Interleukin-22 mediates early host defense against attaching and effacing bacterial pathogens

Biological pathways via which the anthocyanin malvidin alleviated the murine colitis induced by Citrobacter rodentium

Enteropathogenic E. coli (EPEC) is a causal agent for diarrheal diseases and contributes to morbidity and mortality in children under the age of five years. The emergence and rapid spread of antibiotic resistant EPEC strains necessitate the search for novel alternatives to antibiotics. In this study, we used Citrobacter rodentium, a natural mouse pathogen that mimics many aspects of human EPEC infections, to investigate the antimicrobial properties of the blueberry anthocyanin malvidin 3-glucoside (MG) using a multi-omics approach. MG supplementation reversed the bodyweight loss induced by C. rodentium infection and improved colonic hyperplasia and histopathological scores. In the colon tissue, MG supplementation significantly increased the expression of Hace1, a key regulator of TNFα-driven signaling, and impacted multiple pathways, such as TGFβ signaling. MG partially restored C. rodentium-induced microbial dysbiosis and significantly enhanced the abundance of the probiotic Bifidobacterium animalis. Moreover, MG disrupted the interactions of E. coli with other gut microbes. MG significantly mediated several host- and microbiota-derived metabolites, such as cytosine, ureidopropionic acid, and glutaric acid. MG normalized the bioactive lipid oleoylethanolamine, a member of the endocannabinoid system, from the dysregulated level in infected mice, directly contributing to its overall beneficial effects. Our findings provided novel insights into molecular processes via which the flavonoid malvidin exerts its biological effects in the gastrointestinal tract.

Current Knowledge of Th22 Cell and IL-22 Functions in Infectious Diseases

T helper 22 (Th22) cells, a newly defined CD4+ T-cell lineage, are characterized by their distinct cytokine profile, which primarily consists of IL-13, IL-22 and TNF-α. Th22 cells express a wide spectrum of chemokine receptors, such as CCR4, CCR6 and CCR10. The main effector molecule secreted by Th22 cells is IL-22, a member of the IL-10 family, which acts by binding to IL-22R and triggering a complex downstream signaling system. Th22 cells and IL-22 have been found to play variable roles in human immunity. In preventing the progression of infections such as HIV and influenza, Th22/IL-22 exhibited protective anti-inflammatory characteristics, and their deleterious proinflammatory activities have been demonstrated to exacerbate other illnesses, including hepatitis B and Helicobacter pylori infection. Herein, we review the current understanding of Th22 cells, including their definition, differentiation and mechanisms, and the effect of Th22/IL-22 on human infectious diseases. According to studies on Th22 cells, Th22/IL-22 may be a promising therapeutic target and an effective treatment strategy for various infections.

T cell-derived interleukin-22 drives the expression of CD155 by cancer cells to suppress NK cell function and promote metastasis

Although T cells can exert potent anti-tumor immunity, a subset of T helper (Th) cells producing interleukin-22 (IL-22) in breast and lung tumors is linked to dismal patient outcome. Here, we examined the mechanisms whereby these T cells contribute to disease. In murine models of lung and breast cancer, constitutional and T cell-specific deletion of Il22 reduced metastases without affecting primary tumor growth. Deletion of the IL-22 receptor on cancer cells decreases metastasis to a degree similar to that seen in IL-22-deficient mice. IL-22 induced high expression of CD155, which bound to the activating receptor CD226 on NK cells. Excessive activation led to decreased amounts of CD226 and functionally impaired NK cells, which elevated the metastatic burden. IL-22 signaling was also associated with CD155 expression in human datasets and with poor patient outcomes. Taken together, our findings reveal an immunosuppressive circuit activated by T cell-derived IL-22 that promotes lung metastasis.

Raw potato starch alters the microbiome, colon and cecal gene expression, and resistance to Citrobacter rodentium infection in mice fed a Western diet

Resistant starches (RS) are fermented in the cecum and colon to produce short-chain fatty acids and other microbial metabolites that can alter host physiology and the composition of the microbiome. We previously showed that mice fed a Total Western Diet (TWD) based on NHANES data that mimics the composition of a typical American diet, containing resistant potato starch (RPS), produced concentration dependent changes to the cecal short-chain fatty acids, the microbiome composition as well as gene expression changes in the cecum and colon that were most prevalent in mice fed the 10% RPS diet. We were then interested in whether feeding TWD/RPS would alter the resistance to bacterial-induced colitis caused by Citrobacter rodentium (Cr), a mouse pathogen that shares 66.7% of encoded genes with Enteropathogenic Escherichia coli. Mice were fed the TWD for 6 weeks followed by a 3-weeks on the RPS diets before infecting with Cr. Fecal Cr excretion was monitored over time and fecal samples were collected for 16S sequencing. Mice were euthanized on day 12 post-infection and cecal contents collected for 16S sequencing. Cecum and colon tissues were obtained for gene expression analysis, histology and to determine the level of mucosa-associated Cr. Feeding RPS increased the percentage of mice productively infected by Cr and fecal Cr excretion on day 4 post-infection. Mice fed the TWD/10% RPS diet also had greater colonization of colonic tissue at day 12 post-infection and colonic pathology. Both diet and infection altered the fecal and cecal microbiome composition with increased levels of RPS resulting in decreased α-diversity that was partially reversed by Cr infection. RNASeq analysis identified several mechanistic pathways that could be associated with the increased colonization of Cr-infected mice fed 10% RPS. In the distal colon we found a decrease in enrichment for genes associated with T cells, B cells, genes associated with the synthesis of DHA-derived SPMs and VA metabolism/retinoic acid signaling. We also found an increase in the expression of the potentially immunosuppressive gene, Ido1. These results suggest that high-level consumption of RPS in the context of a typical American diet, may alter susceptibility to gastrointestinal bacterial infections.

How autophagy, a potential therapeutic target, regulates intestinal inflammation

Inflammatory bowel disease (IBD) is a group of disorders that cause chronic inflammation in the intestines, with the primary types including ulcerative colitis and Crohn's disease. The link between autophagy, a catabolic mechanism in which cells clear protein aggregates and damaged organelles, and intestinal health has been widely studied. Experimental animal studies and human clinical studies have revealed that autophagy is pivotal for intestinal homeostasis maintenance, gut ecology regulation and other aspects. However, few articles have summarized and discussed the pathways by which autophagy improves or exacerbates IBD. Here, we review how autophagy alleviates IBD through the specific genes (e.g., ATG16L1, IRGM, NOD2 and LRRK2), crosstalk of multiple phenotypes with autophagy (e.g., Interaction of autophagy with endoplasmic reticulum stress, intestinal antimicrobial defense and apoptosis) and autophagy-associated signaling pathways. Moreover, we briefly discuss the role of autophagy in colorectal cancer and current status of autophagy-based drug research for IBD. It should be emphasized that autophagy has cell-specific and environment-specific effects on the gut. One of the problems of IBD research is to understand how autophagy plays a role in intestinal tract under specific environmental factors. A better understanding of the mechanism of autophagy in the occurrence and progression of IBD will provide references for the development of therapeutic drugs and disease management for IBD in the future.

Bacteroides fragilis strain ZY-312 facilitates colonic mucosa regeneration in colitis via motivating STAT3 signaling pathway induced by IL-22 from ILC3 secretion

Introduction

Probiotics play critical roles in relieving inflammatory bowel disease (IBD). However, the underlying mechanism of Bacteroides fragilis strain ZY-312 (B. fragilis) for colonic mucosa regeneration in IBD remains unclear.

Methods

The weight loss, disease activity index (DAI), colon length, and histopathology-associated index (HAI) were evaluated the therapeutic effects of B. fragilis in a DSS-induced colitis mouse model. Colonic mucosa proliferation and apoptosis level, and mucus density were detected by histological stain. Gut microbiota was sequenced by 16srRNA analysis. The expression of signal transducer and activator of transcription 3 (STAT3) phosphorylation in colonic mucosa was detected in B. fragilis-treated mice in colitis. B. fragilis-regulated immunity factors of motivating downstream STAT3 phosphorylation were screened by ELISA and flow cytometry. Lastly, B. fragilis-mediated colonic mucosa regeneration effects were verified though the knockout of STAT3 (Stat3 ^△IEC) and IL-22 (IL-22^-/-) in mice, and inhibitor of STAT3 and IL-22 in co-culture model.

