Novel Fecal Biomarkers That Precede Clinical Diagnosis of Ulcerative Colitis.

BACKGROUND & AIMS: Altered gut microbiota composition and function have been associated with inflammatory bowel diseases, including ulcerative colitis (UC), but the causality and mechanisms remain unknown. METHODS: We applied 16S ribosomal RNA gene sequencing, shotgun metagenomic sequencing, in vitro functional assays, and gnotobiotic colonizations to define the microbial composition and function in fecal samples obtained from a cohort of healthy individuals at risk for inflammatory bowel diseases (pre-UC) who later developed UC (post-UC) and matched healthy control individuals (HCs). RESULTS: Microbiota composition of post-UC samples was different from HC and pre-UC samples; however, functional analysis showed increased fecal proteolytic and elastase activity before UC onset. Metagenomics identified more than 22,000 gene families that were significantly different between HC, pre-UC, and post-UC samples. Of these, 237 related to proteases and peptidases, suggesting a bacterial component to the pre-UC proteolytic signature. Elastase activity inversely correlated with the relative abundance of Adlercreutzia and other potentially beneficial taxa and directly correlated with known proteolytic taxa, such as Bacteroides vulgatus. High elastase activity was confirmed in Bacteroides isolates from fecal samples. The bacterial contribution and functional significance of the proteolytic signature were investigated in germ-free adult mice and in dams colonized with HC, pre-UC, or post-UC microbiota. Mice colonized with or born from pre-UC-colonized dams developed higher fecal proteolytic activity and an inflammatory immune tone compared with HC-colonized mice. CONCLUSIONS: We have identified increased fecal proteolytic activity that precedes the clinical diagnosis of UC and associates with gut microbiota changes. This proteolytic signature may constitute a noninvasive biomarker of inflammation to monitor at-risk populations that can be targeted therapeutically with antiproteases.

Aryl hydrocarbon receptor ligand production by the gut microbiota is decreased in celiac disease leading to intestinal inflammation.

Metabolism of tryptophan by the gut microbiota into derivatives that activate the aryl hydrocarbon receptor (AhR) contributes to intestinal homeostasis. Many chronic inflammatory conditions, including celiac disease involving a loss of tolerance to dietary gluten, are influenced by cues from the gut microbiota. We investigated whether AhR ligand production by the gut microbiota could influence gluten immunopathology in nonobese diabetic (NOD) mice expressing DQ8, a celiac disease susceptibility gene. NOD/DQ8 mice, exposed or not exposed to gluten, were subjected to three interventions directed at enhancing AhR pathway activation. These included a high-tryptophan diet, gavage with Lactobacillus reuteri that produces AhR ligands or treatment with an AhR agonist. We investigated intestinal permeability, gut microbiota composition determined by 16S rRNA gene sequencing, AhR pathway activation in intestinal contents, and small intestinal pathology and inflammatory markers. In NOD/DQ8 mice, a high-tryptophan diet modulated gut microbiota composition and enhanced AhR ligand production. AhR pathway activation by an enriched tryptophan diet, treatment with the AhR ligand producer L. reuteri, or pharmacological stimulation using 6-formylindolo (3,2-b) carbazole (Ficz) decreased immunopathology in NOD/DQ8 mice exposed to gluten. We then determined AhR ligand production by the fecal microbiota and AhR activation in patients with active celiac disease compared to nonceliac control individuals. Patients with active celiac disease demonstrated reduced AhR ligand production and lower intestinal AhR pathway activation. These results highlight gut microbiota-dependent modulation of the AhR pathway in celiac disease and suggest a new therapeutic strategy for treating this disorder.

Pharmacological inactivation of the PI3K p110δ prevents breast tumour progression by targeting cancer cells and macrophages.

