Competition between colitogenic Th1 and Th17 cells contributes to the amelioration of colitis

Dichotomous effects of Galectin-9 in disease modulation in murine models of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a multifaceted disease characterised by compromised integrity of the epithelial barrier, the gut microbiome, and mucosal inflammation. While leukocyte recruitment and infiltration into intestinal tissue are well-studied and targeted in clinical practice, the role of galectins in modulating mucosal immunity remains underexplored. Galectins, a family of lectin-binding proteins, mediate critical interactions between immune cells and the intestinal epithelium. This study investigated the effect of endogenous Galectin-9 (Gal-9), as well as the combined effects with Galectin-3 (Gal-3), in modulating disease progression in murine models of colitis, using global knockout (KO) models for Gal-3, Gal-9, and Gal-3/Gal-9. Global deficiency in both galectins demonstrated improved disease parameters in Dextran sodium sulfate (DSS)-driven colitis. In contrast, in a model of adoptive T cell driven colitis, the addition of recombinant Gal-9 (rGal-9) was associated with reduced intestinal inflammation and an improvement in disease parameters. Further in vitro studies revealed no change in bone marrow-derived macrophage cytokine production in the absence of endogenous Gal-9, whereas the addition of rGal-9 to human macrophages stimulated pro-inflammatory cytokine production. Collectively, these findings demonstrate that Gal-9 plays distinct, context-dependent effects in intestinal inflammation, with both pro-inflammatory and anti-inflammatory effects. The contrasting functions of endogenous and exogenous Gal-9 underscore its complex involvement in IBD pathogenesis and highlight the need to differentiate its physiological function from therapeutic applications.

Microsomal Prostaglandin E Synthase-1 Controls Colonic Prostaglandin E2 Production and Exerts a Protective Effect on Colitis Induced by Trinitrobenzene Sulfonic Acid in Mice

Microsomal prostaglandin E synthase-1 (mPGES-1) is an isozyme of the prostaglandin (PG) E synthase that acts downstream of cyclooxygenase and catalyzes the conversion of PGH2 to PGE2. The impact of genetic deletion of mPGES-1 on the development of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis, a well-established model of inflammatory bowel disease (IBD), was investigated in this study. After administration of TNBS, mice deficient in mPGES-1 (mPGES-1-/- mice) showed more severe colitis than did wild-type (WT) mice. Histological examination revealed that mPGES-1-/- mice had markedly exacerbated symptoms of colitis. mPGES-1 expression was detectable in the colons of WT mice at both the mRNA and protein levels. Lack of mPGES-1 resulted in marked reduction of colonic PGE2 production. Our study also showed a significant increase in colonic expression of interleukin-17A (IL-17A), as well as interferon γ (IFNγ) and tumor necrosis factor α, during colitis in mPGES-1-/- mice compared with that in WT mice. Furthermore, loss of mPGES-1 increased the populations of IL-17A-producing T-helper (Th) 17 and IFNγ-producing Th1 cells in mesenteric lymph nodes. These results suggest that mPGES-1 is the main enzyme responsible for colonic PGE2 production and deficiency of mPGES-1 facilitates the development of colitis and T-cell-mediated immunity. mPGES-1 might, therefore, impact T-cell-related immune response associated with IBD.

A reverse translational approach reveals the protective roles of Mangifera indica in inflammatory bowel disease

Inflammatory bowel diseases (IBDs) are chronic intestinal disorders often characterized by a dysregulation of T cells, specifically T helper (Th) 1, 17 and T regulatory (Treg) repertoire. Increasing evidence demonstrates that dietary polyphenols from Mangifera indica L. extract (MIE, commonly known as mango) mitigate intestinal inflammation and splenic Th17/Treg ratio. In this study, we aimed to dissect the immunomodulatory and anti-inflammatory properties of MIE using a reverse translational approach, by initially using blood from an adult IBD inception cohort and then investigating the mechanism of action in a preclinical model of T cell-driven colitis. Of clinical relevance, MIE modulates TNF-α and IL-17 levels in LPS spiked sera from IBD patients as an ex vivo model of intestinal barrier breakdown. Preclinically, therapeutic administration of MIE significantly reduced colitis severity, pathogenic T-cell intestinal infiltrate and intestinal pro-inflammatory mediators (IL-6, IL-17A, TNF-α, IL-2, IL-22). Moreover, MIE reversed colitis-induced gut permeability and restored tight junction functionality and intestinal metabolites. Mechanistic insights revealed MIE had direct effects on blood vascular endothelial cells, blocking TNF-α/IFN-γ-induced up-regulation of COX-2 and the DP2 receptors. Collectively, we demonstrate the therapeutic potential of MIE to reverse the immunological perturbance during the onset of colitis and dampen the systemic inflammatory response, paving the way for its clinical use as nutraceutical and/or functional food.

Targeted delivery of Fc-fused PD-L1 for effective management of acute and chronic colitis

The PD-1/PD-L1 pathway in mucosal immunity is currently actively explored and considered as a target for inflammatory bowel disease (IBD) treatment. However, systemic PD-L1 administration may cause unpredictable adverse effects due to immunosuppression. Here we show that reactive oxygen species (ROS)-responsive nanoparticles enhance the efficacy and safety of PD-L1 in a mouse colitis model. The nanoparticles control the accumulation and release of PD-L1 fused to Fc (PD-L1-Fc) at inflammatory sites in the colon. The nanotherapeutics shows superiority in alleviating inflammatory symptoms over systemic PD-L1-Fc administration and mitigates the adverse effects of PD-L1-Fc administration. The nanoparticles-formulated PD-L1-Fc affects production of proinflammatory and anti-inflammatory cytokines, attenuates the infiltration of macrophages, neutrophils, and dendritic cells, increases the frequencies of Treg, Th1 and Tfh cells, reshapes the gut microbiota composition; and increases short-chain fatty acid production. In summary, PD-L1-Fc-decorated nanoparticles may provide an effective and safe strategy for the targeted treatment of IBD.