Results

B. fragilis alleviated DSS-induced colitis in mice with less weight loss, DAI, colon length shortening, and HAI. Further the results showed that B. fragilis motivated STAT3 phosphorylation in colonic mucosa with the upregulation of proliferation index Ki-67 and mucus density, the downregulation of apoptosis level, and the modulation of gut microbiota through a Stat3 ^△IEC mice model and STAT3 inhibitor-added model in vitro. Meanhwhile we found that B. fragilis promoted IL-22 production, and increased the percentage of IL-22-secreting type 3 innate lymphocytes (ILC3) in colitis. Consequently, We identified that B. fragilis did not increase the expression of pSTAT3, either proliferation level, mucus density, or alter gut microbiota in IL-22 ^-/- mice.

Discussion

B. fragilis may indirectly motivate ILC3 to secrete IL-22, followed by IL-22-induced STAT3 phosphorylation, hence promoting colonic mucosa regeneration in colitis. It indicates that B. fragilis has the potential to be a biological agent for IBD therapy.

Alterations in fecal β-defensin-3 secretion as a marker of instability of the gut microbiota

Compositional changes in the microbiota (dysbiosis) may be a basis for Irritable Bowel Syndrome (IBS), but biomarkers are currently unavailable to direct microbiota-directed therapy. We therefore examined whether changes in fecal β-defensin could be a marker of dysbiosis in a murine model. Experimental dysbiosis was induced using four interventions relevant to IBS: a mix of antimicrobials, westernized diets (high-fat/high-sugar and high salt diets), or mild restraint stress. Fecal mouse β-defensin-3 and 16S rRNA-based microbiome profiles were assessed at baseline and during and following these interventions. Each intervention, except for mild restraint stress, altered compositional and diversity profiles of the microbiota. Exposure to antimicrobials or a high-fat/high-sugar diet, but not mild restraint stress, resulted in decreased fecal β-defensin-3 compared to baseline. In contrast, exposure to the high salt diet increased β-defensin-3 compared to baseline. Mice exposed to the mix of antimicrobials showed the largest compositional changes and the most significant correlations between β-defensin-3 levels and bacterial diversity. The high salt diet was also associated with significant correlations between changes in β-defensin-3 and bacterial diversity, and this was not accompanied by discernible inflammatory changes in the host. Thus, dietary change or antimicrobial exposure, both recognized factors in IBS exacerbations, induced marked dysbiosis that was accompanied by changes in fecal β-defensin-3 levels. We propose that serial monitoring of fecal β-defensins may serve as a marker of dysbiosis and help identify those IBS patients who may benefit from microbiota-directed therapeutic interventions.

Epithelial talin-1 protects mice from citrobacter rodentium-induced colitis by restricting bacterial crypt intrusion and enhancing t cell immunity

Pathogenic enteric Escherichia coli present a significant burden to global health. Food-borne enteropathogenic E. coli (EPEC) and Shiga toxin-producing E. coli (STEC) utilize attaching and effacing (A/E) lesions and actin-dense pedestal formation to colonize the gastrointestinal tract. Talin-1 is a large structural protein that links the actin cytoskeleton to the extracellular matrix though direct influence on integrins. Here we show that mice lacking talin-1 in intestinal epithelial cells (Tln1Δepi) have heightened susceptibility to colonic disease caused by the A/E murine pathogen Citrobacter rodentium. Tln1Δepi mice exhibit decreased survival, and increased colonization, colon weight, and histologic colitis compared to littermate Tln1fl/fl controls. These findings were associated with decreased actin polymerization and increased infiltration of innate myeloperoxidase-expressing immune cells, confirmed as neutrophils by flow cytometry, but more bacterial dissemination deep into colonic crypts. Further evaluation of the immune population recruited to the mucosa in response to C. rodentium revealed that loss of Tln1 in colonic epithelial cells (CECs) results in impaired recruitment and activation of T cells. C. rodentium infection-induced colonic mucosal hyperplasia was exacerbated in Tln1Δepi mice compared to littermate controls. We demonstrate that this is associated with decreased CEC apoptosis and crowding of proliferating cells in the base of the glands. Taken together, talin-1 expression by CECs is important in the regulation of both epithelial renewal and the inflammatory T cell response in the setting of colitis caused by C. rodentium, suggesting that this protein functions in CECs to limit, rather than contribute to the pathogenesis of this enteric infection.

The role of group 3 innate lymphoid cell in intestinal disease

Group 3 innate lymphoid cells (ILC3s), a novel subpopulation of lymphocytes enriched in the intestinal mucosa, are currently considered as key sentinels in maintaining intestinal immune homeostasis. ILC3s can secrete a series of cytokines such as IL-22 to eliminate intestinal luminal antigens, promote epithelial tissue repair and mucosal barrier integrity, and regulate intestinal immunity by integrating multiple signals from the environment and the host. However, ILC3 dysfunction may be associated with the development and progression of various diseases in the gut. Therefore, in this review, we will discuss the role of ILC3 in intestinal diseases such as enteric infectious diseases, intestinal inflammation, and tumors, with a focus on recent research advances and discoveries to explore potential therapeutic targets.

Th17 Cells: Orchestrators of Mucosal Inflammation and Potential Therapeutic Targets

T helper 17 (Th17) cells represent a specialized subgroup of effector CD4+ T cells known for their role in provoking neutrophil-driven tissue inflammation, particularly within mucosal tissues. Although they are pivotal for defending the host against extracellular bacteria and fungi, they have also been associated with development of various T cell-mediated inflammatory conditions, autoimmune diseases, and even cancer. Notably, Th17 cells exhibit a dual nature, with different Th17 cell subtypes showcasing distinct effector functions and varying capacities to incite autoimmune tissue inflammation. Furthermore, Th17 cells exhibit significant plasticity, which carries important functional implications, both in terms of their expression of cytokines typically associated with other effector T cell subsets and in their interactions with regulatory CD4+ T cells. The intricate balance of Th17 cytokines can also be a double-edged sword in inflammation, autoimmunity, and cancer. Within this article, we delve into the mechanisms that govern the differentiation, function, and adaptability of Th17 cells. We culminate with an exploration of therapeutic potentials in harnessing the power of Th17 cells and their cytokines. Targeted interventions to modulate Th17 responses are emerging as promising strategies for autoimmunity, inflammation, and cancer treatment. By precisely fine-tuning Th17-related pathways, we may unlock new avenues for personalized therapeutic approaches, aiming to restore immune balance, alleviate the challenges of these disorders, and ultimately enhance the quality of life for individuals affected by them.

Short Chain Fatty Acid Metabolism in Relation to Gut Microbiota and Genetic Variability

It is widely accepted that the gut microbiota plays a significant role in modulating inflammatory and immune responses of their host. In recent years, the host-microbiota interface has gained relevance in understanding the development of many non-communicable chronic conditions, including cardiovascular disease, cancer, autoimmunity and neurodegeneration. Importantly, dietary fibre (DF) and associated compounds digested by the microbiota and their resulting metabolites, especially short-chain fatty acids (SCFA), were significantly associated with health beneficial effects, such as via proposed anti-inflammatory mechanisms. However, SCFA metabolic pathways are not fully understood. Major steps include production of SCFA by microbiota, uptake in the colonic epithelium, first-pass effects at the liver, followed by biodistribution and metabolism at the host's cellular level. As dietary patterns do not affect all individuals equally, the host genetic makeup may play a role in the metabolic fate of these metabolites, in addition to other factors that might influence the microbiota, such as age, birth through caesarean, medication intake, alcohol and tobacco consumption, pathogen exposure and physical activity. In this article, we review the metabolic pathways of DF, from intake to the intracellular metabolism of fibre-derived products, and identify possible sources of inter-individual variability related to genetic variation. Such variability may be indicative of the phenotypic flexibility in response to diet, and may be predictive of long-term adaptations to dietary factors, including maladaptation and tissue damage, which may develop into disease in individuals with specific predispositions, thus allowing for a better prediction of potential health effects following personalized intervention with DF.

The Double Game Played by Th17 Cells in Infection: Host Defense and Immunopathology

T-helper 17 (Th17) cells represent a subpopulation of CD4+ T lymphocytes that play an essential role in defense against pathogens. Th17 cells are distinguished from Th1 and Th2 cells by their ability to produce members of the interleukin-17 (IL-17) family, namely IL-17A and IL-17F. IL-17 in turn induces several target cells to synthesize and release cytokines, chemokines, and metalloproteinases, thereby amplifying the inflammatory cascade. Th17 cells reside predominantly in the lamina propria of the mucosa. Their main physiological function is to maintain the integrity of the mucosal barrier against the aggression of infectious agents. However, in an appropriate inflammatory microenvironment, Th17 cells can transform into immunopathogenic cells, giving rise to inflammatory and autoimmune diseases. This review aims to analyze the complex mechanisms through which the interaction between Th17 and pathogens can be on the one hand favorable to the host by protecting it from infectious agents, and on the other hand harmful, potentially generating autoimmune reactions and tissue damage.

