IL-10 producing CD14low monocytes inhibit lymphocyte-dependent activation of intestinal epithelial cells by commensal bacteria

Microfluidic gut-on-a-chip with three-dimensional villi structure

Current in vitro gut models lack physiological relevance, and various approaches have been taken to improve current cell culture models. For example, mimicking the three-dimensional (3D) tissue structure or fluidic environment has been shown to improve the physiological function of gut cells. Here, we incorporated a collagen scaffold that mimics the human intestinal villi into a microfluidic device, thus providing cells with both 3D tissue structure and fluidic shear. We hypothesized that the combined effect of 3D structure and fluidic shear may provide cells with adequate stimulus to induce further differentiation and improve physiological relevance. The physiological function of our '3D gut chip' was assessed by measuring the absorptive permeability of the gut epithelium and activity of representative enzymes, as well as morphological evaluation. Our results suggest that the combination of fluidic stimulus and 3D structure induces further improvement in gut functions. Our work provides insight into the effect of different tissue environment on gut cells.

Gut Microbial Influences on the Mammalian Intestinal Stem Cell Niche

The mammalian intestinal epithelial stem cell (IESC) niche is comprised of diverse epithelial, immune, and stromal cells, which together respond to environmental changes within the lumen and exert coordinated regulation of IESC behavior. There is growing appreciation for the role of the gut microbiota in modulating intestinal proliferation and differentiation, as well as other aspects of intestinal physiology. In this review, we evaluate the diverse roles of known niche cells in responding to gut microbiota and supporting IESCs. Furthermore, we discuss the potential mechanisms by which microbiota may exert their influence on niche cells and possibly on IESCs directly. Finally, we present an overview of the benefits and limitations of available tools to study niche-microbe interactions and provide our recommendations regarding their use and standardization. The study of host-microbe interactions in the gut is a rapidly growing field, and the IESC niche is at the forefront of host-microbe activity to control nutrient absorption, endocrine signaling, energy homeostasis, immune response, and systemic health.

The microbiota and autoimmunity: Their role in thyroid autoimmune diseases

Since the 1970s, the role of infectious diseases in the pathogenesis of Graves' disease (GD) has been an object of intensive research. The last decade has witnessed many studies on Yersinia enterocolitica, Helicobacter pylori and other bacterial organisms and their potential impact on GD. Retrospective, prospective and molecular binding studies have been performed with contrary outcomes. Until now it is not clear whether bacterial infections can trigger autoimmune thyroid disease. Common risk factors for GD (gender, smoking, stress, and pregnancy) reveal profound changes in the bacterial communities of the gut compared to that of healthy controls but a pathogenetic link between GD and dysbiosis has not yet been fully elucidated. Conventional bacterial culture, in vitro models, next generation and high-throughput DNA sequencing are applicable methods to assess the impact of bacteria in disease onset and development. Further studies on the involvement of bacteria in GD are needed and may contribute to the understanding of pathogenetic processes. This review will examine available evidence on the subject.

Lactobacillus paracasei CNCM I-4034 and its culture supernatant modulate Salmonella-induced inflammation in a novel transwell co-culture of human intestinal-like dendritic and Caco-2 cells

Background

The action of probiotics has been studied in vitro in cells isolated from both mice and humans, particularly enterocytes (IECs), dendritic cells (DCs) and co-cultures of peripheral DCs and IECs. Peripheral DCs and murine DCs differ from human gut DCs, and to date there are no data on the action of any probiotic on co-cultured human IECs and human intestinal DCs. To address this issue, a novel transwell model was used. Human IECs (Caco-2 cells) grown in the upper chamber of transwell filters were co-cultured with intestinal-like human DCs grown in the basolateral compartment of the transwells. The system was apically exposed for 4 h to live probiotic L. paracasei CNCM I-4034 obtained from the faeces of breastfed infants or to its cell-free culture supernatant (CFS) and challenged with Salmonella typhi. The secretion of pro- and anti-inflammatory cytokines in the basolateral compartment was determined by immunoassay, and the DC expression pattern of 20 TLR signaling pathway genes was analysed by PCR array.