Berberine as a natural modulator of inflammatory signaling pathways in the immune system: Focus on NF-κB, JAK/STAT, and MAPK signaling pathways

Three main inflammatory signaling pathways include nuclear factor-κB (NF-κB), Janus kinases/Signal transducer and activator of transcriptions (JAKs/STATs), and mitogen-activated protein kinases (MAPKs) play crucial roles in inducing, promoting, and regulating inflammatory responses in the immune system. Importantly, the breakdown of mechanisms that tightly regulate inflammatory signaling pathways can be the underlying cause of uncontrolled inflammatory responses and be associated with the generation and development of several inflammatory diseases. Hence, therapeutic strategies targeting inflammatory signaling pathways and their downstream components may promise to treat inflammatory diseases. Studies over the past two decades have provided important information on the polytrophic pharmacological and biochemical properties of berberine (BBR) as a naturally occurring compound, such as antioxidant, antitumor, antimicrobial, and antiinflammatory activates. Interestingly, the modulatory effects of BBR on inflammatory signaling cascades, which lead to the inhibition of inflammation, have been widely investigated in several in vitro and in vivo studies. For the first time, herein, this comprehensive review attempts to put together these studies and provide important insight into the modulatory effects of BBR on NF-κB, JAKs/STATs, and MAPKs signaling pathways in vitro in various types of immune cells and in vivo in several experimental inflammatory diseases. As the second achievement of this review, we also explore the therapeutic efficacy and antiinflammatory effects of BBR regarding its modulatory action.

CD8+ tissue-resident memory T cells promote liver fibrosis resolution by inducing apoptosis of hepatic stellate cells

Non-alcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease that can progress to liver fibrosis. Recent clinical advance suggests a reversibility of liver fibrosis, but the cellular and molecular mechanisms underlying NASH resolution remain unclarified. Here, using a murine diet-induced NASH and the subsequent resolution model, we demonstrate direct roles of CD8⁺ tissue-resident memory CD8⁺ T (CD8⁺ Trm) cells in resolving liver fibrosis. Single-cell transcriptome analysis and FACS analysis revealed CD69⁺CD103⁻CD8⁺ Trm cell enrichment in NASH resolution livers. The reduction of liver CD8⁺ Trm cells, maintained by tissue IL-15, significantly delayed fibrosis resolution, while adoptive transfer of these cells protected mice from fibrosis progression. During resolution, CD8⁺ Trm cells attracted hepatic stellate cells (HSCs) in a CCR5-dependent manner, and predisposed activated HSCs to FasL-Fas-mediated apoptosis. Histological assessment of patients with NASH revealed CD69⁺CD8⁺ Trm abundance in fibrotic areas, further supporting their roles in humans. These results highlight the undefined role of liver CD8⁺ Trm in fibrosis resolution.

The cellular and molecular mechanisms underlying the resolution of non-alcoholic steatohepatitis remain incompletely understood. Here the authors report a single cell-based analysis that identified CD8 + tissue-resident memory T cells, which contribute to resolution of liver fibrosis potentially via elimination of hepatic stellate cells through Fas-mediated cytotoxicity.

Attenuation of intestinal inflammation in IL-10 deficient mice by a plasmid carrying Lactococcus lactis strain

BACKGROUND

Inflammatory bowel diseases (IBD) are intestinal disorders characterized by inflammation in the gastrointestinal tract (GIT) and to date, no efficient treatments exist. Interleukin-10 (IL-10), one of the most important anti-inflammatory cytokines of the immune response, has been under study due to its potential for IBD therapy; however, systemic treatments lead to undesirable side effects and oral administration is limited due to its quick degradation. To avoid these bottlenecks, we previously engineered an invasive Lactococcus lactis (L. lactis) strain capable of delivering, directly to host cells, a eukaryotic DNA expression vector coding for IL-10 of Mus musculus (pValac:il-10) that diminished inflammation in two induced mouse models of intestinal inflammation. Thus, the aim of this study was to analyze its therapeutic effect in the IL-10-deficient mouse model (IL-10^-/-) that spontaneously and gradually develops an inflammation that modifies the immune system and resembles Crohn's disease (CD) in humans, and evaluate if it would also diminish and/or prevent the onset of this disease.

RESULTS

Oral administration of L. lactis MG1363 FnBPA+ (pValac:il-10) to IL-10^-/- mice not only led to IL-10 production by these, but consequently also diminished the severe development of the disease, with animals showing lower macroscopic scores and histological damages, increased IL-10 levels and tendency to lower pro-inflammatory cytokine levels.

CONCLUSIONS

The results of this study, together with the previously published ones using this DNA delivery-based strategy, show that it is capable of creating and maintaining an anti-inflammatory environment in the GIT and thus effectively diminish the onset of inflammation in various mouse models.

The liver-brain-gut neural arc maintains the Treg cell niche in the gut

Recent clinical and experimental evidence has evoked the concept of the gut-brain axis to explain mutual interactions between the central nervous system and gut microbiota that are closely associated with the bidirectional effects of inflammatory bowel disease and central nervous system disorders^1-4. Despite recent advances in our understanding of neuroimmune interactions, it remains unclear how the gut and brain communicate to maintain gut immune homeostasis, including in the induction and maintenance of peripheral regulatory T cells (pT_reg cells), and what environmental cues prompt the host to protect itself from development of inflammatory bowel diseases. Here we report a liver-brain-gut neural arc that ensures the proper differentiation and maintenance of pT_reg cells in the gut. The hepatic vagal sensory afferent nerves are responsible for indirectly sensing the gut microenvironment and relaying the sensory inputs to the nucleus tractus solitarius of the brainstem, and ultimately to the vagal parasympathetic nerves and enteric neurons. Surgical and chemical perturbation of the vagal sensory afferents at the hepatic afferent level reduced the abundance of colonic pT_reg cells; this was attributed to decreased aldehyde dehydrogenase (ALDH) expression and retinoic acid synthesis by intestinal antigen-presenting cells. Activation of muscarinic acetylcholine receptors directly induced ALDH gene expression in both human and mouse colonic antigen-presenting cells, whereas genetic ablation of these receptors abolished the stimulation of antigen-presenting cells in vitro. Disruption of left vagal sensory afferents from the liver to the brainstem in mouse models of colitis reduced the colonic pT_reg cell pool, resulting in increased susceptibility to colitis. These results demonstrate that the novel vago-vagal liver-brain-gut reflex arc controls the number of pT_reg cells and maintains gut homeostasis. Intervention in this autonomic feedback feedforward system could help in the development of therapeutic strategies to treat or prevent immunological disorders of the gut.

