Commensal gut bacteria: mechanisms of immune modulation

Specific prebiotics modulate gut microbiota and immune activation in HAART-naive HIV-infected adults: results of the "COPA" pilot randomized trial

Intestinal mucosal immune system is an early target for human immunodeficiency virus type 1 (HIV-1) infection, resulting in CD4(+) T-cell depletion, deterioration of gut lining, and fecal microbiota composition. We evaluated the effects of a prebiotic oligosaccharide mixture in highly active antiretroviral therapy (HAART)-naive HIV-1-infected adults. In a pilot double-blind, randomized, placebo-controlled study, 57 HAART-naive HIV-1-infected patients received a unique oligosaccharide mixture (15 or 30 g short chain galactooligosaccharides/long chain fructooligosaccharides/pectin hydrolysate-derived acidic oligosaccharides (scGOS/lcFOS/pAOS) daily) or a placebo for 12 weeks. Microbiota composition improved significantly with increased bifidobacteria, decreased Clostridium coccoides/Eubacterium rectale cluster, and decreased pathogenic Clostridium lituseburense/Clostridium histolyticum group levels upon prebiotic supplementation. In addition, a reduction of soluble CD14 (sCD14), activated CD4(+)/CD25(+) T cells, and significantly increased natural killer (NK) cell activity when compared with control group were seen in the treatment group. The results of this pilot trial highly significantly show that dietary supplementation with a prebiotic oligosaccharide mixture results in improvement of the gut microbiota composition, reduction of sCD14, CD4(+) T-cell activation (CD25), and improved NK cell activity in HAART-naive HIV-infected individuals.

Disparate effects of bacteria and Toll-like receptor-dependant bacterial ligand stimulation on immunoglobulin A transcytosis

BACKGROUND

Recent studies have indicated that epithelial cells of the gut and other mucosal surfaces play an important role in orchestrating host responses to luminal microbes. Intestinal epithelial cells also play an important role in the transport of dimeric secretory immunoglobulin A (IgA) through the polyimmunoglobulin receptor (pIgR). The end product is secretory IgA, which contains a cleaved portion of the pIgR called secretory component. Transcytosis of dIgA may be responsive to various stimuli. We studied the effect of gram-negative (G-) or gram-positive (G+) and Toll-like receptor (TLR) bacterial ligand pathways on IgA transcytosis in vitro.

METHODS

Polarized HT-29 cells, a human intestinal epithelial cell line, were grown to confluence ion a two-chamber cell culture system. Rat dIgA was added to the basal chamber of HT-29 cell monolayers and cells and then stimulated with heat-killed Escherichia coli (ΔE. coli), LPS (TLR-4 pathway ligand), heat-killed Staphylococcus aureus (ΔS. aureus), or peptidoglycan (TLR-2 pathway ligand). IgA transcytosis was determined by ELISA. The pIgR expression was quantitated by flow cytometry and Western blot. HT-29 cell monolayer integrity was monitored by serial measurement of transepithelial electrical resistance.

RESULTS

Transcytosis was stimulated by either ΔE. coli or LPS. This was in part due to upregulation of pIgR expression and augmented intracellular trafficking of dIgA-pIgR complexes.

CONCLUSION

The disparate effects between different bacteria and TLR-4 versus TLR-2 pathways may have implications in host responses at mucosal surfaces.

NF-κB and mucosal homeostasis

NF-κB is well characterized as a primary mediator of inflammatory responses during infection and immune reactions, but it has recently become evident that NF-κB also mediates a potent cytoprotective, homeostatic function under basal conditions. This role is especially evident in the mammalian intestine, which is challenged not only with a range of microbial pathogens, but is also in constant contact with potent proinflammatory commensal bacteria and their products. Present data lead to the overall conclusion that antiapoptotic actions of NF-κB in intestinal epithelial cells dominate tissue responses to many acute inflammatory and injurious challenges, whereas proinflammatory and cell survival functions of NF-κB in macrophages and T cells govern chronic intestinal inflammation. This review focuses on the protective and homeostatic functions of NF-κB, and the importance of NF-κB in determining host-microbe interactions in the intestinal tract.

Modulation of Mucosal Immune Response, Tolerance, and Proliferation in Mice Colonized by the Mucin-Degrader Akkermansia muciniphila

Epithelial cells of the mammalian intestine are covered with a mucus layer that prevents direct contact with intestinal microbes but also constitutes a substrate for mucus-degrading bacteria. To study the effect of mucus degradation on the host response, germ-free mice were colonized with Akkermansia muciniphila. This anaerobic bacterium belonging to the Verrucomicrobia is specialized in the degradation of mucin, the glycoprotein present in mucus, and found in high numbers in the intestinal tract of human and other mammalian species. Efficient colonization of A. muciniphila was observed with highest numbers in the cecum, where most mucin is produced. In contrast, following colonization by Lactobacillus plantarum, a facultative anaerobe belonging to the Firmicutes that ferments carbohydrates, similar cell-numbers were found at all intestinal sites. Whereas A. muciniphila was located closely associated with the intestinal cells, L. plantarum was exclusively found in the lumen. The global transcriptional host response was determined in intestinal biopsies and revealed a consistent, site-specific, and unique modulation of about 750 genes in mice colonized by A. muciniphila and over 1500 genes after colonization by L. plantarum. Pathway reconstructions showed that colonization by A. muciniphila altered mucosal gene expression profiles toward increased expression of genes involved in immune responses and cell fate determination, while colonization by L. plantarum led to up-regulation of lipid metabolism. These indicate that the colonizers induce host responses that are specific per intestinal location. In conclusion, we propose that A. muciniphila modulates pathways involved in establishing homeostasis for basal metabolism and immune tolerance toward commensal microbiota.

In vitro culture conditions for maintaining a complex population of human gastrointestinal tract microbiota

A stable intestinal microbiota is important in maintaining human physiology and health. Although there have been a number of studies using in vitro and in vivo approaches to determine the impact of diet and xenobiotics on intestinal microbiota, there is no consensus for the best in vitro culture conditions for growth of the human gastrointestinal microbiota. To investigate the dynamics and activities of intestinal microbiota, it is important for the culture conditions to support the growth of a wide range of intestinal bacteria and maintain a complex microbial community representative of the human gastrointestinal tract. Here, we compared the bacterial community in three culture media: brain heart infusion broth and high- and low-carbohydrate medium with different growth supplements. The bacterial community was analyzed using denaturing gradient gel electrophoresis (DGGE), pyrosequencing and real-time PCR. Based on the molecular analysis, this study indicated that the 3% fecal inoculum in low-concentration carbohydrate medium with 1% autoclaved fecal supernatant provided enhanced growth conditions to conduct in vitro studies representative of the human intestinal microbiota.