Results

The presence of the live probiotic alone significantly increased IL-1β, IL-6, IL-8, TGF-β2, RANTES and IP-10 levels and decreased IL-12p40, IL-10, TGF- β1 and MIP-1α levels. This release was correlated with a significant increase in the expression of almost all TLR signaling genes. By contrast, incubation of the co-culture with CFS increased IL-1β, IL-6, TGF-β2 and IP-10 production only when Salmonella was present. This induction was correlated with an overall decrease in the expression of all TLR genes except TLR9, which was strongly up-regulated.

Conclusions

The data presented here clearly indicate that L. paracasei CNCM I-4034 significantly increases the release of pro-inflammatory cytokines, enhances TLR signaling pathway activation and stimulates rather than suppresses the innate immune system. Furthermore, our findings provide evidence that the effects of probiotics in the presence of IECs and DCs differ from the effects of probiotics on cultures of each cell type alone, as reported by us earlier. Thus, co-culture systems such as the one described here are needed to characterise the effects of probiotics in vitro, highlighting the potential utility of such co-cultures as a model system.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0408-6) contains supplementary material, which is available to authorized users.

Uropathogenic Escherichia coli modulates innate immunity to suppress Th1-mediated inflammatory responses during infectious epididymitis

Infectious epididymitis in men, a frequent entity in urological outpatient settings, is commonly caused by bacteria originating from the anal region ascending the genitourinary tract. One of the most prevalent pathogens associated with epididymitis is Escherichia coli. In our previous study, we showed that semen quality is compromised in men following epididymitis associated with specific E. coli pathovars. Thus, our aim was to investigate possible differences in immune responses elicited during epididymitis following infection with the uropathogenic E. coli (UPEC) strain CFT073 and the nonpathogenic enteric E. coli (NPEC) strain 470. Employing an in vivo experimental epididymitis model, C57BL/6 mice were infected with UPEC CFT073, NPEC 470, or phosphate-buffered saline (PBS) as a sham control for up to 7 days. After infection with NPEC 470, the expression of proinflammatory cytokines interleukin-1 (IL-1), IL-6, and tumor necrosis factor alpha in the epididymis was significantly increased. Conversely, UPEC CFT073-challenged mice displayed inflammatory gene expression at levels comparable to sham PBS-treated animals. Moreover, by day 7 only NPEC-infected animals showed activation of adaptive immunity evident by a substantial influx of CD3+ and F4/80+ cells in the epididymal interstitium. This correlated with enhanced production of Th1-associated cytokines IL-2 and gamma interferon (IFN-γ). Furthermore, splenocytes isolated from UPEC-infected mice exhibited diminished T-cell responses with significantly reduced secretion of IL-2 and IFN-γ in contrast to NPEC-infected animals. Overall, these findings provide new insights into understanding pathogen-specific modulation of host immunity during acute phases of epididymitis, which may influence severity of disease and clinical outcomes.

Differential modulation of innate immunity in vitro by probiotic strains of Lactobacillus gasseri

Background

Probiotics species appear to differentially regulate the intestinal immune response. Moreover, we have shown that different immune-modulatory abilities can be found among probiotic strains belonging to the same species. In this study, we further addressed this issue while studying L. gasseri, a species that induces relevant immune activities in human patients.

Results

We determined the ability of two strains of L. gasseri, OLL2809 and L13-Ia, to alter cell surface antigen expression, cytokine production and nuclear erythroid 2-related factor 2 (Nrf2)-mediated cytoprotection in murine bone marrow-derived dendritic cells (DCs) and MODE-K cells, which represent an enterocyte model. Differential effects of L. gasseri strains were observed on the expression of surface markers in mature DCs; nevertheless, both strains dramatically induced production of IL-12, TNF-α and IL-10. Distinctive responses to OLL2809 and L13-Ia were also shown in MODE-K cells by analyzing the expression of MHC II molecules and the secretion of IL-6; however, both L. gasseri strains raised intracellular glutathione. Treatment of immature DCs with culture medium from MODE-K monolayers improved cytoprotection and modified the process of DC maturation by down-regulating the expression of co-stimulatory markers and by altering the cytokine profile. Notably, bacteria-conditioned MODE-K cell medium suppressed the expression of the examined cytokines, whereas cytoprotective defenses were significantly enhanced only in DCs exposed to OLL2809-conditioned medium. These effects were essentially mediated by secreted bacterial metabolites.

