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Background Early life stress (ELS) is an environmental trigger believed to promote increased risk of IBD. Our goal was to identify mechanisms whereby ELS in mice affects susceptibility to and/or severity of gut inflammation. Methods We utilized 2 published animal models of ELS. In the first model, newborn mice were separated from the dam daily for 4 to 8 hours starting on postnatal day 2 and then weaned early on postnatal day 17. Control mice were left undisturbed with the dams until weaning on postnatal day 21. In the second model, dams were fed dexamethasone or vehicle ad libitum in drinking water on postpartum days 1 to 14. Plasma and colonic corticosterone were measured in juvenile and adult mice. Colitis was induced in 4-week-old mice via intraperitoneal injection of interleukin (IL)-10 receptor blocking antibody every 5 days for 15 days. Five or 15 days later, colitis scores and transcripts for Tnf, glucocorticoid receptors, and steroidogenic enzymes were measured. Results Mice exposed to ELS displayed reduced plasma and colonic corticosterone. Control animals showed improvements in indices of inflammation following cessation of interleukin-10 receptor blockade, whereas ELS-exposed animals maintained high levels of Tnf and histological signs of colitis. In colitic animals, prior exposure to ELS was associated with significantly lower expression of genes associated with corticosterone synthesis and responsiveness. Finally, TNF stimulation of colonic crypt cells from ELS mice led to increased inhibition of corticosterone synthesis. Conclusions Our study identifies impaired local glucocorticoid production and responsiveness as a potential mechanism whereby ELS predisposes to chronic colitis in susceptible hosts.

Given the gut microbiome's rise as a potential frontier in cancer pathogenesis and therapy, leveraging microbial analyses in the study of breast tumor progression and treatment could unveil novel interactions between commensal bacteria and disease outcomes. In breast cancer, the Hedgehog (Hh) signaling pathway is a potential target for treatment due to its aberrant activation leading to poorer prognoses and drug resistance. There are limited studies that have investigated the influences of orally administered cancer therapeutics, such as Vismodegib (a pharmacological, clinically used Hh inhibitor) on the gut microbiota. Using a 4T1 mammary carcinoma mouse model and 16 S rRNA sequencing, we longitudinally mapped alterations in immunomodulating gut microbes during mammary tumor development. Next, we identified changes in the abundance of commensal microbiota in response to Vismodegib treatment of 4T1 mammary tumor-bearing mice. In addition to remodeling gut microbiota, Vismodegib treatment elicited an increase in proliferative CD8sup+/supT cells in the colonic immune network, without any remarkable gastrointestinal-associated side effects. To our knowledge, this is the first study to assess longitudinal changes in the gut microbiome during mammary tumor development and progression. Our study also pioneers an investigation of the dynamic effects of an orally delivered Hh inhibitor on the gut microbiome and the gut-associated immune-regulatory adaptive effector CD8sup+/supT cells. These findings inform future comprehensive studies on the consortium of altered microbes that can impact potential systemic immunomodulatory roles of Vismodegib.

Exposure to early life stress (ELS) is associated with a greater risk of chronic disease development including depression and cardiovascular disease. Altered gut microbiota has been linked to both depression and cardiovascular disease in mice and humans. Rodent models of early life neglect are used to characterize the mechanistic links between early life stress (ELS) and the risk of disease later in life. However, little is understood about ELS exposure and the gut microbiota in the young mice and the influence of the maternal inheritance of the gut microbiota. We used a mouse model of ELS, maternal separation with early weaning (MSEW), and normally reared mice to determine whether the neonate microbiota is altered, and if so, are the differences attributable to changes in dam microbiota that are then transmitted to their offspring. Individual amplicon sequence variants (ASVs) displayed differential abundance in the microbiota of MSEW compared with normally reared pups at postnatal day ( PD) 28. Additionally, ELS exposure reduced the alpha diversity and altered microbial community composition at PD28. The composition, levels of alpha diversity, and abundance of individual ASVs in the microbiota of dams were similar from MSEW or normally reared cohorts. Thus, the observed shifts in the abundance of individual bacterial ASVs in the neonates and young pups are likely driven by endogenous effects of MSEW in the offspring host and are not due to inherited differences from the dam. This knowledge suggests that exposure to ELS has a direct effect on microbial factors on the risk of chronic disease development.