Rectal administration of Lactobacillus casei DG modifies flora composition and Toll-like receptor expression in colonic mucosa of patients with mild ulcerative colitis

BACKGROUND

An imbalance in gut microbiota seems to contribute to the development of chronic inflammatory disorders of the gastrointestinal tract, such as ulcerative colitis (UC). Although it has been suggested that probiotic supplementation is an effective approach to colitis, its effects on intestinal flora and on mucosal cytokine balance have never been explored.

AIM

To evaluate the effect of Lactobacillus casei (L. casei) DG, a probiotic strain, on colonic-associated microbiota, mucosal cytokine balance, and toll-like receptor (TLR) expression.

METHODS

Twenty-six patients with mild left-sided UC were randomly allocated to one of three groups for an 8-week treatment period: the first group of 7 patients received oral 5-aminosalicylic acid (5-ASA) alone, the second group of 8 patients received oral 5-ASA plus oral L. casei DG, and the third group of 11 patients received oral 5-ASA and rectal L. casei DG. Biopsies were collected from the sigmoid region to culture mucosal-associated microbes and to assess cytokine and TLR messenger RNA (mRNA) levels by quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

5-ASA alone or together with oral L. casei DG failed to affect colonic flora and TLR expression in a significant manner, but when coupled with rectally administered L. casei DG, it modified colonic microbiota by increasing Lactobacillus spp. and reducing Enterobacteriaceae. It also significantly reduced TLR-4 and interleukin (IL)-1β mRNA levels and significantly increased mucosal IL-10.

CONCLUSIONS

Manipulation of mucosal microbiota by L. casei DG and its effects on the mucosal immune system seem to be required to mediate the beneficial activities of probiotics in UC patients.

Altered host-microbe interaction in HIV: a target for intervention with pro- and prebiotics

The intestinal immune system is severely affected by HIV and circulating microbial products from the intestinal tract that provide an ongoing source of systemic inflammation and concomitant viral replication. In addition, HIV-infected individuals can have a deregulated immune response that may hamper the anti-viral capacity of the host. Various probiotic organisms and prebiotic agents have been shown to enhance intestinal epithelial barrier functions, reduce inflammation, and support effective Th-1 responses. As these characteristics may benefit HIV patients, this review aims to provide a theoretical framework for the development of probiotic and prebiotic interventions specifically for this population.

Epithelial microRNAs regulate gut mucosal immunity via epithelium-T cell crosstalk

Colonic homeostasis entails epithelium-lymphocyte cooperation, yet many participants in this process are unknown. We show here that epithelial microRNAs mediate the mucosa-immune system crosstalk necessary for mounting protective T helper type 2 (T(H)2) responses. Abolishing the induction of microRNA by gut-specific deletion of Dicer1 (Dicer1(Δgut)), which encodes an enzyme involved in microRNA biogenesis, deprived goblet cells of RELMβ, a key T(H)2 antiparasitic cytokine; this predisposed the host to parasite infection. Infection of Dicer1(Δgut) mice with helminths favored a futile T(H)1 response with hallmarks of inflammatory bowel disease. Interleukin 13 (IL-13) induced the microRNA miR-375, which regulates the expression of TSLP, a T(H)2-facilitating epithelial cytokine; this indicated a T(H)2-amplification loop. We found that miR-375 was required for RELMβ expression in vivo; miR-375-deficient mice had significantly less intestinal RELMβ, which possibly explains the greater susceptibility of Dicer1(Δgut) mice to parasites. Our findings indicate that epithelial microRNAs are key regulators of gut homeostasis and mucosal immunity.

Host-bacterial symbiosis in health and disease

All animals live in symbiosis. Shaped by eons of co-evolution, host-bacterial associations have developed into prosperous relationships creating mechanisms for mutual benefits to both microbe and host. No better example exists in biology than the astounding numbers of bacteria harbored by the lower gastrointestinal tract of mammals. The mammalian gut represents a complex ecosystem consisting of an extraordinary number of resident commensal bacteria existing in homeostasis with the host's immune system. Most impressive about this relationship may be the concept that the host not only tolerates, but has evolved to require colonization by beneficial microorganisms, known as commensals, for various aspects of immune development and function. The microbiota provides critical signals that promote maturation of immune cells and tissues, leading to protection from infections by pathogens. Gut bacteria also appear to contribute to non-infectious immune disorders such as inflammatory bowel disease and autoimmunity. How the microbiota influences host immune responses is an active area of research with important implications for human health. This review synthesizes emerging findings and concepts that describe the mutualism between the microbiota and mammals, specifically emphasizing the role of gut bacteria in shaping an immune response that mediates the balance between health and disease. Unlocking how beneficial bacteria affect the development of the immune system may lead to novel and natural therapies based on harnessing the immunomodulatory properties of the microbiota.

RIG-I/MDA5/MAVS are required to signal a protective IFN response in rotavirus-infected intestinal epithelium

Rotavirus is a dsRNA virus that infects epithelial cells that line the surface of the small intestine. It causes severe diarrheal illness in children and ∼500,000 deaths per year worldwide. We studied the mechanisms by which intestinal epithelial cells (IECs) sense rotavirus infection and signal IFN-β production, and investigated the importance of IFN-β production by IECs for controlling rotavirus production by intestinal epithelium and virus excretion in the feces. In contrast with most RNA viruses, which interact with either retinoic acid-inducible gene I (RIG-I) or melanoma differentiation-associated gene 5 (MDA5) inside cells, rotavirus was sensed by both RIG-I and MDA5, alone and in combination. Rotavirus did not signal IFN-β through either of the dsRNA sensors TLR3 or dsRNA-activated protein kinase (PKR). Silencing RIG-I or MDA5, or their common adaptor protein mitochondrial antiviral signaling protein (MAVS), significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Overexpression of laboratory of genetics and physiology 2, a RIG-I-like receptor that interacts with viral RNA but lacks the caspase activation and recruitment domains required for signaling through MAVS, significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Rotavirus-infected mice lacking MAVS, but not those lacking TLR3, TRIF, or PKR, produced significantly less IFN-β and increased amounts of virus in the intestinal epithelium, and shed increased quantities of virus in the feces. We conclude that RIG-I or MDA5 signaling through MAVS is required for the activation of IFN-β production by rotavirus-infected IECs and has a functionally important role in determining the magnitude of rotavirus replication in the intestinal epithelium.

Web of ecological interactions in an experimental gut microbiota

The dynamics of all ecosystems are dictated by intrinsic, density-dependent mechanisms and by density-independent environmental forcing. In spite of the importance of the gastrointestinal microbiota in health and disease, the ecology of this system remains largely unknown. Here, we take an ecological approach to gut microbial community analysis, with statistical modelling of time series data from chemostats. This approach removes effects of host forcing, allowing us to describe a network of intrinsic interactions determining the dynamic structure of an experimental gut microbiota. Surprisingly, the main colonization pattern in this simplified model system resembled that of the human infant gut, suggesting a potentially important role of density-dependent interactions in the early gut microbiota. Knowledge of ecological structures in microbial systems may provide us with a means of controlling such systems by modifying the strength and nature of interactions among microbes and between the microbes and their environment.