Interleukin (IL)-22 in common carp (Cyprinus carpio L.): Immune modulation, antibacterial defense, and activation of the JAK-STAT signaling pathway

Interleukin (IL)-22 is an IL-10 family cytokine secreted by CD4⁺ T cells and plays an important role in regulating inflammation and infection elimination. IL-22 homologues have been reported in the teleost, but the functions of IL-22 are still unclear. In this study, we identified two duplicated IL-22 genes in common carp (Cyprinus carpio L.), termed Cc_IL-22A and Cc_IL-22B. Sequence analysis showed that Cc_IL-22A and Cc_IL-22B had four conserved cysteine residues, which could form two intra-chain disulfide bridges. The Cc_IL-22A and Cc_IL-22B were constitutively expressed in various tissues, with the highest expression in the gill. The mRNA expression levels of Cc_IL-22A and Cc_IL-22B were significantly up-regulated in the gill, intestine, head kidney, and spleen of common carp challenged with Aeromonas. hydrophila. In vivo study showed that the expression levels of pro-inflammatory cytokines were significantly up-regulated in the head kidney and spleen when Cc_IL-22A or Cc_IL-22B were over-expressed. Furthermore, the over-expression of Cc_IL-22A and Cc_IL-22B indicated a protective effect on tissues, with only lymphocytic infiltration observed in comparison to the control and pcN3 groups, without obvious change in tissue morphology. Similar stimulatory effects of rIL-22A and rIL-22B were observed in vitro. When HKLs were stimulated with rIL-22A or rIL-22B, the expression levels of critical signaling molecules in the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathway were significantly induced, including JAK1, JAK3, STAT1, and STAT3, as well as pro-inflammatory cytokines (IL-1β and TNF-α). Together, these results suggest that Cc_IL-22A and Cc_IL-22B may regulate inflammatory responses through the JAK-STAT signaling pathway and have a significant impact on the immune defense of common carp against bacterial infection. Therefore, our study provides a new perspective on the functions of Cc_IL-22A and Cc_IL-22B in the immune defense mechanism of fish.

IL-22 and Lactobacillus delbrueckii mitigate alcohol-induced exacerbation of DSS-induced colitis

Ulcerative colitis (UC) is characterized by cycles of active disease flare and inactive disease remission. During UC remission, IL-22 is up-regulated, acting as a hallmark of entrance into UC remission. Recently, we found that in our mouse model of binge alcohol and dextran sodium sulfate (DSS)-induced colitis, alcohol increases severity of UC pathology. In this study, we assessed not only whether alcohol influenced IL-22 expression and thereby perpetuates UC, but also whether recombinant IL-22 (rIL-22) or treatment with a probiotic could alleviate exacerbated symptoms of UC. Levels of large intestine IL-22 were significantly decreased ∼6.9-fold in DSS ethanol compared with DSS vehicle. Examination of lamina propria (LP) cells in the large intestine revealed IL-22+ γδ T cells in DSS vehicle-treated mice were significantly increased, while IL-22+ γδ T cells in DSS ethanol mice were unable to mount this IL-22 response. We administered rIL-22 and found it restored weight loss of DSS ethanol-treated mice. Colonic shortening and increased Enterobacteriaceae were also attenuated. Administration of Lactobacillus delbrueckii attenuated weight loss (p < 0.01), colon length (p < 0.001), mitigated increases in Enterobacteriaceae, increased levels of IL-22, and increased levels of p-STAT3 back to that of DSS vehicle group in DSS ethanol mice. In contrast, sole administration of L. delbrueckii supernatant was not sufficient to reduce UC exacerbation following alcohol. Our findings suggest L. delbrueckii contributes to repair mechanisms by increasing levels of IL-22, resulting in phosphorylation of STAT3, thus attenuating the alcohol-induced increases in intestinal damage after colitis.

Gut to lung translocation and antibiotic mediated selection shape the dynamics of Pseudomonas aeruginosa in an ICU patient

Bacteria have the potential to translocate between sites in the human body, but the dynamics and consequences of within-host bacterial migration remain poorly understood. Here we investigate the link between gut and lung Pseudomonas aeruginosa populations in an intensively sampled ICU patient using a combination of genomics, isolate phenotyping, host immunity profiling, and clinical data. Crucially, we show that lung colonization in the ICU was driven by the translocation of P. aeruginosa from the gut. Meropenem treatment for a suspected urinary tract infection selected for elevated resistance in both the gut and lung. However, resistance was driven by parallel evolution in the gut and lung coupled with organ specific selective pressures, and translocation had only a minor impact on AMR. These findings suggest that reducing intestinal colonization of Pseudomonas may be an effective way to prevent lung infections in critically ill patients.

ILCs-Crucial Players in Enteric Infectious Diseases

Research of the last decade has remarkably increased our understanding of innate lymphoid cells (ILCs). ILCs, in analogy to T helper (Th) cells and their cytokine and transcription factor profile, are categorized into three distinct populations: ILC1s express the transcription factor T-bet and secrete IFNγ, ILC2s depend on the expression of GATA-3 and release IL-5 and IL-13, and ILC3s express RORγt and secrete IL-17 and IL-22. Noteworthy, ILCs maintain a level of plasticity, depending on exposed cytokines and environmental stimuli. Furthermore, ILCs are tissue resident cells primarily localized at common entry points for pathogens such as the gut-associated lymphoid tissue (GALT). They have the unique capacity to initiate rapid responses against pathogens, provoked by changes of the cytokine profile of the respective tissue. Moreover, they regulate tissue inflammation and homeostasis. In case of intracellular pathogens entering the mucosal tissue, ILC1s respond by secreting cytokines (e.g., IFNγ) to limit the pathogen spread. Upon infection with helminths, intestinal epithelial cells produce alarmins (e.g., IL-25) and activate ILC2s to secrete IL-13, which induces differentiation of intestinal stem cells into tuft and goblet cells, important for parasite expulsion. Additionally, during bacterial infection ILC3-derived IL-22 is required for bacterial clearance by regulating antimicrobial gene expression in epithelial cells. Thus, ILCs can limit infectious diseases via secretion of inflammatory mediators and interaction with other cell types. In this review, we will address the role of ILCs during enteric infectious diseases.

The PPARα Regulation of the Gut Physiology in Regard to Interaction with Microbiota, Intestinal Immunity, Metabolism, and Permeability

Peroxisome proliferator-activated receptor alpha (PPARα) is expressed throughout the mammalian gut: in epithelial cells, in the villi of enterocytes and in Paneth cells of intestinal crypts, as well as in some immune cells (e.g., lamina propria macrophages, dendritic cells) of the mucosa. This review examines the reciprocal interaction between PPARα activation and intestinal microbiota. We refer to the published data confirming that microbiota products can influence PPARα signaling and, on the other hand, PPARα activation is able to affect microbiota profile, viability, and diversity. PPARα impact on the broad spectrum of events connected to metabolism, signaling (e.g., NO production), immunological tolerance to dietary antigens, immunity and permeability of the gut are also discussed. We believe that the phenomena described here play a prominent role in gut homeostasis. Therefore, in conclusion we propose future directions for research, including the application of synthetic activators and natural endogenous ligands of PPARα (i.e., endocannabinoids) as therapeutics for intestinal pathologies and systemic diseases assumed to be related to gut dysbiosis.

