Mesenteric Lymph Node Dendritic Cells Research Articles

Anti-inflammatory capacity of selected lactobacilli in experimental colitis is driven by NOD2-mediated recognition of a specific peptidoglycan-derived muropeptide

Background and aimsInflammatory bowel disease (IBD) has been linked to a loss of tolerance towards the resident microflora. Therapeutic use of probiotics is known to be strain specific, but precise...

Granulocyte-macrophage colony stimulating factor blockade promotes ccr9+ lymphocyte expansion in Nod2 deficient mice

Ileal involvement in Crohn's disease (CD) is associated with NOD2 mutations and granulocyte-macrophage colony stimulating factor autoantibodies (GM-CSF Ab), and GM-CSF blockade promotes ileitis in Nod2/Card15-deficient (C15KO) mice. RALDH2-expressing dendritic cells (DC) and IL-4 promote CCR9 imprinting and small bowel homing of T lymphocytes, in conjunction with CCL25 expression by ileal epithelial cells (IEC). We hypothesized that GM-CSF neutralization promotes ileal disease by modulating expression of CCL25 by IEC and CCR9 by T lymphocytes via Nod2-dependent and independent pathways. CCL25 and CCR9 expression were determined in pediatric CD patients stratified by GM-CSF Ab. Ileitis was induced in C15KO mice via GM-CSF Ab administration followed by nonsteroidal antiinflammatory drug (NSAID) exposure, and expression of CCL25, CCR9, FOXP3, intracellular cytokines, and RALDH2 was determined in IEC and immune cell populations. The frequency of CCL25(+) IEC and CCR9(+) T lymphocytes was increased in CD patients with elevated GM-CSF Ab. In the murine model, GM-CSF blockade alone induced IEC CCL25 expression, and reduced the frequency of mesenteric lymph node (MLN) CD4(+) FOXP3(+) cells, while Card15 deficiency alone enhanced MLN DC RALDH2 expression. Both GM-CSF neutralization and Card15 deficiency were required for downregulation of MLN DC IL-10 expression; under these conditions NSAID exposure led to an expansion of IL-4(+) and IL-17(+) CCR9(+) lymphocytes in the ileum. GM-CSF prevents ileal expansion of CCR9(+) lymphocytes via Nod2-dependent and independent pathways. CCR9 blockade may be beneficial in CD patients with elevated GM-CSF Ab.

Expression of Retinaldehyde Dehydrogenase Enzymes in Mucosal Dendritic Cells and Gut-Draining Lymph Node Stromal Cells Is Controlled by Dietary Vitamin A

The vitamin A metabolite retinoic acid (RA) plays a crucial role in mucosal immune responses. We demonstrate in this study that RA-producing retinaldehyde dehydrogenase (RALDH) enzymes are postnatally induced in mesenteric lymph node (MLN) dendritic cells (DCs) and MLN stromal cells. RALDH enzyme activity in lamina propria-derived CD103(+) MLN-DCs did not depend on TLR signaling. Remarkably, RA itself could directly induce RALDH2 in both DCs and stromal cells in vitro. Furthermore, upon provision of a vitamin A-deficient diet, it was found that RA-mediated signaling was strongly reduced within the small intestines, while RALDH2 mRNA and RALDH enzyme activity in lamina propria DCs and MLN-DCs, as well as RALDH2 mRNA expression in MLN stromal cells, were strongly diminished. Moreover, supply of vitamin A to vitamin A-deficient mice restored RA-mediated signaling in the intestine and RALDH activity in lamina propria-derived CD103(+) MLN-DCs. Our results show that RA-dependent signaling within the intestine is indispensable for RALDH activity in the draining MLN.

Crucial roles of B7-H1 and B7-DC expressed on mesenteric lymph node dendritic cells in the generation of antigen-specific CD4+Foxp3+ regulatory T cells in the establishment of oral tolerance