Prebiotic evaluation of cocoa-derived flavanols in healthy humans by using a randomized, controlled, double-blind, crossover intervention study

BACKGROUND

The absorption of cocoa flavanols in the small intestine is limited, and the majority of the flavanols reach the large intestine where they may be metabolized by resident microbiota.

OBJECTIVE

We assessed the prebiotic potential of cocoa flavanols in a randomized, double-blind, crossover, controlled intervention study.

DESIGN

Twenty-two healthy human volunteers were randomly assigned to either a high-cocoa flavanol (HCF) group (494 mg cocoa flavanols/d) or a low-cocoa flavanol (LCF) group (23 mg cocoa flavanols/d) for 4 wk. This was followed by a 4-wk washout period before volunteers crossed to the alternant arm. Fecal samples were recovered before and after each intervention, and bacterial numbers were measured by fluorescence in situ hybridization. A number of other biochemical and physiologic markers were measured.

RESULTS

Compared with the consumption of the LCF drink, the daily consumption of the HCF drink for 4 wk significantly increased the bifidobacterial (P < 0.01) and lactobacilli (P < 0.001) populations but significantly decreased clostridia counts (P < 0.001). These microbial changes were paralleled by significant reductions in plasma triacylglycerol (P < 0.05) and C-reactive protein (P < 0.05) concentrations. Furthermore, changes in C-reactive protein concentrations were linked to changes in lactobacilli counts (P < 0.05, R(2) = -0.33 for the model). These in vivo changes were closely paralleled by cocoa flavanol-induced bacterial changes in mixed-batch culture experiments.

CONCLUSION

This study shows, for the first time to our knowledge, that consumption of cocoa flavanols can significantly affect the growth of select gut microflora in humans, which suggests the potential prebiotic benefits associated with the dietary inclusion of flavanol-rich foods. This trial was registered at clinicaltrials.gov as NCT01091922.

Developmental profiles of mucosal immunity in pre-school children

This study investigated the effect of attending pre-school on mucosal immunity. Children 3.5 to 5 years of age who attended pre-school were observed for a 10 month period. Demographic information was collected on previous childcare experiences, the home environment and clinical information relating to the child and the family. A daily illness log was kept for each child. A multivariate longitudinal analysis of the relation between immunoglobulins in saliva and age, gender, childcare experience, pre-school exposure, number of siblings, environmental tobacco smoke (ETS), atopy and hospitalisation was conducted. There was a positive association of higher IgA levels with the winter season and with children being older than 4 years (P < .001), having attended childcare prior to commencing pre-school (P < .05), and having been exposed to ETS at home (P < .05). Lower IgA levels were associated with being atopic (P < .05). Higher IgG levels were associated with exposure to ETS (P < .001), while lower levels were associated to having atopy. Higher IgM levels were associated with previous childcare experience (P < .01) whilst having been hospitalised was associated with having low salivary IgM levels (P < .01). Lagged analyses demonstrated that immunological parameters were affected by the number of respiratory infections in the preceding 2 months.

Toll-like receptors: a novel target for therapeutic intervention in intestinal and hepatic ischemia-reperfusion injury?

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are transmembrane proteins that act mainly as sensors of microbes, orchestrating an organism's defense against infections, while they sense also host tissue injury by recognizing products of dying cells. Ischemia-reperfusion injury (IRI) represents one of these tissue damage states in which TLR-mediated mechanisms might be implicated.

AREAS COVERED IN THIS REVIEW

The most recent data on TLR signaling and the latest knowledge regarding the involvement of TLRs in the pathogenesis and progression of intestinal and hepatic IRI are presented. The potential effectiveness of TLR-modulating therapy in intestinal and liver IRI is also analyzed.

WHAT THE READER WILL GAIN

A comprehensive summary of the data suggesting TLR involvement in intestinal and hepatic IRI. Knowledge required for developing TLR modulation strategies against intestinal and hepatic IRI.

TAKE HOME MESSAGE

TLRS play a significant role in both intestinal and hepatic IRI pathophysiology. Better understanding of TLR involvement in such processes may enable the invention of novel TLR-based therapies for IRI in the intestine and liver.

Protein glycosylation--an evolutionary crossroad between genes and environment

The majority of molecular processes in higher organisms are performed by various proteins and are thus determined by genes that encode these proteins. However, a significant structural component of at least half of all cellular proteins is not a polypeptide encoded by a single gene, but an oligosaccharide (glycan) synthesized by a network of proteins, resulting from the expression of hundreds of different genes. Relationships between hundreds of individual proteins that participate in glycan biosynthesis are very complex which enables the influence of environmental factors on the final structure of glycans, either by direct effects on individual enzymatic processes, or by induction of epigenetic changes that modify gene expression patterns. Until recently, the complexity of glycan structures prevented large scale studies of protein glycosylation, but recent advances in both glycan analysis and genotyping technologies, enabled the first insights into the intricate field of complex genetics of protein glycosylation. Mutations which inactivate genes involved in the synthesis of common N-glycan precursors are embryonically lethal. However, mutations in genes involved in modifications of glycan antennas are common and apparently contribute largely to individual phenotypic variations that exist in humans and other higher organisms. Some of these variations can be recognized as specific glyco-phenotypes that might represent specific evolutionary advantages or disadvantages. They are however, amenable to environmental influences and are thus less pre-determined than classical Mendelian mutations.

The role of the gut mucosal immunity in the development of tolerance against allergy to food

PURPOSE OF REVIEW

To provide an overview on the role of gut mucosal immunity in the development of tolerance against allergy to food.

RECENT FINDINGS

The gastrointestinal tract, through innate and specific immunologic factors, acts as a defense against ingested antigens. In addition to the mucous membrane integrity and digestion, numerous specific immunologic cells and mediators orchestrate such defensive mechanisms. In case of food antigens, the outcome is usually in favor of tolerance. Defects in that barrier, however, can lead to the development of aberrant immunologic responses, including hypersensitivity reactions.

SUMMARY

The prevailing evidence is that healthy mucosal immunity plus appropriate feeding regimen during early infancy are in favor of food tolerance. However, in addition to genetic predisposition, development of allergy is facilitated by defects in the gut barrier (immune or nonimmune) and the food allergen load.

Inverse association between Helicobacter pylori infection and allergic rhinitis in young Japanese

BACKGROUND AND AIM

The prevalence of allergic disorders, including asthma, atopic dermatitis, and allergic rhinitis has been increasing, and the prevalence of Helicobacter pylori (H. pylori) infection has been decreasing. Chronic bacterial infection during childhood is reported to protect the development of allergic diseases. The aim of the present study was to identify whether H. pylori infection influences the prevalence of allergic rhinitis, which has become a serious social problem, especially in the developed countries.