Exposure to dechlorane 602 induces perturbation of gut immunity and microbiota in female mice

The homeostasis of gut immunity and microbiota are associated with the health of the gut. Dechlorane 602 (Dec 602) with food web magnification potential has been detected in daily food. People who were orally exposed to Dec 602 may encounter increased risk of health problems in the gut. In order to reveal the influence of short-term exposure of Dec 602 on gut immunity and microbiota, adult female C57BL/6 mice were administered orally with Dec 602 (low/high doses: 1.0/10.0 μg/kg body weight per day) for 7 days. Lymphocytes were examined by flow cytometry. Gut microbiota was measured by 16S rRNA gene sequencing. Results showed that fecal IgA was upregulated after exposure to the high dose of Dec 602, suggesting that there might be inflammation in the gut. Then, changes of immune cells in mesenteric lymph nodes and colonic lamina propria were examined. We found that exposure to the high dose of Dec 602 decreased the percentages of the anti-inflammatory T regulatory cells in mesenteric lymph nodes. In colonic lamina propria, the production of gut protective cytokine interleukin-22 by CD4⁺ T cells was decreased, and a decreased trend of interleukin-22 production was also observed in type 3 innate lymphoid cells in the high dose group. Furthermore, an altered microbiota composition toward inflammation in the gut was observed after exposure to Dec 602. Additionally, the altered microbiota correlated with changes of immune parameters, suggesting that there were interactions between influenced microbiota and immune parameters after exposure to Dec 602. Taken together, short-term exposure to Dec 602 induced gut immunity and microbiota perturbations, and this might be the mechanisms for Dec 602 to elicit inflammation in the gut.

Ornithine decarboxylase supports ILC3 responses in infectious and autoimmune colitis through positive regulation of IL-22 transcription

Group 3 innate lymphoid cells (ILC3s) are RORγT+ lymphocytes that are predominately enriched in mucosal tissues and produce IL-22 and IL-17A. They are the innate counterparts of Th17 cells. While Th17 lymphocytes utilize unique metabolic pathways in their differentiation program, it is unknown whether ILC3s make similar metabolic adaptations. We employed single-cell RNA sequencing and metabolomic profiling of intestinal ILC subsets to identify an enrichment of polyamine biosynthesis in ILC3s, converging on the rate-limiting enzyme ornithine decarboxylase (ODC1). In vitro and in vivo studies demonstrated that exogenous supplementation with the polyamine putrescine or its biosynthetic substrate, ornithine, enhanced ILC3 production of IL-22. Conditional deletion of ODC1 in ILC3s impaired mouse antibacterial defense against Citrobacter rodentium infection, which was associated with a decrease in anti-microbial peptide production by the intestinal epithelium. Furthermore, in a model of anti-CD40 colitis, deficiency of ODC1 in ILC3s markedly reduced the production of IL-22 and severity of inflammatory colitis. We conclude that ILC3-intrinsic polyamine biosynthesis facilitates efficient defense against enteric pathogens as well as exacerbates autoimmune colitis, thus representing an attractive target to modulate ILC3 function in intestinal disease.

Non-redundant functions of group 2 innate lymphoid cells

Protective immunity relies on the interplay of innate and adaptive immune cells with complementary and redundant functions. Innate lymphoid cells (ILCs) have recently emerged as tissue-resident, innate mirror images of the T cell system, with which they share lineage-specifying transcription factors and effector machinery1. Located at barrier surfaces, ILCs are among the first responders against invading pathogens and thus could potentially determine the outcome of the immune response2. However, so far it has not been possible to dissect the unique contributions of ILCs to protective immunity owing to limitations in specific targeting of ILC subsets. Thus, all of the available data have been generated either in mice lacking the adaptive immune system or with tools that also affect other immune cell subsets. In addition, it has been proposed that ILCs might be dispensable for a proper immune response because other immune cells could compensate for their absence3-7. Here we report the generation of a mouse model based on the neuromedin U receptor 1 (Nmur1) promoter as a driver for simultaneous expression of Cre recombinase and green fluorescent protein, which enables gene targeting in group 2 ILCs (ILC2s) without affecting other innate and adaptive immune cells. Using Cre-mediated gene deletion of Id2 and Gata3 in Nmur1-expressing cells, we generated mice with a selective and specific deficiency in ILC2s. ILC2-deficient mice have decreased eosinophil counts at steady state and are unable to recruit eosinophils to the airways in models of allergic asthma. Further, ILC2-deficient mice do not mount an appropriate immune and epithelial type 2 response, resulting in a profound defect in worm expulsion and a non-protective type 3 immune response. In total, our data establish non-redundant functions for ILC2s in the presence of adaptive immune cells at steady state and during disease and argue for a multilayered organization of the immune system on the basis of a spatiotemporal division of labour.

Dietary phytate primes epithelial antibacterial immunity in the intestine

Although diet has long been associated with susceptibility to infection, the dietary components that regulate host defense remain poorly understood. Here, we demonstrate that consuming rice bran decreases susceptibility to intestinal infection with Citrobacter rodentium, a murine pathogen that is similar to enteropathogenic E. coli infection in humans. Rice bran naturally contains high levels of the substance phytate. Interestingly, phytate supplementation also protected against intestinal infection, and enzymatic metabolism of phytate by commensal bacteria was necessary for phytate-induced host defense. Mechanistically, phytate consumption induced mammalian intestinal epithelial expression of STAT3-regulated antimicrobial pathways and increased phosphorylated STAT3, suggesting that dietary phytate promotes innate defense through epithelial STAT3 activation. Further, phytate regulation of epithelial STAT3 was mediated by the microbiota-sensitive enzyme histone deacetylase 3 (HDAC3). Collectively, these data demonstrate that metabolism of dietary phytate by microbiota decreases intestinal infection and suggests that consuming bran and other phytate-enriched foods may represent an effective dietary strategy for priming host immunity.

IL-22BP production is heterogeneously distributed in Crohn’s disease

Crohn’s disease (CD), a form of inflammatory bowel disease (IBD), is characterized by impaired epithelial barrier functions and dysregulated mucosal immune responses. IL-22 binding protein (IL-22BP) is a soluble inhibitor regulating IL-22 bioactivity, a cytokine proposed to play protective roles during CD. We and others have shown that IL-22BP is produced in IBD inflamed tissues, hence suggesting a role in CD. In this work, we extended the characterization of IL-22BP production and distribution in CD tissues by applying enzyme-linked immunosorbent assays to supernatants obtained from the culture of endoscopic biopsies of patients, and reverse transcription-quantitative polymerase chain reaction on sorted immune cell subsets. We reveal that IL-22BP levels are higher in inflamed ileums than colons. We observe that in a cell-intrinsic fashion, populations of mononuclear phagocytes and eosinophils express IL-22BP at the highest levels in comparison to other sources of T cells. We suggest the enrichment of intestinal eosinophils could explain higher IL-22BP levels in the ileum. In inflamed colon, we reveal the presence of increased IL-22/IL22BP ratios compared to controls, and a strong correlation between IL-22BP and CCL24. We identify monocyte-derived dendritic cells (moDC) as a cellular subtype co-expressing both cytokines and validate our finding using in vitro culture systems. We also show that retinoic acid induces the secretion of both IL-22BP and CCL24 by moDC. Finally, we report on higher IL-22BP levels in active smokers. In conclusion, our work provides new information relevant to therapeutic strategies modulating IL-22 bioactivity in CD, especially in the context of disease location.

(Not) Home alone: Antigen presenting cell - T Cell communication in barrier tissues

Priming of T cells by antigen presenting cells (APCs) is essential for T cell fate decisions, enabling T cells to migrate to specific tissues to exert their effector functions. Previously, these interactions were mainly explored using blood-derived cells or animal models. With great advances in single cell RNA-sequencing techniques enabling analysis of tissue-derived cells, it has become clear that subsets of APCs are responsible for priming and modulating heterogeneous T cell effector responses in different tissues. This composition of APCs and T cells in tissues is essential for maintaining homeostasis and is known to be skewed in infection and inflammation, leading to pathological T cell responses. This review highlights the commonalities and differences of T cell priming and subsequent effector function in multiple barrier tissues such as the skin, intestine and female reproductive tract. Further, we provide an overview of how this process is altered during tissue-specific infections which are known to cause chronic inflammation and how this knowledge could be harnessed to modify T cell responses in barrier tissue.

Interferon regulatory factor 1 (IRF-1) promotes intestinal group 3 innate lymphoid responses during Citrobacter rodentium infection

Group 3 innate lymphoid cells (ILC3s) are crucial mediators of immunity and epithelial barrier function during immune responses against extracellular bacteria. Here, we identify Interferon regulatory factor 1 (IRF-1), a transcription factor previously associated with type 1 immunity, as an essential regulator of intestinal ILC3 accumulation and effector cytokine production. We demonstrate that IRF-1 is upregulated in the context of infection with the enteropathogen Citrobacter rodentium and that its presence is central for anatomical containment and prevention of pathogen dissemination. We furthermore show that IRF-1 is required in order for intestinal ILC3s to produce large amounts of the protective effector cytokine IL-22 early in the course of infection. On a molecular level, our data indicate that IRF-1 controls ILC3 numbers and their activation by direct transcriptional regulation of the IL-12Rβ1 chain, thereby allowing ILCs to physiologically respond to IL-23 stimulation.