The recruitment of extra-intestinal cells to the injured mucosa promotes healing in radiation enteritis and chemical colitis in a mouse parabiosis model

Mucosal healing occurs through migration and proliferation of cells within injured epithelium, yet these processes may be inadequate for mucosal healing after significant injury where the mucosa is denuded. We hypothesize that extra-intestinal cells can contribute to mucosal healing after injury to the small and large intestine. We generated parabiotic pairs between wild-type and tdTomato mice, which were then subjected to radiation-induced enteritis and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis. We now show that as compared with singleton mice, mice with a parabiotic partner were protected against intestinal damage as revealed by significantly reduced weight loss, reduced expression of pro-inflammatory cytokines, reduced enterocyte apoptosis, and improved crypt proliferation. Donor cells expressed CD45-, Sca-1+, c-kit+, and CXCR4+ and accumulated around the injured crypts but did not transdifferentiate into epithelia, suggesting that extra-intestinal cells play a paracrine role in the healing response, while parabiotic pairings with Rag1-/- mice showed improved healing, indicating that adaptive immune cells were dispensable for mucosal healing. Strikingly, ablation of the bone marrow of the donor parabionts removed the protective effects. These findings reveal that the recruitment of extra-intestinal, bone marrow-derived cells into the injured intestinal mucosa can promote mucosal healing, suggesting novel therapeutic approaches for severe intestinal disease.

Rapid Downregulation of DAB2 by Toll-Like Receptor Activation Contributes to a Pro-Inflammatory Switch in Activated Dendritic Cells

Dendritic cells (DCs) are pivotal in regulating tolerogenic as well as immunogenic responses against microorganisms by directing both the innate and adaptive immune response. In health, phenotypically different DC subsets found in the gut mucosa are maintained in their tolerogenic state but switch to a pro-inflammatory phenotype during infection or chronic autoinflammatory conditions such as inflammatory bowel disease (IBD). The mechanisms that promote the switch among the mucosal DCs from a tolerogenic to an immunogenic, pro-inflammatory phenotype are incompletely understood. We hypothesized that disabled homolog 2 (DAB2), recently described as a negative regulator of DC immunogenicity during their development, is regulated during intestinal inflammation and modulates mucosal DC function. We show that DAB2 is highly expressed in colonic CD11b⁺CD103⁻ DCs, a subset known for its capacity to induce inflammatory Th1/Th17 responses in the colon, and is downregulated predominantly in this DC subset during adoptive T cell transfer colitis. Administration of Dab2-deficient DCs (DC2.4^Dab2−/− cells) modulated the course of DSS colitis in wild-type mice, enhanced mucosal expression of Tnfa, Il6, and Il17a, and promoted neutrophil recruitment. In bone-marrow derived dendritic cells (BMDC), DAB2 expression correlated with CD11b levels and DAB2 was rapidly and profoundly inhibited by TLR ligands in a TRIF- and MyD88-dependent manner. The negative modulation of DAB2 was biphasic, initiated with a quick drop in DAB2 protein, followed by a sustained reduction in Dab2 mRNA. DAB2 downregulation promoted a more functional and activated DC phenotype, reduced phagocytosis, and increased CD40 expression after TLR activation. Furthermore, Dab2 knockout in DCs inhibited autophagy and promoted apoptotic cell death. Collectively, our results highlight the immunoregulatory role for DAB2 in the intestinal dendritic cells and suggest that DAB2 downregulation after microbial exposure promotes their switch to an inflammatory phenotype.

TRAIL suppresses gut inflammation and inhibits colitogeic T-cell activation in experimental colitis via an apoptosis-independent pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cell apoptosis by transducing apoptosis signals. Recently, accumulating evidence demonstrated that TRAIL regulates autoimmune inflammation and immune cell homeostasis in several autoimmune animal models, suggesting a novel immunoregulatory role of TRAIL in autoimmune diseases. However, the impact of TRAIL in inflammatory bowel disease is yet undefined. This study is to address the therapeutic effects and immunoregulatory role of TRAIL in autoimmune gut inflammation. We demonstrated herein that TRAIL significantly suppressed gut inflammation and reduced the severity of colitis in a dextran sodium sulfate (DSS)-induced colitis model. Suppression of gut inflammation was not due to induction of apoptosis in colonic T cells, dendritic cells, or epithelium cells by TRAIL. In contrast, TRAIL directly inhibited activation of colitogenic T cells and development of gut inflammation in an adoptive transfer-induced colitis model. The anti-inflammatory effects of TRAIL on colitis were abolished when T cells from TRAIL receptor (TRAIL-R) knockout mice were adoptively transferred, suggesting that TRAIL regulates autoreactive colitogenic T-cell activation in the development of gut inflammation. Our results demonstrate that TRAIL effectively inhibited colonic T-cell activation and suppressed autoimmune colitis, suggesting a potential therapeutic application of TRAIL in human inflammatory bowel disease.

