The role of TLRs, NLRs, and RLRs in mucosal innate immunity and homeostasis

Gut-CNS-Axis as Possibility to Modulate Inflammatory Disease Activity-Implications for Multiple Sclerosis

In the last decade the role of environmental factors as modulators of disease activity and progression has received increasing attention. In contrast to classical environmental modulators such as exposure to sun-light or fine dust pollution, nutrition is an ideal tool for a personalized human intervention. Various studies demonstrate a key role of dietary factors in autoimmune diseases including Inflammatory Bowel Disease (IBD), rheumatoid arthritis or inflammatory central nervous system (CNS) diseases such as Multiple Sclerosis (MS). In this review we discuss the connection between diet and inflammatory processes via the gut-CNS-axis. This axis describes a bi-directional communication system and comprises neuronal signaling, neuroendocrine pathways and modulation of immune responses. Therefore, the gut-CNS-axis represents an emerging target to modify CNS inflammatory activity ultimately opening new avenues for complementary and adjunctive treatment of autoimmune diseases such as MS.

Gut homeostasis and regulatory T cell induction depend on molecular chaperone gp96 in CD11c+ cells

The intestinal immunity and tolerance are orchestrated by both the innate and the adaptive immune system. Intestinal professional antigen presenting cells (pAPCs) recognize and respond to the gut microbiota through multiple pattern-recognition receptors, including TLRs and NLRs. How gut pAPCs maintain mucosal homeostasis remains incompletely understood. Heat shock protein gp96, also known as grp94, is an essential immune chaperone for TLRs. However, the role of gp96 in regulating CD11c⁺ APCs in the gut immunity and tolerance is unknown. By a genetic strategy, we report here that selective deletion of gp96 from CD11c⁺ cells in mice results in alteration of dendritic cell and T cell subsets in the gut as well as loss of antigen-specific regulatory T cell induction in the mesenteric lymph nodes. Strikingly, these conditional gp96-null mice developed spontaneous colitis, had increased levels of systemic and fecal IgA, and were highly susceptible to chemical-induced colitis. Our findings for the first time demonstrate that gp96 is essential for CD11c⁺ cells to induce regulatory T cells and maintain gut homeostasis, illustrating the importance of protein immune chaperone in safeguarding against immune pathology.

Self-adjuvanting C18 lipid vinil sulfone-PP2A vaccine: study of the induced immunomodulation against Trichuris muris infection

Despite the importance of the adjuvant in the immunization process, very few adjuvants merge with the antigens in vaccines. A synthetic self-adjuvant oleic-vinyl sulfone (OVS) linked to the catalytic region of recombinant serine/threonine phosphatase 2A from the nematode Angiostrongylus costaricensis (rPP2A) was used for intranasal immunization in mice previously infected with Trichuris muris. The animal intranasal immunization with rPP2A-OVS showed a reduction of 99.01% in the number of the nematode eggs and 97.90% in adult. The immunohistochemical analysis of the intestinal sections showed that in immunized animals with lipopeptide the mucus was significantly higher than in the other experimental groups. Also, these animals presented significantly different chemokine, CCL20 and CCL11, levels. However, although the number and size of Tuft cells did not vary between groups, the intensity of fluorescence per cell was significant in the group immunized with the rPP2A-OVS. The results of the present study suggest that mice immunized with the lipopeptide are capable of activating a combined Th17/Th9 response. This strategy of immunization may be of great applicability not only in immunotherapy and immunoprophylaxis to control diseases caused by nematodes but also in pathologies necessitating action at the level of the Th9 response in the intestinal mucosa.

Visualization of Probiotic-Mediated Ca2+ Signaling in Intestinal Epithelial Cells In Vivo

Probiotics, such as lactic acid bacteria (LAB) and Bacillus subtilis var. natto, have been shown to modulate immune responses. It is important to understand how probiotic bacteria impact intestinal epithelial cells (IECs), because IECs are the first line of defense at the mucosal surface barrier and their activities substantially affect the gut microenvironment and immunity. However, to date, their precise mechanism remains unknown due to a lack of analytical systems available for live animal models. Recently, we generated a conditional Ca²⁺ biosensor Yellow Cameleon (YC3.60) transgenic mouse line and established 5D (x, y, z, time, and Ca²⁺) intravital imaging systems of lymphoid tissues including those in Peyer’s patches and bone marrow. In the present study, we further advance our intravital imaging system for intestinal tracts to visualize IEC responses against orally administrated food compounds in real time. Using this system, heat-killed B. subtilis natto, a probiotic TTCC012 strain, is shown to directly induce Ca²⁺ signaling in IECs in mice housed under specific pathogen-free conditions. In contrast, this activation is not observed in the Lactococcus lactis strain C60; however, when we generate germ-free YC3.60 mice and observe the LAB stimulation of IECs in the absence of gut microbiota, C60 is capable of inducing Ca²⁺ signaling. This is the first study to successfully visualize the direct effect of probiotics on IECs in live animals. These data strongly suggest that probiotic strains stimulate IECs under physiological conditions and that their activity is affected by the microenvironment of the small intestine, such as commensal bacteria.

Characterization and Genetic Analyses of New Genes Coding for NOD2 Interacting Proteins

NOD2 contributes to the innate immune response and to the homeostasis of the intestinal mucosa. In response to its bacterial ligand, NOD2 interacts with RICK and activates the NF-κB and MAPK pathways, inducing gene transcription and synthesis of proteins required to initiate a balanced immune response. Mutations in NOD2 have been associated with an increased risk of Crohn’s Disease (CD), a disabling inflammatory bowel disease (IBD). Because NOD2 signaling plays a key role in CD, it is important to further characterize the network of protein interacting with NOD2. Using yeast two hybrid (Y2H) screens, we identified new NOD2 interacting proteins (NIP). The primary interaction was confirmed by coimmunoprecipitation and/or bioluminescence resonance energy transfer (BRET) experiments for 11 of these proteins (ANKHD1, CHMP5, SDCCAG3, TRIM41, LDOC1, PPP1R12C, DOCK7, VIM, KRT15, PPP2R3B, and C10Orf67). These proteins are involved in diverse functions, including endosomal sorting complexes required for transport (ESCRT), cytoskeletal architecture and signaling regulation. Additionally, we show that the interaction of 8 NIPs is compromised with the 3 main CD associated NOD2 mutants (R702W, G908R and 1007fs). Furthermore, to determine whether these NOD2 protein partners could be encoded by IBD susceptibility genes, a transmission disequilibrium test (TDT) was performed on 101 single nucleotide polymorphisms (SNPs) and the main corresponding haplotypes in genes coding for 15 NIPs using a set of 343 IBD families with 556 patients. Overall this work did not increase the number of IBD susceptibility genes but extends the NOD2 protein interaction network and suggests that NOD2 interactome and signaling depend upon the NOD2 mutation profile in CD.