METHODS

We initially investigated the association between the prevalence of H. pylori and pollinosis symptoms in 97 healthy volunteers. We had investigated the association between the serum H. pylori-immunoglobulin (Ig) G antibodies and specific IgE antibodies for pollen, mites, and house dust in 211 consecutive patients.

RESULTS

There were 52.2% (36/69) of H. pylori-negative volunteers with allergic symptoms, which was significantly higher than H. pylori-positive volunteers (14.3%, 4/28, P < 0.05). The risk of pollinosis symptoms by H. pylori infection was 0.148 (95% confidence interval): 0.046-0.475, P < 0.05). The prevalence of H. pylori infection increased according to age, whereas that of specific IgE-positive patients gradually decreased. Among the IgE-positive patients, the prevalence of H. pylori-negative patients was significantly higher than H. pylori-positive patients who were younger in age (P < 0.05).

CONCLUSION

H. pylori infection decreased the pollinosis effects, especially among the younger volunteers. However, the prevalence of pollinosis in patients who were 50 years or older were almost same between H. pylori-positive and H. pylori-negative patients; therefore, the recent increase of pollinosis might relate to not only H. pylori infection, but also change in social environment.

Commensal microflora induce host defense and decrease bacterial translocation in burn mice through toll-like receptor 4

Background

Major burn is associated with decreased gut barrier function and increased bacterial translocation (BT). This study is to investigate whether commensal microflora induce host defense and decrease BT in burn mice.

Methods

First, we treated Wild type (WT) mice with antibiotics in drinking water for 4 weeks to deplete gut commensal microflora. At week 3, drinking water was supplemented with lipopolysaccharide (LPS); a ligand for TLR4, to trigger TLRs in gut. The intestinal permeability, glutathione level, NF-κB DNA-binding activity, TLR4 expression of intestinal mucosa, BT to mesenteric lymph nodes (MLNs), and bacterial killing activity of peritoneal cells were measured after thermal injury. Second, lung of animals were harvested for MPO activity and TNFα mRNA expression assay. Third, WT animals were treated with oral antibiotics with or without LPS supplement after burn. At 48 hr after burn, TLR4 expression of intestinal mucosa and bacterial killing activity of cells were examined. Finally, bacterial killing activity and BT to MLNs after thermal injury in C3H/HeJ (TLR4 mutant) mice were measured.

Results

Burn induced BT to MLNs in WT mice. Commensal depletion decreased TLR4 expression as well as NF-κB activation of intestine, myeloperoxidase (MPO) activity as well as TNFα expression of lung, and bacterial killing activity of peritoneal cells. Oral LPS supplement markedly reduced 81% of burn-induced BT and increased TLR4 expression, MPO activity of lung, as well as bacterial killing activity of peritoneal cells. LPS supplement did not change BT or bacterial killing activity in C3H/HeJ mice.

Conclusions

Collectively, commensal microflora induce TLR4 expression of intestine and bacterial killing activity of inflammatory cells in burn. TLR4 ligand increases bacterial killing activity and decreases burn-induced BT. Taken together with the abolition of LPS effect in TLR4 mutant mice, we conclude that commensal microflora induce host defense and decrease bacterial translocation in burn mice through toll-like receptor 4.

Chemical modulators of the innate immune response alter gypsy moth larval susceptibility to Bacillus thuringiensis

Background

The gut comprises an essential barrier that protects both invertebrate and vertebrate animals from invasion by microorganisms. Disruption of the balanced relationship between indigenous gut microbiota and their host can result in gut bacteria eliciting host responses similar to those caused by invasive pathogens. For example, ingestion of Bacillus thuringiensis by larvae of some species of susceptible Lepidoptera can result in normally benign enteric bacteria exerting pathogenic effects.

Results

We explored the potential role of the insect immune response in mortality caused by B. thuringiensis in conjunction with gut bacteria. Two lines of evidence support such a role. First, ingestion of B. thuringiensis by gypsy moth larvae led to the depletion of their hemocytes. Second, pharmacological agents that are known to modulate innate immune responses of invertebrates and vertebrates altered larval mortality induced by B. thuringiensis. Specifically, Gram-negative peptidoglycan pre-treated with lysozyme accelerated B. thuringiensis-induced killing of larvae previously made less susceptible due to treatment with antibiotics. Conversely, several inhibitors of the innate immune response (eicosanoid inhibitors and antioxidants) increased the host's survival time following ingestion of B. thuringiensis.

Conclusions

This study demonstrates that B. thuringiensis infection provokes changes in the cellular immune response of gypsy moth larvae. The effects of chemicals known to modulate the innate immune response of many invertebrates and vertebrates, including Lepidoptera, also indicate a role of this response in B. thuringiensis killing. Interactions among B. thuringiensis toxin, enteric bacteria, and aspects of the gypsy moth immune response may provide a novel model to decipher mechanisms of sepsis associated with bacteria of gut origin.

Bacteriocin as weapons in the marine animal-associated bacteria warfare: inventory and potential applications as an aquaculture probiotic

As the association of marine animals with bacteria has become more commonly recognized, researchers have increasingly questioned whether these animals actually produce many of the bioactive compounds originally isolated from them. Bacteriocins, ribosomally synthesized antibiotic peptides, constitute one of the most potent weapons to fight against pathogen infections. Indeed, bacteriocinogenic bacteria may prevent pathogen dissemination by occupying the same ecological niche. Bacteriocinogenic strains associated with marine animals are a relevant source for isolation of probiotics. This review draws up an inventory of the marine bacteriocinogenic strains isolated from animal-associated microbial communities, known to date. Bacteriocin-like inhibitory substances (BLIS) and fully-characterized bacteriocins are described. Finally, their applications as probiotics in aquaculture are discussed.

Alcohol, inflammation, and gut-liver-brain interactions in tissue damage and disease development

Chronic inflammation is often associated with alcohol-related medical conditions. The key inducer of such inflammation, and also the best understood, is gut microflora-derived lipopolysaccharide (LPS). Alcohol can significantly increase the translocation of LPS from the gut. In healthy individuals, the adverse effects of LPS are kept in check by the actions and interactions of multiple organs. The liver plays a central role in detoxifying LPS and producing a balanced cytokine milieu. The central nervous system contributes to anti-inflammatory regulation through neuroimmunoendocrine actions. Chronic alcohol use impairs not only gut and liver functions, but also multi-organ interactions, leading to persistent systemic inflammation and ultimately, to organ damage. The study of these interactions may provide potential new targets for therapeutic intervention.