BLT1 in dendritic cells promotes Th1/Th17 differentiation and its deficiency ameliorates TNBS-induced colitis

Leukotriene B4 (LTB4) synthesis is enhanced in the colonic mucosa in patients with inflammatory bowel disease (IBD). BLT1, a high-affinity receptor for LTB4, exhibits no effect on the progression of dextran sodium sulfate (DSS)-induced colitis, which mostly relies on innate immunity. Here, we reported that BLT1 regulates trinitrobenzene sulfonic acid (TNBS)-induced colitis, which reflects CD4+ T-cell-dependent adaptive immune mechanisms of IBD. We found that BLT1 signaling enhanced the progression of colitis through controlling the production of proinflammatory cytokines by dendritic cells (DCs) and modulating the differentiation of Th1 and Th17. BLT1-/- mice displayed an alleviated severity of TNBS-induced colitis with reduced body weight loss and infiltrating cells in the lamina propria. BLT1 deficiency in DCs led to reduced production of proinflammatory cytokines, including IL-6, TNF-α, and IL-12, and these results were further confirmed via treatment with a BLT1 antagonist. The impaired cytokine production by BLT1-/- DCs subsequently led to reduced Th1 and Th17 differentiation both in vitro and in vivo. We further performed a conditional DC reconstitution experiment to assess whether BLT1 in DCs plays a major role in regulating the pathogenesis of TNBS-induced colitis, and the results indicate that BLT1 deficiency in DCs also significantly reduces disease severity. The mechanistic study demonstrated that BLT1-regulated proinflammatory cytokine production through the Gαi βγ subunit-phospholipase Cβ (PLCβ)-PKC pathway. Notably, we found that treatment with the BLT1 antagonist also reduced the production of proinflammatory cytokines by human peripheral blood DCs. Our findings reveal the critical role of BLT1 in regulating adaptive immunity and TNBS-induced colitis, which further supports BLT1 as a potential drug target for adaptive immunity-mediated IBD.

Intestinal barrier regulates immune responses in the liver via IL-10-producing macrophages

The gut-liver axis is of clinical importance as a potential therapeutic target in a wide range of liver diseases; however, the mechanisms underlying interactions between microbial products and immune responses in the liver remain unknown. In this study, we demonstrated that IL-10-producing macrophages contribute to immune tolerance in the inflamed liver under intestinal barrier disruption in a murine tandem model of dextran sulfate sodium (DSS) colitis and concanavalin A (Con A) hepatitis. Intestinal barrier disruption protected mice from subsequent liver injury, and the severity of colitis directly affected susceptibility to such injury. The protective effect of DSS-Con A was canceled in gut-sterilized mice, suggesting that gut microbiota play a substantial role in this process. Altered gut microbiota and their metabolites, along with a disrupted intestinal barrier, directly gave rise to immunological permissiveness in the inflamed liver. We identified 1-methylnicotinamide (1-MNA) as a candidate metabolite capable of suppressing liver injury with the potential to induce IL-10-producing macrophages. Consistently, expression of nicotinamide N-methyltransferase, which converts nicotinamide to 1-MNA, was upregulated in the liver of DSS-Con A mice, and this effect was abrogated by gut sterilization. Collectively, our results provide a mechanistic insight into the regulation of immunological balance in the liver via the gut-liver axis.

Innate lymphoid cells in inflammatory bowel diseases

It is generally believed that inflammatory bowel diseases (IBD) are caused by an aberrant immune response to environmental triggers in genetically susceptible individuals. The exact contribution of the adaptive and innate immune system has not been elucidated. However, recent advances in treatments targeting key inflammatory mediators such as tumour necrosis factor highlight the crucial role of the innate immune system in IBD. Innate lymphoid cells (ILCs) have recently been identified to play an important role in immune mediated inflammatory diseases. In this review we recapitulate the current knowledge on ILCs in IBD.

A breakthrough in probiotics: Clostridium butyricum regulates gut homeostasis and anti-inflammatory response in inflammatory bowel disease

Intestinal immune homeostasis is regulated by gut microbiota, including beneficial and pathogenic microorganisms. Imbalance in gut bacterial constituents provokes host proinflammatory responses causing diseases such as inflammatory bowel disease (IBD). The development of next-generation sequencing technology allows the identification of microbiota alterations in IBD. Several studies have shown reduced diversity in the gut microbiota of patients with IBD. Advances in gnotobiotic technology have made possible analysis of the role of specific bacterial strains in immune cells in the intestine. Using these techniques, we have shown that Clostridium butyricum as a probiotic induces interleukin-10-producing macrophages in inflamed mucosa via the Toll-like receptor 2/myeloid differentiation primary response gene 88 pathway to prevent acute experimental colitis. In this review, we focus on the new approaches for the role of specific bacterial strains in immunological responses, as well as the potential of bacterial therapy for IBD treatments.

Berberine ameliorates TNBS induced colitis by inhibiting inflammatory responses and Th1/Th17 differentiation

Th1 and Th17 cells, and their associated cytokines, have been associated with the pathogenesis of Crohn's disease. Berberine (BBR), a compound long used in traditional Chinese medicines, has been reported to have therapeutic effects in treating experimental colitis. In this study, we show that BBR had a protective effect on mice with TNBS-induced colitis. BBR inhibited levels of IFN-γ, IL-17, IL-6, IL-1β and TNF-α both in the local colon and sera, and transiently increased levels of IL-22. BBR also markedly increased sIgA expression in the colon. BBR had pronounced effects on macrophage populations. Treatment with BBR adjusted the M2/M1 ratio. In addition, BBR exerted effects on adaptive immunity by suppressing numbers of Th1 and Th17 cells, as well as expression levels of their associated cytokines and transcriptional factors. BBR downregulated STAT3 and STAT1 phosphorylation, and inhibited phosphorylation of NF-kB. In vitro experiments showed that BBR inhibited the differentiation of Th17 and, to a lesser degree, Th1 cells, without affecting regulatory T cells. Therefore, we conclude that BBR plays a regulatory role in modulating the balance of immune responses in TNBS-induced colitis. Our study will help us understand the regulatory mechanisms exerted by BBR in the treatment of IBD.