Despite decades of research there is no specific therapy for Acute Pancreatitis (AP). In the current study, we have evaluated the efficacy of pirfenidone, an anti-inflammatory and anti-fibrotic agent which is FDA-approved for treatment of idiopathic pulmonary fibrosis (IPF), in ameliorating local and systemic injury in AP. Our results suggest that treatment with pirfenidone in therapeutic settings (i.e. after initiation of injury), even when administered at the peak of injury, reduces severity of local and systemic injury and inflammation in multiple models of AP. In-vitro evaluation suggests that pirfenidone decreases cytokine release from acini and macrophages and disrupts acinar-macrophage crosstalk. Therapeutic pirfenidone treatment increases IL-10 secretion from macrophages preceding changes in histology and modulates the immune phenotype of inflammatory cells with decreased levels of inflammatory cytokines. Antibody-mediated IL-10 depletion, use of IL-10 Knock Out mice, and macrophage depletion experiments confirmed the role of IL-10 and macrophages in its mechanism of action, as pirfenidone was unable to reduce severity of AP in these scenarios. Since pirfenidone is FDA approved for IPF, a trial evaluating the efficacy of pirfenidone in patients with moderate to severe AP can be initiated expeditiously.Key Words: Acute Pancreatitis, Pirfenidone, Interleukin-10, L-arginine pancreatitis, Systemic inflammation, lung injury.

Meals rich in oxalate are associated with calcium oxalate (CaOx) kidney stone disease. Hydroxy-L-proline (HLP) is an oxalate precursor found in milk and collagen-containing foods. HLP has been shown to induce CaOx crystal formation in rodents. The purpose of this study was to evaluate the effect of HLP-induced oxalate levels on inflammation and renal leukocytes during crystal formation. Male Sprague-Dawley rats (6-8 weeks old) were fed a control diet containing no oxalate for 3 days before being randomized to continue the control diet or 5% HLP for up to 28 days. Blood, 24-hour urine, and kidneys were collected on Days 0, 7, 14, or 28. Urinary oxalate levels, crystal deposition, and renal macrophage markers were evaluated using ion chromatography-mass spectrometry, immunohistochemistry, and qRT-PCR. Renal leukocytes were assessed using flow cytometry and RNA-sequencing. HLP feeding increased urinary oxalate levels and renal crystal formation in animals within 7 days. HLP also increased renal macrophage populations on Days 14 and 28. Transcriptome analysis revealed that renal macrophages from animals fed HLP for 7 days were involved in inflammatory response and disease, stress response to LPS, oxidative stress, and immune cell trafficking. Renal macrophages isolated on Day 14 were involved in cell-mediated immunological pathways, ion homeostasis, and inflammatory response. Collectively, these findings suggest that HLP-mediated oxalate levels induce markers of inflammation, leukocyte populations, and reprograms signaling pathways in macrophages in a time-dependent manner. Additional studies investigating the significance of oxalate on renal macrophages could aid in our understanding of kidney stone formation.

The ICOS pathway has been implicated in the development and functions of regulatory T (Treg) cells, including those producing IL-10. Treg cell–derived IL-10 is indispensable for the establishment and maintenance of intestinal immune homeostasis. We examined the possible involvement of the ICOS pathway in the accumulation of murine colonic Foxp3- and/or IL-10–expressing cells. We show that ICOS deficiency does not impair induction of IL-10 by intestinal CD4 T cells but, instead, triggers substantial reductions in gut-resident and peripherally derived Foxp3+ Treg cells. ICOS deficiency is associated with reduced demethylation of Foxp3 CNS2 and enhanced loss of Foxp3. This instability significantly limits the ability of ICOS-deficient Treg cells to reverse ongoing inflammation. Collectively, our results identify a novel role for ICOS costimulation in imprinting the functional stability of Foxp3 that is required for the retention of full Treg cell function in the periphery.

Genome-wide association studies have identified ICOSLG, which encodes the inducible costimulator ligand (ICOSLG or ICOSL) as a susceptibility locus for inflammatory bowel disease. ICOSL has been implicated in the enhancement of pattern recognition receptor signaling in dendritic cells, induction of IL-10 production by CD4 T cells, and the generation of high-affinity antibodies to specific antigens—all of which can potentially explain its involvement in gastrointestinal inflammation. Here, we show that murine ICOSL deficiency results in significant enrichment of IL-10–producing CD4 T cells particularly in the proximal large intestine. Transient depletion of IL-10–producing cells from adult ICOSL-deficient mice induced severe colonic inflammation that was prevented when mice were first treated with metronidazole. ICOSL-deficient mice displayed reduced IgA and IgG antibodies in the colon mucus and impaired serum antibody recognition of microbial antigens, including flagellins derived from mucus-associated bacteria of the Lachnospiraceae family. Confirming the synergy between ICOSL and IL-10, ICOSL deficiency coupled with CD4-specific deletion of the Il10 gene resulted in juvenile onset colitis that was impeded when pups were fostered by ICOSL-sufficient dams. In this setting, we found that both maternally acquired and host-derived antibodies contribute to the life anti-commensal antibody repertoire that mediates this protection in early life. Collectively, our findings reveal a partnership between ICOSL-dependent anti-commensal antibodies and IL-10 in adaptive immune regulation of the microbiota in the large intestine. Furthermore, we identify ICOSL deficiency as an effective platform for exploring the functions of anti-commensal antibodies in host–microbiota mutualism.

