-bound Toll-like receptors (TLRs) are frontline guardians in the mammalian innate immune system. They primarily function to recognize pathogen-associated molecular patterns (PAMPs) of invading microorganisms and on activation mount rapid, nonspecific innate responses and trigger sequential delayed specific adaptive cellular responses, which are mediated by complex signal transduction pathways involving adaptor molecules, costimulatory ligands and receptors, kinases, transcription factors, and modulated gene expression. Increasing evidence of multiple functionality and diversity suggests TLRs play critical roles in noninfective medical conditions such as cardiovascular, gastrointestinal, neurologic, musculoskeletal, obstetric, renal, liver, and dermatologic diseases, allergy, autoimmunity, and tissue regeneration. The significance of TLR heterogeneity underscores the possibility for establishing a universal immunobiological model to explain all human disease. Novel immunomodulatory therapies targeting specific or multiple TLRs may in the future offer new tools to combat or eradicate pathogenesis potentially transforming the landscape of current medical treatments.

Inulin and oligofructose: review of experimental data on immune modulation

Diet modulates immune functions in different ways and affects host resistance to infections. In addition to the essential nutrients in food, nonessential food constituents such as nondigestible carbohydrates also affect the immune system. First results from human intervention studies suggest that the intake of inulin (IN) and oligofructose (OF) has beneficial effects on the gut-associated lymphoid tissue. At the level of the systemic immune system, however, only minor effects have been observed in healthy adult human subjects. In contrast, data from studies with infants suggest that supplementation with a prebiotic mixture positively affects postnatal immune development and increases fecal secretory IgA. Animal studies confirm the observations from human trials and give more insight into the immune tissue- specific effects of IN/OF. A clear outcome of the animal studies is that the intestinal immune system and especially the immune cells associated with the Peyer's patches are responsive to a dietary supplement of IN/OF and/or their metabolites. The mechanisms of IN/OF include indirect effects such as a shift in the composition of the intestinal flora and the enhanced production of immunoregulatory SCFA and perhaps other bacterial metabolites. Few data suggest direct effects of IN/OF via carbohydrate receptors on intestinal epithelial cells and immune cells. In conclusion, prebiotic IN/OF clearly modulate immunological processes at the level of the gut-associated lymphoid tissue, which may be associated with significant health benefits in infants and patients with intestinal inflammatory diseases.

Activation of enteroendocrine cells via TLRs induces hormone, chemokine, and defensin secretion

Enteroendocrine cells are known primarily for their production of hormones that affect digestion, but they might also be implicated in sensing and neutralizing or expelling pathogens. We evaluate the expression of TLRs and the response to specific agonists in terms of cytokines, defensins, and hormones in enteroendocrine cells. The mouse enteroendocrine cell line STC-1 and C57BL/6 mice are used for in vitro and in vivo studies, respectively. The presence of TLR4, 5, and 9 is investigated by RT-PCR, Western blot, and immunofluorescence analyses. Activation of these receptors is studied evaluating keratinocyte-derived chemokine, defensins, and cholecystokinin production in response to their specific agonists. In this study, we show that the intestinal enteroendocrine cell line STC-1 expresses TLR4, 5, and 9 and releases cholecystokinin upon stimulation with the respective receptor agonists LPS, flagellin, and CpG-containing oligodeoxynucleotides. Release of keratinocyte-derived chemokine and beta-defensin 2 was also observed after stimulation of STC-1 cells with the three TLR agonists, but not with fatty acids. Consistent with these in vitro data, mice showed increased serum cholecystokinin levels after oral challenge with LPS, flagellin, or CpG oligodeoxynucleotides. In addition to their response to food stimuli, enteroendocrine cells sense the presence of bacterial Ags through TLRs and are involved in neutralizing intestinal bacteria by releasing chemokines and defensins, and maybe in removing them by releasing hormones such as cholecystokinin, which induces contraction of the muscular tunica, favoring the emptying of the distal small intestine.