Innate lymphoid cells (ILC) are involved with different immune responses. Here the authors show that Interferon regulatory factor 1 (IRF1) is important for intestinal ILC3 accumulation during Citrobacter rodentium infection and promotes release of the protective cytokine IL-22 and response to IL-23.

Role of IL-22 in intestinal microenvironment and potential targeted therapy through diet

IL-22 is a type 2 receptor cytokine in IL-10 family. IL-22 is usually secreted by innate and adaptive immune cells and takes its effects on non-hematopoietic cells. Through activate STAT3 pathway, IL-22 plays an important role in infection clearance and tissue regeneration, which is critical for barrier integrate and homeostasis. Abnormal activation of IL-22 signal was observed in inflammation diseases, autoimmune diseases, and cancers. We review the recent discoveries about the mechanism and regulation of IL-22 signal pathway from the perspective of intestinal micro-environment. Diet-based IL-22 target therapeutic strategies and their potential clinical significance will also be discussed.

The IL-20RB receptor and the IL-20 signaling pathway in regulating host defense in oral mucosal candidiasis

Pseudomembranous candidiasis (thrush), erythematous candidiasis, and fungal esophagitis are infections of the barrier mucosa of the upper gastrointestinal tract. The majority of these infections are caused by Candida albicans, an opportunistic fungal pathogen that frequently exists as a harmless commensal on mucosal surfaces lining the gastrointestinal tract. Oral infections are initiated in the superficial stratified squamous epithelium, in which keratinocytes are the most abundant host cells and are the initial points of contact with C. albicans present in saliva. Intrinsic features of oral keratinocytes are likely to play important roles in host defense and tissue homeostasis in oral candidiasis. One understudied pathway that may be important for modulating oral candidiasis is the IL-20 cytokine signaling pathway that employs keratinocyte IL-20RB receptors as ligands for IL-19, IL-20, and IL-24. We report that production of human oral keratinocyte il24 mRNA and protein are stimulated during co-culture with C. albicans. To test the role of the IL-20 family signaling pathway in oral candidiasis, Il20rb^-/- mice (lacking the IL-20RB receptor) were compared to wild-type mice in a murine model of oropharyngeal candidiasis. Fungal burdens and percent loss in body weight were determined. Despite comparable fungal burdens, the Il20rb^-/- mice exhibited less weight loss over the course of their infection compared to the B6 mice, suggestive of reduced overall disease consequences in the mutant mice. Interference with IL-20 family cytokine signaling may be useful for augmenting the ability of the host to defend itself against pathogens.

Long-term use of broad-spectrum antibiotics affects Ly6Chi monocyte recruitment and IL-17A and IL-22 production through the gut microbiota in tumor-bearing mice treated with chemotherapy

The protective effects of antibiotics against infection in cancer patients treated with chemotherapy remains unclear and related studies have been performed in healthy or pathogen-infected animal models. Here, we aimed to study the effects of antibiotic use on intestinal infection in tumor-bearing mice treated with chemotherapy and to determine the underlying mechanisms. Subcutaneous CT26 tumor-bearing mice were assigned to four groups: the control (Ctrl) group without any treatment, the antibiotic (ATB) group treated with a mixture of ampicillin, streptomycin, and colistin, the 5-fluorouracil (FU) group treated with four cycles of intraperitoneal injections of FU, and the ATB + FU group treated with the combination of ATB and FU. Gut microbial composition was determined and mesenteric lymph nodes (mLNs) were isolated for bacterial culturing. Intestinal permeability and integrity were assessed and the expression of cytokines was analyzed by quantitative PCR, ELISA, or flow cytometry (FCM). Monocytes in the colonic lamina propria (LP) were measured by FCM. Compared with the Ctrl and FU groups, the numbers of positive bacterial culturing results for mLNs were higher, and gut bacterial compositions were altered in the ATB and ATB + FU groups, with significantly decreased alpha diversity in the ATB + FU group. Intestinal integrity regarding the expression of tight junction proteins and intestinal permeability were not impaired significantly after treatments, but the colons were shorter in the ATB + FU group. The expression levels of intestinal IL-17A and IL-22, as well as the percentages of IL-17A⁺ cells in the colonic LP of the ATB + FU group, were lower than those in the FU group. The percentages of Ly6C^hi monocytes in the colonic LP were lower, but those in the spleen were higher in the ATB + FU group than in the FU group. The mRNA levels of colonic CCL8 were reduced in the ATB + FU group. Antibiotic use is associated with an increased incidence of intestinal infections in tumor-bearing mice treated with chemotherapy, which might in turn be associated with a dysregulated gut microbiota that inhibits colonic monocyte recruitment and IL-17A and IL-22 production.

Research progress on Th17 and T regulatory cells and their cytokines in regulating atherosclerosis

Background

Coronary heart disease due to atherosclerosis is the leading cause of death worldwide. Atherosclerosis is considered a chronic inflammatory state in the arterial wall that promotes disease progression and outcome, and immune cells play an important role in the inflammatory process.

Purpose

We review the mechanisms of CD4+ T subsets, i.e., helper T17 (Th17) cells and regulatory T cells (Tregs), in regulating atherosclerosis, focusing on the role of interleukin (IL)-17, IL-10, and other cytokines in this disease and the factors influencing the effects of these cytokines.

Results

IL-17 secreted by Th17 cells can promote atherosclerosis, but few studies have reported that IL-17 can also stabilize atherosclerotic plaques. Tregs play a protective role in atherosclerosis, and Th17/Treg imbalance also plays an important role in atherosclerosis.

Conclusion

The immune response is important in regulating atherosclerosis, and studying the mechanism of action of each immune cell on atherosclerosis presents directions for the treatment of atherosclerosis. Nevertheless, the current studies are insufficient for elucidating the mechanism of action, and further in-depth studies are needed to provide a theoretical basis for clinical drug development.

Systems to model the personalized aspects of microbiome health and gut dysbiosis

The human gut microbiome is a complex and dynamic microbial entity that interacts with the environment and other parts of the body including the brain, heart, liver, and immune system. These multisystem interactions are highly conserved from invertebrates to humans, however the complexity and diversity of human microbiota compositions often yield a context that is unique to each individual. Yet commonalities remain across species, where a healthy gut microbiome will be rich in symbiotic commensal biota while an unhealthy gut microbiota will be experiencing abnormal blooms of pathobiont bacteria. In this review we discuss how omics technologies can be applied in a personalized approach to understand the microbial crosstalk and microbial-host interactions that affect the delicate balance between eubiosis and dysbiosis in an individual gut microbiome. We further highlight the strengths of model organisms in identifying and characterizing these conserved synergistic and/or pathogenic host-microbe interactions. And finally, we touch upon the growing area of personalized therapeutic interventions targeting gut microbiome.

Activated T cells are the cellular source of IL-22 that enhances proliferation and survival of lymphocytes in Nile tilapia

As a pleiotropic cytokine mainly secreted by CD4⁺ T cells, interleukin (IL)-22 plays an important role in immune regulation and infection elimination. Despite IL-22 homologues have been identified in non-mammal, whether and how IL-22 participates in the adaptive immune response of early vertebrates have not been fully addressed. In this study, we identified an evolutionarily conserved IL-22 from Nile tilapia Oreochromis niloticus (defined as OnIL-22), proved by its properties regarding sequence, gene structure, functional domain, tertiary structure and phylogeny. IL-22 was broadly expressed in lymphoid-related tissues of tilapia, and with relatively higher levels in skin, gill, intestine and liver. The expression of OnIL-22 in spleen lymphocytes was markedly induced at the adaptive immune stage after Streptococcus agalactiae infection. Moreover, once lymphocytes were activated by PMA plus ionomycin or T-cell specific mitogen PHA in vitro, OnIL-22 expression was obviously up-regulated at both mRNA and protein levels. These results thus suggest that activated T cells produce IL-22 to take part in the adaptive immune response of tilapia. Furthermore, treatment of lymphocytes with recombinant OnIL-22 increased the expression of genes related to proliferation and survival, and further promoted the proliferation and reduced the apoptosis of lymphocytes during bacterial infection or T-cell activation. These cellular effects of IL-22 seem to be associated with JAK1/STAT3 axis downstream of IL-22, because IL-22 application not only elevated the mRNA expression of JAK1 and STAT3, but also enhanced their phosphorylation in lymphocytes. Altogether, we suggest that activated T cells produce IL-22 to promote lymphocyte proliferation and survival probability via JAK1/STAT3 signaling pathway, thus participating in adaptive immune response of Nile tilapia. Our study therefore provides helpful perspective for understanding the function and mechanism of adaptive immune system in teleost.