Conclusions

We have demonstrated that L. gasseri strains possess distinctive abilities to modulate in vitro DCs and enterocytes. In particular, our results highlight the potential of metabolites secreted by L. gasseri to influence enterocyte-DC crosstalk. Regulation of cellular mechanisms of innate immunity by selected probiotic strains may contribute to the beneficial effects of these bacteria in gut homeostasis.

Selenium and zinc internalized by Lactobacillus buchneri Lb26 (DSM 16341) and Bifidobacterium lactis Bb1 (DSM 17850): improved bioavailability using a new biological approach

BACKGROUND

Minerals, often referred to as micronutrients, are one of the 5 fundamental groups of nutrients needed to sustain life. Micronutrient malnutrition affects >50% of the worldwide population. In particular, zinc (Zn) deficiency is considered an emerging public health problem in India and in other developing countries. Selenium (Se) is another trace mineral essential for humans and animals. Dietary Se exists primarily as selenomethionine and selenocysteine. In addition, Se may be present in its inorganic form (selenite) in some vegetables. To increase the daily intake of these minerals, numerous food supplements containing different inorganic and organic forms of Zn or Se are commercially available. At any rate, it is quite well known that inorganic salts have a very low bioavailability. Organic salts, commonly based on gluconate, orotate, citrate, or other molecules, are characterized by a higher systemic effect. The innovative opportunity of using certain species of probiotics enriched with the 2 minerals could represent an interesting alternative to these preparations. Diet integration with bacteria able to internalize Zn and Se may embody a new application of probiotics.

METHODS

To overcome the difficulties of in vivo animal or human trials, in this work a cell culture model using Caco-2 cells in bicameral chambers (Transwell system) was developed and validated to quantify the bioavailability of some commercial forms of Se and Zn compared with the organic forms accumulated intracellularly by Lactobacillus buchneri Lb26 (DSM 16341) and Bifidobacterium lactis Bb1 (DSM 17850), respectively.

RESULTS

The experimental data collected demonstrated a significantly higher bioavailability of Se and Zn internalized by L. buchneri Lb26 (DSM 16341) and B. lactis Bb1 (DSM 17850), respectively, compared with the inorganic and even organic forms tested. In particular, the Se accumulated at the intracellular level by L. buchneri Lb26 proved to be 5.9, 9.4, and 65 times more absorbable than sodium selenite, seleno-L-methionine, and seleno-L-cysteine, respectively. In contrast, Zn internalized by B. lactis Bb1 showed an absorption that was >16 times higher by Caco-2 cells compared with zinc gluconate and a 31.5 times higher absorption compared with zinc sulfate. Most notably, Se and Zn internalized by the 2 probiotics studied are the only forms able to reach the Transwell basolateral compartment at a concentration higher than the concentration found in the apical compartment, therefore suggesting a considerably higher in vivo ability to be absorbed into the bloodstream. Both organic and inorganic forms of Se and Zn were predominantly found in the apical compartment, thus demonstrating their poor ability to diffuse into the cell and become bioavailable in all subcellular areas.

CONCLUSIONS

The opportunity of delivering minerals in a highly bioavailable form by means of a probiotic bacterium has not been deeply investigated to date. This is the first study reporting quantitative data on the bioavailability and percentage of absorption of minerals internalized by specific probiotics. The most noticeable aspect is the significantly higher absorption of both probiotic Se and Zn compared with their organic forms, with particular reference to seleno-L-methionine, seleno-L-cysteine, and zinc gluconate.