Patient selection for PI3K-targeted solid cancer treatment was based on the PIK3CA/PTEN mutational status. However, it is increasingly clear that this is not a good predictor of the response of breast cancer cells to the anti-proliferative effect of PI3K inhibitors, indicating that isoform(s) other than p110α may modulate cancer cells sensitivity to PI3K inhibition. Surprisingly, we found that although no mutations in the p110δ subunit have been detected thus far in breast cancer, the expression of p110δ becomes gradually elevated during human breast cancer progression from grade I to grade III. Moreover, pharmacological inactivation of p110δ in mice abrogated the formation of tumours and the recruitment of macrophages to tumour sites and strongly affected the survival, proliferation and apoptosis of grafted tumour cells. Pharmacological inactivation of p110δ in mice with defective macrophages or in mice with normal macrophages but grafted with p110δ-lacking tumours suppressed only partly tumour growth, indicating a requisite role of p110δ in both macrophages and cancer cells in tumour progression. Adoptive transfer of δD910A/D910A macrophages into mice with defected macrophages suppressed tumour growth, eliminated the recruitment of macrophages to tumour sites and prevented metastasis compared with mice that received WT macrophages further establishing that inactivation of p110δ in macrophage prevents tumour progression. Our work provides the first in vivo evidence for a critical role of p110δ in cancer cells and macrophages during solid tumour growth and may pave the way for the use of p110δ inhibitors in breast cancer treatment.

L. plantarum WCFS1 enhances Treg frequencies by activating DCs even in absence of sampling of bacteria in the Peyer Patches.

Probiotics such as L. plantarum WCFS1 can modulate immune responses in healthy subjects but how this occurs is still largely unknown. Immune-sampling in the Peyer Patches has been suggested to be one of the mechanisms. Here we studied the systemic and intestinal immune effects in combination with a trafficking study through the intestine of a well-established immunomodulating probiotic, i.e. L. plantarum WCFS1. We demonstrate that not more than 2-3 bacteria were sampled and in many animals not any bacterium could be found in the PP. Despite this, L. plantarum was associated with a strong increase in infiltration of regulatory CD103+ DCs and generation of regulatory T cells in the spleen. Also, a reduced splenic T helper cell cytokine response was observed after ex vivo restimulation. L. plantarum enhanced Treg cells and attenuated the T helper 2 response in healthy mice. We demonstrate that, in healthy mice, immune sampling is a rare phenomenon and not required for immunomodulation. Also in absence of any sampling immune activation was found illustrating that host-microbe interaction on the Peyer Patches was enough to induce immunomodulation of DCs and T-cells.

Modulation of Dendritic-Epithelial Cell Responses against Sphingomonas Paucimobilis by Dietary Fibers.

Non-fermenting Gram-negative bacilli, such as Sphingomonas paucimobilis (S.paucimobilis), are among the most widespread causes of nosocomial infections. Up to now, no definitive guidelines exist for antimicrobial therapy for S. paucimobilis infections. As we have shown that some dietary fibers exhibit pronounced immune-regulatory properties, we hypothesized that specific immune active dietary fibers might modulate the responses against S. paucimobilis. We studied the immunomodulatory effects of dietary fibers against S. paucimobilis on cytokine release and maturation of human dendritic cells (DCs) in co-cultures of DCs and intestinal epithelial cells (IECs). S. paucimobilis infection resulted in increased release of pro-inflammatory cytokines and chemokines by DCs/IECs; these effects were strongly attenuated by specific dietary fibers. Chicory inulin, sugar beet pectin, and both starches had the strongest regulatory effects. IL-12 and TNF-α were drastically diminished upon exposure to chicory inulin and sugar beet pectin, or both starches. High-maize 260, was more effective in the reduction of chemokine release than the others fibers tested. In summary, chicory inulin, sugar beet pectin, High-maize 260, and Novelose 330 attenuate S. paucimobilis-induced cytokines. These results demonstrate that dietary fibers with a specific chemical composition can be used to manage immune responses against pathogens such as S. paucimobilis.

Focus on PTEN Regulation.

The role of phosphatase and tensin homolog on chromosome 10 (PTEN) as a tumor suppressor has been for a long time attributed to its lipid phosphatase activity against PI(3,4,5)P3, the phospholipid product of the class I PI3Ks. Besides its traditional role as a lipid phosphatase at the plasma membrane, a wealth of data has shown that PTEN can function independently of its phosphatase activity and that PTEN also exists and plays a role in the nucleus, in cytoplasmic organelles, and extracellularly. Accumulating evidence has shed light on diverse physiological functions of PTEN, which are accompanied by a complex regulation of its expression and activity. PTEN levels and function are regulated transcriptionally, post-transcriptionally, and post-translationally. PTEN is also sensitive to regulation by its interacting proteins and its localization. Herein, we summarize the current knowledge on mechanisms that regulate the expression and enzymatic activity of PTEN and its role in human diseases.