Contribution of Innate Lymphoid Cells in Supplementing Cytokines Produced by CD4+ T Cells During Acute and Chronic SIV Infection of the Colon

HIV/SIV (simian immunodeficiency virus) infection leads to a loss of CD4+ T helper (Th) cells in number and function that begins during the acute phase and persists through the chronic phase of infection. In particular, there is a drastic decrease of Th17 and Th22 cells in the HIV/SIV-infected gastrointestinal (GI) tract as a source of interleukin (IL)-17 and IL-22. These cytokines are vital in the immune response to extracellular pathogens and maintenance of the GI tract. However, innate lymphoid cells (ILCs) are a source of IL-17 and IL-22 during the early stages of an immune response in mucosal tissue and remain vital cytokine producers when the immune response is persistent. Here, we wanted to determine whether ILCs are a source of IL-17 and IL-22 in the SIV-infected colon and could compensate for the loss of Th17 and Th22 cells. As a control, we evaluated the frequency and number of ILCs expressing interferon-gamma (IFNγ) and tumor necrosis factor-alpha (TNFα). We determined the frequency and number of cytokine expressing ILC subsets and T cell subsets within leukocytes from the colons of uninfected as well as acute and chronic SIV-infected colons without in vitro mitogenic stimulation. In the present study, we find that: (1) the frequency of IL-22, IFNγ, and TNFα but not IL-17 producing ILCs is increased in the acutely infected colon and remains high during the chronically infected colon relative to cytokine expressing ILCs in the uninfected colon, (2) ILCs are a significant source of IL-22, IFNγ, and TNFα but not IL-17 when CD4+ T lymphocytes in the gut lose their capacity to secrete these cytokines during SIV infection, and (3) the changes in the cytokines expressed by ILCs relative to CD4+ T cells in the infected colon were not due to increases in the frequency or number of ILCs in relation to T lymphocytes found in the tissue.

ZBTB46 defines and regulates ILC3s that protect the intestine

RORγt is a lineage-specifying transcription factor that is expressed by immune cells that are enriched in the gastrointestinal tract and promote immunity, inflammation and tissue homeostasis1-15. However, fundamental questions remain with regard to the cellular heterogeneity among these cell types, the mechanisms that control protective versus inflammatory properties and their functional redundancy. Here we define all RORγt+ immune cells in the intestine at single-cell resolution and identify a subset of group 3 innate lymphoid cells (ILC3s) that expresses ZBTB46, a transcription factor specifying conventional dendritic cells16-20. ZBTB46 is robustly expressed by CCR6+ lymphoid-tissue-inducer-like ILC3s that are developmentally and phenotypically distinct from conventional dendritic cells, and its expression is imprinted by RORγt, fine-tuned by microbiota-derived signals and increased by pro-inflammatory cytokines. ZBTB46 restrains the inflammatory properties of ILC3s, including the OX40L-dependent expansion of T helper 17 cells and the exacerbated intestinal inflammation that occurs after enteric infection. Finally, ZBTB46+ ILC3s are a major source of IL-22, and selective depletion of this population renders mice susceptible to enteric infection and associated intestinal inflammation. These results show that ZBTB46 is a transcription factor that is shared between conventional dendritic cells and ILC3s, and identify a cell-intrinsic function for ZBTB46 in restraining the pro-inflammatory properties of ILC3s and a non-redundant role for ZBTB46+ ILC3s in orchestrating intestinal health.

Role of Nutrient-sensing Receptor GPRC6A in Regulating Colonic Group 3 Innate Lymphoid Cells and Inflamed Mucosal Healing

BACKGROUND AND AIMS

Group 3 innate lymphoid cells [ILC3s] sense environmental signals and are critical in gut homeostasis and immune defence. G-protein-coupled receptors [GPCRs] mediate cellular responses to diverse environmental signals. However, the GPCRs' regulation mechanisms of ILC3s is largely unknown.

METHODS

We used wild-type [WT] and GPRC6A-/- mice to investigate the role of GPRC6A in the population and the function of ILC3s. We then purified ILC3s from WT and GPRC6A-/- mice. Colitis was induced in WT mice and GPRC6A-/- mice through dextran sodium sulphate [DSS] administration or C. rodentium infection. Furthermore L-arginine, a selective GPRC6A agonist, was administered to mice with colitis.

RESULTS

We found that colonic ILC3s expressed GPRC6A. The deficiency of GPRC6A decreased ILC3-derived interleukin-22 [IL-22] production and the number of proliferating ILC3s, which led to increased susceptibility to colon injury and pathogen infection and impaired inflamed mucosal healing. Further studies showed that L-arginine, a GPRC6A agonist, promoted colonic ILC3 expansion and function via the mammalian target of rapamycin complex 1 [mTORC1] signalling in vitro. In addition, L-arginine attenuated DSS-induced colitis in vivo. This was associated with a significant increase in IL-22 secretion by ILC3s.

CONCLUSIONS

Our findings unveil a role for the nutrient-sensing receptor GPRC6A in colonic ILC3 function and identify a novel ILC3 receptor signalling pathway modulating inflamed mucosal healing.

Akkermansia muciniphila Reduces Peritonitis and Improves Intestinal Tissue Wound Healing after a Colonic Transmural Defect by a MyD88-Dependent Mechanism

Anastomotic leakage is a major complication following colorectal surgery leading to peritonitis, complications, and mortality. Akkermansia muciniphila has shown beneficial effects on the gut barrier function. Whether A. muciniphila reduces peritonitis and mortality during colonic leakage is unknown. Whether A. muciniphila can directly modulate the expression of genes in the colonic mucosa in humans has never been studied. We investigated the effects of a pretreatment (14 days) with live A. muciniphila prior to surgical colonic perforation on peritonitis, mortality, and wound healing. We used mice with an inducible intestinal-epithelial-cell-specific deletion of MyD88 (IEC-MyD88 KO) to investigate the role of the innate immune system in this context. In a proof-of-concept pilot study, healthy humans were exposed to A. muciniphila for 2 h and colonic biopsies taken before and after colonic instillation for transcriptomic analysis. Seven days after colonic perforation, A.-muciniphila-treated mice had significantly lower mortality and severity of peritonitis. This effect was associated with significant improvements of wound histological healing scores, higher production of IL22, but no changes in the mucus layer thickness or genes involved in cell renewal, proliferation, or differentiation. All these effects were abolished in IEC-MyD88 KO mice. Finally, human subjects exposed to A. muciniphila exhibited an increased level of the bacterium at the mucus level 2 h after instillation and significant changes in the expression of different genes involved in the regulation of cell cycling, gene transcription, immunity, and inflammation in their colonic mucosa. A. muciniphila improves wound healing during transmural colonic wall defect through mechanisms possibly involving IL22 signaling and requiring MyD88 in the intestinal cells. In healthy humans, colonic administration of A. muciniphila is well tolerated and changes the expression of genes involved in the immune pathways.

Gut Microbiota Modulation as a Novel Therapeutic Strategy in Cardiometabolic Diseases

The human gut harbors microbial ecology that is in a symbiotic relationship with its host and has a vital function in keeping host homeostasis. Inimical alterations in the composition of gut microbiota, known as gut dysbiosis, have been associated with cardiometabolic diseases. Studies have revealed the variation in gut microbiota composition in healthy individuals as compared to the composition of those with cardiometabolic diseases. Perturbation of host-microbial interaction attenuates physiological processes and may incite several cardiometabolic disease pathways. This imbalance contributes to cardiometabolic diseases via metabolism-independent and metabolite-dependent pathways. The aim of this review was to elucidate studies that have demonstrated the complex relationship between the intestinal microbiota as well as their metabolites and the development/progression of cardiometabolic diseases. Furthermore, we systematically itemized the potential therapeutic approaches for cardiometabolic diseases that target gut microbiota and/or their metabolites by following the pathophysiological pathways of disease development. These approaches include the use of diet, prebiotics, and probiotics. With the exposition of the link between gut microbiota and cardiometabolic diseases, the human gut microbiota therefore becomes a potential therapeutic target in the development of novel cardiometabolic agents.