AbstractOral tolerance is a key feature of intestinal immunity, generating systemic tolerance to fed antigens. However, the molecular mechanism mediating oral tolerance remains unclear. In this study, we examined the role of the B7 family members of costimulatory molecules in the establishment of oral tolerance. Deficiencies of B7-H1 and B7-DC abrogated the oral tolerance, accompanied by enhanced antigen-specific CD4+ T-cell response and IgG1 production. Mesenteric lymph node (MLN) dendritic cells (DCs) displayed higher levels of B7-H1 and B7-DC than systemic DCs, whereas they showed similar levels of CD80, CD86, and B7-H2. MLN DCs enhanced the antigen-specific generation of CD4+Foxp3+ inducible regulatory T cells (iTregs) from CD4+Foxp3− T cells rather than CD4+ effector T cells (Teff) relative to systemic DCs, owing to the dominant expression of B7-H1 and B7-DC. Furthermore, the antigen-specific conversion of CD4+Foxp3− T cells into CD4+Foxp3+ iTregs occurred in MLNs greater than in peripheral organs during oral tolerance under steady-state conditions, and such conversion required B7-H1 and B7-DC more than other B7 family members, whereas it was severely impaired under inflammatory conditions. In conclusion, our findings suggest that B7-H1 and B7-DC expressed on MLN DCs are essential for establishing oral tolerance through the de novo generation of antigen-specific CD4+Foxp3+ iTregs.

Innate immune responses to human rotavirus in the neonatal gnotobiotic piglet disease model

Intestinal and systemic dendritic cell (DC) frequencies, serum and small intestinal content cytokines and uptake/binding of human rotavirus (HRV) virus-like particles (VLP) were studied in HRV acutely infected or mock-inoculated neonatal gnotobiotic piglets. Intestinal, mesenteric lymph node (MLN) and splenic plasmacytoid DCs (pDCs), conventional DCs (cDCs) and macrophages/monocytes were assessed by flow cytometry. In infected pigs, serum and small intestinal content interferon-α (IFN-α) were highest, interleukin-12 (IL-12) was lower and IL-10, tumour necrosis factor-α and IL-6 were minimal. Compared with mock-inoculated piglets, frequencies of total intestinal DCs were higher; splenic and MLN DC frequencies were lower. Most intestinal pDCs, but few cDCs, were IFN-α(+) and intestinal macrophages/monocytes were negative for IFN-α. Serum IFN-α levels and IFN-α(+) intestinal pDCs were highly correlated, suggesting IFN-α production in vivo by intestinal pDCs (r=0·8; P<0·01). The intestinal pDCs and cDCs, but not intestinal macrophages/monocytes, of HRV-infected piglets showed significantly lower VLP uptake/binding compared with mock-inoculated piglets, suggesting higher activation of pDCs and cDCs in infected piglets. Both intestinal pDCs and cDCs were activated (IFN-α(+) and lower VLP binding) after HRV infection, suggesting their role in induction of HRV-specific immunity. Dose-effects of HRV on serum IFN-α and IFN-α(+) DCs were studied by infecting piglets with 100-fold higher HRV dose. A high dose increased parameters associated with inflammation (diarrhoea, intestinal pathology) but serum IFN-α and IFN-α(+) DCs were similar between both groups. The pDCs have both anti- and pro-inflammatory functions. Stimulation of the anti-inflammatory effects of pDCs after the high dose, without increasing their pro-inflammatory impacts, may be critical to reduce further immunopathology during HRV infection.

Characterization of FasL expression of rat Mesenteric Lymph Node Dendritic Cells during Inflammatory Bowel Disease (IBD)

Strong evidence demonstrates that a breakdown of tolerance against intestinal microflora is a major factor in the pathogenesis of IBD. Dendritic cells (DCs) appear to play a role in modulating the innate and adaptive immune response. During IBD DCs are activated and the toll like receptors upregulated. The DC populations present in inflamed and control mesenteric lymph nodes (MLNs) are unknown.AIMTo examine the expression of FasL on MLN DC during acute colitis.METHODSAcute colitis was induced in Sprague Dawley rats by administration of trinitrobenzene sulfonic acid (TNBS i.c.). At 72 hours the rats were sacrificed and the colons removed and scored for macroscopic damage. The cecum and small intestine were exteriorized and the MLN chain identified. After dissection of overlying mesenteric fat, the MLN were removed. The lymph nodes adjacent to the cecum were also removed. Isolation of DC and phenotypic characterization of FasL expression were performed by flow cytometry.RESULTSAnimals receiving TNBS had significantly higher damage scores than untreated animals (p&lt;0.0001). Expression of FasL on MLN DC was significantly higher in colitis animals (83%) than in controls (38% p&lt;0.05).CONCLUSIONOur results suggest that loss of FasL expression on MLN DC may be one of the mechanisms that contribute to the inappropriate apoptosis and subsequent T cell accumulation that occurs in IBD. Supported by 5F31DK077584.