Inflammation and the Intestinal Barrier: Leukocyte-Epithelial Cell Interactions, Cell Junction Remodeling, and Mucosal Repair

The intestinal tract is lined by a single layer of columnar epithelial cells that forms a dynamic, permeable barrier allowing for selective absorption of nutrients, while restricting access to pathogens and food-borne antigens. Precise regulation of epithelial barrier function is therefore required for maintaining mucosal homeostasis and depends, in part, on barrier-forming elements within the epithelium and a balance between pro- and anti-inflammatory factors in the mucosa. Pathologic states, such as inflammatory bowel disease, are associated with a leaky epithelial barrier, resulting in excessive exposure to microbial antigens, recruitment of leukocytes, release of soluble mediators, and ultimately mucosal damage. An inflammatory microenvironment affects epithelial barrier properties and mucosal homeostasis by altering the structure and function of epithelial intercellular junctions through direct and indirect mechanisms. We review our current understanding of complex interactions between the intestinal epithelium and immune cells, with a focus on pathologic mucosal inflammation and mechanisms of epithelial repair. We discuss leukocyte-epithelial interactions, as well as inflammatory mediators that affect the epithelial barrier and mucosal repair. Increased knowledge of communication networks between the epithelium and immune system will lead to tissue-specific strategies for treating pathologic intestinal inflammation.

Targeting mast cells: Uncovering prolific therapeutic role in myriad diseases

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases.

Transcriptome analysis reveals regional and temporal differences in mucosal immune system development in the small intestine of neonatal calves

Background

Postnatal development of the mammalian mucosal immune system is crucial for responding to the rapid colonization by commensal bacteria and possible exposure to pathogens. This study analyzed expression patterns for mRNAs and their relationship with microRNAs (miRNAs) in the bovine small intestine during the critical neonatal period (0 to 42 days). This analysis revealed molecular mechanisms regulating the postnatal development of the intestinal mucosal immune system.

Results

Small intestine samples (jejunum and ileum) were collected from newborn male, Holstein calves immediately post-partum (n = 3) and at 7 (n = 5), 21 (n = 5), and 42 (n = 5) days of age and the transcriptomes were profiled using RNA-Seq. When analyzing all time points collectively, greater expression of genes encoding the complement functional pathway, as well as lower expression of genes encoding Toll-like receptors and NOD-like receptors were observed in the jejunum when compared to the ileum. In addition, significant changes in the expression of immune-related genes were detected within the first week post-partum in both jejunum and ileum. For example, increased expression of genes encoding tight junction proteins (claudin 1, claudin 4 and occludin), an antimicrobial peptide (Regenerating Islet-Derived 3-γ), NOD-like receptors (NACHT, LRR and PYD domain-containing protein 3), regulatory T cell marker (forkhead box P3), and both anti-inflammatory (interleukin 10) and pro-inflammatory (interleukin 8) cytokines was observed throughout the small intestine of 7-day-old calves when compared to newborn calves. Moreover, the expression of mucosal immune-related genes were either positively or negatively correlated with total bacterial population depending on both intestinal region and age. The integrated analysis of miRNAs and mRNAs supported the conclusion that miRNAs may regulate temporal changes in the expression of genes encoding tight junction proteins (miR-335), cytokines (miR-335) and bacterial recognition (miR-100) during the first week of small intestine development.

Conclusion

The rapid development of transcriptional differences between jejunum and ileum reveal that these two intestinal regions make distinct contributions to the intestinal mucosal immune system during the early neonatal period. In addition, transcriptome analysis indicates that the first week after birth is a very dynamic developmental period for the intestinal mucosal immune system and these changes may be regulated by both miRNAs and microbial colonization. Findings from this study indicate that a detailed analysis of both the abundance and diversity of the colonizing microbiome may be necessary to understand factors regulating the rapid development of the mucosal immune system during the first week of life.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2957-y) contains supplementary material, which is available to authorized users.

Influence of orally fed a select mixture of Bacillus probiotics on intestinal T-cell migration in weaned MUC4 resistant pigs following Escherichia coli challenge

Efficient strategies for treating enteritis caused by F4⁺ enterotoxigenic Escherichia coli (ETEC)/verocytotoxigenic Escherichia coli (VTEC)/enteropathogenic E. coli (EPEC) in mucin 4 resistant (MUC4 RR; supposed to be F4ab/ac receptor–negative [F4ab/acR⁻]) pigs remain elusive. A low (3.9 × 10⁸ CFU/day) or high (7.8 × 10⁸ CFU/day) dose of Bacillus licheniformis and Bacillus subtilis spore mixture (BLS-mix) was orally administered to MUC4 RR piglets for 1 week before F4⁺ ETEC/VTEC/EPEC challenge. Orally fed BLS-mix upregulated the expression of TLR4, NOD2, iNOS, IL-8, and IL-22 mRNAs in the small intestine of pigs challenged with E. coli. Expression of chemokine CCL28 and its receptor CCR10 mRNAs was upregulated in the jejunum of pigs pretreated with high-dose BLS-mix. Low-dose BLS-mix pretreatment induced an increase in the proportion of peripheral blood CD4⁻CD8⁻ T-cell subpopulations and high-dose BLS-mix induced the expansion of CD4⁻CD8⁻ T cells in the inflamed intestine. Immunostaining revealed that considerable IL-7Rα–expressing cells accumulated at the lamina propria of the inflamed intestines after E. coli challenge, even in pigs pretreated with either low- or high-dose BLS-mix, although Western blot analysis of IL-7Rα expression in the intestinal mucosa did not show any change. Our data indicate that oral administration of the probiotic BLS-mix partially ameliorates E. coli-induced enteritis through facilitating upregulation of intestinal IL-22 and IκBα expression, and preventing loss of intestinal epithelial barrier integrity via elevating ZO-1 expression. However, IL-22 also elicits an inflammatory response in inflamed intestines as a result of infection with enteropathogenic bacteria.