Microbiota-reactive CD4+ T memory (TM) cells are generated during intestinal infections and inflammation, and can revert to pathogenic CD4+ T effector (TE) cells, resulting in chronicity of inflammatory bowel disease (IBD). Unlike TE cells, TM cells have a low rate of metabolism unless they are activated by reencountering cognate antigen. Here, we show that the combination of cell activation and metabolic checkpoint inhibition (CAMCI), by targeting key metabolic regulators mTORC and AMPK, resulted in cell death and anergy, but enhanced the induction of the regulatory subset. Parenteral application of this treatment with a synthetic peptide containing multiple flagellin T cell epitopes (MEP1) and metabolic inhibition successfully prevented the development of CD4+ T cell-driven colitis. Microbiota-specific CD4+ T cells, especially the pathogenic TE subsets, were decreased 10-fold in the intestinal lamina propria. Furthermore, using the CAMCI strategy, we were able to prevent antigen-specific TM cell formation upon initial antigen encounter, and ablate existing TM cells upon reactivation in mice, leading to an altered transcriptome in the remaining CD4+ T cells after ablation. Microbiota flagellin-specific CD4+ T cells from patients with Crohn's disease were ablated in a similar manner after CAMCI in vitro, with half of the antigen-specific T cells undergoing cell death. These results indicate that parenteral activation of microbiota-specific CD4+ T cells with concomitant metabolic inhibition is an effective way to ablate pathogenic CD4+ TM cells and to induce T regulatory (Treg) cells that provide antigen-specific and bystander suppression, supporting a potential immunotherapy to prevent or ameliorate IBD.

The nonimmune roles of Tregs have been described in various tissues, including the BM. In this study, we comprehensively phenotyped marrow Tregs, elucidating their key features and tissue-specific functions. We show that marrow Tregs are migratory and home back to the marrow. For trafficking, marrow Tregs use S1P gradients, and disruption of this axis allows for specific targeting of the marrow Treg pool. Following Treg depletion, the function and phenotype of both mesenchymal stromal cells (MSCs) and hematopoietic stem cells (HSCs) was impaired. Transplantation also revealed that a Treg-depleted niche has a reduced capacity to support hematopoiesis. Finally, we found that marrow Tregs are high producers of IL-10 and that Treg-secreted IL-10 has direct effects on MSC function. This is the first report to our knowledge revealing that Treg-secreted IL-10 is necessary for stromal cell maintenance, and our work outlines an alternative mechanism by which this cytokine regulates hematopoiesis., Bone marrow Tregs regulate stromal cell function to maintain hematopoiesis through IL-10 and provide a potential therapeutic avenue for stromal manipulation.

High salt diets (HSD) promote both inflammation and immunosuppression as shown in numerous studies utilizing salt-sensitive or hypertensive models. However, mechanisms involved in the homeostatic immune response to HSD, alone, have not been fully elucidated. Regulatory T cells (FOXP3 + CD4 + T cells) play a role in host protection against disease or environmental stressors. Further, recent studies show that RORt + expression by Tregs may represent a functional adaptation by Tregs in response to alterations to the diet. Thus, we hypothesized that these Treg populations may expand in response to HSD alone, and a hypertensive insult prior to the HSD blunts this response. We designed experiments to determine whether Tregs and RORt + Tregs expand in response to HSD or with LNAME hypertension followed by HSD. We evaluated the following groups in male C57BL/6J mice: NSD (normal salt diet, 0.4% NaCl), LNAME/NSD (0.5mg/ml for 3-wks in drinking water, followed by 3-wks NSD), HSD (4% NaCl+1% NaCl in drinking water, 2-wks), or LNAME/HSD (0.5mg/mL for 3-wks in drinking water, with 1-wk NSD followed by 2-wks HSD). Following immune cell isolation, we utilized flow cytometry to phenotype renal and colonic T cells. Data are expressed as frequency of means (% of CD4 + TCRbeta + T cells)±SEM (n=3-8/group) compared to NSD. In kidneys, HSD significantly expanded Tregs and RORt + Tregs, while LNAME/HSD group was unchanged compared to controls (% Treg: NSD: 5.7±0.5; L-NAME: 6.5±0.5; HSD: 9.2±1.0**; LNAME/HSD: 6.2±0.3; % RORt + Treg: NSD: 0.4±0.07; L-NAME: 0.6±0.13; HSD: 1.8±0.41***; LNAME/HSD: 0.6±0.14; **p+ Tregs, whereas the LNAME/HSD group had no change in these T cell populations (% Treg: NSD: 36±2; LNAME: 42±1; HSD: 46±2*; LNAME/HSD: 43±2; % RORt + Tregs: NSD: 16±1; LNAME: 19±1; HSD: 23±1*; LNAME/HSD: 20±2; *p+ Tregs expand in response to HSD in the kidney and colon, with a greater magnitude of expansion by RORt + Tregs. However, this expansion of T cell populations is not evident in mice pre-exposed to a hypertensive insult. We propose that HSD stimulates pathways that promote Treg expansion, which may be associated with salt-resistance and protective mechanisms.