[Inflammatory bowel diseases and enteric microbiota]

Intestinal mucosal layers are colonized by a complex microbiota that provides beneficial effects under normal physiological conditions, but is capable of contributing to chronic inflammatory disease such as inflammatory bowel disease (IBD) in susceptible individuals. Studies have shown that the enteric microbiota may drive the development of the gut immune system and can induce immune homeostasis as well as contribute to the development of IBD although the precise etiology is still unknown. Therefore, intestinal microbes seem to play a key role in the disease pathogenesis. Especially, dysbiosis, which is a shift in the composition of enteric microbiota to a nonphysiologic composition, is associated with one or more defects in mucosal immune functions, including microbe recognition, barrier function, intercellular communication, and anti-microbial effector mechanisms. This review focuses on the impact of enteric microbiota on the development and perpetuation of IBD. In addition, interactions with enteric bacteria and mucosal cells, including intestinal epithelial cells, dendritic cells, and T cells, to induce immune responses at mucosal surfaces have been discussed in the point of IBD pathogenesis. Further extension of the knowledge of enteric microbiota may lead to insights on the pathogenesis and new therapeutic strategies for IBD.

Probiotics and prebiotics in atopic dermatitis: review of the theoretical background and clinical evidence

The prevalence of atopic dermatitis (AD) has risen over the past decades, especially in western societies. According to the revised hygiene hypothesis this increase is caused by a changed intestinal colonization pattern during infancy, which has an impact on the immune system. Manipulating the intestinal microflora with pro-, pre- or synbiotics is an innovative way to prevent or treat AD. This review provides an overview of the theoretical basis for using probiotics and prebiotics in AD and presents the current evidence from randomized controlled trials (RCTs) regarding prevention and treatment of AD and food allergy in children with pro-, pre- and synbiotics. Seven RCTs on prevention and 12 RCTs on treatment were found by searching the Pubmed, Embase and Cochrane databases. Results of these trials are conflicting. In conclusion, at this moment there is not enough evidence to support the use of pro-, pre- or synbiotics for prevention or treatment of AD in children in clinical practice.

Curcumin induces the tolerogenic dendritic cell that promotes differentiation of intestine-protective regulatory T cells

The gut is home to a large number of Treg, with both CD4(+) CD25(+) Treg and bacterial antigen-specific Tr1 cells present in normal mouse intestinal lamina propria. It has been shown recently that intestinal mucosal DC are able to induce Foxp3(+) Treg through production of TGF-beta plus retinoic acid (RA). However, the factors instructing DC toward this mucosal phenotype are currently unknown. Curcumin has been shown to possess a number of biologic activities including the inhibition of NF-kappaB signaling. We asked whether curcumin could modulate DC to be tolerogenic whose function could mimic mucosal DC. We report here that curcumin modulated BM-derived DC to express ALDH1a and IL-10. These curcumin-treated DC induced differentiation of naïve CD4(+) T cells into Treg resembling Treg in the intestine, including both CD4(+)CD25(+) Foxp3(+) Treg and IL-10-producing Tr1 cells. Such Treg induction required IL-10, TGF-beta and retinoic acid produced by curcumin-modulated DC. Cell contact as well as IL-10 and TGF-beta production were involved in the function of such induced Treg. More importantly, these Treg inhibited antigen-specific T-cell activation in vitro and inhibited colitis due to antigen-specific pathogenic T cells in vivo.

The K5 capsule of Escherichia coli strain Nissle 1917 is important in stimulating expression of Toll-like receptor 5, CD14, MyD88, and TRIF together with the induction of interleukin-8 expression via the mitogen-activated protein kinase pathway in epithelial cells

Escherichia coli strain Nissle 1917, which has been widely used as a probiotic for the treatment of inflammatory bowel disorders, expresses a K5 capsule, the expression of which is often associated with extraintestinal and urinary tract isolates of E. coli. Previously, it had been shown that the expression of a K5 capsule by Nissle 1917 was important in mediating interactions with epithelial cells and the extent of chemokine expression. In this paper, we show that infection with Nissle 1917 induces expression of Toll-like receptor 4 (TLR4) and TLR5 in Caco-2 cells and that maximal induction of TLR5 required the K5 capsule. In addition, purified K5 polysaccharide was capable of inducing expression of TLR5 and mCD14 and potentiated the activity of both TLR4 and TLR5 agonists to increase the proinflammatory response. Infection with Nissle 1917 also increased the expression of the adaptor molecules MyD88 and TRIF, which was K5 capsule dependent. By Western blot analysis, it was possible to show that induction of interleukin-8 by Nissle 1917 was predominantly through the mitogen-activated protein (MAP) kinase pathway and that expression of the K5 capsule was important for activation of the MAP kinase pathway. This paper provides new information on the function of the K5 capsule in mediating interactions between Nissle 1917 and epithelial cells and the mechanisms that underlie the probiotic properties of Nissle 1917.

A novel probiotic mixture exerts a therapeutic effect on experimental autoimmune encephalomyelitis mediated by IL-10 producing regulatory T cells

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system (CNS). One potential therapeutic strategy for MS is to induce regulatory cells that mediate immunological tolerance. Probiotics, including lactobacilli, are known to induce immunomodulatory activity with promising effects in inflammatory diseases. We tested the potential of various strains of lactobacilli for suppression of experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

METHODOLOGY/PRINCIPAL FINDINGS

The preventive effects of five daily-administered strains of lactobacilli were investigated in mice developing EAE. After a primary screening, three Lactobacillus strains, L. paracasei DSM 13434, L. plantarum DSM 15312 and DSM 15313 that reduced inflammation in CNS and autoreactive T cell responses were chosen. L. paracasei and L. plantarum DSM 15312 induced CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) in mesenteric lymph nodes (MLNs) and enhanced production of serum TGF-beta1, while L. plantarum DSM 15313 increased serum IL-27 levels. Further screening of the chosen strains showed that each monostrain probiotic failed to be therapeutic in diseased mice, while a mixture of the three lactobacilli strains suppressed the progression and reversed the clinical and histological signs of EAE. The suppressive activity correlated with attenuation of pro-inflammatory Th1 and Th17 cytokines followed by IL-10 induction in MLNs, spleen and blood. Additional adoptive transfer studies demonstrated that IL-10 producing CD4(+)CD25(+) Tregs are involved in the suppressive effect induced by the lactobacilli mixture.

CONCLUSIONS/SIGNIFICANCE

Our data provide evidence showing that the therapeutic effect of the chosen mixture of probiotic lactobacilli was associated with induction of transferable tolerogenic Tregs in MLNs, but also in the periphery and the CNS, mediated through an IL-10-dependent mechanism. Our findings indicate a therapeutic potential of oral administration of a combination of probiotics and provide a more complete understanding of the host-commensal interactions that contribute to beneficial effects in autoimmune diseases.

Molecular modulation of intestinal epithelial barrier: contribution of microbiota

The daunting task required of the gut-barrier to prevent luminal pathogens and harmful substances from entering into the internal milieu and yet promoting digestion and absorption of nutrients requires an exquisite degree of coordination between the different architectural units of this barrier. The complex integration and execution of these functions are superbly carried out by the intestinal mucosal (IM) surface. Exposed to trillions of luminal microbes, the IM averts threats by signaling to the innate immune system, through pattern recognition receptors (PRR), to respond to the commensal bacteria by developing tolerance (hyporesponsiveness) towards them. This system also acts by protecting against pathogens by elaborating and releasing protective peptides, cytokines, chemokines, and phagocytic cells. The IM is constantly sampling luminal contents and making molecular adjustments at its frontier. This article describes the topography of the IM and the mechanisms of molecular adjustments that protect the internal milieu, and also describes the role of the microbiota in achieving this goal.

