Dendritic cells in oral tolerance in the gut

Re-evaluation of dietary interventions in rheumatoid arthritis: can we improve patient conversations around food choices?

Rheumatoid arthritis (RA) is one of over 100 different types of autoimmune conditions. In RA, the cells of the immune system attack the tissue lining the joints, triggering inflammation. A large body of research suggests that the underlying trigger(s) of RA are unique to an individual. For example, increased risk of RA can be driven by smoking tobacco in one individual and mercury exposure in another. Due to the development of next-generation sequencing technology, the critical role of the microbiota in shaping RA risk has been elucidated. Therefore, it is surprising that diet, arguably the most important lever in shaping the gut microbiota, is ineffective in the treatment of RA, even in a sub-set of patients. To attempt to rationalise this apparent paradox, we conducted an umbrella review to address the question as to whether diet can affect outcomes in RA.

Microbiota-gut-brain axis: interplay between microbiota, barrier function and lymphatic system

The human gastrointestinal tract, boasting the most diverse microbial community, harbors approximately 100 trillion microorganisms comprising viruses, bacteria, fungi, and archaea. The profound genetic and metabolic capabilities of the gut microbiome underlie its involvement in nearly every facet of human biology, from health maintenance and development to aging and disease. Recent recognition of microbiota - gut - brain axis, referring to the bidirectional communication network between gut microbes and their host, has led to a surge in interdisciplinary research. This review begins with an overview of the current understandings regarding the influence of gut microbes on intestinal and blood-brain barrier integrity. Subsequently, we discuss the mechanisms of the microbiota - gut - brain axis, examining the role of gut microbiota-related neural transmission, metabolites, gut hormones and immunity. We propose the concept of microbiota-mediated multi-barrier modulation in the potential treatment in gastrointestinal and neurological disorders. Furthermore, the role of lymphatic network in the development and maintenance of barrier function is discussed, providing insights into lesser-known conduits of communication between the microbial ecosystem within the gut and the brain. In the final section, we conclude by describing the ongoing frontiers in understanding of the microbiota - gut - brain axis's impact on human health and disease.

Gut dysbiosis promotes the breakdown of oral tolerance mediated through dysfunction of mucosal dendritic cells

While dysbiosis in the gut is implicated in the impaired induction of oral tolerance generated in mesenteric lymph nodes (MesLNs), how dysbiosis affects this process remains unclear. Here, we describe that antibiotic-driven gut dysbiosis causes the dysfunction of CD11c⁺CD103⁺ conventional dendritic cells (cDCs) in MesLNs, preventing the establishment of oral tolerance. Deficiency of CD11c⁺CD103⁺ cDCs abrogates the generation of regulatory T cells in MesLNs to establish oral tolerance. Antibiotic treatment triggers the intestinal dysbiosis linked to the impaired generation of colony-stimulating factor 2 (Csf2)-producing group 3 innate lymphoid cells (ILC3s) for regulating the tolerogenesis of CD11c⁺CD103⁺ cDCs and the reduced expression of tumor necrosis factor (TNF)-like ligand 1A (TL1A) on CD11c⁺CD103⁺ cDCs for generating Csf2-producing ILC3s. Thus, antibiotic-driven intestinal dysbiosis leads to the breakdown of crosstalk between CD11c⁺CD103⁺ cDCs and ILC3s for maintaining the tolerogenesis of CD11c⁺CD103⁺ cDCs in MesLNs, responsible for the failed establishment of oral tolerance.

Interplay between Gut Lymphatic Vessels and Microbiota

Lymphatic vessels play a distinctive role in draining fluid, molecules and even cells from interstitial and serosal spaces back to the blood circulation. Lymph vessels of the gut, and especially those located in the villi (called lacteals), not only serve this primary function, but are also responsible for the transport of lipid moieties absorbed by the intestinal mucosa and serve as a second line of defence against possible bacterial infections. Here, we briefly review the current knowledge of the general mechanisms allowing lymph drainage and propulsion and will focus on the most recent findings on the mutual relationship between lacteals and intestinal microbiota.