Innate lymphoid cells (ILCs) and CD4+ T cells produce IL-22, which is critical for intestinal immunity. The microbiota is central to IL-22 production in the intestines; however, the factors that regulate IL-22 production by CD4+ T cells and ILCs are not clear. Here, we show that microbiota-derived short-chain fatty acids (SCFAs) promote IL-22 production by CD4+ T cells and ILCs through G-protein receptor 41 (GPR41) and inhibiting histone deacetylase (HDAC). SCFAs upregulate IL-22 production by promoting aryl hydrocarbon receptor (AhR) and hypoxia-inducible factor 1α (HIF1α) expression, which are differentially regulated by mTOR and Stat3. HIF1α binds directly to the Il22 promoter, and SCFAs increase HIF1α binding to the Il22 promoter through histone modification. SCFA supplementation enhances IL-22 production, which protects intestines from inflammation. SCFAs promote human CD4+ T cell IL-22 production. These findings establish the roles of SCFAs in inducing IL-22 production in CD4+ T cells and ILCs to maintain intestinal homeostasis., Intestinal IL-22 has important regulatory effects on the barrier and intestinal diseases and its production is controlled by the intestinal microbiome. Here the authors show that intestinal immune cell production of IL-22 is regulated by short chain fatty acids via an aryl hydrocarbon receptor and HIF1α-mediated mechanism that protects mice from intestinal inflammation.

Microbiota-reactive CD4

Inflammatory bowel diseases (IBD) are chronic disorders of the gastrointestinal tract with peak onset during adolescence. The etiology of IBD remains poorly understood, but is believed to involve genetic susceptibility, improper immune regulation, and environmental factors. Psychological stress is one environmental trigger that has been associated with an increased risk of inflammatory diseases. Specifically, previous studies have linked early life stress (ELS) with hypothalamic–pituitary–adrenal (HPA) axis dysfunction leading to adverse health outcomes later in life. Our goal was to determine whether ELS in mice affects susceptibility to, and severity of, colitis – induced subsequent to stress exposure. We used an established mouse model of ELS, maternal separation with early weaning (MSEW), in which newborn mice are separated from their mothers for 4–8 hours daily from day of life (DOL) 2 until early weaning on DOL 17. Then, starting on DOL 28, colitis was induced in MSEW mice and their normally-reared (NR) counterparts by transient blockade of the interleukin-10 receptor (IL-10R). Prior to induction of colitis, MSEW mice showed systemic and colon-specific depletion of corticosterone relative to NR mice. In addition, MSEW mice with active colitis harbored significantly reduced numbers of colonic Foxp3+ T cells compared to colitic NR mice. Finally, whereas NR mice were mostly in remission by 15 days following cessation of IL-10R blockade, MSEW mice showed consistently elevated Tnf in the proximal colon and sustained epithelial damage. Our results suggest that ELS-mediated HPA-axis dysfunction causes hypo-corticosteronism, which may subsequently promote prolonged colonic inflammation in susceptible hosts.

Tuberculosis (TB), caused by Mycobacterium tuberculosis infection, is a leading cause of mortality and morbidity, causing ∼1.5 million deaths annually. CD4+ T cells and several cytokines, such as the Th1 cytokine IFN-γ, are critical in the control of this infection. Conversely, the immunosuppressive cytokine IL-10 has been shown to dampen Th1 cell responses to M. tuberculosis infection impairing bacterial clearance. However, the critical cellular source of IL-10 during M. tuberculosis infection is still unknown. Using IL-10 reporter mice, we show in this article that during the first 14 d of M. tuberculosis infection, the predominant cells expressing IL-10 in the lung were Ly6C+ monocytes. However, after day 21 postinfection, IL-10–expressing T cells were also highly represented. Notably, mice deficient in T cell–derived IL-10, but not mice deficient in monocyte-derived IL-10, showed a significant reduction in lung bacterial loads during chronic M. tuberculosis infection compared with fully IL-10–competent mice, indicating a major role for T cell–derived IL-10 in TB susceptibility. IL-10–expressing cells were detected among both CD4+ and CD8+ T cells, expressed high levels of CD44 and Tbet, and were able to coproduce IFN-γ and IL-10 upon ex vivo stimulation. Furthermore, during M. tuberculosis infection, Il10 expression in CD4+ T cells was partially regulated by both IL-27 and type I IFN signaling. Together, our data reveal that, despite the multiple immune sources of IL-10 during M. tuberculosis infection, activated effector T cells are the major source accounting for IL-10–induced TB susceptibility.