Effects of bacterial products on enterocyte-macrophage interactions in vitro

We describe a coculture model of a human intestinal epithelial cell line and human peripheral blood monocytes in which monocytes differentiate into cells with features of resident intestinal macrophages. Caco-2 cells are grown on the lower surface of a semipermeable filter with pore size of 3 μm (Transwells) until they differentiate into enterocytes. Peripheral-blood monocytes are added and the co-culture incubated for two days. Monocytes migrate through the pores of the membrane, come into direct contact with the basolateral surfaces of the epithelial cell monolayer, and develop characteristics of resident intestinal macrophages including downregulation of CD14 expression and reduced pro-inflammatory cytokine responses (IL-8, TNF and IL-1β) to bacterial products. The apical application of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) resulted in an increased number of integrated monocytes, but abrogated the downregulation of CD14 expression and the diminished cytokine responses. MDP also reduced tight-junctional integrity, whilst LPS had no effect. These data indicate that LPS and MDP have significant pathophysiological effects on enterocyte-monocyte interactions, and confirm other studies that demonstrate that enterocytes and their products influence monocyte differentiation. This model may be useful in providing insights into the interaction between monocytes, epithelial cells and intestinal bacteria in health and disease.

Pivotal Advance: Bifidobacteria and Gram-negative bacteria differentially influence immune responses in the proinflammatory milieu of celiac disease

CD is a chronic inflammatory disorder of the small intestine that presents in genetically predisposed individuals following gluten consumption. In this study, the effects of Bifidobacterium (Bifidobacterium bifidum IATA-ES2 and Bifidobacterium longum ATCC15707) and Gram-negative bacteria (Bacteroides fragilis DSM2451, Escherichia coli CBL2, and Shigella CBD8 isolated from CD patients), alone and in the presence of CD triggers (gliadins and/or IFN-gamma) on surface marker expression and cytokine production by PBMCs, were determined. These effects were also evaluated in cocultures of PBMCs and Caco-2 cells. The Gram-negative bacteria induced higher secretion of Th1-type proinflammatory cytokines (IL-12 and/or IFN-gamma) than the Bifidobacterium strains. Shigella CBD8 and E. coli CBL2 up-regulated mainly HLA-DR and CD40 expression involved in Th1 activation, and Bifidobacterium strains up-regulated CD83 expression. Specific interactions among the studied bacteria, gliadins, and IFN-gamma, which favored the CD immune features, were also detected. Therefore, intestinal bacteria could be additional factors that regulate the ability of monocytes recruited to the mucosa to respond to gliadins and IFN-gamma in CD patients, influencing the course of the disease.

Heat- and formalin-inactivated probiotic bacteria induce comparable cytokine patterns in intestinal epithelial cell-leucocyte cocultures

The mode of inactivation of probiotic bacteria may profoundly affect their immune-modulatory properties to the point of reversal of effects in in vitro human intestinal epithelial-like cell cultures (Caco-2). To further investigate the influence of inactivation treatment on cytokine production, three probiotic strains were evaluated-live, heat-inactivated, and formalin-inactivated strains-for their impact on interleukin (IL) 6, IL-8, and IL-10 production in Caco-2-leucocyte cocultures. The tested bacteria induced strain-specific production of IL-6, IL-8, and IL-10. No suppressive effects on cytokine synthesis were observed. Live microorganisms seemed to be slightly more potent inducers of cytokine production than nonviable strains, but differences to inactivated bacteria were not statistically significant. Our results indicate that heat and formalin treatments of probiotic microorganisms are equivalent inactivation methods in terms of induction of IL-6, IL-8, and IL-10 production in Caco-2-peripheral blood mononuclear cell cocultures and do not invert immune-modulatory effects.

Novel and future medical management of inflammatory bowel disease

The treatment of inflammatory bowel disease (IBD) is undergoing rapid and profound change. Entirely new approaches are being developed that reflect a greater understanding of how to control the inflammatory process. These began with inflixumab therapy for Crohn's disease. Additional tumor necrosis antibodies will soon be employed, and other biological agents are being investigated. Probiotics, helminth ova therapy, alternative and complementary treatments, leukocytophoresis, and bone-marrow and stem-cell transplantation are additional exciting regimens that are being explored. Although some of these approaches provide marked improvement in these parameters, others are unproven or fraught with adverse effects and complications. Still, control of ulcerative colitis and Crohn's is improving with more changes likely to come.