TIR-domain-containing adapter-inducing interferon-β (TRIF) regulates Th17-mediated intestinal immunopathology in colitis

Gastrointestinal mucosa reserves abundant Th17 cells where host response to commensal bacteria maintains Th17-cell generation. Although functional heterogeneity and dynamic plasticity of Th17 cells appear to be involved in chronic inflammatory disorders, how their plasticity is regulated in intestinal mucosa is unknown. Here we show that innate TRIF signaling regulates intestinal Th17-cell generation and plasticity during colitis. Absence of TRIF in mice resulted in increased severity of experimental colitis, which was associated with aberrant generation of Th17 cells especially of interferon (IFN)-γ-expressing Th17 cells in the lamina propria. The abnormal generation and plasticity of Th17 cells involved impaired expression of interleukin (IL)-27p28 by lamina propria macrophages but not dendritic cells. Treatment of TRIF-deficient mice with IL-27p28 during colitis reduced the number and IFN-γ expression of Th17 cells in the intestine. In vitro, TRIF-deficient macrophages induced more Th17 cells than wild-type (WT) macrophages during co-culture with WT naive T cells in response to cecal bacterial antigen. Many of Th17 cells induced by TRIF-deficient macrophages expressed IFN-γ due to impaired expression of IL-27p28 by macrophages and defective activation of STAT1 in T cells. These results outline TRIF-dependent regulatory mechanism by which host response to intestinal bacteria maintains Th17-cell-mediated pathology during colitis.

Protective effects of Fc-fused PD-L1 on two different animal models of colitis

OBJECTIVE

Programmed death-ligand 1 (PD-L1) has been shown to negatively regulate immune responses via its interaction with PD-1 receptor. In this study, we investigated the effects of PD-L1-Fc treatment on intestinal inflammation using two murine models of inflammatory colitis induced by dextran sulfate sodium (DSS) and T-cell transfer.

DESIGN

The anti-colitis effect of adenovirus expressing Fc-conjugated PD-L1 (Ad/PD-L1-Fc) and recombinant PD-L1-Fc protein was evaluated in DSS-treated wild-type and Rag-1 knockout (KO) mice. We examined differentiation of T-helper cells, frequency of innate immune cells, and cytokine production by dendritic cells (DCs) in the colon from DSS-treated mice after PD-L1-Fc administration. In Rag-1 KO mice reconstituted with CD4 CD45RB(high) T cells, we assessed the treatment effect of PD-L1-Fc protein on the development of colitis.

RESULTS

Administration of Ad/PD-L1-Fc significantly ameliorated DSS-induced colitis, which was accompanied by diminished frequency of interleukin (IL)-17A-producing CD4 T cells and increased interferon-γ-producing CD4 T cells in the colon of DSS-fed mice. The anti-colitic effect of PD-L1-Fc treatment was also observed in DSS-treated Rag-1 KO mice, indicating lymphoid cell independency. PD-L1-Fc modulated cytokine production by colonic DCs and the effect was dependent on PD-1 expression. Furthermore, PD-L1-Fc protein could significantly reduce the severity of colitis in CD4 CD45RB(high) T-cell-transferred Rag-1 KO mice.

CONCLUSIONS

Based on the protective effect of PD-L1-Fc against DSS-induced and T-cell-induced colitis, our results suggest that PD-1-mediated inhibitory signals have a crucial role in limiting the development of colonic inflammation. This implicates that PD-L1-Fc may provide a novel therapeutic approach to treat inflammatory bowel disease.

Experimental Models of Inflammatory Bowel Diseases

The understanding of the intestinal inflammation occurring in the inflammatory bowel diseases (IBD) has been immeasurably advanced by the development of the now numerous murine models of intestinal inflammation. The usefulness of this research tool in IBD studies has been enabled by our improved knowledge of mucosal immunity and thus our improved ability to interpret the complex responses of mice with various causes of colitis; in addition, it has been powered by the availability of models in which the mice have specific genetic and/or immunologic defects that can be related to the origin of the inflammation. Finally, and more recently, it has been enhanced by our newly acquired ability to define the intestinal microbiome under various conditions and thus to understand how intestinal microorganisms impact on inflammation. In this brief review of murine models of intestinal inflammation we focus mainly on the most often used models that are, not incidentally, also the models that have yielded major insights into IBD pathogenesis.

Imbalances of CD4(+) T-cell subgroups in Crohn's disease and their relationship with disease activity and prognosis

BACKGROUND AND AIM

The CD4(+) T-cell subgroups play central pathophysiological roles in Crohn's disease (CD); however, their clinical relevance requires additional clarification and remains controversial. We investigated their balance in Chinese CD patients and explored their clinical significance.

METHODS

Peripheral blood mononuclear cells and serum were collected from 46 Chinese CD patients and 23 healthy donors. Circulating Treg, Th1, Th2, and Th17 cells were flow cytometrically analyzed. Subgroup-restricted transcription factor expression was determined by real-time polymerase chain reaction. Serum concentrations of the main cytokines produced by each subgroup were measured by cytometric bead arrays or enzyme-linked immunosorbent assay.

RESULTS

Lower Treg proportion (6.0 ± 1.2% vs 7.8 ± 1.5%, P = 0.030), FOXP3 mRNA expression (0.58-fold, P = 0.030), and circulating soluble TGFβ-1 (19.1 ± 9.9 vs 32.7 ± 16.8 ng/mL, P = 0.038) were observed in CD patients versus controls. The Th1 and Th17 proportions were higher in CD patients (17.8 ± 6.6% vs 7.8 ± 1.5%, P < 0.001; and 3.7 ± 1.8% vs 1.8 ± 0.7%, P = 0.022, respectively), as were transcription factors T-bet (4.6-fold, P = 0.043) and RORγt (14-fold, P < 0.001) and related cytokines (P < 0.05). Th2 proportion, GATA3 mRNA expression, and serum interleukin-4 concentration in CD patients were similar to controls (P > 0.05). Treg/Th1 and Treg/Th17 ratios were higher in inactive versus active CD patients (0.6 ± 0.4 vs 0.3 ± 0.1, P = 0.022; and 3.7 ± 2.0 vs 1.7 ± 1.4, P = 0.013, respectively). During follow-up, patients with lower Treg/Th1 and Treg/Th17 ratios were at higher recurrence risk.

CONCLUSIONS

Imbalances among Treg, Th1, and Th17 subgroups were found in Chinese CD patients. Treg/Th1 and Treg/Th17 ratios are associated with disease activity and are potential prognostic indicators for predicting CD recurrence.