Congenital Deficiency of Conventional Dendritic Cells Promotes the Development of Atopic Dermatitis-Like Inflammation

Atopic dermatitis (AD) is a common pruritic inflammatory skin disease characterized by impaired epidermal barrier function and dysregulation of Thelper-2 (T_H2)-biased immune responses. While the lineage of conventional dendritic cells (cDCs) are implicated to play decisive roles in T-cell immune responses, their requirement for the development of AD remains elusive. Here, we describe the impact of the constitutive loss of cDCs on the progression of AD-like inflammation by using binary transgenic (Tg) mice that constitutively lacked CD11c^hi cDCs. Unexpectedly, the congenital deficiency of cDCs not only exacerbates the pathogenesis of AD-like inflammation but also elicits immune abnormalities with the increased composition and function of granulocytes and group 2 innate lymphoid cells (ILC2) as well as B cells possibly mediated through the breakdown of the Fms-related tyrosine kinase 3 ligand (Flt3L)-mediated homeostatic feedback loop. Furthermore, the constitutive loss of cDCs accelerates skin colonization of Staphylococcus aureus (S. aureus), that associated with disease flare. Thus, cDCs maintains immune homeostasis to prevent the occurrence of immune abnormalities to maintain the functional skin barrier for mitigating AD flare.

Essential role of submandibular lymph node dendritic cells in protective sublingual immunotherapy against murine allergy

While sublingual immunotherapy (SLIT) is known as an allergen-specific treatment for type-1 allergies, how it controls allergic pathogenesis remains unclear. Here, we show the prerequisite role of conventional dendritic cells in submandibular lymph nodes (ManLNs) in the effectiveness of SLIT for the treatment of allergic disorders in mice. Deficiency of conventional dendritic cells or CD4⁺Foxp3⁺ regulatory T (T_reg) cells abrogates the protective effect of SLIT against allergic disorders. Furthermore, sublingual antigenic application primarily induces antigen-specific CD4⁺Foxp3⁺ T_reg cells in draining ManLNs, in which it is severely impaired in the absence of cDCs. In ManLNs, migratory CD11b⁺ cDCs are superior to other conventional dendritic cell subsets for the generation of antigen-specific CD4⁺Foxp3⁺ T_reg cells, which is reflected by their dominancy in the tolerogenic features to favor this program. Thus, ManLNs are privileged sites in triggering mucosal tolerance mediating protect effect of SLIT on allergic disorders that requires a tolerogenesis of migratory CD11b⁺ conventional dendritic cells.

Noriaki Miyanaga and Hideaki Takagi et al. identify an essential role for migratory dendritic cells in mediating immunotherapy treatment against allergies in mice. They show that submandibular lymph node dendritic cells induce regulatory T cells, and their absence abrogates the effectiveness of immunotherapy treatment.

The Wnt-β-Catenin-IL-10 Signaling Axis in Intestinal APCs Protects Mice from Colitis-Associated Colon Cancer in Response to Gut Microbiota

Loss of immune tolerance to gut microflora is inextricably linked to chronic intestinal inflammation and colitis-associated colorectal cancer (CAC). The LRP5/6 signaling cascade in APCs contributes to immune homeostasis in the gut, but whether this pathway in APCs protects against CAC is not known. In the current study, using a mouse model of CAC, we show that the LRP5/6-β-catenin-IL-10 signaling axis in intestinal CD11c⁺ APCs protects mice from CAC by regulating the expression of tumor-promoting inflammatory factors in response to commensal flora. Genetic deletion of LRP5/6 in CD11c⁺ APCs in mice (LRP5/6^ΔCD11c) resulted in enhanced susceptibility to CAC. This is due to a microbiota-dependent increased expression of proinflammatory factors and decreased expression of the immunosuppressive cytokine IL-10. This condition could be improved in LRP5/6^ΔCD11c mice by depleting the gut flora, indicating the importance of LRP5/6 in mediating immune tolerance to the gut flora. Moreover, mechanistic studies show that LRP5/6 suppresses the expression of tumor-promoting inflammatory factors in CD11c⁺ APCs via the β-catenin-IL-10 axis. Accordingly, conditional activation of β-catenin specifically in CD11c⁺ APCs or in vivo administration of IL-10 protected LRP5/6^ΔCD11c mice from CAC by suppressing the expression of inflammatory factors. In summary, in this study, we identify a key role for the LRP5/6-β-catenin-IL-10 signaling pathway in intestinal APCs in resolving chronic intestinal inflammation and protecting against CAC in response to the commensal flora.

Can Probiotics and Diet Promote Beneficial Immune Modulation and Purine Control in Coronavirus Infection?

Infection caused by the SARS-CoV-2 coronavirus worldwide has led the World Health Organization to declare a COVID-19 pandemic. Because there is no cure or treatment for this virus, it is emergingly urgent to find effective and validated methods to prevent and treat COVID-19 infection. In this context, alternatives related to nutritional therapy might help to control the infection. This narrative review proposes the importance and role of probiotics and diet as adjunct alternatives among the therapies available for the treatment of this new coronavirus. This review discusses the relationship between intestinal purine metabolism and the use of Lactobacillus gasseri and low-purine diets, particularly in individuals with hyperuricemia, as adjuvant nutritional therapies to improve the immune system and weaken viral replication, assisting in the treatment of COVID-19. These might be promising alternatives, in addition to many others that involve adequate intake of vitamins, minerals and bioactive compounds from food.