Toxoplasma gondii: Impaired maturation and pro-inflammatory response of dendritic cells in MIF-deficient mice favors susceptibility to infection

Macrophage migration inhibitory factor (MIF) has been found to be involved in host resistance to several parasitic infections. To determine the mechanisms of MIF-dependent responses to Toxoplasma gondii, we investigated host resistance in MIF−/− mice (BALB/c background) during natural oral infection. We focused on the potential involvement of MIF in Dendritic Cell (DC) maturation and IL-12 production. Following oral T. gondii infection, wild type mice developed a strong IL-12 response with an adequate maturation of their draining mesenteric lymph node DC (MLNDC) population and were resistant to challenge with either 40 or 100 cysts (ME49 strain). In contrast, similarly infected MIF−/− mice mounted a weak IL-12 response, displayed immature MLNDCs in the early phases of infection and rapidly succumbed to both type of challenges. Lack of maturation and IL-12 production of DCs in response to T. gondii antigens was confirmed by in vitro studies, and these effects were reversed following treatment with recombinant MIF. These findings demonstrate that MIF-induced early DC maturation and IL-12 production mediate resistance to T. gondii infection.

Langerin‐expressing dendritic cells in gut‐associated lymphoid tissues

Dendritic cells (DCs) are key regulators of the immune system. They act as professional antigen-presenting cells and are capable of activating naive T cells and stimulating the growth and differentiation of B cells. According to their molecular expression, DCs can be divided into several subsets with different functions. We focus on DC subsets expressing langerin, a C-type lectin. Langerin expression is predominant in skin DCs, but langerin-expressing DCs also exist in mucosal tissue and can be induced by immunization and sometimes by nutrient deficiency. Topical transcutaneous immunization induces langerin(+)CD8 alpha(-) DCs in mesenteric lymph nodes (MLNs), which mediate the production of antigen-specific immunoglobulin A antibody in the intestine. Yet, in one recent study, langerin(+) DCs were generated in gut-associated lymphoid tissue and contributed to the suppressive intestinal immune environment in the absence of retinoic acid. In this review, we focus on the phenotypic and functional characteristics of langerin(+) DCs in the mucosal tissues, especially MLNs.

Abstract 5199: Oral Administration of an Active Form Vitamin D 3 Decreases Atherosclerosis in Mice via Modulating Immune Cell Phenotypes and Functions

Background and Objectives: Recent several clinical studies demonstrated the low level of plasma vitamin D 3 would be a risk of cardiovascular events. An active form vitamin D 3 not only regulates bone metabolisms but also has an immunosuppressive and anti-inflammatory actions which target dendritic cells (DCs) and T lymphocytes. Vitamin D 3 has been reported to inhibit the maturation of DCs and to induce regulatory T cells (Tregs) in experimental autoimmune disease models. We hypothesized an active form vitamin D 3 (calcitriol), could prevent atherosclerosis through changing immune responses. Method and Results : Six-week-apolipoprotein E knockout mice on a standard diet were orally administered 200 ng calcitriol dissolved in carboxymethyl cellulose (n=12) or carboxymethyl cellulose alone (n=15; control) twice a week for 12 weeks and atherosclerosis was assessed at 18 weeks old. Calcitriol administration decreased atherosclerotic lesion 39.1 % at aortic sinus compared to control group (mean plaque area: 0.18±0.05×10 6 vs. 0.27±0.07×10 6 μ m 2 , p&lt;0.01) without lowering cholesterol. The drug was also shown to reduce the infiltration of inflammatory cells to the atherosclerotic lesions by immunohistochemistry. To evaluate the induction of Tregs and immature state of DCs (iDC) in small intestine and other organs, we examined the ratio of Tregs and iDC by flow cytometry in mesenteric lymph nodes (MLNs) and spleens. Calcitriol markedly increased CD4 + CD25 + FoxP3 + Tregs in MLNs by 17.1% and spleens by 23.4% (p&lt;0.01), and further reduced the mature state (CD11c + CD80 + CD86 + ) DCs in MLNs by 10.6% (p=0.02) compared to control. RT-PCR demonstrated mRNA expressions of CD80 and interferon-gamma were markedly decreased in MLNs and spleens in calcitriol-treated group, respectively. Conclusion : An active form vitamin D 3 could prevent the development of atherosclerosis via changing the function or differentiation of DCs and T lymphocytes. At least, we demonstrated calcitriol increased the number of Tregs and reduced the mature state DCs in the present study, though further studies are required to examine the role of iDC and Tregs in this process. This treatment could be a potential immunotherapy for preventing atherosclerosis and must contribute to the clinics.