Resistant starches differentially stimulate Toll-like receptors and attenuate proinflammatory cytokines in dendritic cells by modulation of intestinal epithelial cells.

SCOPE: Main objectives of this study were (1) to demonstrate direct signaling of starch on human dendritic cells (DCs), (2) to study whether this is mediated by the pattern recognition receptors such as Toll-like receptors (TLRs) and (3) to study whether intestinal epithelial cells (IECs) are involved in modulating the starch induced immune activation of DCs. METHODS AND RESULTS: Two different types of resistant starch, High-maize® 260 (RS2) and Novelose® 330 (RS3) were characterized for their starch content and particle size. Human DCs and reporter cells for TLRs were incubated with starches and analyzed for NF-kB/AP-1 activation. Complex coculture systems were applied to study the cross-talk. High-maize® 260 predominantly binds to TLR2 while Novelose® 330 binds to TLR2 and TLR5. The strong immune-stimulating effects of High-maize® 260 were attenuated by starch-exposed IECs illustrating the regulatory function of IECs. Despite these attenuating effects, DCs kept producing Th1 cytokines. CONCLUSION: Resistant starch possesses direct signaling capacity on human DCs in a starch-type-dependent manner. IECs regulate these responses. High-maize® 260 skews toward a more regulatory phenotype in coculture systems of DCs, IEC, and T cells.

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-1ß, IL-6, IL-8, TGF-ß2, RANTES and IP-10 levels and decreased IL-12p40, IL-10, TGF- ß1 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-1ß, IL-6, TGF-ß2 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.

The impact of dietary fibers on dendritic cell responses in vitro is dependent on the differential effects of the fibers on intestinal epithelial cells.

SCOPE: In the present study, the direct interaction of commonly consumed fibers with epithelial or dendritic cells (DCs) was studied. METHODS AND RESULTS: The fibers were characterized for their sugar composition and chain length profile. When in direct contact, fibers activate DCs only mildly. This was different when DCs and fibers were co-cultured together with supernatants from human epithelial cells (Caco spent medium). Caco spent medium enhanced the production of IL-12, IL-1Ra, IL-6, IL-8, TNF-α, MCP-1 (monocyte chemotactic protein), and MIP-1α but this was strongly attenuated by the dietary fibers. This attenuating effect on proinflammatory cytokines was dependent on the interaction of the fibers with Toll-like receptors as it was reduced by Pepinh-myd88. The interaction of galacto-oligosaccharides, chicory inulin, wheat arabinoxylan, barley ß-glucan with epithelial cells and DCs led to changes in the production of the Th1 cytokines in autologous T cells, while chicory inulin, and barley ß-glucan reduced the Th2 cytokine IL-6. The Treg-promoting cytokine IL-10 was induced by galacto-oligosaccharides whereas chicory inulin decreased the IL-10 production. CONCLUSIONS: Our results suggest that dietary fibers can modulate the host immune system not only by the recognized mechanism of effects on microbiota but also by direct interaction with the consumer's mucosa. This modulation is dietary fiber type dependent.

Lactobacillus rhamnosus and its cell-free culture supernatant differentially modulate inflammatory biomarkers in Escherichia coli-challenged human dendritic cells.

The intestinal immune system maintains a delicate balance between immunogenicity against invading pathogens and tolerance to the commensal microbiota and food antigens. Different strains of probiotics possess the ability to finely regulate the activation of dendritic cells (DC), polarising the subsequent activity of T-cells. Nevertheless, information about their underlying mechanisms of action is scarce. In the present study, we investigated the immunomodulatory effects of a potentially probiotic strain, Lactobacillus rhamnosus CNCM I-4036, and its cell-free culture supernatant (CFS) on human DC challenged with Escherichia coli. The results showed that the levels of pro-inflammatory cytokines such as IL-1ß, IL-6, IL-8 and IL-12p70 were higher in the cells treated with live L. rhamnosus than in the cells treated with the CFS. In the presence of E. coli, the supernatant was more effective than the probiotic bacteria in reducing the secretion of pro-inflammatory cytokines. In addition, live L. rhamnosus potently induced the production of transforming growth factor (TGF)-ß1 and TGF-ß2, whereas the CFS increased the secretion of TGF-ß1. However, in the presence of E. coli, both treatments restored the levels of TGF-ß. The probiotic strain L. rhamnosus CNCM I-4036 and its CFS were able to activate the Toll-like receptor signalling pathway, enhancing innate immunity. The two treatments induced gene transcription of TLR-9. Live L. rhamnosus activated the expression of TLR-2 and TLR-4 genes, whereas the CFS increased the expression of TLR-1 and TLR-5 genes. In response to the stimulation with probiotic/CFS and E. coli, the expression of each gene tested was notably increased, with the exception of TNF-α and NFKBIA. In conclusion, the CFS exhibited an extraordinary ability to suppress the production of pro-inflammatory cytokines by DC, and may be used as an effective and safer alternative to live bacteria.