Functional P2X7Receptor Polymorphisms (His155Tyr, Arg307Gln, Glu496Ala) in Patients with Crohn's Disease

Genetic factors contribute to inflammatory bowel diseases. Recently, the P2X(7) receptor was found to be a key player in caspase-1-mediated processing of the proinflammatory cytokines, interleukin-1beta and interleukin-18. We therefore aimed to determine whether the gain-of-function single nucleotide polymorphism (SNP) His155Tyr and the loss-of-function SNP Arg307Gln and Glu496Ala were associated with susceptibility to Crohn's disease (CD). For association analysis, 681 unrelated CD patients and 736 healthy controls were enrolled. Furthermore, 490 CD trios were included for segregation analysis. Genotyping was performed by the application of the TaqMan(R) MGB biallelic discrimination system. The Arg307Gln polymorphism revealed a borderline significant difference in genotype frequencies between CD patients and controls (P = 0.06) without implying any pathological significance because of low case numbers. Case-control statistics for the variants His155Tyr and Glu496Ala showed no association with CD phenotype (P = 0.19 and 0.99). Subsequent family-based transmission disequilibrium test did not prove an association of the investigated single-nucleotide polymorphisms with CD. In conclusion, the analysed intragenetic variants of the P2X(7) receptor may not be a susceptibility factor for CD.

Starch microparticles as vaccine adjuvant

The demand for new vaccine adjuvants is well documented. New purified antigens from parasites, bacterial or viral pathogens, as well as recombinant subunit antigens and synthetic peptides, are often inherently weak immunogens; therefore, they need some kind of adjuvant to help initiate an immune response. In addition, there are very few adjuvants using the potential of the mucosal immune system, which may play an important role in the defence against air- and food-borne infections. Starch is a natural biocompatible and biodegradable polymer that is suitable for the production of various particulate adjuvant formulations, which can induce mucosal as well as systemic immune responses. This review gives an account of the different starch adjuvants used in immunisation studies. In particular, the properties of polyacryl starch microparticles as an oral vaccine adjuvant that induce protective immune responses in mice challenge experiments are summarised. In addition, a diphtheria booster vaccine has been proposed to be used to proving the concept in man and the possibilities to design an efficient vaccine formulation for human use are discussed.

Identification and expression of Toll-like receptors 1-10 in selected bovine and ovine tissues

Members of the Toll-like receptor (TLR) family are vital to immune function through the sensing of pathogenic agents and initiation of an appropriate immune response. More specifically, tissue and cell specific TLR expression patterns have been correlated with the ability to respond to various pathogenic challenges. Bovine sequence exists for 4 of the 10 human TLR Reference Sequences and no ovine TLR sequence has been reported. The main goal of this study was to determine if homologues of human TLRs 1-10 exist within the cattle and sheep. Subsequent to this, quantitative real time PCR assays were to be developed to produce transcript expression profiles in cattle skin and sheep gut-associated lymphoid tissue, as these epithelial tissues are the primary sites of host/pathogen interactions for numerous pathogens. Our findings show that homologues of human TLRs 1-10 do indeed exist within both cattle and sheep, with respective bovine and ovine homologues sharing at least 95% nucleotide sequence identity and 83-90% identity to the corresponding human Reference Sequences. Conservation of the amino acid sequence between homologous ruminant and human TLRs ranged between 84 and 97%. Quantitative real time PCR (qPCR) assays confirmed expression of all 10 TLRs within ovine jejunum, Peyer's patch and mesenteric lymph nodes. While in bovine skin all TLRs apart from TLR6 were detected. The most abundant TLR transcripts within the ovine jejunum were TLRs 3, 5 and 6, while TLRs 6, 7 and 10 were abundant in both ovine Peyer's patch and mesenteric lymph node. In bovine skin TLRs 2 and 7 were most abundant. In all tissues tested TLR4 expression was at the lower limit of detection.