Dynamics of CD11c+ dendritic cell subsets in lymph nodes draining the site of intestinal nematode infection

Helminth parasites drive dominant Th2 responses through an as yet unidentified pathway. We have previously shown that the rodent gastrointestinal nematode Nippostrongylus brasiliensis secretes products which selectively activate in vitro-derived dendritic cells to induce Th2 responses on in vivo transfer. We now show that, during active infection with this parasite, the draining mesenteric lymph node dendritic cell population is altered significantly. Although there is substantial expansion of DC numbers during infection, the CD86hi-CD8αint-CD11b− subset is markedly diminished, and expression levels of CD40, CD86 and CD103 are reduced. Notably, the reduced frequency of CD8αint DCs is evident only in those mesenteric lymph nodes draining the anterior site of infestation. In infections with the longer lived Heligmosomoides polygyrus, the proportion of CD8αint DCs in the MLNC falls to below 10% of total DC numbers by 35 days post-infection. Further, infection alters TLR responsiveness, as IL-12 production (as measured by ex vivo intracellular staining of CD11c+ DCs) in response to LPS stimulation is reduced, while IL-6, TNF-α and in particular, IL-10 all increase following infection with either nematode parasite. These changes suggest the possibility that helminth parasites modulate gastrointestinal immunity both by inhibiting migration of CD8αint DCs to the draining lymph nodes, and modifying DC responsiveness in a manner which favours a Th2 outcome.

Role of &amp;#946;7 Integrins in Intestinal Lymphocyte Homing and Retention

Lymphocytes involved in intestinal immune response are found in organized immune inductive sites of the gut-associated lymphoid tissues (GALT) such as Peyer's patches (PP), mesenteric lymph nodes (MLN) and diffuse effector sites of gut epithelium and lamina propria (LP). beta(7) integrins are responsible for efficient trafficking and retention of lymphocytes in these sites. Naïve and effector lymphocytes use alpha(4)beta(7) integrin to extravasate from blood to gut mucosal tissues of GALT, MLN and LP via interactions with Mucosal Addressin Cell Adhesion Molecule-1 (MAdCAM-1). The alpha(E)beta(7) integrin facilitates retention of effector and memory lymphocytes in the gut epithelial layer via interactions with E-cadherin. Mucosal dendritic cells (DCs) regulate the expression of the gut homing receptors alpha(4)beta(7) integrin and the chemokine receptor CCR9 on activated effector and regulatory lymphocytes in a retinoic acid-dependent manner. CD103 (alpha(E) integrin) identifies a subset of mucosal DCs in MLN and small intestine LP that have an enhanced ability to induce gut-tropic receptors on responding lymphocytes. The interactions between beta(7) integrin and their ligands are also implicated in the pathogenesis and progression of inflammatory bowel diseases (IBDs), intestinal parasitic infections and graft-versus-host diseases. During intestinal inflammation, beta(7) integrin-dependent and -independent pathways contribute to lymphocytes recruitment to the intestinal tissues and disease pat-hogenesis. Recent works have explored the potential of therapeutic targeting of alpha(4) and beta(7) integrins in IBDs. Here, we review the current understanding of the role of beta(7) integrins in intestinal lymphocyte trafficking and retention in health and disease.