Cross-talk between probiotic bacteria and the host immune system

Among the numerous purported health benefits attributed to probiotic bacteria, their capacity to interact with the immune system of the host is now supported by an increasing number of in vitro and in vivo experiments. In addition to these, a few well-controlled human intervention trials aimed at preventing chronic immune dysregulation have been reported. Even though the precise molecular mechanisms governing the cross-talk between these beneficial bacteria and the intestinal ecosystem remain to be discovered, a new and fascinating phase of research has been initiated in this area as demonstrated by a series of recent articles. This article summarizes the status and latest progress of the field in selected areas and aims at identifying key questions that remain to be addressed, especially concerning the translocation of ingested bacteria, the identification of major immunomodulatory compounds of probiotics, and specific aspects of the host-microbe cross-talk. The interaction with immunocompetent cells and the role of secretory IgA in gut homeostasis are also evoked. Finally, a brief overview is provided on the potential use of recombinant DNA technology to enhance the health benefits of probiotic strains and to unravel specific mechanisms of the host-microbe interaction.

Innate resistance to Entamoeba histolytica in murine models

Hamano et al. have recently reported that in murine models of amebiasis, innate resistance is associated with nonhemopoietic cells and depends on the activity of interleukin-10. This article raises the issue of the importance of predisposition to amebic colitis and discusses which host factors have a role in innate resistance to invasive disease. Resistance studies that elucidate the mechanisms involved in parasite clearance or parasite invasion are essential to understanding the incidence of amebiasis in humans.

Human MICL (CLEC12A) is differentially glycosylated and is down-regulated following cellular activation

C-type lectins are the most diverse and prevalent lectin family in immunity. Particular interest has recently been attracted by the C-type lectin-like receptors on NK cells, which appear to regulate the activation/inhibitory balance of these cells, controlling cytotoxicity and cytokine production. We previously identified a human C-type lectin-like receptor, closely related to both the beta-glucan receptor and the lectin-like receptor for oxidized-LDL, named MICL (myeloid inhibitory C-type lectin-like receptor), which we had shown using chimeric analysis to function as an inhibitory receptor. Using a novel MICL-specific monoclonal antibody, we show here that human MICL is expressed primarily on myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells. Although MICL was highly N-glycosylated in primary cells, the level of glycosylation was found to vary between cell types. MICL surface expression was down-regulated during inflammatory/activation conditions in vitro, as well as during an in vivo model of acute inflammation, which we characterize here. This suggests that human MICL may be involved in the control of myeloid cell activation during inflammation.

Probiotic bacteria Bifidobacterium animalis MB5 and Lactobacillus rhamnosus GG protect intestinal Caco-2 cells from the inflammation-associated response induced by enterotoxigenic Escherichia coli K88

Probiotic bacteria may provide protection against intestinal damage induced by pathogens, but the underlying mechanisms are still largely unknown. We investigated whether Bifidobacterium animalis MB5 and Lactobacillus rhamnosus GG (LGG) protected intestinal Caco-2 cells from the inflammation-associated response induced by enterotoxigenic Escherichia coli (ETEC) K88, by inhibiting pathogen attachment to the cells, which is the first step of ETEC pathogenicity, and regulating neutrophil recruitment, a crucial component of inflammation. A partial reduction of ETEC adhesion was exerted by probiotics and their culture supernatant fractions either undigested or digested with proteases. ETEC viability was unaffected by the presence of B. animalis, LGG or their supernatant fractions in the culture medium, indicating an absence of probiotic bactericidal activity. Probiotics and their supernatant fractions, either undigested or digested with proteases, strongly inhibited the neutrophil transmigration caused by ETEC. Both B. animalis and LGG counteracted the pathogen-induced up regulation of IL-8, growth-related oncogene-alpha and epithelial neutrophil-activating peptide-78 gene expression, which are chemokines essential for neutrophil migration. Moreover, the probiotics prevented the ETEC-induced increased expression of IL-1beta and TNF-alpha and decrease of transforming growth factor-alpha, which are regulators of chemokine expression. These results indicate that B. animalis MB5 and LGG protect intestinal cells from the inflammation-associated response caused by ETEC K88 by partly reducing pathogen adhesion and by counteracting neutrophil migration, probably through the regulation of chemokine and cytokine expression.