Colorectal carcinoma: Importance of colonic environment for anti-cancer response and systemic immunity

The intestinal environment is considered to play an important role both in colorectal tumor development and in the evolution and modulation of mucosal immunity. Studies in animals reared in germ-free (GF, without any intestinal microflora) versus conventional (CV, with regular microflora in bowel) conditions can aid in clarifying the influence of bacteria on carcinogenesis and anti-cancer immune responses in situ. The lower incidence of colon cancers and better immunological parameters in GF animals versus CV ones after chemically-induced carcinogenesis raises questions about specific characteristics of the immunological networks in each respective condition. Different levels of tolerance/regulatory mechanisms in the GF versus CV animals may influence the development of immune responses not only at the level of mucosal, but also at the systemic, immunity. We hypothesize that GF animals can better recognize and respond to evolving neoplasias in the bowel as a consequence of their less-tolerogenic immunity (i.e., due to their more limited exposure to antigens to become tolerated against at the intestinal level). In this paper, we review the role of bacteria in modulating gut environment and mucosal immunity, their importance in cancer development, and aspects of immune regulation (both at local and systemic level) that can be modified by bacterial microflora. Lastly, the use of GF animals in comparison with conventionally-raised animals is proposed as a suitable and potent model for understanding the inflammatory network and its effect on cancer immunity especially during colorectal cancer development.

Influence of different litter materials on cecal microbiota colonization in broiler chickens

A chicken growth study was conducted to determine if litter type influenced gut microbiota and performance in broilers. Seven bedding materials were investigated and included soft and hardwood sawdust, softwood shavings, shredded paper, chopped straw, rice hulls, and reused softwood shavings. Microbial profiling was done to investigate changes in cecal bacterial communities associated with litter material and age. Cecal microbiota were investigated at 14 and 28 d of age (n = 12 birds/litter material). At both ages, the cecal microbiota of chickens raised on reused litter was significantly (P < 0.05) different from that of chickens raised on any of the other litter materials, except softwood shavings at d 28. Cecal microbiota was also significantly different between birds raised on shredded paper and rice hulls at both ages. Age had a significant influence on cecal microbiota composition regardless of litter material. Similarity in cecal microbial communities among birds raised on the same litter treatment was greater at 28 d of age (29 to 40%) than at 14 d of age (25 to 32%). Bird performance on the different litter materials was measured by feed conversion ratio, live weight, and feed intake. Significant (P < 0.05) differences were detected in live weight at 14 d of age and feed intake at 14 and 28 d of age among birds (n = 160/treatment) raised on some of the different litter materials. However, no significant (P > 0.05) differences were observed in feed conversion ratio among birds raised on any of the 7 different litter materials at either 14 or 28 d of age. The type of litter material can influence colonization and development of cecal microbiota in chickens. Litter-induced changes in the gut microbiota may be partially responsible for some of the significant differences observed in early rates of growth; therefore, litter choice may have an important role in poultry gut health particularly in the absence of in-feed antibiotics.

Influence of microbial environment on autoimmunity

During protective immune responses, the adaptive arm of the immune system requires activation by signals provided by innate immunity and driven by microbial stimuli. Whether the same rules apply to autoimmune diseases involving clonal self-reactive T and B lymphocytes--a process referred to here as 'adaptive autoimmunity'--is not quite clear. Nevertheless, in these diseases, the innate-adaptive connection is likely to be influenced by the microbial environment. This review integrates the results of experiments analyzing autoimmunity in sterile versus nonsterile conditions and experiments testing the role of innate immune receptor signaling in autoimmunity. It proposes that autoimmune diseases can be divided into two groups, the pathogenesis of which either follows the rules of innate-adaptive connection or does not.

Covalent inhibition of bacterial quorum sensing

Chemical coordination of gene expression among bacteria as a function of population density is regulated by a mechanism known as 'quorum sensing' (QS). QS in Pseudomonas aeruginosa, an opportunistic pathogen that causes disease in immunocompromised patients, is mediated by binding of the transcriptional activator, LasR, to its ligand, 3-oxo-C(12)-HSL, leading to population-wide secretion of virulence factors and biofilm formation. We have targeted QS in P. aeruginosa with a set of electrophilic probes designed to covalently bind Cys79 in the LasR binding pocket, leading to specific inhibition of QS-regulated gene expression and concomitant reduction of virulence factor secretion and biofilm formation. This first example of covalent modification of a QS receptor provides a new tool to study molecular mechanisms of bacterial group behavior and could lead to new strategies for targeting bacterial virulence.

Commensal bacteria regulate Toll-like receptor 3-dependent inflammation after skin injury

The normal microflora of the skin includes staphylococcal species that will induce inflammation when present below the dermis but are tolerated on the epidermal surface without initiating inflammation. Here we reveal a previously unknown mechanism by which a product of staphylococci inhibits skin inflammation. This inhibition is mediated by staphylococcal lipoteichoic acid (LTA), and acts selectively on keratinocytes triggered through Toll-like receptor (TLR) 3. The significance of this is seen by observations that TLR3 activation is required for normal inflammation after injury, and that keratinocytes require TLR3 to respond to RNA from damaged cells with the release of inflammatory cytokines. Staphylococcal LTA inhibits both inflammatory cytokine release from keratinocytes and inflammation triggered by injury through a TLR2-dependent mechanism. These findings show for the first time that the skin epithelium requires TLR3 for normal inflammation after wounding and that the microflora can modulate specific cutaneous inflammatory responses.

Infectious serologies and autoantibodies in inflammatory bowel disease: insinuations at a true pathogenic role

The aim of this study was to reevaluate the role of infection in inflammatory bowel disease (IBD). Sera from 119 patients with IBD [80 with Crohn's disease (CD); 39 with ulcerative colitis] and 98 healthy controls were assessed using the Bio-Rad BioPlex 2200 for the presence of Toxoplasma gondii, cytomegalovirus, Epstein-Barr virus, Treponema pallidum, and Saccharomyces cerevisiae. Hepatitis B virus, hepatitis C virus (HCV), and anti-Helicobacter pylori antibodies were assessed by ELISA. In addition, sera were tested for a panel of antibodies associated with thrombophilia as well as various autoantibodies. Titers of antibodies toward HCV and T. gondii, and S. cerevisiae were higher in IBD patients than in controls, while the H. pylori autoantibodies were less prevalent among the patient population. Several thrombophilia-associated antibodies were more common in CD patients, and a single patient had a thromboembolic event. Our results show an excess of anti-HCV and anti-T. gondii antibodies among patients with IBD compared to healthy controls. Whereas the former may be the result of immunosuppression from the inflammatory disease itself or from the medications used to treat it, the latter association suggests that T. gondii is involved in the etiopathogenesis of IBD, and especially CD, in humans, as has been shown in the murine model. However, our findings also reiterate the positive association between CD and anti-S. cerevisiae antibodies as well as the negative association with H. pylori infections. These, in turn, lend indirect support to the "hygiene hypothesis" in IBD as well as the newly proposed role of commensal bacteria in the initiation of the disease process.