Core Fucosylation of Intestinal Epithelial Cells Protects Against Salmonella Typhi Infection via Up-Regulating the Biological Antagonism of Intestinal Microbiota

The fucosylated carbohydrate moieties on intestinal epithelial cells (IECs) are involved in the creation of an environmental niche for commensal and pathogenic bacteria. Core fucosylation catalyzed by fucosyltransferase 8 (Fut8) is the major fucosylation pattern on the N-glycans of the surface glycoproteins on IECs, however, the role of IECs core fucosylation during infection remains unclear. This study was conducted to investigate the interaction between IECs core fucosylation and gut microbiota, and the effects of this interaction on protecting Salmonella enterica subsp. enterica serovar Typhi (S. Typhi) infection. Firstly, the Fut8^+/+ and Fut8^+/– mice were infected with S. Typhi. The level of IECs core fucosylation and protein expression of intestinal mucosa were then detected by LCA blot and Western blot, respectively. The gut microbiota of Fut8^+/+ and Fut8^+/– mice before and after S. Typhi infection was assessed by 16S rRNA sequencing. Our results showed that core fucosylation was ubiquitous expressed on the intestinal mucosa of mice and had significant effects on their gut microbiota. Fut8^+/– mice was more susceptive to S. Typhi infection than Fut8^+/+ mice. Interestingly, infection of S. Typhi upregulated the core fucosylation level of IECs and increased the abundances of beneficial microorganisms such as Lactobacillus and Akkermansia spp. Further in vitro and in vivo studies demonstrated that Wnt/β-catenin signaling pathway mediated the elevation of IECs core fucosylation level upon infection of S. Typhi. Taken together, our data in this study revealed that the IECs core fucosylation plays an important role in protecting against S. Typhi infection via up-regulating the biological antagonism of intestinal microbiota.

The Influence of Maternal-Foetal Parameters on Concentrations of Zonulin and Calprotectin in the Blood and Stool of Healthy Newborns during the First Seven Days of Life. An Observational Prospective Cohort Study

Background: It can be hypothetically assumed that maternal and perinatal factors influence the intestinal barrier. Methods: The study was conducted with 100 healthy, full-term newborns breastfed in the first week of life, with similar analyses for their mothers. Zonulin and calprotectin levels were used as intestinal permeability markers. Results: The median (range) zonulin concentrations (ng/mL) were in mothers: serum, 21.39 (6.39–57.54); stool, 82.23 (42.52–225.74); and newborns: serum cord blood, 11.14 (5.82–52.34); meconium, 54.15 (1.36–700.65); and stool at age seven days, 114.41 (29.38–593.72). Calprotectin median (range) concentrations (µg/mL) in mothers were: stool, 74.79 (3.89–211.77); and newborns: meconium, 154.76 (6.93–8884.11); and stool at age seven days 139.12 (11.89–627.35). The use of antibiotics during pregnancy resulted in higher zonulin concentrations in umbilical-cord serum and calprotectin concentrations in newborn stool at seven days, while antibiotic therapy during labour resulted in higher zonulin concentrations in the stool of newborns at seven days. Zonulin concentrations in the stool of newborns (at seven days) who were born via caesarean section were higher compared to with vaginal birth. With further analyses, caesarean section was found to have a greater effect on zonulin concentrations than prophylactic administration of antibiotics in the perinatal period. Pregnancy mass gain >18 kg was associated with higher calprotectin concentrations in maternal stool. Body Mass Index (BMI) increase >5.7 during pregnancy was associated with decreased zonulin concentrations in maternal stool and increased calprotectin concentrations in stool of mothers and newborns at seven days. There was also a negative correlation between higher BMI increase in pregnancy and maternal zonulin stool concentrations and a positive correlation between BMI increase in pregnancy and maternal calprotectin stool concentrations. Conclusion: Maternal-foetal factors such as caesarean section, antibiotic therapy during pregnancy, as well as change in mother’s BMI during pregnancy may increase intestinal permeability in newborns. Changes in body mass during pregnancy can also affect intestinal permeability in mothers. However, health consequences associated with increased intestinal permeability during the first days of life are unknown. Additionally, before the zonulin and calprotectin tests can be adopted as universal diagnostic applications to assess increased intestinal permeability, validation of these tests is necessary.