OBJECTIVES/GOALS: The overall goal of this study was to determine the effect of early life stress (ELS) on the intestinal CD4+ T cell immune compartment, at homeostasis and after induction of experimental Inflammatory Bowel Disease (IBD). METHODS/STUDY POPULATION: We used a mouse model of ELS, maternal separation with early weaning (MSEW). We used IL-10 reporter mice to enable analysis of IL-10-producing cells. Mice were examined on postnatal day 28 to determine the impact of ELS on gut regulatory T cells. Plasma levels of corticosterone (rodent stress response hormone) was determined by ELISA. Colitis was induced in MSEW and normal rear (NR) mice via intraperitoneal injection of α-IL-10R every 5 days until day 15. Mice were euthanized on days 20 and 30. Colonic tissue sections were stained for histological analysis. Remaining tissue was further processed for flow cytometric analysis of CD4+ T cells and innate lymphoid cells. RESULTS/ANTICIPATED RESULTS: Plasma corticosterone was elevated in MSEW mice compared to their NR counterparts at 4 weeks of age. We observed that the MSEW stress protocol does not affect the baseline colonic CD4+ T cell or innate lymphoid cell populations. There was a reduction in the intestinal CD4+ T cells and regulatory T cells on day 20 in α-IL-10R MSEW mice compared to NR counterparts. This difference disappeared by day 30. Histological scoring showed no difference in disease severity between α-IL-10R treated MSEW and NR mice on day 20. However, on day 30, when α-IL-10R NR mice are recovering from colitis, MSEW mice showed persistent histological inflammation, mainly attributable to sustained epithelial damage. DISCUSSION/SIGNIFICANCE OF IMPACT: Our results suggest that ELS prolongs intestinal inflammation and impairs epithelial repair. Future studies will focus on elucidating the mechanisms responsible for ELS-dependent impairment of mucosal repair in experimental colitis.

Humans and other species of mammals are hosts to an array of microbial communities collectively referred to as the microbiota. The microbiota comprises prokaryotes (bacteria and archaea), viruses (bacteriophages as well as eukaryotic viruses), and eukarya or the meiofauna (mainly fungi and protozoa). As revealed by the Human Microbiome Project, specialized subcommunities colonize barrier surfaces of the digestive, respiratory, and urogenital tracts, and skin. Our immune system is believed to have evolved to ensure peaceful coexistence with these microorganisms that aid in immune homeostasis, pathogen resistance, and digestion in exchange for a nutrient-rich habitat. There is a perpetual cross-talk between the microbiota and the immune system throughout an individual's life. Specific modulation of this microbiota, particularly in infancy, has important long-term health consequences. Addition of specific symbionts to the microbiota can provide tangible health benefits. Reconstitution of a dysbiotic microbiota continues to be utilized or explored as therapy for inflammatory diseases.

The ICOS pathway has been implicated in the development and functions of regulatory T cells (Treg cells) including those producing IL-10. Treg cell-derived IL-10 is indispensable for the establishment and maintenance of intestinal immune homeostasis. We examined the possible involvement of the ICOS pathway in the accumulation of murine colonic Foxp3- and/or IL-10-expressing cells. We show that, ICOS deficiency does not impair induction of IL-10 by intestinal CD4 T cells, but instead triggers substantial reductions in gut-resident and peripherally-derived Foxp3(+) Treg cells. ICOS deficiency is associated with reduced demethylation of Foxp3 CNS2 and enhanced loss of Foxp3. This instability significantly limits the ability of ICOS-deficient Treg cells to reverse ongoing inflammation. Collectively, our results identify a novel role for ICOS co-stimulation in imprinting the functional stability of Foxp3 that is required for the retention of full Treg cell function in the periphery.

The intestinal microbiota is comprised of millions of microorganisms that reside in the gastrointestinal tract and consistently interact with the host. Host factors such as diet and disease status affect the composition of the microbiota, while the microbiota itself produces metabolites that can further manipulate host physiology. Dysbiosis of the intestinal microbiota has been characterized in patients with certain metabolic diseases, some of which involve damage to the host intestinal epithelial barrier and alterations in the immune system. In this review, we will discuss the consequences of dietdependent bacterial dysbiosis in the gastrointestinal tract, and how the associated interaction with epithelial and immune cells impacts metabolic diseases.

Inflammatory bowel diseases (IBD) are chronic autoinflammatory conditions in which the immune system loses tolerance to gastrointestinal microbes. The role of humoral immunity in IBD is largely undefined. We examined the potential of T-dependent antibodies to prevent intestinal inflammation using mouse models of IBD. For this, we used mice without inducible T cell costimulator ligand (ICOSL). Icosl−/− mice produce significantly fewer T-dependent antibodies. When tested, we found Icosl−/− mice had similar IgA binding but significantly reduced IgG binding to mucosally-associated microbes. Additionally, Icosl−/− mice have more CD4 T cells producing IL-10, an immunosuppressive cytokine, in the colon. We hypothesized that T-dependent antibodies and IL-10 cooperatively promote intestinal homeostasis. To test this, we temporarily eliminated IL-10 producing cells from adult mice. Icosl−/−, but not wild type or IgA−/− mice, rapidly developed colitis under these conditions. This colitis could be prevented if mice were first depleted of Gram-positive or anaerobic bacterial flora. We further investigated the synergy between these T-dependent antibodies and IL-10 utilizing mice with a codeletion of CD4 T cell-derived IL-10 (Il10cKO) and ICOSL. This codeletion resulted in colitis before 28 days of age. However, fostering Icosl−/− Il10cKO mice on wild-type mothers delayed this early-onset inflammation. This suggests T-dependent antibodies conveyed through breastmilk are protective against early-onset colitis. Collectively, our results suggest that IL-10 and T-dependent antibodies toward mucosa-associated Gram-positive anaerobes continually cooperate to maintain intestinal homeostasis throughout the lifespan.