Th1/Th17 Immune Response Is Induced by Mesenteric Lymph Node Dendritic Cells in Crohn's Disease

Dendritic cells (DCs) possess the most potent ability to induce acquired immunity. However, their involvement in the pathogenesis of Crohn's disease (CD) has not yet been determined. We aimed to establish the immune status of mesenteric lymph nodes, the major gut-associated lymphoid tissue, and isolated DCs and determine their involvement in the pathogenesis of CD. CD4(+) T cells and DCs were isolated from mesenteric lymph nodes of CD, ulcerative colitis, and normal control. The immune status of CD4(+) T cells was analyzed by cytokine production and transcriptional profile. Surface phenotype of DCs was analyzed by flow cytometry. Cytokine production by myeloid DCs was analyzed by real-time polymerase chain reaction and exogenous bacterial stimulation. Immune stimulating activity of DCs was determined by mixed lymphocyte reaction. In CD, mesenteric lymph node CD4(+) T cells produced higher amounts of interferon-gamma and interleukin (IL)-17 compared with ulcerative colitis and normal control, and this was dictated by increased T-bet and retinoic acid-related orphan receptor-gamma expression. Three subtypes of DCs, myeloid DC, plasmacytoid DC, and mature DC, were identified in all groups. When stimulated with exogenous bacterial derivative, myeloid DCs from CD produced a higher amount of IL-23 and a lower amount of IL-10. Myeloid DCs from CD induced stronger T helper cell (Th)1 immune response in mixed lymphocyte reaction compared with those from ulcerative colitis and normal control. Our findings revealed that mesenteric lymph node is the key pathogenic location of CD elicited by the unique cytokine milieu produced by DCs leading to a dysregulated Th1/Th17 immune response.

Toll-Like Receptor 5-Dependent Regulation of Inflammation in Systemic Salmonella enterica Serovar Typhimurium Infection

Salmonella enterica, a gram-negative pathogen, causes a spectrum of human infections including enterocolitis and typhoid fever. We previously showed that Salmonella flagellin played a role in suppressing intestinal mucosal inflammation in a murine model of acute enterocolitis. In this study, we examined the role of flagellin in the typhoid-like systemic murine Salmonella infection by measuring bacterial proliferation, inflammation, leukocyte recruitment, and cellular apoptosis in Peyer's patches (PPs), mesenteric lymph node (MLN), and spleen. We found that relative to an isogenic wild-type (WT) strain, aflagellate Salmonella exhibited increased proliferation at 4 days postinfection in PPs and MLN but not spleen. The aflagellate mutant also elicited increased local and systemic secretion of inflammatory cytokines such as interleukin-1beta, gamma interferon, and tumor necrosis factor alpha and enhanced surface expression of ICAM-1 on macrophages and dendritic cells (DCs). Furthermore, the recruitment of macrophages and DCs in PPs and MLN, but not spleen, was enhanced upon infection with aflagellate Salmonella. The relative differences between WT and aflagellate Salmonella were highly attenuated in Toll-like receptor 5-deficient (TLR5(-/-)) mice, indicating involvement of TLR5-dependent signaling. Interestingly, infection with the aflagellate mutant also resulted in decreased levels of T-cell apoptosis in PPs relative to infection with WT Salmonella. We postulate that the initial lack of detection of the aflagellate mutant in the mucosa permits increased proliferation within the host and enhances inflammatory signaling in nonepithelial cell types, which subsequently promotes leukocyte recruitment. In contrast, lack of difference in any disease parameter measured in the spleen likely reflects that Salmonella expression of flagellin is downregulated in this organ. Thus, the characteristic inflammatory pathology of Salmonella infection occurs only in PPs and to a lesser extent in MLN during the initial phases of infection and these early responses are dependent on TLR5.

Dendritic Cells from Peyer’s Patches and Mesenteric Lymph Nodes Differ from Spleen Dendritic Cells in their Response to Commensal Gut Bacteria

Commensal gut bacteria have potent effects on the immune system, which are partially mediated by intestinal dendritic cells (DC). Distinct commensals confer different properties to in vitro-generated DC. The aim of the present study was to reveal strain-dependent maturation patterns in primary DC. To this end, we compared the response of mouse Peyer's patch (PP) DC, mesenteric lymph node (MLN) DC and spleen DC to the commensal bacteria, Bifidobacterium longum Q46, Lactobacillus acidophilus X37 and Escherichia coli Nissle 1917. Bacterial maturation of DC occurred independently of tissue origin. Expression of CCR7 and CD103 on the surface of MLN DC, necessary for the induction of gut-homing regulatory T cells, increased with stimulation by Gram-positive commensals. Bacteria-dependent cytokine production (IL-6, IL-10 and TNF-alpha) was similar in spleen and MLN DC, and contaminant cells in these DC preparations produced IFN-gamma in response to L. acidophilus. In contrast, PP DC produced IL-6 only in response to E. coli, little IL-10 and no TNF-alpha, and this low cytokine production was not due to inhibition by IL-10 or TGF-beta. Bifidobacteria downregulate IL-6, TNF-alpha and IL-12 production induced in in vitro-generated DC by L. acidophilus. Similar inhibition was observed in splenic DC, but not in MLN DC. MLN cells responded to bacterial stimulation with higher IFN-gamma production than spleen cells, possibly due to the presence of more responsive natural killer cells. Commensal bacteria therefore play specific roles in the gut immune system distinguishable from the effect they would have if recognized by the systemic immune system.