Inflammation triggers ILC3 patrolling of the intestinal barrier

An orchestrated cellular network, including adaptive lymphocytes and group 3 innate lymphoid cells (ILC3s), maintains intestinal barrier integrity and homeostasis. T cells can monitor environmental insults through constitutive circulation, scanning tissues and forming immunological contacts, a process named immunosurveillance. In contrast, the dynamics of intestinal ILC3s are unknown. Using intravital imaging, we observed that villus ILC3s were largely immotile at steady state but acquired migratory ‘patrolling’ attributes and enhanced cytokine expression in response to inflammation. We showed that T cells, the chemokine CCL25 and bacterial ligands regulated intestinal ILC3 behavior and that loss of patrolling behavior by interleukin-22 (IL-22)-producing ILC3s altered the intestinal barrier through increased epithelial cell death. Collectively, we identified notable differences between the behavior of ILC3s and T cells, with a prominent adaptation of intestinal ILC3s toward mucosal immunosurveillance after inflammation.

Serafini and colleagues show that intestinal villus ILC3s, which are largely immotile at steady state, develop a patrolling behavior in response to inflammation.

Sex-Dependent Hepatoprotective Role of IL-22 Receptor Signaling in Non-Alcoholic Fatty Liver Disease-Related Fibrosis

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) is a major health problem with complex pathogenesis. Although sex differences in NAFLD pathogenesis have been reported, the mechanisms underlying such differences remain understudied. Interleukin (IL)22 is a pleiotropic cytokine with both protective and/or pathogenic effects during liver injury. IL22 was shown to be hepatoprotective in NAFLD-related liver injury. However, these studies relied primarily on exogenous administration of IL22 and did not examine the sex-dependent effect of IL22. Here, we sought to characterize the role of endogenous IL22-receptor signaling during NAFLD-induced liver injury in males and females.

METHODS

We used immunofluorescence, flow cytometry, histopathologic assessment, and gene expression analysis to examine IL22 production and characterize the intrahepatic immune landscape in human subjects with NAFLD (n = 20; 11 men and 9 women) and in an in vivo Western high-fat diet-induced NAFLD model in IL22RA knock out mice and their wild-type littermates.

RESULTS

Examination of publicly available data sets from 2 cohorts with NAFLD showed increased hepatic IL22 gene expression in females compared with males. Furthermore, our immunofluorescence analysis of liver sections from NAFLD subjects (n = 20) showed increased infiltration of IL22-producing cells in females. Similarly, IL22-producing cells were increased in wild-type female mice with NAFLD and the hepatic IL22/IL22 binding protein messenger RNA ratio correlated with expression of anti-apoptosis genes. The lack of endogenous IL22-receptor signaling (IL22RA knockout) led to exacerbated liver damage, inflammation, apoptosis, and liver fibrosis in female, but not male, mice with NAFLD.

CONCLUSIONS

Our data suggest a sex-dependent hepatoprotective antiapoptotic effect of IL22-receptor signaling during NAFLD-related liver injury in females.

Blocking GARP-mediated activation of TGF-β1 did not alter innate or adaptive immune responses to bacterial infection or protein immunization in mice

Abstract

Transmembrane protein GARP binds latent TGF-β1 to form GARP:(latent)TGF-β1 complexes on the surface of several cell types including Tregs, B-cells, and platelets. Upon stimulation, these cells release active TGF-β1. Blocking TGF-β1 activation by Tregs with anti-GARP:TGF-β1 mAbs overcomes resistance to PD1/PD-L1 blockade and induces immune-mediated regressions of murine tumors, indicating that Treg-derived TGF-β1 inhibits anti-tumor immunity. TGF-β1 exerts a vast array of effects on immune responses. For example, it favors differentiation of T_H17 cells and B-cell switch to IgA production, two important processes for mucosal immunity. Here, we sought to determine whether treatment with anti-GARP:TGF-β1 mAbs would perturb immune responses to intestinal bacterial infection. We observed no aggravation of intestinal disease, no systemic dissemination, and no alteration of innate or adaptative immune responses upon oral gavage of C. rodentium in highly susceptible Il22r^−/− mice treated with anti-GARP:TGF-β1 mAbs. To examine the effects of GARP:TGF-β1 blockade on Ig production, we compared B cell- and T_H cell- responses to OVA or CTB protein immunization in mice carrying deletions of Garp in Tregs, B cells, or platelets. No alteration of adaptive immune responses to protein immunization was observed in the absence of GARP on any of these cells. Altogether, we show that antibody-mediated blockade of GARP:TGF-β1 or genetic deletion of Garp in Tregs, B cells or platelets, do not alter innate or adaptive immune responses to intestinal bacterial infection or protein immunization in mice. Anti-GARP:TGF-β1 mAbs, currently tested for cancer immunotherapy, may thus restore anti-tumor immunity without severely impairing other immune defenses.

Précis

Immunotherapy with GARP:TGF-β1 mAbs may restore anti-tumor immunity without impairing immune or inflammatory responses required to maintain homeostasis or host defense against infection, notably at mucosal barriers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00262-021-03119-8.

IL-24 intrinsically regulates Th17 cell pathogenicity in mice

In certain instances, Th17 responses are associated with severe immunopathology. T cell–intrinsic mechanisms that restrict pathogenic effector functions have been described for type 1 and 2 responses but are less well studied for Th17 cells. Here, we report a cell-intrinsic feedback mechanism that controls the pathogenicity of Th17 cells. Th17 cells produce IL-24, which prompts them to secrete IL-10. The IL-10–inducing function of IL-24 is independent of the cell surface receptor of IL-24 on Th17 cells. Rather, IL-24 is recruited to the inner mitochondrial membrane, where it interacts with the NADH dehydrogenase (ubiquinone) 1 α subcomplex subunit 13 (also known as Grim19), a constituent of complex I of the respiratory chain. Together, Grim19 and IL-24 promote the accumulation of STAT3 in the mitochondrial compartment. We propose that IL-24–guided mitochondrial STAT3 constitutes a rheostat to blunt extensive STAT3 deflections in the nucleus, which might then contribute to a robust IL-10 response in Th17 cells and a restriction of immunopathology in experimental autoimmune encephalomyelitis.

Oral Administration with Live Attenuated Citrobacter rodentium Protects Immunocompromised Mice from Lethal Infection

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) are important causative agents for foodborne diseases worldwide. Besides antibiotic treatment, vaccination has been deemed as the most effective strategy for preventing EPEC- and EHEC-caused foodborne illnesses. Despite substantial progress made in identifying promising antigens and efficacious vaccines, no vaccines against EPEC or EHEC have yet been licensed. Mice are inherently resistant to EPEC and EHEC infections; infection with Citrobacter rodentium (CR), the murine equivalent of EPEC and EHEC, in mice has been widely used as a model to study bacterial pathogenesis and develop novel vaccine strategies. Mirroring the severe outcomes of EPEC and EHEC infections in immunocompromised populations, immunocompromised mouse strains such as interleukin-22 knockout (Il22^-/-) are susceptible to CR infection with severe clinical symptoms and mortality. Live attenuated bacterial vaccine strategies have been scarcely investigated for EPEC and EHEC infections, in particular in immunocompromised populations associated with severe outcomes. Here we examined whether live attenuated CR strain with rational genetic manipulation generates protective immunity against lethal CR infection in the susceptible Il22^-/- mice. Our results demonstrate that oral administration of live ΔespFΔushA strain promotes efficient systemic and humoral immunity against a wide range of CR virulence determinants, thus protecting otherwise lethal CR infection, even in immunocompromised Il22^-/- mice. This provides a proof of concept of live attenuated vaccination strategy for preventing CR infection in immunocompromised hosts associated with more severe symptoms and lethality.

The Transcription Factor ThPOK Regulates ILC3 Lineage Homeostasis and Function During Intestinal Infection

Innate lymphoid cells (ILCs) have been identified as a heterogeneous population of lymphocytes that mirrors the cytokine and transcriptional profile of adaptive T cells. The dynamic balance between key transcription factors determines the heterogeneity, plasticity, and functions of ILC subsets. The transcription factor ThPOK is highly conserved in biological evolution and exerts pivotal functions in the differentiation of T cells. However, the function of ThPOK in ILC3s has not been identified. Here, we found that ThPOK regulated the homeostasis of ILC3s, as mice lacking ThPOK showed decreased NKp46⁺ ILC3s and increased CCR6^- NKp46^- ILC3s. ThPOK-deficient mice were more sensitive to S. typhimurium infection due to the impaired IFN-γ secretion of NKp46⁺ ILC3s. Furthermore, ThPOK participates in ILC3-mediated control of C. rodentium infection by negatively regulating IL-17A secretion. ThPOK preserves the identity of NKp46⁺ ILC3s by repressing RORγt, which indirectly releases T-bet expression. On the molecular level, ThPOK directly binds to Rorc and Il23r to restrain their expression which further modulates IL-17A secretion. Collectively, our analysis revealed a critical role of ThPOK in the homeostasis and functions of ILC3 subsets.