Inflammatory bowel disease, gut bacteria and probiotic therapy

Crohn's disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel disease (IBD) and both diseases lead to high morbidity and health care costs. Complex interactions between the immune system, enteric commensal bacteria and host genotype are thought to underlie the development of IBD although the precise aetiology of this group of diseases is still unknown. The understanding of the composition and complexity of the normal gut microbiota has been greatly aided by the use of molecular methods and is likely to be further increased with the advent of metagenomics and metatranscriptomics approaches, which will allow an increasingly more holistic assessment of the microbiome with respect to both diversity and function of the commensal gut microbiota. Studies thus far have shown that the intestinal microbiota drives the development of the gut immune system and can induce immune homeostasis as well as contribute to the development of IBD. Probiotics which deliver some of the beneficial immunomodulatory effects of the commensal gut microbiota and induce immune homeostasis have been proposed as a suitable treatment for mild to moderate IBD. This review provides an overview over the current understanding of the commensal gut microbiota, its interactions with the mucosal immune system and its capacity to induce both gut homeostasis as well as dysregulation of the immune system. Bacterial-host events, including interactions with pattern recognition receptors (PRRs) expressed on epithelial cells and dendritic cells (DCs) and the resultant impact on immune responses at mucosal surfaces will be discussed.

Salmonella Typhimurium type III secretion effectors stimulate innate immune responses in cultured epithelial cells

Recognition of conserved bacterial products by innate immune receptors leads to inflammatory responses that control pathogen spread but that can also result in pathology. Intestinal epithelial cells are exposed to bacterial products and therefore must prevent signaling through innate immune receptors to avoid pathology. However, enteric pathogens are able to stimulate intestinal inflammation. We show here that the enteric pathogen Salmonella Typhimurium can stimulate innate immune responses in cultured epithelial cells by mechanisms that do not involve receptors of the innate immune system. Instead, S. Typhimurium stimulates these responses by delivering through its type III secretion system the bacterial effector proteins SopE, SopE2, and SopB, which in a redundant fashion stimulate Rho-family GTPases leading to the activation of mitogen-activated protein (MAP) kinase and NF-κB signaling. These observations have implications for the understanding of the mechanisms by which Salmonella Typhimurium induces intestinal inflammation as well as other intestinal inflammatory pathologies.

Salmonella Typhimurium is one of the most common causes of food-borne illness in the United States and a major cause of diarrheal diseases in developing countries. This pathogen induces diarrhea by stimulating inflammation in the intestinal tract. This study shows that S. Typhimurium delivers molecules into epithelial cells with the capacity to stimulate the production of pro-inflammatory substances. This mechanism may help the pathogen to initiate the inflammatory response in the intestinal epithelium. This study provides insight into the mechanisms by which Salmonella Typhimurium causes diarrhea.

Extra-adrenal glucocorticoid synthesis in the intestinal epithelium: more than a drop in the ocean?

Glucocorticoids (GC) are lipophilic hormones commonly used as therapeutics in acute and chronic inflammatory disorders such as inflammatory bowel disease due to their attributed anti-inflammatory and immunosuppressive actions. Although the adrenal glands are the major source of endogenous GC, there is increasing evidence for the production of extra-adrenal GC in the brain, thymus, skin, vasculature, and the intestine. However, the physiological relevance of extra-adrenal-produced GC remains still ambiguous. Therefore, this review attracts attention to discuss possible biological benefits of extra-adrenal-synthesized GC, especially focusing on the impact of locally synthesized GC in the regulation of intestinal immune responses.

TLR ligand decreases mesenteric ischemia and reperfusion injury-induced gut damage through TNF-alpha signaling

Ischemic gut contributes to the development of sepsis and organ failure in critically ill patients. Toll-like receptors (TLRs) have been reported to mediate the pathophysiology of organ damage following ischemia/reperfusion (I/R) injury. We hypothesize that LPS, a ligand for TLR4, decreases mesenteric I/R injury-induced gut damage through tumor necrosis factor alpha (TNF-alpha) signaling. First, wild-type (WT) mice were fed with oral antibiotics for 4 weeks to deplete the intestinal commensal microflora. At week 3, drinking water was supplemented with LPS (10 microg/microL) to trigger TLRs. The intestinal mucosa was harvested for TLR4 protein, caspase 3 activity, and terminal deoxynucleotide transferase labeling assay. Second, WT and Tnfrsf1a mice received 30-min ischemia and 30-min reperfusion (30I-30R) or 30I-180R of the intestine; intestinal permeability and lipid peroxidation of the intestine were examined. Third, WT and Tnfrsf1a mice were fed with oral antibiotics with or without LPS and received 30I-180R of the intestine. The intestinal mucosa was harvested for lipid peroxidation; glutathione (GSH) level; nuclear factor kappaB (NF-kappaB) and AP-1 DNA-binding activity; Bcl-w, TNF-alpha, and CXCR2 mRNA expression; and HSP70 protein assay. Commensal depletion increased caspase 3 activity as well as villi apoptosis and decreased TLR4 expression of the intestinal mucosa. LPS increased TLR4 expression and decreased villi apoptosis. Commensal depletion augmented 30I-180R-induced intestine permeability as well as lipid peroxidation and decreased GSH level in WT mice but not in Tnfrsf1a mice. LPS decreased 30I-180R-induced intestinal permeability as well as lipid peroxidation and increased GSH level of the intestinal mucosa in WT mice but not in Tnfrsf1a mice. Commensal depletion with 30I-180R increased NF-kappaB and AP-1 DNA-binding activity, HSP70 protein expression, and decreased Bcl-w and TNF-alpha mRNA expression of the intestinal mucosa in WT mice but not in Tnfrsf1a mice. Collectively, commensal microflora induces TLR4 expression and decreases apoptosis of the intestinal mucosa. Commensal depletion enhances I/R-induced gut damage. LPS prevents I/R-induced intestinal permeability, lipid peroxidation, and decrease in GSH level. Given that the preventive effect of LPS on I/R-induced gut damage and NF-kappaB activity of the intestine is abolished in Tnfrsf1a mice, we conclude that TLR ligand decreases mesenteric I/R injury-induced gut damage through TNF-alpha signaling.