Stability of Reference Gene Expression After Porcine Sapelovirus Infection in Porcine Intestinal Epithelial Cells

Intestinal epithelial cells, which serve as the first physical barrier to protect intestinal tract from external antigens, have an important role in the local innate immunity. Screening of reference genes that have stable expression levels after viral infection in porcine intestinal epithelial cells is critical for ensuring the reliability of the expression analysis on anti-infection genes in porcine intestinal epithelial cells. In this study, nine common reference genes in pigs, including ACTB, B2M, GAPDH, HMBS, SDHA, HPRT1, TBP, YWHAZ, and RPL32, were chosen as the candidate reference genes. Porcine sapelovirus (PSV) was used as a model virus to infect porcine intestinal epithelial cell line (IPEC-J2). The expression stability of the nine genes was assessed by the geNorm, NormFinder, and BestKeeper software. Moreover, RefFinder program was used to evaluate the analytical results of above three softwares, and a relative expression experiment of selected target gene was used to verify the analysis results. The comprehensive results indicated that the gene combination of TBP and RPL32 has the most stable expression, which could be considered as an appropriate reference gene for research on gene expression after PSV infection in IPEC-J2cells. The results provided essential data for expression analysis of anti-infection genes in porcine intestinal epithelial cells.

The absence of microbiota delays the inflammatory response to Cryptococcus gattii

The inflammatory response plays a crucial role in infectious diseases, and the intestinal microbiota is linked to maturation of the immune system. However, the association between microbiota and the response against fungal infections has not been elucidated. Our aim was to evaluate the influence of microbiota on Cryptococcus gattii infection. Germ-free (GF), conventional (CV), conventionalized (CVN-mice that received feces from conventional animals), and LPS-stimulated mice were infected with C. gattii. GF mice were more susceptible to infection, showing lower survival, higher fungal burden in the lungs and brain, increased behavioral changes, reduced levels of IFN-γ, IL-1β and IL-17, and lower NFκBp65 phosphorylation compared to CV mice. Low expression of inflammatory cytokines was associated with smaller yeast cells and polysaccharide capsules (the main virulence factor of C. gattii) in the lungs, and less tissue damage. Furthermore, macrophages from GF mice showed reduced ability to engulf, produce ROS, and kill C. gattii. Restoration of microbiota (CVN mice) or LPS administration made GF mice more responsive to infection, which was associated with increased survival and higher levels of inflammatory mediators. This study is the first to demonstrate the influence of microbiota in the host response against C. gattii.

Association of NOD1, CXCL16, STAT6 and TLR4 gene polymorphisms with Malaysian patients with Crohn's disease

Crohn's disease (CD) is a prominent type of inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract. CD is known to have higher prevalence in the Western countries, but the number of cases has been increasing in the past decades in Asia, including Malaysia. Therefore, there is a need to investigate the underlining causes of CD that may shed light on its prevention and treatment. In this study, genetic polymorphisms in NOD1 (rs2075820), CXCL16 (rs2277680), STAT6 (rs324015) and TLR4 (rs4986791) genes were examined in a total of 335 individuals (85 CD patients and 250 healthy controls) with PCR-RFLP approach. There was no significant association observed between NOD1 rs2075820 and STAT6 rs324015 with the onset of CD in the studied cohort. However, the G allele of CXCL16 rs2277680 was found to have a weak association with CD patients (P = 0.0482; OR = 1.4310). The TLR4 rs4986791 was also significantly associated to CD. Both the homozygous C genotype (P = 0.0029; OR = 0.3611) and C allele (P = 0.0069; OR = 0.4369) were observed to confer protection against CD. On the other hand, the heterozygous C/T genotype was a risk genotype (P = 0.0015; OR = 3.1392). Further ethnic-stratified analysis showed that the significant associations in CXCL16 rs2277680 and TLR4 rs4986791 were accounted by the Malay cohort. In conclusion, the present study reported two CD-predisposing loci in the Malay CD patients. However, these loci were not associated to the onset of CD in Chinese and Indian patients.

Scavenger receptor SRA attenuates TLR4-induced microglia activation in intracerebral hemorrhage

Scavenger receptor A (SRA) has been shown to participate in the pattern recognition of pathogen infection. However, its role in intracerebral hemorrhage has not been well defined. In this study, we detected SRA and TLR4 expression and inflammatory response of microglia treated with erythrocyte lysate in vitro, and observed the cerebral water content and neurological deficit of ICH mice in vivo. We found that SRA deficiency leads to greater sensitivity to erythrocyte lysate-induced inflammatory response. SRA down-regulated inflammatory response expression in microglia by suppressing TLR4-induced activation. Collectively, we have identified the molecular linkage between SRA and the TLR4 signaling pathways in ICH. And our results reveal that SRA has important clinical implications for TLR-targeted immunotherapeutical strategy in ICH.