Role of intestinal epithelial cells in immune effects mediated by gram-positive probiotic bacteria: involvement of toll-like receptors

The mechanisms by which probiotic bacteria exert their effects on the immune system are not completely understood, but the epithelium may be a crucial player in the orchestration of the effects induced. In a previous work, we observed that some orally administered strains of lactic acid bacteria (LAB) increased the number of immunoglobulin A (IgA)-producing cells in the small intestine without a concomitant increase in the CD4(+) T-cell population, indicating that some LAB strains induce clonal expansion only of B cells triggered to produce IgA. The present work aimed to study the cytokines induced by the interaction of probiotic LAB with murine intestinal epithelial cells (IEC) in healthy animals. We focused our investigation mainly on the secretion of interleukin 6 (IL-6) necessary for the clonal expansion of B cells previously observed with probiotic bacteria. The role of Toll-like receptors (TLRs) in such interaction was also addressed. The cytokines released by primary cultures of IEC in animals fed with Lactobacillus casei CRL 431 or Lactobacillus helveticus R389 were determined. Cytokines were also determined in the supernatants of primary cultures of IEC of unfed animals challenged with different concentrations of viable or nonviable lactobacilli and Escherichia coli, previously blocked or not with anti-TLR2 and anti-TLR4. We concluded that the small intestine is the place where a major distinction would occur between probiotic LAB and pathogens. This distinction comprises the type of cytokines released and the magnitude of the response, cutting across the line that separates IL-6 necessary for B-cell differentiation, which was the case with probiotic lactobacilli, from inflammatory levels of IL-6 for pathogens.

Norepinephrine, dopamine and dexamethasone modulate discrete leukocyte subpopulations and cytokine profiles from human PBMC

The interplay between the immune and neuroendocrine systems is intense, with the cross-talk between these two systems increasing during stress circumstances. Stress events culminate with hormonal pathway activation elevating the plasma levels of glucocorticoids and catecholamines. The majority of the works evaluating the effects of stress hormones on immune cells have utilized in vivo animal models or clinical studies. This work evaluates the effects of norepinephrine, dopamine, dexamethasone, and the combination of norepinephrine and dexamethasone on cellular activation and expression of immunoregulatory cytokines and chemokines by human PBMC in vitro. Norepinephrine and dopamine increased lymphocyte activation accompanied by augmented Th1 and Th2 type cytokine production. Dexamethasone reduced cell activation and decreased frequencies of cytokine producing cells and chemokine production. The action of norepinephrine together with dexamethasone resulted in immunosupression. The observed effects of hormones and neurotransmitters on leukocyte subsets likely underlie their immunomodulatory action in vivo.

Place of probiotics

PURPOSE OF REVIEW

This review reports on the recent progress understanding mechanisms of action and clinical applications of probiotics.

RECENT FINDINGS

New insights on regulating mechanisms of intestinal commensal bacteria to prevent and treat different gastrointestinal diseases have been reported. Some probiotics, though not all, exert beneficial effects by modulating the mucosal barrier function and immune activity. It seems that a combination of different probiotics is more effective than a single strain. It was demonstrated that not only viable bacteria administered to the intestinal tract but also isolated probiotic DNA is active, even if injected subcutaneously. There is reasonable evidence to recommend probiotics in infectious diarrhoea for prevention and treatment (mainly in children) and to prevent antibiotic-induced gastrointestinal side effects. Furthermore, probiotics are effective in maintaining remission in ulcerative colitis and preventing and treating pouchitis. Promising positive effects were published in major surgery patients (gastric resection, pancreatic resection, liver transplantation) and in severe necrotising acute pancreatitis.

SUMMARY

Increasing knowledge on probiotics is exciting, but in the near future it must be defined which probiotics (single strains or a combination) are most effective in specific diseases. Well-designed, randomized clinical trials are still required to further define the role of probiotics as preventive and therapeutic agents.