Cytokines and Soluble Receptors in Breast Milk as Enhancers of Oral Tolerance Development

The postpartum period is an important window during which environmental factors can shape the life-long health of the infant. This time period often coincides with substantial milk consumption either in the form of breast milk or from cow's milk sources, such as infant formulas. Although breast milk is the most beneficial source of nutrients for infants during the first 6 months after birth, its role in regulating food allergy development, through regulation of oral tolerance, is still controversial. Breast milk contains several factors that can impact mucosal immune function, including immune cells, antibodies, microbiota, oligosaccharides, cytokines, and soluble receptors. However, there is considerable variation in the assessed levels of cytokines and soluble receptors between studies and across the lactation period. Most of these cytokines and soluble receptors are absent, or only found in limited quantities, in commercial baby formulas. Differences in content of these pluripotent factors, which impact on both the mother and the neonate, could contribute to the controversy surrounding the role of breast milk regulating oral tolerance. This review highlights current knowledge about the importance of cytokines and soluble receptors in breast milk on the development of oral tolerance and tolerance-relateddisorders. Understanding the mechanisms by which such milk components might promote oral tolerance could aid in the development of improved strategies for allergy prevention.

Canonical Wnt Signaling in CD11c+ APCs Regulates Microbiota-Induced Inflammation and Immune Cell Homeostasis in the Colon

Aberrant Wnt/β-catenin signaling occurs in several inflammatory diseases, including inflammatory bowel disease and inflammatory bowel disease-associated colon carcinogenesis. However, its role in shaping mucosal immune responses to commensals in the gut remains unknown. In this study, we investigated the importance of canonical Wnt signaling in CD11c⁺ APCs in controlling intestinal inflammation. Using a mouse model of ulcerative colitis, we demonstrated that canonical Wnt signaling in intestinal CD11c⁺ APCs controls intestinal inflammation by imparting an anti-inflammatory phenotype. Genetic deletion of Wnt coreceptors, low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) in CD11c⁺ APCs in LRP5/6^ΔCD11c mice, resulted in enhanced intestinal inflammation with increased histopathological severity of colonic tissue. This was due to microbiota-dependent increased production of proinflammatory cytokines and decreased expression of immune-regulatory factors such as IL-10, retinoic acid, and IDO. Mechanistically, loss of LRP5/6-mediated signaling in CD11c⁺ APCs resulted in altered microflora and T cell homeostasis. Furthermore, our study demonstrates that conditional activation of β-catenin in CD11c⁺ APCs in LRP5/6^ΔCD11c mice resulted in reduced intestinal inflammation with decreased histopathological severity of colonic tissue. These results reveal a mechanism by which intestinal APCs control intestinal inflammation and immune homeostasis via the canonical Wnt-signaling pathway.

Critical role of plasmacytoid dendritic cells in induction of oral tolerance

BACKGROUND

Exposure to dietary constituents through the mucosal surface of the gastrointestinal tract generates oral tolerance that prevents deleterious T cell-mediated immunity. Although oral tolerance is an active process that involves emergence of CD4⁺ forkhead box p3 (Foxp3)⁺ regulatory T (Treg) cells in gut-associated lymphoid tissues (GALTs) for suppression of effector T (Teff) cells, how antigen-presenting cells initiate this process remains unclear.

OBJECTIVE

We sought to determine the role of plasmacytoid dendritic cells (pDCs), which are known as unconventional antigen-presenting cells, in establishment of oral tolerance.

METHODS

GALT-associated pDCs in wild-type mice were examined for their ability to induce differentiation of CD4⁺ Teff cells and CD4⁺Foxp3⁺ Treg cells in vitro. Wild-type and pDC-ablated mice were fed oral antigen to compare their intestinal generation of CD4⁺Foxp3⁺ Treg cells and induction of oral tolerance to protect against Teff cell-mediated allergic inflammation.

RESULTS

GALT-associated pDCs preferentially generate CD4⁺Foxp3⁺ Treg cells rather than CD4⁺ Teff cells, and such generation requires an autocrine loop of TGF-β for its robust production. A deficiency of pDCs abrogates antigen-specific de novo generation of CD4⁺Foxp3⁺ Treg cells occurring in GALT after antigenic feeding. Furthermore, the absence of pDCs impairs development of oral tolerance, which ameliorates the progression of delayed-type hypersensitivity and systemic anaphylaxis, as well as allergic asthma, accompanied by an enhanced antigen-specific CD4⁺ Teff cell response and antibody production.

CONCLUSION

pDCs are required for establishing oral tolerance to prevent undesirable allergic responses, and they might serve a key role in maintaining gastrointestinal immune homeostasis.