Bropirimine inhibits osteoclast differentiation through production of interferon-β

Bropirimine is a synthetic agonist for toll-like receptor 7 (TLR7). In this study, we investigated the effects of bropirimine on differentiation and bone-resorbing activity of osteoclasts in vitro. Bropirimine inhibited osteoclast differentiation of mouse bone marrow-derived macrophages (BMMs) induced by receptor activator of nuclear factor κB ligand (RANKL) in a concentration-dependent manner. Furthermore, it suppressed the mRNA expression of nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1), a master transcription factor for osteoclast differentiation, without affecting BMM viability. Bropirimine also inhibited osteoclast differentiation induced in co-cultures of mouse bone marrow cells (BMCs) and mouse osteoblastic UAMS-32 cells in the presence of activated vitamin D3. Bropirimine partially suppressed the expression of RANKL mRNA in UAMS-32 cells induced by activated vitamin D3. Finally, the anti-interferon-β (IFN-β) antibody restored RANKL-dependent differentiation of BMMs into osteoclasts suppressed by bropirimine. These results suggest that bropirimine inhibits differentiation of osteoclast precursor cells into osteoclasts via TLR7-mediated production of IFN-β.

Recent advances on anti-HIV vaginal delivery systems development

A review of the recent outcomes regarding technologies to prevent vaginal transmission of HIV, mainly by using antiretroviral (ARV) drugs formulated as microbicides. An introduction about the HIV transmission mechanisms by the vaginal route is included, together with the recent challenges faced for development of successful microbicide products. The outcomes of clinical evaluations are mentioned, and the different formulation strategies studied to-date, with the requirements, advantages, disadvantages and limitations of each dosage-form type, are presented. Finally, the recent attempts to apply various types of nanotechnologies in order to develop advanced microbicide-products and overcome existing limitations, are discussed.

Compartmentalizing intestinal epithelial cell toll-like receptors for immune surveillance

Toll-like receptors (TLRs) are membrane-bound microbial sensors that mediate important host-to-microbe responses. Cell biology aspects of TLR function have been intensively studied in professional immune cells, in particular the macrophages and dendritic cells, but not well explored in other specialized epithelial cell types. The adult intestinal epithelial cells are in close contact with trillions of enteric microbes and engage in lifelong immune surveillance. Mature intestinal epithelial cells, in contrast to immune cells, are highly polarized. Recent studies suggest that distinct mechanisms may govern TLR traffic and compartmentalization in these specialized epithelial cells to establish and maintain precise signaling of individual TLRs. We, using immune cells as references, discuss here the shared and/or unique molecular machineries used by intestinal epithelial cells to control TLR transport, localization, processing, activation, and signaling. A better understanding of these mechanisms will certainly generate important insights into both the mechanism and potential intervention of leading digestive disorders, in particular inflammatory bowel diseases.

Activation of NLRC4 downregulates TLR5-mediated antibody immune responses against flagellin

Bacterial flagellin is a unique pathogen-associated molecular pattern (PAMP), which can be recognized by surface localized Toll-like receptor 5 (TLR5) and the cytosolic NOD-like receptor (NLR) protein 4 (NLRC4) receptors. Activation of the TLR5 and/or NLRC4 signaling pathways by flagellin and the resulting immune responses play important roles in anti-bacterial immunity. However, it remains unclear how the dual activities of flagellin that activate the TLR5 and/or NLRC4 signaling pathways orchestrate the immune responses. In this study, we assessed the effects of flagellin and its mutants lacking the ability to activate TLR5 and NLRC4 alone or in combination on the adaptive immune responses against flagellin. Flagellin that was unable to activate NLRC4 induced a significantly higher antibody response than did wild-type flagellin. The increased antibody response could be eliminated when macrophages were depleted in vivo. The activation of NLRC4 by flagellin downregulated the flagellin-induced and TLR5-mediated immune responses against flagellin.

TLR2 and AP-1/NF-kappaB are involved in the regulation of MMP-9 elicited by heat killed Listeria monocytogenes in human monocytic THP-1 cells

BACKGROUND

MMP-9 is crucial for a normal immune response, but excessive release of this enzyme leads to severe tissue damage. Listeria monocytogenes (LM) is an opportunistic food-borne pathogen causing listerosis, meningitis and sepsis. Heat killed Listeria monocytogenes (HKLM) activates immune system and leads production of cytokines and chemokines. However, nothing is known about the involvement of HKLM in MMP-9 regulation. Therefore we investigated the role of HKLM in the regulation of MMP-9 gene expression in THP-1 cells.

METHODS

Commercially available heat killed Listeria monocytogenes was used in this study. HKLM-induced MMP-9 expression was assessed with quantitative real-time qPCR and ELISA. Action of HKLM in different signaling pathways were studied by using THP-1-XBlue™ cells (THP-1-cells with NF-κB/AP-1 reporter construct), THP-1-XBlue™-defMyD cells (MyD88(-/-) THP-1 cells), anti-TLR2 mAb and pharmacological inhibitors. Phospho and total proteins were determined by Western blotting.

RESULTS

Increased MMP-9 production (mRNA: 395-Fold; Protein: 8141 pg/ml; P < 0.05) was observed in HKLM stimulated THP-1 cells as compared to the un-stimulated THP-1 cells. This production of MMP-9 was completely abrogated by anti-TLR2 blocking mAb (P = 0.0024). Furthermore, THP-1-XBlue™-defMyD cells were unable to produce MMP-9 in response to HKLM. HKLM- induced activation of NF-kappaB/AP-1 was also observed in THP-1-XBlue™ Cells. In addition, inhibitors of JNK (SP600125), MEK/ERK (U0126; PD98056), p38 MAPK (SB203580) and NF-kappaB (BAY 11-7085, Triptolide and Resveratrol) significantly suppressed (P < 0.05) HKLM-stimulated MMP-9 expression.

CONCLUSION

Our results indicate that HKLM activates TLR2 and NF-κB/AP-1 signaling pathways, leading to up-regulation of MMP-9 production in THP-1 cells. Thus, MMP-9 could be an appropriate therapeutic target to stop severe tissue damage caused by infection or chronic inflammation.

Dendritic cell functions: Learning from microbial evasion strategies

Dendritic cells (DCs) are specialized antigen presenting cells (APC) that are fundamental to initiate both immunity and tolerance. DCs play a 'sentinel' role to protect our body from potential pathogens and induce tolerogenic responses toward harmless antigens. The flexibility of DCs or macrophages to adapt to the environment and to respond accordingly can be hijacked by pathogens for their own interest to transform a potentially immunogenic APC into a tolerogenic cell with clear consequences in pathogen clearance. While these immune evasion mechanisms can be detrimental for the host, they can highlight important molecular pathways in DCs necessary for their function. In this review we will mention several mechanisms employed by pathogens to evade DC patrolling function.