Classical Th1 cells obtain colitogenicity by co-existence of RORγt-expressing T cells in experimental colitis

BACKGROUND

Both Th1 and Th17 cell types are involved in the pathogenesis of chronic intestinal inflammation. We recently demonstrated that retinoid-related orphan receptor gamma t (RORγt)-expressing Th17 cells are progenitor cells for alternative Th1 cells, which have the potential to induce colitis. However, the involvement of classical Th1 (cTh1) cells generated directly from naive T cells without RORγt expression in the pathogenesis of colitis remains poorly understood.

METHODS

We performed a series of in vivo experiments using a murine chronic colitis model induced by adoptive transfer of splenic CD4CD45RB(high) T cells obtained from wild-type, RORγt(gfp/gfp), or RORγt(gfp/gfp) mice into RAG-2(-/-) mice.

RESULTS

RAG-2(-/-) mice receiving transfer of in vitro-manipulated RORγt(gfp/gfp) Th1 cells developed colitis. RAG-2(-/-) mice co-transferred with splenic CD4CD45RB(high) T cells obtained from wild-type mice and RORγt(gfp/gfp) mice developed colitis with a significant increase in RORγt cTh1 cell numbers when compared with noncolitic mice transferred with splenic CD4CD45RB(high) T cells obtained from RORγt(gfp/gfp) mice. Furthermore, RAG-2(-/-) mice transferred with in vivo-manipulated RORγt(gfp/gfp) cTh1 cells developed colitis with a significant increase in RORγt(gfp/gfp) cTh1 cell numbers.

CONCLUSIONS

These findings indicate that both alternative Th1 cells and cTh1 cells have the potential to be colitogenic in an adaptive transfer model. The development of cTh1 cells was dependent on the co-existence of RORγt-expressing T cells, suggesting a critical role for the interactions of these cell types in the development of chronic intestinal inflammation.

Macrophages and dendritic cells emerge in the liver during intestinal inflammation and predispose the liver to inflammation

The liver is a physiological site of immune tolerance, the breakdown of which induces immunity. Liver antigen-presenting cells may be involved in both immune tolerance and activation. Although inflammatory diseases of the liver are frequently associated with inflammatory bowel diseases, the underlying immunological mechanisms remain to be elucidated. Here we report two murine models of inflammatory bowel disease: RAG-2^−/− mice adoptively transferred with CD4⁺CD45RB^high T cells; and IL-10^−/− mice, accompanied by the infiltration of mononuclear cells in the liver. Notably, CD11b⁻CD11c^lowPDCA-1⁺ plasmacytoid dendritic cells (DCs) abundantly residing in the liver of normal wild-type mice disappeared in colitic CD4⁺CD45RB^high T cell-transferred RAG-2^−/− mice and IL-10^−/− mice in parallel with the emergence of macrophages (Mφs) and conventional DCs (cDCs). Furthermore, liver Mφ/cDCs emerging during intestinal inflammation not only promote the proliferation of naïve CD4⁺ T cells, but also instruct them to differentiate into IFN-γ-producing Th1 cells in vitro. The emergence of pathological Mφ/cDCs in the liver also occurred in a model of acute dextran sulfate sodium (DSS)-induced colitis under specific pathogen-free conditions, but was canceled in germ-free conditions. Last, the Mφ/cDCs that emerged in acute DSS colitis significantly exacerbated Fas-mediated hepatitis. Collectively, intestinal inflammation skews the composition of antigen-presenting cells in the liver through signaling from commensal bacteria and predisposes the liver to inflammation.

A single strain of Clostridium butyricum induces intestinal IL-10-producing macrophages to suppress acute experimental colitis in mice

Imbalance in gut bacterial composition provokes host proinflammatory responses causing diseases such as colitis. Colonization with a mixture of Clostridium species from clusters IV and XIVa was shown to suppress colitis through the induction of IL-10-producing regulatory T (Treg) cells. We demonstrate that a distinct Clostridium strain from cluster I, Clostridium butyricum (CB), prevents acute experimental colitis in mice through induction of IL-10, an anti-inflammatory cytokine. However, while CB treatment had no effect on IL-10 production by T cells, IL-10-producing F4/80(+)CD11b(+)CD11c(int) macrophages accumulated in the inflamed mucosa after CB treatment. CB directly triggered IL-10 production by intestinal macrophages in inflamed mucosa via the TLR2/MyD88 pathway. The colitis-preventing effect of CB was negated in macrophage-specific IL-10-deficient mice, suggesting that induction of IL-10 by intestinal macrophages is crucial for the probiotic action of CB. Collectively, CB promotes IL-10 production by intestinal macrophages in inflamed mucosa, thereby preventing experimental colitis in mice.

C-C motif chemokine receptor 9 positive macrophages activate hepatic stellate cells and promote liver fibrosis in mice

Chemokine receptors mediate migration of immune cells into the liver, thereby promoting liver inflammation. C-C motif chemokine receptor (CCR) 9(+) macrophages are crucial in the pathogenesis of acute liver inflammation, but the role and underlying mechanisms of this macrophage subset in chronic liver injury and subsequent liver fibrosis are not fully understood. We confirmed that tumor necrosis factor alpha (TNF-α)-producing CCR9(+) macrophages accumulated during the initiation of carbon tetrachloride (CCl4 )-induced liver injury, and CCR9 deficiency attenuated the degree of liver damage. Accumulation of CCR9(+) macrophages persisted prominently during the process of liver fibrosis induced by repetitive CCl4 or thioacetamide (TAA)/leptin administration. Increased CCR9 expression was also found on activated hepatic stellate cells (HSCs). Importantly, experimental liver fibrosis was significantly ameliorated in CCR9(-/-) mice compared with wild-type (WT) mice, assessed by α-smooth muscle actin (α-SMA) immunostain, Sirius red staining, and messenger RNA (mRNA) expression levels of α-SMA, collagen 1α1, transforming growth factor (TGF)-β1, and tissue inhibitor of metalloproteinase (TIMP)-1. Accumulated CD11b(+) macrophages in CCl4 -treated WT mice showed marked increases in TNF, NO synthase-2, and TGF-β1 mRNA expression compared with CCR9(-/-) mice, implying proinflammatory and profibrogenic properties. Hepatic CD11b(+) macrophages from CCl4 -treated WT mice (i.e., CCR9(+) macrophages), but not CD8(+) T lymphocytes or non-CD11b(+) cells, significantly activated HSCs in vitro compared with those from CCR9(-/-) mice. TNF-α or TGF-β1 antagonism attenuated CCR9(+) macrophage-induced HSC activation. Furthermore, C-C motif chemokine ligand (CCL) 25 mediated migration and, to a lesser extent, activation of HSCs in vitro.