IL-10 produced by T cells and CD11b+ cells utilizes TLR2 signaling and FimA antigen to inhibit early IFN-γ T cell responses to Porphyromonas gingivalis. P.g., a Gram-negative bacterium, is one of the main etiological agents of the chronic inflammatory disease, periodontitis. Disease progression is thought to occur as a result of an inadequate immune response, which although happens locally, can also occur distally as a result of the dissemination of P.g. into the circulation. As IL-10 and TLR2 are pivotal molecules in the immune response that P.g. elicits, we hypothesized that TLR2-mediated IL-10 production, following the initial systemic exposure to P.g., inhibits the IFN-γ T cell response. To address this hypothesis, mice were primed with P.g., and the types of cells producing IL-10 and the capacity of T cells to produce IFN-γ following blocking or neutralization of IL-10 were assessed. Our results showed that upon initial encounter with P.g., splenic T cells and CD11b+ cells produce IL-10, which when neutralized, resulted in a substantial increase in IFN-γ production by T cells. Furthermore, IL-10 production was dependent on TLR2/1 signaling, partly in response to the major surface protein, FimA of P.g. In addition, P.g. stimulation resulted in the up-regulation of PD-1 and its ligand PD-L1 on CD4 T cells and CD11b+ cells, respectively. Up-regulation of PD-1 was partially dependent on IL-10 but independent of TLR2 or FimA. These results highlight the role of IL-10 in inhibiting T cell responses to the initial systemic P.g. exposure and suggest multiple inhibitory mechanisms potentially used by P.g. to evade the hostˈs immune response, thus allowing its persistence in the host.

Recognizing Escaped Commensals In order to coexist peacefully, the billions of bacteria in our gut and our immune system have reached a détente. An intestinal mucosal firewall exists, so bacteria remain localized to the gut, where the immune system is tightly regulated so that these bacteria are tolerated. Enteric infections, however, lead to a breach in this mucosal firewall, resulting in exposure of the peripheral immune system to the intestinal bacterial contents. What is the result? Using oral Toxoplasma gondii infection in mice, Hand et al. (p. 1553 , published online 23 August) show that, besides the T. gondii –specific T cell response, a commensal bacteria–specific T cell response is elicited. The CD4 + T cell–specific response was tracked to a commensal-derived flagellin, and these T cells expanded after T. gondii infection and formed long-lived memory cells able to respond to subsequent challenges. Thus, enteric infections can lead to the formation of commensal bacteria–specific, long-lived memory T cells that reside throughout the body—which may play a role in intestinal pathologies such as inflammatory bowel disease.

Vitamin D deficiency is implicated in autoimmune disease. We therefore evaluated the effects of 1α,25-dihydroxyvitamin D(3) (1,25-D(3)), the active form of vitamin D, on the development of T helper 1 (Th1), Th17, and Th9 cells, which are implicated in the pathogenesis of different types of autoimmunity. 1,25-D(3) compromised the development of Th17 and Th9 cells, including IL-22-expressing cells while simultaneously increasing the frequency of IL-10-competent cells. Relative to Th17 and Th9 cells, the effects of 1,25-D(3) on Th1 cells were modest, reflecting the significantly reduced levels of the receptor for vitamin D in this lineage. The use of cells deficient in IL-10 or antibodies that block IL-10 signaling abolished the inhibitory effect of 1,25-D(3) on Th9 cells but had no effect on inhibition of Th17 cell frequencies. Thus, the induction of IL-10 in cultures of Th9 cells is an important mechanism by which 1,25-D(3) compromises Th9 development but does not explain inhibition of Th17 cells. A survey of select representatives of the Th17 transcriptome revealed that the levels of mRNA that encode RORγt, IL-17A, IL-17F, IL-23R, and IL-22, were reduced by 1,25-D(3), whereas IL-21 and aryl hydrocarbon receptor mRNA remained unchanged. These data suggest that vitamin D deficiency may promote autoimmunity by favoring the inordinate production of Th17 and Th9 cells at the expense of regulatory IL-10-producing T cells.