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.

Intestinal microbiota as modulators of the immune system and neuroimmune system: impact on the host health and homeostasis

Many immune-based intestinal disorders, such as ulcerative colitis and Crohn's disease, as well as other illnesses, may have the intestines as an initial cause or aggravator in the development of diseases, even apparently not correlating directly to the intestine. Diabetes, obesity, multiple sclerosis, depression, and anxiety are examples of other illnesses discussed in the literature. In parallel, importance of the gut microbiota in intestinal homeostasis and immunologic conflict between tolerance towards commensal microorganisms and combat of pathogens is well known. Recent researches show that the immune system, when altered by the gut microbiota, influences the state in which these diseases are presented in the patient directly and indirectly. At the present moment, a considerable number of investigations about this subject have been performed and published. However, due to difficulties on correlating information, several speculations and hypotheses are generated. Thus, the present review aims at bringing together how these interactions work-gut microbiota, immune system, and their influence in the neuroimmune system.

Emerging role of Toll-like receptor 4 in hepatocellular carcinoma

Toll-like receptor (TLR) signaling has been implicated in inflammatory-related cancers. The upregulation of TLR signaling in hepatocellular carcinoma (HCC) suggests that it may play an essential role in the prognosis of chronic and inflammatory diseases that ultimately culminate in HCC. Here, we provide evidence about the involvement of the TLR pathway in the initiation, progression, and metastasis of HCC. The differential expression of TLR in epithelial cells has also been discussed. In particular, we emphasize the physiological role of TLR4 in the development and pathogenesis of HCC and propose novel and promising approaches for HCC therapeutics with the aid of TLR ligands.

Expression of Toll-like receptors in the mucosa of patients with ulcerative colitis

Patients with ulcerative colitis (UC) have a high risk of developing colorectal cancer. The aim of the present study was to evaluate the expression pattern of Toll-like receptors (TLRs) in the colonic mucosa of patients with UC. Colonic mucosal biopsy specimens were collected during colonoscopy from 30 patients with UC and 30 patients with normal findings as controls. The protein and mRNA expression levels of TLRs 1-4 and TLR9 were measured by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction analysis, respectively. The results showed that the mRNA and protein expression of TLR2, TLR4 and TLR9, but not TLR1 and TLR3, was significantly increased in the colonic mucosa of patients with UC compared with that in the normal controls. TLR (TLR2, TLR4 and TLR9) immunoreactivity was found in the cytoplasm of epithelial cells in the mucosa, and occasionally in the endothelium of small vessels of the stromal tissues. In conclusion, TLR2, TLR4 and TLR9 expression may be important in the biological pathogenesis of UC. TLR alterations in the innate response system may contribute to the pathogenesis of UC.

Dendritic cell-epithelial cell crosstalk in the gut

Intestinal epithelial cells are fundamental to maintain barrier integrity and to participate in food degradation and absorption, but they can also decipher signals coming from the outside world and 'educate' the immune system accordingly. In particular, they interact with dendritic cells (DCs) and other intraepithelial immune cells to drive tolerogenic responses under steady state, but they can also release immune mediators to recruit inflammatory cells and to elicit immunity to infectious agents. When these interactions are deregulated, immune disorders can develop. In this review, we discuss some important features of epithelial cells and DCs and their fruitful interactions.

Effect of Sulforaphane on NOD2 via NF-κB: implications for Crohn's disease

Background

Sulforaphane has well established anti-cancer properties and more recently anti-inflammatory properties have also been determined. Sulforaphane has been shown to inhibit PRR-mediated pro-inflammatory signalling by either directly targeting the receptor or their downstream signalling molecules such as the transcription factor, NF-κB. These results raise the possibility that PRR-mediated inflammation could be suppressed by specific dietary bioactives. We examined whether sulforaphane could suppress NF-κB via the NOD2 pathway.

Methods

Human embryonic kidney 293T (HEK293T) cells were stably transfected with NOD2 variants and the NF-κB reporter, pNifty2-SEAP. The cells were co-treated with sulforaphane and MDP and secreted alkaline phosphatase (SEAP) production was determined.

Results

We found that sulforaphane was able to significantly suppress the ligand-induced NF-κB activity at physiologically relevant concentrations, achievable via the consumption of broccoli within the diet.

Conclusions

These results demonstrate that the anti-inflammatory role of sulforaphane is not restricted to LPS-induced inflammatory signalling. These data add to the growing evidence that PRR activation can be inhibited by specific phytochemicals and thus suggests that diet could be a way of controlling inflammation. This is particularly important for a disease like Crohn’s disease where diet can play a key role in relieving or exacerbating symptoms.

Safety of Bifidobacterium animalis subsp. lactis (B. lactis) strain BB-12-supplemented yogurt in healthy adults on antibiotics: a phase I safety study

Probiotics are live microorganisms that, when administered in sufficient doses, provide health benefits on the host. The United States Food and Drug Administration (FDA) requires phase I safety studies for probiotics when the intended use of the product is as a drug. The purpose of the study was to determine the safety of Bifidobacterium animalis subsp lactis (B. lactis) strain BB-12 (BB-12)-supplemented yogurt when consumed by a generally healthy group of adults who were prescribed a 10-day course of antibiotics for a respiratory infection. Secondary aims were to assess the ability of BB-12 to affect the expression of whole blood immune markers associated with cell activation and inflammatory response. A phase I, double-blinded, randomized controlled study was conducted in compliance with FDA guidelines for an Investigational New Drug (IND). Forty participants were randomly assigned to consume 4 ounces of either BB-12 -supplemented yogurt or non-supplemented control yogurt daily for 10 d. The primary outcome was to assess safety and tolerability, assessed by the number of reported adverse events. A total of 165 non-serious adverse events were reported, with no differences between the control and BB-12 groups. When compared to the control group, B lactis fecal levels were modestly higher in the BB-12-supplemented group. In a small subset of patients, changes in whole blood expression of genes associated with regulation and activation of immune cells were detected in the BB-12-supplemented group. BB-12-supplemented yogurt is safe and well tolerated when consumed by healthy adults concurrently taking antibiotics. This study will form the basis for future randomized clinical trials investigating the potential immunomodulatory effects of BB-12-supplemented yogurt in a variety of disease states.