GPR81, a Cell-Surface Receptor for Lactate, Regulates Intestinal Homeostasis and Protects Mice from Experimental Colitis

At mucosal sites such as the intestine, the immune system launches robust immunity against invading pathogens while maintaining a state of tolerance to commensal flora and ingested food Ags. The molecular mechanisms underlying this phenomenon remain poorly understood. In this study, we report that signaling by GPR81, a receptor for lactate, in colonic dendritic cells and macrophages plays an important role in suppressing colonic inflammation and restoring colonic homeostasis. Genetic deletion of GPR81 in mice led to increased Th1/Th17 cell differentiation and reduced regulatory T cell differentiation, resulting in enhanced susceptibility to colonic inflammation. This was due to increased production of proinflammatory cytokines (IL-6, IL-1β, and TNF-α) and decreased expression of immune regulatory factors (IL-10, retinoic acid, and IDO) by intestinal APCs lacking GPR81. Consistent with these findings, pharmacological activation of GPR81 decreased inflammatory cytokine expression and ameliorated colonic inflammation. Taken together, these findings identify a new and important role for the GPR81 signaling pathway in regulating immune tolerance and colonic inflammation. Thus, manipulation of the GPR81 pathway could provide novel opportunities for enhancing regulatory responses and treating colonic inflammation.

Comparative phenotypic and functional analysis of migratory dendritic cell subsets from human oral mucosa and skin

Antigen exposure to oral mucosa is generally thought to lead to immune tolerance induction. However, very little is known about the subset composition and function of dendritic cells (DC) migrating from human oral mucosa. Here we show that migratory DC from healthy human gingival explants consist of the same phenotypic subsets in the same frequency distribution as DC migrating from human skin. The gingival CD1a+ Langerhans cell and interstitial DC subsets lacked CXCR4 expression in contrast to their cutaneous counterparts, pointing to different migration mechanisms, consistent with previous observations in constructed skin and gingival equivalents. Remarkably, without any exogenous conditioning, gingival explants released higher levels of inflammatory cytokines than human skin explants, resulting in higher DC migration rates and a superior ability of migrated DC to prime allogeneic T cells and to induce type-1 effector T cell differentiation. From these observations we conclude that rather than an intrinsic ability to induce T cell tolerance, DC migrating from oral mucosa may have a propensity to induce effector T cell immunity and maintain a high state of alert against possible pathogenic intruders in the steady state. These findings may have implications for oral immunization strategies.

Alterations in cytokine gene expression profile in colon mucosa of Inflammatory Bowel Disease patients on different therapeutic regimens

Inflammatory bowel disease (IBD) is assumed to be caused by genetic and environmental factors that interact together in promoting intestinal immune dysregulation where cytokines have validated role. However, the underlying intimate mechanisms in the human IBD involving cytokines still needs to be supplemented especially in the clinical context. The aim of this study was to investigate the expression of some inflammatory and regulatory cytokines (IL-17A, IL-23, IL-6, TGFβ1, and IL-10) as well as of the transcription factor FoxP3 in mucosal samples of IBD and non-IBD patients. We assessed the mRNA relative quantities (RQ) of the above-mentioned cytokines and the transcription factor FoxP3 in paired colonic samples (inflamed and adjacent normal mucosa) from 37 patients with IBD and in normal mucosal tissue in 12 persons without IBD by performing a qRT-PCR assay and tested the protein levels of target cytokines in serum samples. The patients were divided into three groups: without any therapy (n=10), on 5-ASA (n=11) and on immunosuppressants (Azathioprine±5-ASA/corticosteroids) (n=16) in order to compare the RQ values for each therapeutic group. All investigated genes were found upregulated in the inflamed mucosa of IBD patients in the following order: IL-6>FoxP3>TGFβ1>IL-23>IL-17A>IL-10. We also observed that the gene expression of FoxP3 and IL-6 were substantially higher in the inflamed mucosal tissue of the IBD patients than the adjacent normal mucosa (p=0.035, p=0.03 respectively). Differences between higher mRNA expression of FoxP3 and IL-6 in inflamed tissue were considered significant in patients with ulcerative colitis (UC) (p=0.011, p=0.000 respectively) and with Crohn's disease (CD) (p=0.008, p=0.000 respectively) in comparison to the normal mucosa of non-IBD persons and we found increased TGFβ1 in CD patients alone (p=0.041). Furthermore, IL-6 and TGFβ1 were overexpressed (RQ>10) in non-inflamed mucosa from IBD patients compared to the normal mucosa from the controls. When we compared the gene expression for paired mucosa in the immunosuppressive treated group with the 5-ASA treated group we observed opposite changes in IL-6 and TGFβ1 expression. Additionally, we found higher serum levels of IL-23 (p=0.008), TGFβ1 and IL-6 in IBD patients compared to non-IBD patients. The obtained specific expression profile consisting of IL-6, TGFβ1, IL-10 and FoxP3 may represent a transcriptional hallmark for IBD. Furthermore, we found that treatment with immunosuppressive therapy was more beneficial for driving cytokine expression to restore immune regulation in patients with IBD, unlike the 5-ASA therapy.