CONCLUSION

Accumulated CD11b(+) macrophages are critical for activating HSCs through the CCR9/CCL25 axis and therefore promote liver fibrosis. CCR9 antagonism might be a novel therapeutic target for liver fibrosis.

Immune aspects of the pathogenesis of inflammatory bowel disease

Although the precise etiologies of inflammatory bowel disease (IBD) (ulcerative colitis and Crohn's disease) remain obscure, several reports have indicated that dysfunction of the mucosal immune system plays an important role in its pathogenesis. Recent progress with genome-wide association studies has identified many IBD susceptibility genes. In individuals with genetic risk, abnormal interactions between the host immune system and gut flora, and dysregulation of cellular responses such as autophagy and ER stress, induce an abnormal host immune response in the gut resulting in intestinal inflammation. Research progress animal models in IBD, and in human IBD, has identified several key molecules in IBD pathogenesis such as TNFα and adhesion molecules, and molecular targeting therapies based on these molecules have been developed. Here, we review immunological aspects in IBD pathogenesis and the development of immunoregulatory therapy.

The Th17 pathway and inflammatory diseases of the intestines, lungs, and skin

The recent discovery of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment-such as the intestinal and respiratory tracts and the skin-where most of the Th17 cells in the body reside, dysregulated immunity to self (or the extended self, the diverse microbiota that normally colonize these tissues) can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and on genome-wide association studies that implicate this immune pathway in human disease involving these tissues.

MyD88-dependent interleukin-10 production from regulatory CD11b⁺Gr-1(high) cells suppresses development of acute cerulein pancreatitis in mice

We explored the role of the MyD88 signaling pathway. This pathway mediates the recognition of pathogen-associated molecular patterns and damage-associated molecular patterns via Toll-like receptors (TLRs) and/or IL-1/IL-18 via each cytokine receptor in a murine model of acute pancreatitis induced by cerulein administration. Our analysis revealed that: various TLRs and MyD88 molecules were constitutively expressed in the pancreas of cerulein-treated and untreated wild-type (WT) mice. MyD88⁻/⁻ mice administered cerulein developed severe pancreatitis as compared with MyD88⁺/⁺ WT mice. The number of IL-10-expressing CD11b⁺Gr-1(high) cells in cerulein-administered MyD88⁻/⁻ mice was significantly decreased. This was in accordance with a reciprocal increase in the infiltration of CD4⁺ T cells as compared with that in control MyD88⁺/⁺ mice. WT mice pretreated with antibiotics and administered cerulein developed milder pancreatitis as compared with control cerulein-administered mice without antibiotic treatment. The MyD88 signaling pathway contributes to the induction of regulatory IL-10-producing macrophages/myeloid-derived suppressor cells, possibly in response to non-bacterial components in the damaged pancreas. These results provide a new concept for therapeutic strategies against acute pancreatitis.

Delivery of IL-12p40 ameliorates DSS-induced colitis by suppressing IL-17A expression and inflammation in the intestinal mucosa

IL-12p40 homodimer is a natural antagonist of IL-12 and IL-23, which are potent pro-inflammatory cytokines required for Th1 and Th17 immune responses, respectively. It has been reported that Th17 response is involved in inflammatory bowel disease (IBD), a chronic disorder of the digestive system with steadily increasing incidence. Here, we investigated the effects of IL-12p40 delivered via recombinant adenovirus (rAd/IL-12p40) or mesenchymal stem cells (MSC/IL-12p40) in a dextran sulfate sodium salt (DSS)-induced colitis model. Injection of rAd/IL-12p40 or MSC/IL-12p40 efficiently attenuated colitis symptoms and tissue damage, leading to an increased survival rate. Moreover, IL-12p40 delivery suppressed IL-17A, but enhanced IFN-γ production from mesenteric lymph node cells, supporting the preferential suppression of IL-23 by IL-12p40 homodimer in vitro and the suppression of Th17 responses in vivo. Our results demonstrate that IL-12p40 delivery ameliorates DSS-induced colitis by suppressing IL-17A production and inflammation in the intestinal mucosa, providing an effective new therapeutic strategy for IBDs.

RORγt-dependent IL-17A-producing cells in the pathogenesis of intestinal inflammation

The hypothesis of helper T (T(h))1/T(h)2 cytokine balance proposed by Mosmann and Coffman is often invoked to explain the development of inflammatory diseases, including inflammatory bowel diseases (IBD). Recently, however, a newly identified class of T(h) cells-T(h)17 cells, which produce T(h)17 family cytokines-has been recognized as an essential subpopulation in the development of almost all kinds of human and animal inflammatory diseases, rather than T(h)1 and T(h)2 cells. A representative T(h)17 family cytokine, interleukin (IL)-17A, is produced by not only T(h)17 cells, but also by other types of cells, such as T-cell receptor γδ T cells, natural killer (NK) T cells, NK cells, myeloid cells, and innate lymphoid cells, which may also be critically involved in the initiation and persistence of IBD. Here we review recent advances in the study of such IL-17A-producing cells in the pathogenesis of IBD.

CCL2-induced migration and SOCS3-mediated activation of macrophages are involved in cerulein-induced pancreatitis in mice

BACKGROUND & AIMS

Acute pancreatitis is a common inflammatory disease mediated by damage to acinar cells and subsequent pancreatic inflammation with recruitment of leukocytes. We investigated the pathologic roles of innate immune cells, especially macrophages, in cerulein- and L-arginine-induced acute pancreatitis in mice.