Collaborative action of Toll-like and NOD-like receptors as modulators of the inflammatory response to pathogenic bacteria

Early sensing of pathogenic bacteria by the host immune system is important to develop effective mechanisms to kill the invader. Microbial recognition, activation of signaling pathways, and effector mechanisms are sequential events that must be highly controlled to successfully eliminate the pathogen. Host recognizes pathogens through pattern-recognition receptors (PRRs) that sense pathogen-associated molecular patterns (PAMPs). Some of these PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-like receptors (NLRs), retinoic acid-inducible gene-I- (RIG-I-) like receptors (RLRs), and C-type lectin receptors (CLRs). TLRs and NLRs are PRRs that play a key role in recognition of extracellular and intracellular bacteria and control the inflammatory response. The activation of TLRs and NLRs by their respective ligands activates downstream signaling pathways that converge on activation of transcription factors, such as nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1) or interferon regulatory factors (IRFs), leading to expression of inflammatory cytokines and antimicrobial molecules. The goal of this review is to discuss how the TLRs and NRLs signaling pathways collaborate in a cooperative or synergistic manner to counteract the infectious agents. A deep knowledge of the biochemical events initiated by each of these receptors will undoubtedly have a high impact in the design of more effective strategies to control inflammation.

Immunomodulation by gut microbiota: role of Toll-like receptor expressed by T cells

A close relationship exists between gut microbiota and immune responses. An imbalance of this relationship can determine local and systemic immune diseases. In fact the immune system plays an essential role in maintaining the homeostasis with the microbiota that normally resides in the gut, while, at the same time, the gut microbiota influences the immune system, modulating number and function of effector and regulatory T cells. To achieve this aim, mutual regulation between immune system and microbiota is achieved through several mechanisms, including the engagement of toll-like receptors (TLRs), pathogen-specific receptors expressed on numerous cell types. TLRs are able to recognize ligands from commensal or pathogen microbiota to maintain the tolerance or trigger the immune response. In this review, we summarize the latest evidences about the role of TLRs expressed in adaptive T cells, to understand how the immune system promotes intestinal homeostasis, fights invasion by pathogens, and is modulated by the intestinal microbiota.

Multiple roles of toll-like receptor 4 in colorectal cancer

Toll-like receptor (TLR) signaling has been implicated in the inflammatory responses in intestinal epithelial cells (IECs). Such inflammatory signals mediate complex interactions between commensal bacteria and TLRs and are required for IEC proliferation, immune response, repair, and homeostasis. The upregulation of certain TLRs in colorectal cancer (CRC) tissues suggests that TLRs may play an essential role in the prognosis of chronic and inflammatory diseases that ultimately culminate in CRC. Here, we provide a comprehensive review of the literature on the involvement of the TLR pathway in the initiation, progression, and metastasis of CRC, as well as inherited genetic variation and epigenetic regulation. The differential expression of TLRs in epithelial cells has also been discussed. In particular, we emphasize the physiological role of TLR4 in CRC development and pathogenesis, and propose novel and promising approaches for CRC therapeutics with the aid of TLR ligands.

Mucosal Inflammatory Response to Salmonella typhimurium Infection

The human intestinal epithelium consists of a single layer of epithelial cells that forms a barrier against food antigens and the resident microbiota within the lumen. This delicately balanced organ functions in a highly sophisticated manner to uphold the fidelity of the intestinal epithelium and to eliminate pathogenic microorganisms. On the luminal side, this barrier is fortified by a thick mucus layer, and on the serosal side exists the lamina propria containing a resident population of immune cells. Pathogens that are able to breach this barrier disrupt the healthy epithelial lining by interfering with the regulatory mechanisms that govern the normal balance of intestinal architecture and function. This disruption results in a coordinated innate immune response deployed to eliminate the intruder that includes the release of antimicrobial peptides, activation of pattern-recognition receptors, and recruitment of a variety of immune cells. In the case of Salmonella enterica serovar typhimurium (S. typhimurium) infection, induction of an inflammatory response has been linked to its virulence mechanism, the type III secretion system (T3SS). The T3SS secretes protein effectors that exploit the host’s cell biology to facilitate bacterial entry and intracellular survival, and to modulate the host immune response. As the role of the intestinal epithelium in initiating an immune response has been increasingly realized, this review will highlight recent research that details progress made in understanding mechanisms underlying the mucosal inflammatory response to Salmonella infection, and how such inflammatory responses impact pathogenic fitness of this organism.

Cross-talk between probiotic lactobacilli and host immune system

The mechanism by which probiotic lactobacilli affect the immune system is strain specific. As the immune system is a multicompartmental system, each strain has its way to interact with it and induce a visible and quantifiable effect. This review summarizes the interplay existing between the host immune system and probiotic lactobacilli, that is, with emphasis on lactobacilli as a prototype probiotic genus. Several aspects including the bacterial-host cross-talk with the mucosal and systemic immune system are presented, as well as short sections on the competing effect towards pathogenic bacteria and their uses as delivery vehicle for antigens.