Intestinal Colonization of IL-2 Deficient Mice with Non-Colitogenic B. vulgatus Prevents DC Maturation and T-Cell Polarization

Background IL-2 deficient (IL-2−/−) mice mono-colonized with E. coli mpk develop colitis whereas IL-2−/−-mice mono-colonized with B. vulgatus mpk do not and are even protected from E. coli mpk induced colitis.Methodology/Principal FindingsWe investigated if mono-colonization with E. coli mpk or B. vulgatus mpk differentially modulates distribution, activation and maturation of intestinal lamina propria (LP) dendritic cells (DC). LP DC in mice mono-colonized with protective B. vulgatus mpk or co-colonized with E. coli mpk/B. vulgatus mpk featured a semi-mature LP DC phenotype (CD40loCD80loMHC-IIhi) whereas mono-colonization with colitogenic E. coli mpk induced LP DC activation and maturation prior to onset of colitis. Accordingly, chemokine receptor (CCR) 7 surface expression was more strikingly enhanced in mesenteric lymph node DC from E. coli mpk than B. vulgatus mpk mono- or co-colonized mice. Mature but not semi-mature LP DC promoted Th1 polarization. As B. vulgatus mpk promotes differentiation of semi-mature DC presumably by IL-6, mRNA and protein expression of IL-6 was investigated in LP DC. The data demonstrated that IL-6 mRNA and protein was increased in LP DC of B. vulgatus mpk as compared to E. coli mpk mono-colonized IL-2−/−-mice. The B. vulgatus mpk mediated suppression of CCR7 expression and DC migration was abolished in IL-6−/−-DC in vitro.Conclusions/SignificanceFrom this data we conclude that the B. vulgatus triggered IL-6 secretion by LP DC in absence of proinflammatory cytokines such as IL-12 or TNF-α induces a semi-mature LP DC phenotype, which might prevent T-cell activation and thereby the induction of colitis in IL-2−/−-mice. The data provide new evidence that IL-6 might act as an immune regulatory cytokine in the mucosa by targeting intestinal DC.

Gastrointestinal Dendritic Cells Promote Th2 Skewing via OX40L

Mice can be sensitized to food proteins by oral administration with the adjuvant cholera toxin (CT), such that they undergo anaphylaxis when rechallenged with the sensitizing allergen. In contrast, feeding of Ags alone leads to oral tolerance. Our aim was to define the mechanisms by which gastrointestinal dendritic cells (DCs) participate in the deviation of tolerance to allergic sensitization in the gut in response to CT. BALB/c mice were fed with CT or PBS. The impact of CT on DC subsets in the mesenteric lymph node (MLN) was assessed by flow cytometry. Ag presentation assays were performed with DCs isolated from the MLN of PBS- or CT-fed mice, using OVA-specific CD4(+) T cells as responder cells. Gene expression in MLN DCs was determined by real-time PCR, and neutralizing Abs were used to test the function of OX40 ligand (OX40L) in Th2 skewing. Oral administration of CT induced an increase in the total CD11c(+) population in the MLN. CT induced a selective increase in migration of the CD11c(+)CD11b(-)CD8alpha(-) DC subset and the maturation of all DC subsets. Maturation of DCs in vivo enhanced T cell proliferation and cytokine secretion. Oral CT induced up-regulation of Jagged-2 and OX40L by MLN DCs. Neutralizing anti-OX40L Abs completely abrogated the CT-induced Th2 cytokine response. We show that oral CT induces selective DC migration, maturation, and T cell priming activity in the MLN. Th2 skewing is mediated by OX40L, and we speculate that this molecule may be an important inducer of allergic sensitization to food allergens.