IL-22 regulates inflammatory responses to agricultural dust-induced airway inflammation

IL-22 is a unique cytokine that is upregulated in many chronic inflammatory diseases, including asthma, and modulates tissue responses during inflammation. However, the role of IL-22 in the resolution of inflammation and how this contributes to lung repair processes are largely unknown. Here, we tested the hypothesis that IL-22 signaling is critical in inflammation resolution after repetitive exposure to agricultural dust. Using an established mouse model of organic dust extract-induced lung inflammation, we found that IL-22 knockout mice have an enhanced response to agricultural dust as evidenced by an exacerbated increase in infiltrating immune cells and lung pathology as compared to wild-type controls. We further identified that, in response to dust, IL-22 is expressed in airway epithelium and in Ym1+ macrophages found within the parenchyma in response to dust. The increase in IL-22 expression was accompanied by increases in IL-22 receptor IL-22R1 within the lung epithelium. In addition, we found that alveolar macrophages in vivo as well as THP-1 cells in vitro express IL-22, and this expression is modulated by dust exposure. Furthermore, subcellular localization of IL-22 appears to be in the Golgi of resting THP1 human monocytes, and treatment with dust extracts is associated with IL-22 release into the cytosolic compartment from the Golgi reservoirs during dust extract exposure. Taken together, we have identified a significant role for macrophage-mediated IL-22 signaling that is activated in dust-induced lung inflammation in mice.

PD-1 signaling facilitates activation of lymphoid tissue inducer cells by restraining fatty acid oxidation

Anti-programmed death-1 (PD-1) immunotherapy that aims to restore T cell activity in cancer patients frequently leads to immune-related adverse events such as colitis. However, the underlying mechanism is still elusive. Here, we find that Pdcd1-deficient mice exhibit disrupted gut microbiota and aggravated dextran sulfate sodium (DSS)-induced colitis. In addition to T cells, PD-1 is also substantially expressed in colonic lymphoid tissue inducer (LTi) cells. During DSS-induced colitis, LTi cell activation is accompanied by increased PD-1 expression, whereas PD-1 deficiency results in reduced interleukin-22 (IL-22) production by LTi cells and exacerbated inflammation. Mechanistically, activated LTi cells reprogram their metabolism toward carbohydrate metabolism and fatty acid synthesis, while fatty acid oxidation (FAO) is unchanged. However, PD-1 deficiency leads to significantly elevated FAO in LTi cells, which in turn attenuates their activation and IL-22 production. Consistently, FAO suppression efficiently restores IL-22 production in Pdcd1^-/- LTi cells. Thus, our study provides unforeseen mechanistic insight into colitis occurrence during anti-PD-1 immunotherapy through LTi cell metabolic reconfiguration.

Group 3 innate lymphoid cell pyroptosis represents a host defence mechanism against Salmonella infection

Group 3 innate lymphoid cells (ILC3s) produce interleukin (IL)-22 and coordinate with other cells in the gut to mount productive host immunity against bacterial infection. However, the role of ILC3s in Salmonella enterica serovar Typhimurium (S. Typhimurium) infection, which causes foodborne enteritis in humans, remains elusive. Here we show that S. Typhimurium exploits ILC3-produced IL-22 to promote its infection in mice. Specifically, S. Typhimurium secretes flagellin through activation of the TLR5-MyD88-IL-23 signalling pathway in antigen presenting cells (APCs) to selectively enhance IL-22 production by ILC3s, but not T cells. Deletion of ILC3s but not T cells in mice leads to better control of S. Typhimurium infection. We also show that S. Typhimurium can directly invade ILC3s and cause caspase-1-mediated ILC3 pyroptosis independently of flagellin. Genetic ablation of Casp1 in mice leads to increased ILC3 survival and IL-22 production, and enhanced S. Typhimurium infection. Collectively, our data suggest a key host defence mechanism against S. Typhimurium infection via induction of ILC3 death to limit intracellular bacteria and reduce IL-22 production.

A secondary metabolite drives intraspecies antagonism in a gut symbiont that is inhibited by cell-wall acetylation

The mammalian microbiome encodes numerous secondary metabolite biosynthetic gene clusters; yet, their role in microbe-microbe interactions is unclear. Here, we characterized two polyketide synthase gene clusters (fun and pks) in the gut symbiont Limosilactobacillus reuteri. The pks, but not the fun, cluster encodes antimicrobial activity. Forty-one of 51 L. reuteri strains tested are sensitive to Pks products; this finding was independent of strains' host origin. Sensitivity to Pks was also established in intraspecies competition experiments in gnotobiotic mice. Comparative genome analyses between Pks-resistant and -sensitive strains identified an acyltransferase gene (act) unique to Pks-resistant strains. Subsequent cell-wall analysis of wild-type and act mutant strains showed that Act acetylates cell-wall components, providing resistance to Pks-mediated killing. Additionally, pks mutants lost their competitive advantage, while act mutants lost their Pks resistance in in vivo competition assays. These findings provide insight into how closely related gut symbionts can compete and co-exist in the gastrointestinal tract.

Bringing to Light the Risk of Colorectal Cancer in Inflammatory Bowel Disease: Mucosal Glycosylation as a Key Player

Colitis-associated cancer is a major complication of inflammatory bowel disease remaining an important clinical challenge in terms of diagnosis, screening, and prognosis. Inflammation is a driving factor both in inflammatory bowel disease and cancer, but the mechanism underlying the transition from colon inflammation to cancer remains to be defined. Dysregulation of mucosal glycosylation has been described as a key regulatory mechanism associated both with colon inflammation and colorectal cancer development. In this review, we discuss the major molecular mechanisms of colitis-associated cancer pathogenesis, highlighting the role of glycans expressed at gut epithelial cells, at lamina propria T cells, and in serum proteins in the regulation of intestinal inflammation and its progression to colon cancer, further discussing its potential clinical and therapeutic applications.

Airway epithelial STAT3 inhibits allergic inflammation via upregulation of stearoyl-CoA desaturase 1

BACKGROUND

Airway epithelial cells (AECs) play a crucial role in the induction and development of allergic inflammation through the development and activation of immune cells, including Th2 cells and ILC2s. Recent studies have revealed that STAT3 expressed in epithelial cells protects against pathogens and maintains homeostasis in the intestine. However, the roles of STAT3 in airway epithelium are poorly understood. Therefore, we sought to elucidate the roles of airway epithelial STAT3 in allergic airway inflammation.

METHODS

Allergic airway inflammation was induced by intratracheal administration of house dust mite (HDM) extract in doxycycline-induced AEC-specific STAT3-deficient (STAT3-cKO) mice and their genetic control (STAT3-WT) mice. Airway inflammation was evaluated by flow cytometric analysis of bronchoalveolar lavage fluid cells and histological analysis of the lung. Purified airway epithelial cells were analyzed by quantitative PCR and RNA-sequencing (RNA-seq).

RESULTS

HDM-induced airway inflammation was exacerbated in STAT3-cKO mice compared with STAT3-WT mice. RNA-seq analyses revealed that Scd1, coding stearoyl-CoA desaturase 1, was most significantly upregulated in HDM-treated STAT3-WT mice compared to HDM-treated STAT3-cKO mice. Notably, the administration of an SCD1 inhibitor exacerbated HDM-induced airway inflammation. AECs of HDM-treated STAT3-cKO mice and those of HDM-treated SCD1 inhibitor-injected mice shared 45 differentially expressed genes (DEGs). Gene enrichment analysis of the DEGs revealed that the enriched ontology clusters included fatty acid biosynthetic process and regulation of lipid biosynthetic process, suggesting the involvement of the STAT3-SCD1-lipid metabolism axis in suppressing allergic inflammation.

CONCLUSIONS

STAT3 is crucial for suppressing HDM-induced allergic airway inflammation, possibly inducing SCD1 expression in AECs.