The development of Th17 cells is accompanied by the acquisition of responsiveness to both IL-12 and IL-23, cytokines with established roles in the development and/or function of Th1 and Th17 cells, respectively. IL-12 signaling promotes antigen-dependent Th1 differentiation but, in combination with IL-18, allows the antigen-independent perpetuation of Th1 responses. On the other hand, while IL-23 is dispensable for initial commitment to the Th17 lineage, it promotes the pathogenic function of the Th17 cells. In this study, we have examined the overlap between Th1 and Th17 cells in their responsiveness to common pro-inflammatory cytokines and how this affects the antigen-independent cytokine responses of Th17 cells. We found that in addition to the IL-1 receptor, developing Th17 cells also up-regulate the IL-18 receptor. Consequently, in the presence of IL-1β or IL-18, and in the absence of TCR activation, Th17 cells produce Th17 lineage cytokines in a STAT3-dependent manner when stimulated with IL-23, and IFN© via a STAT4-dependent mechanism when stimulated with IL-12. Thus, building on previous findings of antigen-induced plasticity of Th17 cells, our results indicate that this potential of Th17 cells extends to their cytokine-dependent antigen-independent responses. Collectively, our data suggest a model whereby signaling via either IL-1β or IL-18 allows for bystander responses of Th17 cells to pathogens or pathogen products that differentially activate innate cell production of IL-12 or IL-23.

Extrathymic induction of regulatory T (T reg) cells is essential to the regulation of effector T cell responses in the periphery. In addition to Foxp3, T reg cell expression of suppressive cytokines, such as IL-10, is essential for peripheral tolerance, particularly in the intestines. TGF-β has been shown to induce expression of Foxp3 as well as IL10 and the vitamin A metabolite; all-trans retinoic acid (RA [at-RA]) has been found to enhance the former. We report that in contrast to its enhancement of TGF-β–mediated Foxp3 induction, at-RA potently inhibits the TGF-β–mediated induction of Il10 in naive CD4 T cells. Thus, mucosal DC subsets that are active producers of at-RA inhibit induction of Il10 in naive CD4 T cells while promoting induction of Foxp3. Accordingly, mice with vitamin A deficiency have increased numbers of IL-10–competent T reg cells. Activation of DCs by certain Toll-like receptors (TLRs), particularly TLR9, suppresses T cell induction of Foxp3 and enables induction of Il10. Collectively, our data indicate that at-RA has reciprocal effects on the induction of Foxp3 and Il10 in developing CD4+ T reg cells and suggest that TLR9-dependent inhibition of at-RA production by antigen-presenting cells might represent one mechanism to promote the development of IL-10–expressing T cells.

Development of T helper (Th) 17 cells requires transforming growth factor (TGF)-beta and interleukin (IL)-6 and is independent of the Th1 pathway. Although T cells that produce interferon (IFN)-gamma are a recognized feature of Th17 cell responses, mice deficient for STAT4 and T-bet-two prototypical Th1 transcription factors-are protected from autoimmunity associated with Th17 pathogenesis. To examine the fate and pathogenic potential of Th17 cells and origin of IFN-gamma-producing T cells that emerge during Th17 immunity, we developed IL-17F reporter mice that identify cells committed to expression of IL-17F and IL-17A. Th17 cells required TGF-beta for sustained expression of IL-17F and IL-17A. In the absence of TGF-beta, both IL-23 and IL-12 acted to suppress IL-17 and enhance IFN-gamma production in a STAT4- and T-bet-dependent manner, albeit with distinct efficiencies. These results support a model of late Th17 developmental plasticity with implications for autoimmunity and host defense.

Recent progress in our understanding of mechanisms by which the immunosuppressive cytokine interleukin-10 (IL-10) participates in an ever-increasing diversity of T-cell lineages to maintain immune homeostasis has broadened the framework for defining regulatory and effector T cells and has blurred the lines between them. In this review, we highlight established and emerging roles for IL-10 produced by distinct CD4(+) T-cell lineages that underlie its non-redundant role in curbing immune responses to the intestinal microbiota at steady state and its role to limit T-cell-driven inflammation in responses to pathogens.

CD4(+) regulatory T cells (T(reg) cells) that produce interleukin 10 (IL-10) are important contributors to immune homeostasis. We generated mice with a 'dual-reporter' system of the genes encoding IL-10 and the transcription factor Foxp3 to track T(reg) subsets based on coordinate or differential expression of these genes. Secondary lymphoid tissues, lung and liver had enrichment of Foxp3(+)IL-10(-) T(reg) cells, whereas the large and small intestine had enrichment of Foxp3(+)IL-10(+) and Foxp3(-)IL-10(+) T(reg) cells, respectively. Although negative for Il10 expression, both Foxp3(+) and Foxp3(-) CD4(+) thymic precursor cells gave rise to peripheral IL-10(+) T(reg) cells, with only Foxp3(-) precursor cells giving rise to all T(reg) subsets. Each T(reg) subset developed in IL-10-deficient mice, but this was blocked by treatment with antibody to transforming growth factor-beta. Thus, Foxp3(+) and Foxp3(-) precursor cells give rise to peripheral IL-10-expressing T(reg) cells by a mechanism dependent on transforming growth factor-beta and independent of IL-10.