Inulin, oligofructose and immunomodulation

Diet is known to modulate immune functions in multiple ways and to affect host resistance to infections. Besides the essential nutrients, non-essential food constituents such as non-digestible carbohydrates may also have an impact on the immune system, especially in the area of the gut-associated lymphoid tissue (GALT). Recent data now provide first evidence that prebiotics such as inulin/oligofructose (IN/OF) modulate functions of the immune system. In animal studies IN/OF primarily activated immune cells in Peyer's patches including IL-10 production and natural killer (NK) cell cytotoxicity. Other immune functions modulated by IN/OF included the concentration of secretory IgA in ileum and caecum, splenic NK cell cytotoxicity as well as splenocyte cytokine production. In different tumour models, a lower incidence of tumours was observed, which in the case of colonic tumours was associated with enhanced NK cell cytotoxicity in the GALT. Few human studies so far have investigated the effects of IN/OF alone or in combination with other dietary supplements on immunocompetence. Supplementation of IN/OF resulted in minor changes of systemic immune functions such as decrease in phagocytic activity. No data are available on the effects of IN/OF on the GALT in man. The mechanisms of the reported effects of IN/OF on the immune system are currently investigated and include: (i) direct effects of lactic acid-producing bacteria or bacterial constituents on immune cells; (ii) the production of SCFA and binding to SCFA receptors on leucocytes. In conclusion, the current data suggest that IN/OF primarily modulate immune parameters in the GALT, but splenocytes are also activated by IN/OF. Human studies are needed to find out whether IN/OF have the potential to modulate systemic immunity in well-nourished individuals and to lower the risk of diseases such as colon cancer.

Defects in mucosal immunity leading to Crohn's disease

Crohn's disease (CD) is characterized by patchy transmural inflammation involving any part of the intestinal tract. Animal models have provided a great deal of insight into the pathogenesis of CD, but no animal model has recapitulated the full spectrum of manifestations witnessed in human disease. The defects in mucosal immunity in CD can be divided into those that involve the epithelial barrier, those that involve the innate immune response, and finally, defects in the adaptive immune response. Defects in the epithelial barrier in CD include an increase in intestinal permeability, increased adherence of bacteria, and decreased expression of defensins. Murine and human studies have demonstrated an increased expression of T-helper 1 (Th1) cytokines by lamina propria lymphocytes. This increased Th1 cytokine expression is driven by interleukin-12 (IL-12)/IL-23 and tumor necrosis factor-like 1A (TL1A) production by antigen-presenting cells, resulting in Tbet expression by CD4+ T cells. Another dimension of the inappropriate immune response in CD is T-cell and B-cell reactivity to luminal microbes. With the identification of the nucleotide-binding oligomerization domain 2 (NOD2) gene as a susceptibility gene, defects in the innate immune response are beginning to be explored. One may consider a model in which defective innate immune clearance of pathogens or commensal bacteria in CD leads to an inappropriate adaptive immune response to the commensal flora.

Beta-defensin-2 expression is regulated by TLR signaling in intestinal epithelial cells

The intestinal epithelium serves as a barrier to the intestinal flora. In response to pathogens, intestinal epithelial cells (IEC) secrete proinflammatory cytokines. To aid in defense against bacteria, IEC also secrete antimicrobial peptides, termed defensins. The aim of our studies was to understand the role of TLR signaling in regulation of beta-defensin expression by IEC. The effect of LPS and peptidoglycan on beta-defensin-2 expression was examined in IEC lines constitutively or transgenically expressing TLRs. Regulation of beta-defensin-2 was assessed using promoter-reporter constructs of the human beta-defensin-2 gene. LPS and peptidoglycan stimulated beta-defensin-2 promoter activation in a TLR4- and TLR2-dependent manner, respectively. A mutation in the NF-kappaB or AP-1 site within the beta-defensin-2 promoter abrogated this response. In addition, inhibition of Jun kinase prevents up-regulation of beta-defensin-2 protein expression in response to LPS. IEC respond to pathogen-associated molecular patterns with expression of the antimicrobial peptide beta-defensin-2. This mechanism may protect the intestinal epithelium from pathogen invasion and from potential invaders among the commensal flora.