Mechanisms of Pediatric Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD), including Crohn disease and ulcerative colitis, is characterized by chronic intestinal inflammation due to a complex interaction of genetic determinants, disruption of mucosal barriers, aberrant inflammatory signals, loss of tolerance, and environmental triggers. Importantly, the incidence of pediatric IBD is rising, particularly in children younger than 10 years. In this review, we discuss the clinical presentation of these patients and highlight environmental exposures that may affect disease risk, particularly among people with a background genetic risk. With regard to both children and adults, we review advancements in understanding the intestinal epithelium, the mucosal immune system, and the resident microbiota, describing how dysfunction at any level can lead to diseases like IBD. We conclude with future directions for applying advances in IBD genetics to better understand pathogenesis and develop therapeutics targeting key pathogenic nodes.

Mucus sialylation determines intestinal host-commensal homeostasis.

Intestinal mucus forms the first line of defense against bacterial invasion while providing nutrition to support microbial symbiosis. How the host controls mucus barrier integrity and commensalism is unclear. We show that terminal sialylation of glycans on intestinal mucus by ST6GALNAC1 (ST6), the dominant sialyltransferase specifically expressed in goblet cells and induced by microbial pathogen-associated molecular patterns, is essential for mucus integrity and protecting against excessive bacterial proteolytic degradation. Glycoproteomic profiling and biochemical analysis of ST6 mutations identified in patients show that decreased sialylation causes defective mucus proteins and congenital inflammatory bowel disease (IBD). Mice harboring a patient ST6 mutation have compromised mucus barriers, dysbiosis, and susceptibility to intestinal inflammation. Based on our understanding of the ST6 regulatory network, we show that treatment with sialylated mucin or a Foxo3 inhibitor can ameliorate IBD.

M cell maturation and cDC activation determine the onset of adaptive immune priming in the neonatal Peyer's patch.

Early-life immune development is critical to long-term host health. However, the mechanisms that determine the pace of postnatal immune maturation are not fully resolved. Here, we analyzed mononuclear phagocytes (MNPs) in small intestinal Peyer's patches (PPs), the primary inductive site of intestinal immunity. Conventional type 1 and 2 dendritic cells (cDC1 and cDC2) and RORgt+ antigen-presenting cells (RORgt+ APC) exhibited significant age-dependent changes in subset composition, tissue distribution, and reduced cell maturation, subsequently resulting in a lack in CD4+ T cell priming during the postnatal period. Microbial cues contributed but could not fully explain the discrepancies in MNP maturation. Type I interferon (IFN) accelerated MNP maturation but IFN signaling did not represent the physiological stimulus. Instead, follicle-associated epithelium (FAE) M cell differentiation was required and sufficient to drive postweaning PP MNP maturation. Together, our results highlight the role of FAE M cell differentiation and MNP maturation in postnatal immune development.

A Map of Toll-like Receptor Expression in the Intestinal Epithelium Reveals Distinct Spatial, Cell Type-Specific, and Temporal Patterns.

Signaling by Toll-like receptors (TLRs) on intestinal epithelial cells (IECs) is critical for intestinal homeostasis. To visualize epithelial expression of individual TLRs in vivo, we generated five strains of reporter mice. These mice revealed that TLR expression varied dramatically along the length of the intestine. Indeed, small intestine (SI) IECs expressed low levels of multiple TLRs that were highly expressed by colonic IECs. TLR5 expression was restricted to Paneth cells in the SI epithelium. Intestinal organoid experiments revealed that TLR signaling in Paneth cells or colonic IECs induced a core set of host defense genes, but this set did not include antimicrobial peptides, which instead were induced indirectly by inflammatory cytokines. This comprehensive blueprint of TLR expression and function in IECs reveals unexpected diversity in the responsiveness of IECs to microbial stimuli, and together with the associated reporter strains, provides a resource for further study of innate immunity.

Enteric neuro-immune interactions in intestinal health and disease.

The enteric nervous system is an autonomous neuronal circuit that regulates many processes far beyond the peristalsis in the gastro-intestinal tract. This circuit, consisting of enteric neurons and enteric glial cells, can engage in many intercellular interactions shaping the homeostatic microenvironment in the gut. Perhaps the most well documented interactions taking place, are the intestinal neuro-immune interactions which are essential for the fine-tuning of oral tolerance. In the context of intestinal disease, compelling evidence demonstrates both protective and detrimental roles for this bidirectional neuro-immune signaling. This review discusses the different immune cell types that are recognized to engage in neuronal crosstalk during intestinal health and disease. Highlighting the molecular pathways involved in the neuro-immune interactions might inspire novel strategies to target intestinal disease.