The K5 capsule of Escherichia coli strain Nissle 1917 is important in mediating interactions with intestinal epithelial cells and chemokine induction

Escherichia coli strain Nissle 1917 has been widely used as a probiotic for the treatment of inflammatory bowel disorders and shown to have immunomodulatory effects. Nissle 1917 expresses a K5 capsule, the expression of which often is associated with extraintestinal and urinary tract isolates of E. coli. In this paper, we investigate the role of the K5 capsule in mediating interactions between Nissle 1917 and intestinal epithelial cells. We show that the loss of capsule significantly reduced the level of monocyte chemoattractant protein 1 (MCP-1), RANTES, macrophage inflammatory protein 2alpha (MIP-2alpha), MIP-2beta, interleukin-8, and gamma interferon-inducible protein 10 induction by Nissle 1917 in both Caco-2 cells and MCP-1 induction in ex vivo mouse small intestine. The complementation of the capsule-minus mutation confirmed that the effects on chemokine induction were capsule specific. The addition of purified K5, but not K1, capsular polysaccharide to the capsule-minus Nissle 1917 at least in part restored chemokine induction to wild-type levels. The purified K5 capsular polysaccharide alone was unable to stimulate chemokine production, indicating that the K5 polysaccharide was acting to mediate interactions between Nissle 1917 and intestinal epithelial cells. The induction of chemokine by Nissle 1917 was generated predominantly by interaction with the basolateral surface of Caco-2 cells, suggesting that Nissle 1917 will be most effective in inducing chemokine expression where the epithelial barrier is disrupted.

Campylobacter jejuni drives MyD88-independent interleukin-6 secretion via Toll-like receptor 2

Gastrointestinal disease caused by Campylobacter jejuni is characterized by localized inflammation and the destruction of the epithelial cell barrier that forms host innate protection against pathogens. This can lead to an imbalance in fluid transport across the gastrointestinal tract, resulting in severe diarrhea. The mechanisms of host cell receptor recognition of C. jejuni and downstream immune signaling pathways leading to this inflammatory disease, however, remain unclear. The aim of this study was to analyze the mechanisms involved in C. jejuni induction of the acute-phase inflammatory response regulator interleukin-6 (IL-6). Polarized intestinal epithelial Caco-2 monolayers responded to infections with Salmonella enterica serovar Typhimurium and eight isolates of C. jejuni by an increase in levels of expression and secretion of IL-6. No such IL-6 response, however, was produced upon infection with the human commensal organism Lactobacillus rhamnosus GG. The IL-6 signaling pathway was further characterized using short interfering RNA complexes to block gene expression. The inhibition of myeloid differentiation primary response protein 88 (MyD88) expression in this manner did not affect C. jejuni-induced IL-6 secretion, suggesting a MyD88-independent route to IL-6 signal transduction in C. jejuni-infected human epithelial cells. However, a significant reduction in levels of IL-6 was evident in the absence of Toll-like receptor 2 (TLR-2) expression, implying a requirement for TLR-2 in C. jejuni recognition. Caco-2 cells were also treated with heat-inactivated and purified membrane components of C. jejuni to isolate the factor responsible for triggering IL-6 signaling. The results demonstrate that C. jejuni surface polysaccharides induce IL-6 secretion from intestinal epithelial cells via TLR-2 in a MyD88-independent manner.

Host-microbe communication within the GI tract

The gastrointestinal tract is a biologically diverse and complicated system which carries out essential physiological functions that support human health, while at the same time maintaining itself as an isolated environment to prevent infection and systemic disease. To maintain homeostasis in the gut, communication between the host and residing microbial communities must occur to identify and eliminate potential pathogens which could colonize and cause damage through aggressive pro-inflammatory responses by the mucosal immune system. To prevent such events, a number of host and bacterial-mediated mechanisms are utilized to monitor the environment and initiate appropriate immune responses to invading pathogens. An essential component of this communication process between gastrointestinal microflora and the host involves distinguishing indigenous species from pathogens through ligand-receptor interactions which lead to various signaling events in host cells. Such events generally result in the development of mucosal immunity and immunological tolerance. While these signaling pathways provide a highly effective means of communication between the gut microflora and the host, pathogens have developed mechanisms to manipulate these pathways to evade detection by the immune system to persist and cause disease. These adaptations include cell surface modifications and the expression of various virulence factors in response to different immunological and hormonal components produced by the host.

The cell-envelope proteome of Bifidobacterium longum in an in vitro bile environment

Host–bacteria interactions are often mediated via surface-associated proteins. The identification of these proteins is an important goal of bacterial proteomics. To address how bile can influence the cell-envelope proteome of Bifidobacterium longum biotype longum NCIMB 8809, we analysed its membrane protein fraction using stable isotope labelling of amino acids in cell culture (SILAC). We were able to identify 141 proteins in the membrane fraction, including a large percentage of the theoretical transporters of this species. Moreover, the envelope-associated soluble fraction was analysed using different subfractionation techniques and differential in-gel fluorescence electrophoresis (DIGE). This approach identified 128 different proteins. Some of them were well-known cell wall proteins, but others were highly conserved cytoplasmic proteins probably displaying a ‘moonlighting’ function. We were able to identify 11 proteins in the membrane fraction and 6 proteins in the envelope-associated soluble fraction whose concentration varied in the presence of bile. Bile promoted changes in the levels of proteins with important biological functions, such as some ribosomal proteins and enolase. Also, oligopeptide-binding proteins were accumulated on the cell surface, which was reflected in a different tripeptide transport rate in the cells grown with bile. The data reported here will provide the first cell-envelope proteome map for B. longum, and may contribute to understanding the bile tolerance of these bacteria.

Up-regulation of intestinal Toll-Like receptors and cytokines expressions change after TPN administration and a lack of enteral feeding

BACKGROUND

Total parenteral nutrition (TPN) increases the risk of severe infectious complications such as septic shock, which are believed to be the result of a breakdown of intestinal barrier function and subsequent bacterial translocation. Toll-like receptors (TLRs) comprise a family of membrane proteins that serve as pattern recognition receptors for a variety of microbe-derived molecules and stimulate innate immune responses to microbes. Alteration of intraepithelial lymphocytes (IELs) to TPN administration has been studied extensively. However, few studies have examined the effect of TPN administration on intestinal TLRs. We hypothesized that the expressions of intestinal TLRs and cytokines may change with TPN administration and a lack of enteral feeding.

MATERIALS AND METHODS

TPN-treated mice and sham operation mice (control) were killed at 10 days after operation. mRNA expression of intestinal cytokines and TLRs were analyzed with reverse transcription-polymerase chain reaction (RT-PCR) methods. Change in IEL populations was analyzed with flow cytometry.

RESULTS

RT-PCR showed varying expression levels of TLRs at different sites on the small intestine and colon. TLR4, TLR5, TLR7, and TLR9 mRNAs were up-regulated in response to TPN administration, particularly in the distal small intestine.

CONCLUSIONS

Up-regulation of TLRs in intestine in response to TPN administration and a lack of enteral nutrition may be associated with an increased risk of septic shock due to bacterial translocation caused by Interferon gamma-mediated intestinal epithelial cell apoptosis.