Genome-wide association study identifies peanut allergy-specific loci and evidence of epigenetic mediation in US children

Food allergy (FA) affects 2–10% of U.S. children and is a growing clinical and public health problem. Here we conduct the first genome-wide association study of well-defined FA, including specific subtypes (peanut, milk, and egg) in 2,759 U.S. participants (1,315 children; 1,444 parents) from the Chicago Food Allergy Study; and identify peanut allergy (PA)-specific loci in the HLA-DR and -DQ gene region at 6p21.32, tagged by rs7192 (p=5.5×10⁻⁸) and rs9275596 (p=6.8×10⁻¹⁰), in 2,197 participants of European ancestry. We replicate these associations in an independent sample of European ancestry. These associations are further supported by meta-analyses across the discovery and replication samples. Both single-nucleotide polymorphisms (SNPs) are associated with differential DNA methylation levels at multiple CpG sites (p<5×10⁻⁸); and differential DNA methylation of the HLA-DQB1 and HLA-DRB1 genes partially mediate the identified SNP-PA associations. This study suggests that the HLA-DR and -DQ gene region likely poses significant genetic risk for PA.

A potential role for regulatory T-cells in the amelioration of DSS induced colitis by dietary non-digestible polysaccharides

Inflammatory bowel diseases (IBD) including ulcerative colitis (UC) and Crohn's disease (CD) are chronic relapsing inflammatory disorders of the gastrointestinal tract. The interaction between a disturbed microbial composition, the intestinal mucosal barrier and the mucosal immune system plays an important role in IBD and its chronicity. It has been indicated that due to the altered microbial composition the balance between T regulatory cells (Treg) and T helper cells (Th) 17 is disturbed, leading to an inflammatory state. The present study shows that oral intake of a specific multi fibre mix (MF), designed to match the fibre content of a healthy diet, counteracts IBD-like intestinal inflammation and weight loss in dextran sodium sulphate treated mice. This reduction in inflammation might be brought about, at least in part, by the MF-induced decrease in inflammatory cytokines, increase in IL-10 and the relative increase in Treg cells in the mesenteric lymph nodes (MLN). Moreover, the Treg percentage in the MLN correlates with the percentage of tolerogenic lamina propria derived CD103+RALDH+dendritic cells in the MLN, suggesting that these play a role in the observed effects. In children with CD exclusive enteral nutrition (EEN) is a widely used safe and effective therapy. Optimizing enteral nutritional concepts with the tested fibre mix, know to modulate the gut microbiota composition, SCFA production and inflammatory status (as indicated by the present study) could possibly further improve efficacy in inducing remission.

Plasmacytoid dendritic cells of the gut: relevance to immunity and pathology

Plasmacytoid dendritic cells (pDCs) are bone marrow-derived immune cells with the ability to express copious amounts of type I and III interferon (IFN) and can differentiate into antigen-presenting dendritic cells as a result of stimulation by pathogen-derived nucleic acid. These powerful combined functionalities allow pDCs to bridge the innate and adaptive immune systems resulting in a concerted pathogen response. The contribution of pDCs to gastrointestinal immunity is only now being elucidated and is proving to be a critical component in systemic immunity. This review will explore the immunology of pDCs and will discuss their involvement in human disease and tolerance with an emphasis on those in the gastrointestinal lymphoid tissue.

Identification and characterization of intestinal antigen-presenting cells involved in uptake and processing of a nontoxic recombinant chimeric mucosal immunogen based on cholera toxin using imaging flow cytometry

Intragastric immunization with recombinant chimeric immunogen, SBR-CTA2/B, constructed from the saliva-binding region (SBR) of Streptococcus mutans antigen AgI/II and the A2/B subunits of cholera toxin (CT) induces salivary and circulating antibodies against S. mutans that protect against dental caries. We previously found that SBR-CTA2/B activated dendritic cells (DC) in the Peyer's patches (PP) and mesenteric lymph nodes (MLN). To identify the cells involved in the intestinal uptake of SBR-CTA2/B and the initiation of immune responses, mice were immunized intragastrically with fluorescein-labeled SBR-CTA2/B or SBR, and intestinal cells were examined by imaging flow cytometry after fluorescent staining for cell surface markers. SBR-CTA2/B was preferentially taken up by CD103(+) DC in the PP and by both CD103(+) and CD11c(+) DC in intestinal lamina propria (LP), whereas SBR was taken up to a lesser extent by PP CD11c(+) DC, within 2 to 16 h. By 16 h, CD103(+) and CD11c(+) DC containing fluorescein-labeled SBR-CTA2/B were found in MLN and showed upregulation of the chemokine receptor CCR7. Large numbers of SBR-CTA2/B-containing DC were found interacting with CD4(+) (T helper) cells, which costained for nuclear transcription factors T-bet or RORγt, identifying them as Th1 or Th17 cells. In contrast, SBR-containing CD11c(+) DC interacted preferentially with GATA3(+) (Th2) cells. No SBR- or SBR-CTA2/B-containing DC were found interacting with Foxp3(+) (T regulatory) cells. We conclude that the coupling of SBR to CTA2/B enhances its immunogenicity by promoting uptake by DC in both PP and LP and that these antigen-containing DC migrated to MLN and interacted preferentially with Th1 and Th17 cells to induce active immune responses.