Lactobacillus amylovorus inhibits the TLR4 inflammatory signaling triggered by enterotoxigenic Escherichia coli via modulation of the negative regulators and involvement of TLR2 in intestinal Caco-2 cells and pig explants

Inflammation derived from pathogen infection involves the activation of toll-like receptor (TLR) signaling. Despite the established immunomodulatory activities of probiotics, studies relating the ability of such bacteria to inhibit the TLR signaling pathways are limited or controversial. In a previous study we showed that Lactobacillus amylovorus DSM 16698T, a novel lactobacillus isolated from unweaned pigs, protects the intestinal cells from enterotoxigenic Escherichia coli (ETEC) K88 infection through cytokine regulation. In the present study we investigated whether the ability of L. amylovorus to counteract the inflammatory status triggered by ETEC in intestine is elicited through inhibition of the TLR4 signaling pathway. We used the human intestinal Caco-2/TC7 cells and intestinal explants isolated from 5 week-old crossbreed Pietrain/Duroc/Large-White piglets, treated with ETEC, L. amylovorus or L. amylovorus cell free supernatant, either alone or simultaneously with ETEC. Western blot analysis showed that L. amylovorus and its cell free supernatant suppress the activation of the different steps of TLR4 signaling in Caco-2/TC7 cells and pig explants, by inhibiting the ETEC induced increase in the level of TLR4 and MyD88, the phosphorylation of the IKKα, IKKβ, IκBα and NF-κB subunit p65, as well as the over-production of inflammatory cytokines IL-8 and IL-1β. The immunofluorescence analysis confirms the lack of phospho-p65 translocation into the nucleus. These anti-inflammatory effects are achieved through modulation of the negative regulators Tollip and IRAK-M. We also found that L. amylovorus blocks the up-regulation of the extracellular heat shock protein (Hsp)72 and Hsp90, that are critical for TLR4 function. By using anti-TLR2 antibody, we demonstrate that TLR2 is required for the suppression of TLR4 signaling activation. These results may contribute to develop therapeutic interventions using L. amylovorus in intestinal disorders of piglets and humans.

Triennial Growth Symposium--Novel roles for vitamin D in animal immunity and health

Recent years have seen significant advances in the generation, validation, and implementation of nutritional supplements for food production animals. Examination of their impact on animal performance and health requires collaboration among animal scientists, nutritionists, biochemists, immunologists, veterinarians, and others. Each provides a unique perspective on the mechanisms of action, short and long-term impacts, and most effective strategies for implementation into continuously evolving industrial practices. In this review we provide a comparative immunology perspective on the impact of vitamin D on animal performance and health, describe the differential contributions of vitamin D3 and of a commercial hydroxylated version of vitamin D3, 25-hydroxyvitamin D3 (25(OH)D3 or HyD) to swine immunity, and highlight recent advances in the technologies that can be used to dissect the cellular and molecular mechanisms that impact production animal immunity and health. Among others, we pay particular attention to how these novel approaches help decrease the variability often observed in immune-associated datasets. From a practical perspective, this is critical for evaluation of in vivo effects for this nutritional supplement as small but meaningful changes to specific immune responses are typical under normal physiological conditions. Furthermore, as the range of reagents and technologies expands for comparative animal models, it is imperative that continued efforts are placed on the capacity to compare results across different experimental platforms.

Immune-epithelial crosstalk at the intestinal surface

The intestinal tract is one of the most complex organs of the human body. It has to exercise various functions including food and water absorption, as well as barrier and immune regulation. These functions affect not only the gut itself, but influence the overall health of the organism. Diseases involving the gastrointestinal tract such as inflammatory bowel disease and colorectal cancer therefore severely affect the patient's quality of life and can become life-threatening. Intestinal epithelial cells (IECs) play an important role in intestinal inflammation, infection, and cancer development. IECs not only constitute the first barrier in the gut against the lumen, they also constantly signal information about the gut lumen to immune cells, thereby influencing their behaviour. In contrast, by producing various antimicrobial peptides, IECs shape the microbial community within the gut. IECs also respond to cytokines and other mediators of immune cells in the lamina propria. Interactions between epithelial cells and immune cells in the intestine are responsible for gut homeostasis, and modulations of this crosstalk have been reported in studies of gut diseases. This review discusses the wide field of immune-epithelial interactions and shows the importance of immune-epithelial crosstalk in the intestine to gut homeostasis and the overall health status.

Intestinal microbiota reduces genotoxic endpoints induced by high-energy protons

Ionizing space radiation causes oxidative DNA damage and triggers oxidative stress responses, and compromised DNA repair mechanisms can lead to increased risk of carcinogenesis. Young adult mice with developed innate and adaptive immune systems that harbored either a conventional intestinal microbiota (CM) or an intestinal microbiota with a restricted microbial composition (RM) were irradiated with a total dose of 1 Gy delivered by high-energy protons (2.5 GeV/n, LET = 0.2-2 keV/μm) or silicon or iron ions (850 MeV/n, LET ≈ 50 keV/μm and 1 GeV/n, LET = 150 keV/μm, respectively). Six hours after whole-body irradiation, acute chromosomal DNA lesions were observed for RM mice but not CM mice. High-throughput rRNA gene sequencing of intestinal mucosal bacteria showed that Barnesiella intestinihominis and unclassified Bacterodiales were significantly more abundant in male RM mice than CM mice, and phylotype densities changed in irradiated mice. In addition, Helicobacter hepaticus and Bacteroides stercoris were higher in CM than RM mice. Elevated levels of persistently phosphorylated γ-H2AX were observed in RM mice exposed to high-energy protons compared to nonirradiated RM mice, and they also were associated with a decrease of the antioxidant glutathione in peripheral blood measured at four weeks after irradiation. After radiation exposure, CM mice showed lower levels of γ-H2AX phosphorylation than RM mice and an increase in specific RM-associated phylotypes, indicating a down-regulating force on DNA repair by differentially abundant phylotypes in RM versus a radiation-sensitive complex CM.

Drosophila at the intersection of infection, inflammation, and cancer

Recent studies show that both cellular and humoral aspects of innate immunity play important roles during tumor progression. These interactions have traditionally been explored in vertebrate model systems. In recent years, Drosophila has emerged as a genetically tractable model system for studying key aspects of tumorigenesis including proliferation, invasion, and metastasis. The absence of adaptive immunity in Drosophila provides a unique opportunity to study the interactions between innate immune system and cancer in different genetic contexts. In this review, I discuss recent advances made by using Drosophila models of cancer to study the role of innate immune pathways Toll/Imd, JNK, and JAK-STAT, microbial infection and inflammation during tumor progression.