Commensal bacteria in the gut: learning who our friends are

PURPOSE OF REVIEW

Recent evidence has shown that commensal bacteria regulate intestinal physiology, development, and function. This review focuses on new insights into the effects of these organisms on health and disease.

RECENT FINDINGS

Gastrointestinal tract development and function is determined by communication between the intestinal epithelium and commensal bacteria. Important regulatory interactions between these cells are being defined with early evidence indicating both beneficial and harmful consequences to the host. A subgroup of these bacteria overlaps with probiotic organisms that have preventative and therapeutic potential for diarrhea, inflammatory bowel disease (IBD), atopy, and other diseases, whereas evidence indicates some "nonpathogenic" commensal bacteria may promote an environment conducive to IBD, cancer, and other diseases.

SUMMARY

Progress in understanding the relation between commensal bacteria and human health is likely to promote the identification of new approaches to disease prevention and treatment.

Modulation of Cytokine Release by Differentiated CACO-2 Cells in a Compartmentalized Coculture Model with Mononuclear Leucocytes and Nonpathogenic Bacteria

To further investigate the interaction between human mononuclear leucocytes [peripheral blood mononuclear cells (PBMC)] and enterocytes, the effect of a confluent layer of differentiated CACO-2 cells on cytokine kinetics during challenge with bacteria in a compartmentalized coculture model was investigated. Nonpathogenic Escherichia coli were added either to the apical or the basolateral compartment of this transwell cell culture system, the latter of which contained human leucocytes. The synthesis of tumour necrosis factor (TNF-alpha) and interleukin (IL)-12 was significantly suppressed by CACO-2 cells when leucocytes were stimulated directly with bacteria. This suppression was not paralleled by changes in the production of IL-10, IL-6 and transforming growth factor (TGF)-beta. When the bacteria were applied apically to the CACO-2 cell layer, the production of TNF-alpha, IL-12, IL-1beta, IL-8, IL-6, IL-10, TGF-beta and interferon-gamma was pronouncedly lower as compared to the bacterial stimulation of leucocytes beneath the CACO-2 cells. In the latter experiments, IL-6, IL-8 and TNF-alpha were the cytokines being mostly induced by apical addition of E. coli. Quantitative mRNA expression analysis revealed that IL-8 gene expression was equally induced in both CACO-2 and PBMC after apical stimulation with bacteria. Of note, bacteria-stimulated CACO-2 cells produced little or no cytokines in the absence of leucocytes, supporting the concept of leucocyte-epithelial cell cross-talk in modulating cytokine responses in the gut mucosa.

Zinc Oxide Protects Cultured Enterocytes from the Damage Induced by Escherichia coli

There is some evidence that zinc oxide (ZnO) protects against intestinal diseases. However, despite the suggestions that ZnO may have an antibacterial effect, the mechanisms of this protective effect have not yet been elucidated. We investigated the potential benefits of ZnO in protecting intestinal cells from damage induced by enterotoxigenic Escherichia coli (ETEC, strain K88) and the related mechanisms, using human Caco-2 enterocytes. Cell permeability, measured as transepithelial electrical resistance (TEER), was unaffected by 0.01 and 1 mmol/L ZnO treatments and moderately increased by 5 mmol/L ZnO, compared with untreated cells. Transfer of (14)C-inulin was slightly increased by 5 mmol/L ZnO compared with untreated cells; transfer was unaffected by lower concentrations. The TEER and (14)C-inulin transfer were lower in ETEC-infected cells than in uninfected cells. Treatment of ETEC exposure with 0.2 mmol/L ZnO prevented disruption of membrane integrity. The ETEC was able to adhere to enterocytes and, to some extent, invade the cells. The ZnO treatment reduced bacterial adhesion and blocked bacterial invasion. The ETEC infection upregulated the expression of the inflammatory cytokines interleukin-8, growth-related oncogene-alpha and tumor necrosis factor-alpha, and reduced that of the anti-inflammatory cytokine transforming growth factor-beta, compared with uninfected cells. The addition of 0.2 or 1 mmol/L ZnO counteracted the alteration of cytokine mRNA levels caused by ETEC. The protective effects of ZnO were not due to any antibacterial activity, because the viability of ETEC grown in a medium containing ZnO was unaffected. In conclusion, ZnO may protect intestinal cells from ETEC infection by inhibiting the adhesion and internalization of bacteria, preventing the increase of tight junction permeability and modulating cytokine gene expression.