Retinoic acid receptor signaling levels and antigen dose regulate gut homing receptor expression on CD8+ T cells

Recent studies have highlighted a central role for intestinal dendritic cells (DCs) and vitamin A metabolite retinoic acid (RA) in the generation of α4β7+ CCR9+“gut tropic” effector T cells. Here, using RA-responsive element reporter mice, we demonstrate that both splenic and mesenteric lymph node (MLN) DCs enhanced retinoic acid receptor (RAR) signaling in CD8+ T cells; however, only a subset of MLN DCs, expressing the integrin α-chain CD103, induced an early RAR signal that is required for efficient CCR9 induction. MLN-primed CD8+ T cells also received enhanced RAR-dependent signals compared with splenic-primed CD8+ T cells in vivo. Further DC-mediated induction of gut homing receptors was inhibited at a high antigen dose without influencing RAR signaling events, and resulted in less efficient CD8+ T-cell entry into the small intestinal mucosa. These results highlight a complex interplay between antigen dose and DC subset-induced RAR signaling events in the generation of tissue tropic effector T-cell subsets.

Dendritic Cell Populations in Colon and Mesenteric Lymph Nodes of Patients With Crohn's Disease

Dendritic cells (DCs) are key cells in innate and adaptive immune responses that determine the pathophysiology of Crohn's disease. Intestinal DCs migrate from the mucosa into mesenteric lymph nodes (MLNs). A number of different markers are described to define the DC populations. In this study we have identified the phenotype and localization of intestinal and MLN DCs in patients with Crohn's disease and non-IBD patients based on these markers. We used immunohistochemistry to demonstrate that all markers (S-100, CD83, DC-SIGN, BDCA1-4, and CD1a) showed a different staining pattern varying from localization in T-cell areas of lymph follicles around blood vessels or single cells in the lamina propria and in the MLN in the medullary cords and in the subcapsular sinuses around blood vessels and in the T-cell areas. In conclusion, all different DC markers give variable staining patterns so there is no marker for the DC.

Mesenteric dendritic cells from germ-free mice cause less T-cell stimulation but still induce ?4?7 integrin

Intestinal dendritic cells (DCs) have properties that distinguish them from DCs in other tissues. The intestinal microbiota influences the generation of the gut immune system but it is not known whether bacteria influence tissue-specific properties of intestinal DCs. In this study intestinal and non-intestinal DCs from germ-free (GF) and conventional (CONV) mice were compared. Mesenteric lymph node (MLN) DCs from GF mice were less stimulatory for T cells than their counterparts from CONV mice. Responses stimulated by Peyer’s patch (PP) DCs and peripheral lymph node (PLN) DCs were similar in GF and CONV mice. DCs from GF mice were competent for the generation of cytokine-producing effector T cells with interferon (IFN)-g production dominant. Gut (MLN and PP) DCs had tissue-specific properties that distinguished them from PLN DCs: lower CD40 expression, the presence of a major CD11blo DC subset and the ability to generate large numbers of T cells expressing the gut-homing integrin α 4β7. These differential properties of gut and PLN DCs were observed in both GF and CONV mice. These data suggest that the microbiota enhance the stimulatory capacity of MLN DCs but are not required for the generation of a number of distinctive properties of gut DCs. Key words: dendritic cells, bacteria, germ-free animals, intestinal microbiota

A functionally specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-β– and retinoic acid–dependent mechanism

Foxp3+ regulatory T (T reg) cells play a key role in controlling immune pathological re actions. Many develop their regulatory activity in the thymus, but there is also evidence for development of Foxp3+ T reg cells from naive precursors in the periphery. Recent studies have shown that transforming growth factor (TGF)-β can promote T reg cell development in culture, but little is known about the cellular and molecular mechanisms that mediate this pathway under more physiological conditions. Here, we show that after antigen activation in the intestine, naive T cells acquire expression of Foxp3. Moreover, we identify a population of CD103+ mesenteric lymph node dendritic cells (DCs) that induce the devel opment of Foxp3+ T reg cells. Importantly, promotion of T reg cell responses by CD103+ DCs is dependent on TGF-β and the dietary metabolite, retinoic acid (RA). These results newly identify RA as a cofactor in T reg cell generation, providing a mechanism via which functionally specialized gut-associated lymphoid tissue DCs can extend the repertoire of T reg cells focused on the intestine.