Three main factors define changes in fecal microbiota associated with feeding modality in infants.

OBJECTIVES: There are many differences in the fecal infant microbiota associated with various feeding methods. The aim of this study was to examine the major differences in the fecal microbiota of breast-fed (BF) and formula-fed (FF) infants and to describe the principal bacterial components that would explain the variability in the predominant bacterial families and genus clusters. METHODS: Fecal samples from 58 infants, 31 of whom were exclusively BF and 27 of whom were exclusively FF with a standard formula in agreement with the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition recommendations, were analyzed by fluorescent in situ hybridization combined with flow cytometry. Principal component analysis was used to maximize the information gained for the predominant bacterial families and genus clusters using a minimal number of bacterial groups. RESULTS: The predominant detected group was Bifidobacterium, followed by Enterobacteriaceae and Bacteroides in both BF and FF infants. The Lactobacillus group was the only independent variable associated with FF infants. We also found that 3 principal components were sufficient to describe the association between the bacterial group, genus, and species studied in BF and FF infants; however, these components differed between BF and FF infants. For the former, the 3 factors found were Bifidobacterium/Enterobacteriaceae, Lactobacillus/Bacteroides, and Clostridium coccoides/Atopobium; for the latter, Bifidobacterium/Enterobacteriaceae, Bacteroides and C coccoides were observed. CONCLUSIONS: There is a clear clustering of components of infant microbiota based on the feeding method.

Cell-free culture supernatant of Bifidobacterium breve CNCM I-4035 decreases pro-inflammatory cytokines in human dendritic cells challenged with Salmonella typhi through TLR activation.

Dendritic cells (DCs) constitute the first point of contact between gut commensals and our immune system. Despite growing evidence of the immunomodulatory effects of probiotics, the interactions between the cells of the intestinal immune system and bacteria remain largely unknown. Indeed,, the aim of this work was to determine whether the probiotic Bifidobacterium breve CNCM I-4035 and its cell-free culture supernatant (CFS) have immunomodulatory effects in human intestinal-like dendritic cells (DCs) and how they respond to the pathogenic bacterium Salmonella enterica serovar Typhi, and also to elucidate the molecular mechanisms involved in these interactions. Human DCs were directly challenged with B. breve/CFS, S. typhi or a combination of these stimuli for 4 h. The expression pattern of genes involved in Toll-like receptor (TLR) signaling pathway and cytokine secretion was analyzed. CFS decreased pro-inflammatory cytokines and chemokines in human intestinal DCs challenged with S. typhi. In contrast, the B. breve CNCM I-4035 probiotic strain was a potent inducer of the pro-inflammatory cytokines and chemokines tested, i.e., TNF-α, IL-8 and RANTES, as well as anti-inflammatory cytokines including IL-10. CFS restored TGF-ß levels in the presence of Salmonella. Live B.breve and its supernatant enhanced innate immune responses by the activation of TLR signaling pathway. These treatments upregulated TLR9 gene transcription. In addition, CFS was a more potent inducer of TLR9 expression than the probiotic bacteria in the presence of S. typhi. Expression levels of CASP8 and IRAK4 were also increased by CFS, and both treatments induced TOLLIP gene expression. Our results indicate that the probiotic strain B. breve CNCM I-4035 affects the intestinal immune response, whereas its supernatant exerts anti-inflammatory effects mediated by DCs. This supernatant may protect immune system from highly infectious agents such as Salmonella typhi and can down-regulate pro-inflammatory pathways.