New generation of oral mucosal vaccines targeting dendritic cells

As most infectious organisms gain entry at mucosal surfaces, there is a great deal of interest in developing vaccines that elicit effective mucosal immune responses against pathogen challenge. Targeted vaccination is one of the most effective methods available to prevent and control infectious diseases. Mucosal vaccines can offer lower costs, better accessibility, needle free delivery, and a higher capacity for mass immunizations during pandemics. Both local mucosal immunity and robust systemic responses can be achieved through mucosal vaccination. Recent progress in understanding the molecular and cellular components of the mucosal immune system have allowed for the development of a novel mucosal vaccine platform utilizing specific dendritic cell-targeting peptides and orally administered lactobacilli to elicit efficient antigen specific immune responses against infections, including Bacillus anthracis in experimental models of disease.

A mechanistic role for leptin in human dendritic cell migration: differences between ileum and colon in health and Crohn's disease

Dendritic cells (DC) migrate to lymph nodes on expression of C-C motif chemokine receptor 7 (CCR7) and control immune activity. Leptin, an immunomodulatory adipokine, functions via leptin receptors, signaling via the long isoform of receptor, LepRb. Leptin promotes DC maturation and increases CCR7 expression on blood DC. Increased mesenteric fat and leptin occur early in Crohn's disease (CD), suggesting leptin-mediated change in intestinal CCR7 expression on DC as a pro-inflammatory mechanism. We have demonstrated CCR7 expression and capacity to migrate to its ligand macrophage inflammatory protein 3β in normal human ileal DC but not colonic or blood DC. In CD, functional CCR7 was expressed on DC from all sites. Only DC populations containing CCR7-expressing cells produced LepRb; in vitro exposure to leptin also increased expression of functional CCR7 in intestinal DC in a dose-dependent manner. In conclusion, leptin may regulate DC migration from gut, in homeostatic and inflammatory conditions, providing a link between mesenteric obesity and inflammation.

Dendritic cell expression of the signaling molecule TRAF6 is critical for gut microbiota-dependent immune tolerance

The intracellular signaling molecule TRAF6 is critical for Toll-like receptor (TLR)-mediated activation of dendritic cells (DCs). We now report that DC-specific deletion of TRAF6 (TRAF6ΔDC) resulted, unexpectedly, in loss of mucosal tolerance, characterized by spontaneous development of T helper 2 (Th2) cells in the lamina propria and eosinophilic enteritis and fibrosis in the small intestine. Loss of tolerance required the presence of gut commensal microbiota but was independent of DC-expressed MyD88. Further, TRAF6ΔDC mice exhibited decreased regulatory T (Treg) cell numbers in the small intestine and diminished induction of iTreg cells in response to model antigen. Evidence suggested that this defect was associated with diminished DC expression of interleukin-2 (IL-2). Finally, we demonstrate that aberrant Th2 cell-associated responses in TRAF6ΔDC mice could be mitigated via restoration of Treg cell activity. Collectively, our findings reveal a role for TRAF6 in directing DC maintenance of intestinal immune tolerance through balanced induction of Treg versus Th2 cell immunity.

Functional RNA delivery targeted to dendritic cells by synthetic nanoparticles

Dendritic cells (DCs) are essential to many aspects of immune defense development and regulation. They provide important targets for prophylactic and therapeutic delivery. While protein delivery has had considerable success, RNA delivery is still expanding. Delivering RNA molecules for RNAi has shown particular success and there are reports on successful delivery of mRNA. Central, therein, is the application of cationic entities. Following endocytosis of the delivery vehicle for the RNA, cationic entities should promote vesicular membrane perturbation, facilitating cytosolic release. The present review explains the diversity of DC function in immune response development and control. Promotion of delivered RNA cytosolic release is discussed, relating to immunoprophylactic and therapeutic potential, and DC endocytic machinery is reviewed, showing how DC endocytic pathways influence the handling of internalized material. The potential advantages for application of replicating RNA are presented and discussed, in consideration of their value and development in the near future.