Mucosal T cells: mediators or guardians of inflammatory bowel disease?

Because the mucosal immune system is continuously exposed to a myriad of potentially harmful environmental antigens, it frequently reacts with antiinflammatory/regulatory T cell responses driven by TGF-beta-producing TH3 cells and IL-10-producing regulatory T cells. Intestinal inflammation in patients with inflammatory bowel diseases is thought to result from an overwhelming uncontrolled activation of the mucosal immune system induced by antigens of the normal luminal flora in genetically susceptible individuals. Inflammatory bowel disease appears to be mediated by subsets of CD4 T lymphocytes or NK T cells secreting high levels of proinflammatory cytokines such as TNF-alpha. The increased expression of integrins/addressins in the inflamed gut and the increased expression of adhesion molecules on T cells facilitate migration of these pathogenic T cell subsets into the lamina propria. Additionally, the local activation of antiapoptotic pathways in pathogenic T lymphocytes leads to a further accumulation of these cells in the lamina propria, causing perpetuation and chronicity of inflammatory bowel disease. This concept is underlined by the finding that most potent immunosuppressive drugs used in treatment of inflammatory bowel disease seem to work by inducing T cell apoptosis via inhibition of STAT-3 and NFkappaB-dependent antiapoptotic pathways. Taken together, distinct T cell subsets appear to act as mediators or guardians of inflammatory bowel disease, and thus they play a central role in controlling the delicate balance between proinflammatory and antiinflammatory immune responses in the gut.

IKK beta and phosphatidylinositol 3-kinase/Akt participate in non-pathogenic Gram-negative enteric bacteria-induced RelA phosphorylation and NF-kappa B activation in both primary and intestinal epithelial cell lines

Pathogenic and enteroinvasive bacteria have been shown to trigger the I kappa B/NF-kappa B transcriptional system and proinflammatory gene expression in epithelial cells. In this study, we investigated the molecular mechanism of the commensal Gram-negative Bacteroides vulgatus-induced NF-kappa B signal transduction in intestinal epithelial cells (IEC). We report that B. vulgatus induced interleukin-1 receptor-associated kinase-1 degradation, I kappa B alpha phosphorylation/degradation, RelA and Akt phosphorylation, as well as NF-kappa B DNA binding and NF-kappa B transcriptional activity in rat non-transformed IEC-6 cells. B. vulgatus- but not interleukin-1 beta-mediated NF-kappa B transcriptional activity was inhibited by dominant negative (dn) toll-like receptor 4. Of importance, B. vulgatus induced I kappa B alpha phosphorylation/degradation and IKK alpha/beta and RelA phosphorylation in primary IEC derived from germ-free or mono-associated HLA-B27 transgenic and wild type rats, demonstrating the physiological relevance of non-pathogenic bacterial signaling in IEC. Adenoviral delivery of dn IKK beta or treatment with wortmannin inhibited B. vulgatus-induced endogenous RelA Ser-536 and GST-p65TAD (Ser-529/Ser-536) phosphorylation as well as NF-kappa B transcriptional activity in IEC-6 cells, suggesting a critical role of IKK beta and phosphatidylinositol 3-kinase/Akt in bacteria-induced RelA phosphorylation and NF-kappa B activation. Interestingly, B. vulgatus-induced I kappa B alpha degradation and NF-kappa B transcriptional activity in IEC transwell cultures were inhibited in the presence of lymphocytes. We propose that non-pathogenic B. vulgatus activates the NF-kappa B signaling pathway through both I kappa B degradation and RelA phosphorylation but that immune cells mediate tolerance of IEC to this commensal bacteria.