In vitro cell and tissue models for studying host-microbe interactions: a review.

Ideally, cell models should resemble the in vivo conditions; however, in most in vitro experimental models, epithelial cells are cultivated as monolayers, in which the establishment of functional epithelial features is not achieved. To overcome this problem, co-culture experiments with probiotics, dendritic cells and intestinal epithelial cells and three-dimensional models attempt to reconcile the complex and dynamic interactions that exist in vivo between the intestinal epithelium and bacteria on the luminal side and between the epithelium and the underlying immune system on the basolateral side. Additional models include tissue explants, bioreactors and organoids. The present review details the in vitro models used to study host-microbe interactions and explores the new tools that may help in understanding the molecular mechanisms of these interactions.

Sources, isolation, characterisation and evaluation of probiotics.

According to the FAO and the WHO, probiotics are 'live microorganisms which, when administered in adequate amounts, confer a health benefit on the host'. The strains most frequently used as probiotics include lactic acid bacteria and bifidobacteria, which are isolated from traditional fermented products and the gut, faeces and breast milk of human subjects. The identification of microorganisms is the first step in the selection of potential probiotics. The present techniques, including genetic fingerprinting, gene sequencing, oligonucleotide probes and specific primer selection, discriminate closely related bacteria with varying degrees of success. Additional molecular methods, such as denaturing gradient gel electrophoresis/temperature gradient gel electrophoresis and fluorescence in situ hybridisation, are employed to identify and characterise probiotics. The ability to examine fully sequenced genomes has accelerated the application of genetic approaches to the elucidation of the functional roles of probiotics. One of the best-demonstrated clinical benefits of probiotics is the prevention and treatment of acute and antibiotic-associated diarrhoea;however, there is mounting evidence for a potential role for probiotics in the treatment of allergies and intestinal, liver and metabolic diseases. There are various mechanisms by which probiotics exert their beneficial effects: regulation of intestinal permeability, normalisation of host intestinal microbiota, improvement of gut immune barrier function, and adjustment between pro- and anti-inflammatory cytokines. The number of studies carried out to test the effects of probiotics in vitro and in animals is enormous. However, the most reliable method of assessing the therapeutic benefits of any probiotic strain is the use of randomised, placebo-controlled trials, which are reviewed in this article [corrected].

Isolation, identification and characterisation of three novel probiotic strains (Lactobacillus paracasei CNCM I-4034, Bifidobacterium breve CNCM I-4035 and Lactobacillus rhamnosus CNCM I-4036) from the faeces of exclusively breast-fed infants.

The aim of the present study was to isolate, identify and characterise novel strains of lactic acid bacteria and bifidobacteria with probiotic properties from the faeces of exclusively breast-fed infants. Of the 4680 isolated colonies, 758 exhibited resistance to low pH and tolerance to high concentrations of bile salts; of these, only forty-two exhibited a strong ability to adhere to enterocytes in vitro. The identities of the isolates were confirmed by 16S ribosomal RNA (rRNA) sequencing, which permitted the grouping of the forty-two bacteria into three different strains that showed more than 99 % sequence identity with Lactobacillus paracasei, Lactobacillus rhamnosus and Bifidobacterium breve, respectively. The strain identification was confirmed by sequencing the 16S-23S rRNA intergenic spacer regions. Strains were assayed for enzymatic activity and carbohydrate utilisation, and they were deposited in the Collection Nationale de Cultures de Microorganismes (CNCM) of the Institute Pasteur and named L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036. The strains were susceptible to antibiotics and did not produce undesirable metabolites, and their safety was assessed by acute ingestion in immunocompetent and immunosuppressed BALB/c mouse models. The three novel strains inhibited in vitro the meningitis aetiological agent Listeria monocytogenes and human rotavirus infections. B. breve CNCM I-4035 led to a higher IgA concentration in faeces and plasma of mice. Overall, these results suggest that L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036 should be considered as probiotic strains, and their human health benefits should be further evaluated.

Competitive inhibition of three novel bacteria isolated from faeces of breast milk-fed infants against selected enteropathogens.