METHODS

Acute pancreatitis was induced by sequential peritoneal administration of cerulein to mice. We determined serum concentrations of amylase and lipase, pancreatic pathology, and features of infiltrating mononuclear cells. We performed parabiosis surgery to assess the hemodynamics of pancreatic macrophages.

RESULTS

Almost all types of immune cells, except for CD11b(high)CD11c(-) cells, were detected in the pancreas of healthy mice. However, activated CD11b(high)CD11c(-) cells, including Gr-1(low) macrophages and Gr-1(high) cells (granulocytes and myeloid-derived suppressor cells), were detected in damaged pancreas after cerulein administration. CCL2(-/-) mice given cerulein injections developed significantly less severe pancreatitis, with less infiltration of CD11b(high)CD11c(-)Gr-1(low) macrophages, but comparable infiltration of myeloid-derived suppressor cells, compared with cerulein-injected wild-type mice. Parabiosis and bone marrow analyses of these mice revealed that the CD11b(high)CD11c(-)Gr-1(low) macrophages had moved out of the bone marrow. Furthermore, mice with macrophage-specific deletion of suppressor of cytokine signaling 3 given injections of cerulein developed less severe pancreatitis and Gr-1(low) macrophage produced less tumor necrosis factor-α than wild-type mice given cerulein, although the absolute number of CD11b(high)CD11c(-)Gr-1(low) macrophages was comparable between strains. Induction of acute pancreatitis by L-arginine required induction of macrophage migration by CCL2, via the receptor CCR2.

CONCLUSIONS

Cerulein induction of pancreatitis in mice involves migration of CD11b(high)CD11c(-)Gr-1(low) macrophage from the bone marrow (mediated by CCL2 via CCR2) and suppressor of cytokine signaling 3-dependent activation of macrophage. These findings might lead to new therapeutic strategies for acute pancreatitis.

New insights into the immunological changes in IL-10-deficient mice during the course of spontaneous inflammation in the gut mucosa

IL-10 is a regulatory cytokine that plays a major role in the homeostasis of the gut and this is illustrated by the fact that IL-10^−/− mice develop spontaneous colitis. In this study, IL-10^−/− mice were analyzed for immunological changes during colitis development. We found a reduced frequency of regulatory T cells CD4⁺CD25⁺Foxp3⁺ and higher frequency of activated T cells in the colon that precedes the macroscopic signs of the disease. Production of IL-17 and IFN-γ was higher in the colon. Colitis progression culminates with the reduction of CD4⁺LAP⁺ regulatory T cells in the intestine. Frequency of B1 cells and the secretory IgA production were both elevated. Despite these alterations, 16-week-old IL-10^−/− mice could be rendered tolerant by a continuous feeding protocol. Our study provides detailed analysis of changes that precede colitis and it also suggests that oral tolerance could be used to design novel alternative therapies for the disease.

Proinflammatory cytokines in the pathogenesis of inflammatory bowel diseases

The cytokine responses characterizing the inflammatory bowel diseases are the key pathophysiologic elements that govern the initiation, evolution, and, ultimately, the resolution of these forms of inflammation. Studies during the last 2 decades now provide a detailed (but not yet complete) picture of the nature of these responses. The first tier of cytokine responses are governed by the T-cell differentiation patterns dominating the disease. In Crohn's disease, the major cytokines arise from T-helper cell (Th) 1 and Th17 CD4(+) T-cell differentiation and consist of interferon-γ and interleukin (IL)-17/IL-22 generated by these types of differentiation. The relative importance of these cytokines to Crohn's inflammation is still unclear, although evidence is mounting that interferon-γ is primus inter pare (first among equals). In contrast, in ulcerative colitis, a Th2-like differentiation process is paramount, which results in expansion of natural killer T cells producing IL-13 (and perhaps IL-5). These disease-specific cytokine patterns give rise to a second tier of cytokines that span the Th1/Th17-Th2 divide and act as upstream facilitators and downstream mediators of inflammation. These cytokines include the well-known tumor necrosis factor-α, IL-1β, IL-6 triumphirate, as well as a more recently studied cytokine known as TL1A (tumor necrosis factor-like ligand). In this review, we will explore this cytokine landscape with the view of providing an understanding of how recent and future anticytokine therapies actually function.

Upregulated IL-7 receptor α expression on colitogenic memory CD4+ T cells may participate in the development and persistence of chronic colitis

We have previously demonstrated that IL-7 is essential for the persistence of colitis as a survival factor of colitogenic IL-7Rα-expressing memory CD4(+) T cells. Because IL-7Rα is broadly expressed on various immune cells, it is possible that the persistence of colitogenic CD4(+) T cells is affected by other IL-7Rα-expressing non-T cells. To test this hypothesis, we conducted two adoptive transfer colitis experiments using IL-7Rα(-/-) CD4(+)CD25(-) donor cells and IL-7Rα(-/-) × RAG-2(-/-) recipient mice, respectively. First, IL-7Rα expression on colitic lamina propria (LP) CD4(+) T cells was significantly higher than on normal LP CD4(+) T cells, whereas expression on other colitic LP immune cells, (e.g., NK cells, macrophages, myeloid dendritic cells) was conversely lower than that of paired LP cells in normal mice, resulting in predominantly higher expression of IL-7Rα on colitogenic LP CD4(+) cells, which allows them to exclusively use IL-7. Furthermore, RAG-2(-/-) mice transferred with IL-7Rα(-/-) CD4(+)CD25(-) T cells did not develop colitis, although LP CD4(+) T cells from mice transferred with IL-7Rα(-/-) CD4(+)CD25(-) T cells were differentiated to CD4(+)CD44(high)CD62L(-) effector-memory T cells. Finally, IL-7Rα(-/-) × RAG-2(-/-) mice transferred with CD4(+)CD25(-) T cells developed colitis similar to RAG-2(-/-) mice transferred with CD4(+)CD25(-) T cells. These results suggest that IL-7Rα expression on colitogenic CD4(+) T cells, but not on other cells, is essential for the development of chronic colitis. Therefore, therapeutic approaches targeting the IL-7/IL-7R signaling pathway in colitogenic CD4(+) T cells may be feasible for the treatment of inflammatory bowel diseases.