IL-10-producing Th1 cells and disease progression are regulated by distinct CD11c⁺ cell populations during visceral leishmaniasis

IL-10 is a critical regulatory cytokine involved in the pathogenesis of visceral leishmaniasis caused by Leishmania donovani and clinical and experimental data indicate that disease progression is associated with expanded numbers of CD4⁺ IFNγ⁺ T cells committed to IL-10 production. Here, combining conditional cell-specific depletion with adoptive transfer, we demonstrate that only conventional CD11c(hi) DCs that produce both IL-10 and IL-27 are capable of inducing IL-10-producing Th1 cells in vivo. In contrast, CD11c(hi) as well as CD11c(int/lo) cells isolated from infected mice were capable of reversing the host protective effect of diphtheria toxin-mediated CD11c⁺ cell depletion. This was reflected by increased splenomegaly, inhibition of NO production and increased parasite burden. Thus during chronic infection, multiple CD11c⁺ cell populations can actively suppress host resistance and enhance immunopathology, through mechanisms that do not necessarily involve IL-10-producing Th1 cells.

Lymphotoxin-beta receptor expression and its related signaling pathways govern dendritic cell homeostasis and function

Dendritic cells (DCs) play a fundamental function, either positive or detrimental, in regulating immune responses. Numerous specialized DC subsets exist in different organs. However, the trophic factors regulating their origin, location, homeostasis and functions remains to be fully understood. Recent evidence indicates that signaling via the lymphotoxin β receptor (LTβR) can function as a trophic signaling system for specific DCs. LTβR is part of a complex signaling network that provides both positive and inhibitory signals to DC subsets. In this review, we focus on the role of LTβR expressed in DC subsets and its associated signaling pathways that regulate DC homeostasis and function. Therapeutically targeting the LTβR signaling pathway could support the development of a beneficial immune response for the host.

Specific oral tolerance induction for the treatment of food allergy

The morbidity of food allergy in children has a tendency to increase these years. Double-blind placebo-controlled food challenge (DBPCFC) is the gold standard for the diagnosis of food allergy, and the standard treatment for food allergy is strict food avoidance. However, long-time strict food avoidance is difficult in everyday life, and may lead to malnutrition and even can increase the risk for developing severe anaphylaxis after accidental ingestion. Specific oral tolerance induction (SOTI) is a new and possible way to treat food allergy, which is performed by limited ingestion of the allergen to make the body become unresponsive to it. However, the effectiveness, safety and economic benefit are still controversial, because of the deficiency of DBPCFC. Our paper will introduce the methods and mechanism of SOTI, compare it with traditional treatments for food allergy, and discuss the possibility of clinical use of SOTI.

Lactobacillus rhamnosus GG and Bifidobacterium animalis MB5 induce intestinal but not systemic antigen-specific hyporesponsiveness in ovalbumin-immunized rats

Probiotics may modulate the host immune response by mechanisms not yet fully understood. We evaluated the modulation of intestinal and systemic antigen-specific immune response by Lactobacillus rhamnosus GG (LGG) or Bifidobacterium animalis MB5 in tolerized and immunized rats. Three groups of rats received orally LGG, B. animalis, or PBS (control) for 28 d. Each group was divided into two subgroups of tolerized or immunized rats receiving orally ovalbumin (OVA; 7 mg) or PBS on d 7, 9, and 11. All rats were immunized with OVA (300 μg) on d 14 and 21. In tolerized rats, the OVA-induced proliferative response of mesenteric lymph nodes (MLN) and spleen cells did not differ from control, indicating that the two probiotics maintained the tolerance. LGG and B. animalis in immunized rats reduced the OVA-induced proliferative response in MLN (P < 0.01) but not in spleen, whereas the proliferative response to anti-CD3 and concanavalin A of MLN and spleen cells as well as the delayed-type hypersensitivity reaction were not affected by probiotic treatment, indicating OVA-specific hyporesponsiveness restricted to intestinal immunity. This hyporesponsiveness was associated with CD4+CD25+Foxp3+ T cell expansion (P < 0.01) and increased IL-10 and TGFβ after LGG (P < 0.05), and increased apoptosis after B. animalis (P < 0.001) in MLN. In conclusion, we report a novel activity of LGG and B. animalis in inducing OVA-specific hyporesponsiveness in MLN of OVA-immunized rats that can be useful for a therapeutic strategy to prevent undesirable reactions to immunogenic antigens in the gut.