New vaccines against influenza virus

Vaccination is one of the most effective and cost-benefit interventions that prevent the mortality and reduce morbidity from infectious pathogens. However, the licensed influenza vaccine induces strain-specific immunity and must be updated annually based on predicted strains that will circulate in the upcoming season. Influenza virus still causes significant health problems worldwide due to the low vaccine efficacy from unexpected outbreaks of next epidemic strains or the emergence of pandemic viruses. Current influenza vaccines are based on immunity to the hemagglutinin antigen that is highly variable among different influenza viruses circulating in humans and animals. Several scientific advances have been endeavored to develop universal vaccines that will induce broad protection. Universal vaccines have been focused on regions of viral proteins that are highly conserved across different virus subtypes. The strategies of universal vaccines include the matrix 2 protein, the hemagglutinin HA2 stalk domain, and T cell-based multivalent antigens. Supplemented and/or adjuvanted vaccination in combination with universal target antigenic vaccines would have much promise. This review summarizes encouraging scientific advances in the field with a focus on novel vaccine designs.

The role of probiotics and prebiotics in inducing gut immunity

The gut immune system is influenced by many factors, including dietary components and commensal bacteria. Nutrients that affect gut immunity and strategies that restore a healthy gut microbial community by affecting the microbial composition are being developed as new therapeutic approaches to treat several inflammatory diseases. Although probiotics (live microorganisms) and prebiotics (food components) have shown promise as treatments for several diseases in both clinical and animal studies, an understanding of the molecular mechanisms behind the direct and indirect effects on the gut immune response will facilitate better and possibly more efficient therapy for diseases. In this review, we will first describe the concept of prebiotics, probiotics, and symbiotics and cover the most recently well-established scientific findings regarding the direct and indirect mechanisms by which these dietary approaches can influence gut immunity. Emphasis will be placed on the relationship of diet, the microbiota, and the gut immune system. Second, we will highlight recent results from our group, which suggest a new dietary manipulation that includes the use of nutrient products (organic selenium and Lithothamnium muelleri) and probiotics (Saccharomyces boulardii UFMG 905 and Bifidobacterium sp.) that can stimulate and manipulate the gut immune response, inducing intestinal homeostasis. Furthermore, the purpose of this review is to discuss and translate all of this knowledge into therapeutic strategies and into treatment for extra-intestinal compartment pathologies. We will conclude by discussing perspectives and molecular advances regarding the use of prebiotics or probiotics as new therapeutic strategies that manipulate the microbial composition and the gut immune responses of the host.

Keeping the bowel regular: the emerging role of Treg as a therapeutic target in inflammatory bowel disease

The understanding of the intricate mechanisms by which gut immune cells interact with each other and the intestinal flora is constantly developing. The mucosal immune system must retain the ability to mount a prompt response to intestinal pathogens while maintaining tolerance for commensal organisms. Effector T lymphocytes drive inflammation, whereas their actions are counteracted by populations of regulatory T cells (Treg), which act as an endogenous suppressor of mucosal inflammation. There is growing evidence that a loss of this delicate counterbalance is important in the etiology of inflammatory bowel disease (IBD). Here, we review studies highlighting alterations in Treg in the pathogenesis of IBD. Observations of dynamic changes in Treg activity with successful IBD treatment have highlighted their functional importance and potential to also serve as a biomarker of disease activity and to predict response to therapy. Furthermore, we explore the potential for adoptive transfer of Treg as part of IBD treatment.

Nondigestible oligosaccharides exert nonprebiotic effects on intestinal epithelial cells enhancing the immune response via activation of TLR4-NFκB

SCOPE

Prebiotic effects of non absorbable glucids depend mainly on digestion by the colonic microbiota. Our aim was to assess nonprebiotic, direct effects of 4 prebiotics, namely fructooligosaccharides, inulin, galactooligosaccharides, and goat's milk oligosaccharides on intestinal epithelial cells.

METHODS AND RESULTS

Prebiotics were tested in intestinal epithelial cell 18 (IEC18), HT29, and Caco-2 cells. Cytokine secretion was measured by ELISA and modulated with pharmacological probes and gene silencing. Prebiotics induced the production of growth-related oncogene, (GROα), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 2 (MIP2) in IEC18 cells, with an efficacy that was 50-80% that of LPS. Prebiotics did not change RANTES expression, which was robustly induced by LPS in IEC18 cells. Cytokine secretion was suppressed by Bay11-7082, an inhibitor of IκB-α phosphorylation. The response was markedly decreased by Myd88 or TLR4 gene knockdown. Prebiotics also elicited cytokine production in HT29 but not in Caco-2 cells, consistent with reduced and vestigial expression of TLR4 in these cell lines, respectively. Prebiotic-induced MCP-1 secretion was reduced also in colonic explants from TLR4 KO mice compared with the controls.

CONCLUSIONS

We conclude that prebiotics are TLR4 ligands in intestinal epithelial cells and that this may be a relevant mechanism for their in vivo effects.

Antimicrobial peptides and gut microbiota in homeostasis and pathology

We survive because we adapted to a world of microorganisms. All our epithelial surfaces participate in keeping up an effective barrier against microbes while not initiating ongoing inflammatory processes and risking collateral damage to the host. Major players in this scenario are antimicrobial peptides (AMPs). Such broad-spectrum innate antibiotics are in part produced by specialized cells but also widely sourced from all epithelia as well as circulating inflammatory cells. AMPs belong to an ancient defense system found in all organisms and participated in a preservative co-evolution with a complex microbiome. Particularly interesting interactions between host barrier and microbiota can be found in the gut. The intestinal cell lining not only has to maintain a tightly regulated homeostasis during its high-throughput regeneration, but also a balanced relationship towards an extreme number of mutualistic or commensal inhabitants. Recent research suggests that advancing our understanding of the circumstances of such balanced and sometimes imbalanced interactions between gut microbiota and host AMPs should have therapeutic implications for different intestinal disorders.