Numerous in vitro and in vivo studies conducted using different probiotic micro-organisms have demonstrated their ability to interfere with the growth and virulence of a variety of enteropathogens. The reported beneficial effects of the use of probiotics to complement antibiotic therapy or prevent diarrhoea or gastrointestinal infection in infants have increased in recent years. In the present study, we demonstrated the capacity of supernatants obtained from three novel probiotics (Lactobacillus paracasei CNCM I-4034, Bifidobacterium breve CNCM I-4035 and Lactobacillus rhamnosus CNCM I-4036) isolated from the faeces of breastfed infants to inhibit the growth of enterotoxigenic and enteropathogenic (EPEC) bacteria, such as Escherichia coli, Salmonella and Shigella. To assess their potential antimicrobial activity, the 17 and 24 h cell-free supernatants broth concentrates (10×) having 1, 2 or 4 % of the three probiotics were incubated with EPEC bacteria strains. After 17 h of co-culture, the supernatants were able to inhibit the growth of E. coli, Salmonella and Shigella up to 40, 55 and 81 %, respectively. However, the inhibitory capacity of some supernatants was maintained or completely lost when the supernatants (pH 3·0) were neutralised (pH 6·5). Overall, these results demonstrated that L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036 produce compounds that exhibited strain-specific inhibition of enterobacteria and have the potential to be used as probiotics in functional foods.

Probiotic mechanisms of action.

Probiotics are live microorganisms that provide health benefits to the host when ingested in adequate amounts. The strains most frequently used as probiotics include lactic acid bacteria and bifidobacteria. Probiotics have demonstrated significant potential as therapeutic options for a variety of diseases, but the mechanisms responsible for these effects have not been fully elucidated yet. Several important mechanisms underlying the antagonistic effects of probiotics on various microorganisms include the following: modification of the gut microbiota, competitive adherence to the mucosa and epithelium, strengthening of the gut epithelial barrier and modulation of the immune system to convey an advantage to the host. Accumulating evidence demonstrates that probiotics communicate with the host by pattern recognition receptors, such as toll-like receptors and nucleotide-binding oligomerization domain-containing protein-like receptors, which modulate key signaling pathways, such as nuclear factor-ĸB and mitogen-activated protein kinase, to enhance or suppress activation and influence downstream pathways. This recognition is crucial for eliciting measured antimicrobial responses with minimal inflammatory tissue damage. A clear understanding of these mechanisms will allow for appropriate probiotic strain selection for specific applications and may uncover novel probiotic functions. The goal of this systematic review was to explore probiotic modes of action focusing on how gut microbes influence the host.

Human intestinal dendritic cells decrease cytokine release against Salmonella infection in the presence of Lactobacillus paracasei upon TLR activation.

Probiotic bacteria have been shown to modulate immune responses and could have therapeutic effects in allergic and inflammatory disorders. However, little is known about the signalling pathways that are engaged by probiotics. Dendritic cells (DCs) are antigen-presenting cells that are involved in immunity and tolerance. Monocyte-derived dendritic cells (MoDCs) and murine DCs are different from human gut DCs; therefore, in this study, we used human DCs generated from CD34+ progenitor cells (hematopoietic stem cells) harvested from umbilical cord blood; those DCs exhibited surface antigens of dendritic Langerhans cells, similar to the lamina propria DCs in the gut. We report that both a novel probiotic strain isolated from faeces of exclusively breast-fed newborn infants, Lactobacillus paracasei CNCM I-4034, and its cell-free culture supernatant (CFS) decreased pro-inflammatory cytokines and chemokines in human intestinal DCs challenged with Salmonella. Interestingly, the supernatant was as effective as the bacteria in reducing pro-inflammatory cytokine expression. In contrast, the bacterium was a potent inducer of TGF-ß2 secretion, whereas the supernatant increased the secretion of TGF-ß1 in response to Salmonella. We also showed that both the bacteria and its supernatant enhanced innate immunity through the activation of Toll-like receptor (TLR) signalling. These treatments strongly induced the transcription of the TLR9 gene. In addition, upregulation of the CASP8 and TOLLIP genes was observed. This work demonstrates that L. paracasei CNCM I-4034 enhanced innate immune responses, as evidenced by the activation of TLR signalling and the downregulation of a broad array of pro-inflammatory cytokines. The use of supernatants like the one described in this paper could be an effective and safe alternative to using live bacteria in functional foods.