CD4+ T cells emerge from thymic selection programmed for fixed antigenic specificity. However, with the exception of natural regulatory T cells (nTreg cells), they are multipotent for alternative developmental programs that diverge contingent upon the peripheral microenvironment in which antigen is first recognized. Antigen recognition in the presence of proinflammatory cytokines elicited from antigen-presenting cells (APCs) or other innate immune cells by microbe-associated molecular patterns (MAMPs) drives the differentiation of antigen-naive CD4+ T cells into distinct effector T cell subsets that are characterized by expression of signature cytokines that orchestrate different patterns of immunity. The intestines harbor the largest collection of CD4+ T cells in the body, including the largest number of effector T cells at homeostasis. Intestinal effector T cell responses are generally directed against antigens derived from microbes that penetrate innate barrier defenses in the gut, whether derived from the largest and most diverse commensal microbiota, or pathogenic bacteria, viruses, helminthic parasites, or fungi. In certain disease states, effector T cells can also be reactive to dietary or self-antigens. Whereas the physiologic role of effector T cell responses is pathogen eradication, when inadequately restrained or dysregulated, effector T cell responses can cause injury to host tissues and lead to chronic, immune-mediated disease.

IL-22 plays an important role in mucosal epithelial cell homeostasis. Using a dextran sodium sulfate-induced mouse model of acute colitis, we observed an IL-23–dependent up-regulation of IL-22 in the middle and distal colon at the onset of epithelial cell damage. This heightened IL-22 correlated with an influx of innate immune cells, suggesting an important role in colonic epithelial protection. Freshly isolated colon-infiltrating neutrophils produced IL-22 contingent upon IL-23 signaling, and IL-22 production was augmented by TNF-α. Importantly, the depletion of neutrophils resulted in diminished IL-22 levels in the colon, and the transfer of IL-22–competent neutrophils to Il22a -deficient mice protected the colonic epithelium from dextran sodium sulfate-induced damage. In addition, IL-22–producing neutrophils targeted colonic epithelial cells to up-regulate the antimicrobial peptides, RegIIIβ and S100A8. This study establishes a role for neutrophils in providing IL-22–dependent mucosal epithelial support that contributes to the resolution of colitis.

The emergence of the adaptive immune system in vertebrates set the stage for evolution of an advanced symbiotic relationship with the intestinal microbiota. The defining features of specificity and memory that characterize adaptive immunity have afforded vertebrates the mechanisms for efficiently tailoring immune responses to diverse types of microbes, whether to promote mutualism or host defence. These same attributes can put the host at risk of immune-mediated diseases that are increasingly linked to the intestinal microbiota. Understanding how the adaptive immune system copes with the remarkable number and diversity of microbes that colonize the digestive tract, and how the system integrates with more primitive innate immune mechanisms to maintain immune homeostasis, holds considerable promise for new approaches to modulate immune networks to treat and prevent disease.

The vitamin-A metabolite retinoic acid normally favours immune tolerance in the gut. But in coeliac disease — an intestinal inflammatory disorder due to adverse reactivity to a dietary protein — it may do just the opposite. See Letter p.220 The vitamin A metabolite retinoic acid is shown to act synergistically with the cytokine interleukin-15 (IL-15) to induce IL-12p70 production by intestinal dendritic cells, thereby promoting an inflammatory T-cell response to dietary antigens. IL-15 is upregulated in the guts of patients with coeliac disease, and this new work points to a previously unknown involvement of IL-15 and retinoic acid in promoting an inflammatory immune response to gluten.

Crohn's disease and ulcerative colitis are the two major forms of chronic relapsing inflammatory disorders of the human intestines collectively referred to as inflammatory bowel disease (IBD). Though a complex set of autoinflammatory disorders that can be precipitated by diverse genetic and environmental factors, a feature that appears common to IBD pathogenesis is a dysregulated effector T cell response to the commensal microbiota. Due to the heightened effector T cell activity in IBD, developmental and functional pathways that give rise to these cells are potential targets for therapeutic intervention. In this review, we highlight recent advances in our understanding of effector T cell biology in the context of intestinal immune regulation and speculate on their potential clinical significance.

Background Fecal microbiota transplants (FMT) are an effective treatment for patients with gut microbe dysbiosis suffering from recurrent C. difficile infections. To further understand how FMT reconstitutes the patient’s gut commensal microbiota, we have analyzed the colonization potential of the donor, recipient and recipient post transplant fecal samples using transplantation in gnotobiotic mice. Results A total of nine samples from three human donors, recipient’s pre and post FMT were transplanted into gnotobiotic mice. Microbiome analysis of three donor fecal samples revealed the presence of a high relative abundance of commensal microbes from the family Bacteriodaceae and Lachnospiraceae that were almost absent in the three recipient pre FMT fecal samples (