S-adenosyl-L-methionine supplementation alleviates damaged intestinal epithelium and inflammatory infiltration caused by Mat2a deficiency.

Methionine is important for intestinal development and homeostasis in various organisms. However, the underlying mechanisms are poorly understood. Here, we demonstrate that the methionine adenosyltransferase gene Mat2a is essential for intestinal development and that the metabolite S-adenosyl-L-methionine (SAM) plays an important role in intestinal homeostasis. Intestinal epithelial cell (IEC)-specific knockout of Mat2a exhibits impaired intestinal development and neonatal lethality. Mat2a deletion in the adult intestine reduces cell proliferation and triggers IEC apoptosis, leading to severe intestinal epithelial atrophy and intestinal inflammation. Mechanistically, we reveal that SAM maintains the integrity of differentiated epithelium and protects IECs from apoptosis by suppressing the expression of caspases 3 and 8 and their activation. SAM supplementation improves the defective intestinal epithelium and reduces inflammatory infiltration sequentially. In conclusion, our study demonstrates that methionine metabolism and its intermediate metabolite SAM play essential roles in intestinal development and homeostasis in mice.

Bacterial indole-3-lactic acid affects epithelium-macrophage crosstalk to regulate intestinal homeostasis.

Tryptophan and its derivatives perform a variety of biological functions; however, the role and specific mechanism of many tryptophan derivatives in intestinal inflammation remain largely unclear. Here, we identified that an Escherichia coli strain (Ec-TMU) isolated from the feces of tinidazole-treated individuals, and indole-3-lactic acid (ILA) in its supernatant, decreased the susceptibility of mice to dextran sulfate sodium-induced colitis. Ec-TMU and ILA contribute to the relief of colitis by inhibiting the production of epithelial CCL2/7, thereby reducing the accumulation of inflammatory macrophages in vitro and in vivo. Mechanistically, ILA downregulates glycolysis, NF-κB, and HIF signaling pathways via the aryl hydrocarbon receptor, resulting in decreased CCL2/7 production in epithelial cells. Clinical evidence suggests that the fecal ILA level is negatively correlated with the progression indicator of inflammatory bowel diseases. These results demonstrate that ILA has the potential to regulate intestinal homeostasis by modulating epithelium-macrophage interactions.

Modelling the dynamics of mammalian gut homeostasis.

Homeostatic balance in the intestinal epithelium relies on a fast cellular turnover, which is coordinated by an intricate interplay between biochemical signalling, mechanical forces and organ geometry. We review recent modelling approaches that have been developed to understand different facets of this remarkable homeostatic equilibrium. Existing models offer different, albeit complementary, perspectives on the problem. First, biomechanical models aim to explain the local and global mechanical stresses driving cell renewal as well as tissue shape maintenance. Second, compartmental models provide insights into the conditions necessary to keep a constant flow of cells with well-defined ratios of cell types, and how perturbations can lead to an unbalance of relative compartment sizes. A third family of models address, at the cellular level, the nature and regulation of stem fate choices that are necessary to fuel cellular turnover. We also review how these different approaches are starting to be integrated together across scales, to provide quantitative predictions and new conceptual frameworks to think about the dynamics of cell renewal in complex tissues.

RANKL and RANK in Cancer Therapy.

Receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) are key regulators of mammalian physiology such as bone metabolism, immune tolerance and antitumor immunity, and mammary gland biology. Here, we explore the multiple functions of RANKL/RANK in physiology and pathophysiology and discuss underlying principles and strategies to modulate the RANKL/RANK pathway as a therapeutic target in immune-mediated cancer treatment.

Toll-like receptor 13-mediated signaling protects against the development of colon cancer.

Appropriate host-microbiota interactions are essential for maintaining intestinal homeostasis; hence, an imbalance in these interactions leads to inflammation-associated intestinal diseases. Toll-like receptors (TLRs) recognize microbial ligands and play a key role in host-microbe interactions in health and disease. TLR13 has a well-established function in enhancing host defenses against pathogenic bacteria. However, its role in maintaining intestinal homeostasis and controlling colitis-associated colon cancer (CAC) is largely unknown. This study aimed to investigate the involvement of TLR13-mediated signaling in intestinal homeostasis and colonic tumorigenesis using ex vivo cell and in vivo CAC animal model. Tlr13-deficient mice were prone to dextran sodium sulfate (DSS)-induced colitis. During the early stages of the CAC regimen (AOM/DSS-treated), Tlr13 deficiency led to severe ulcerative colitis. Moreover, Tlr13-deficient mice exhibited increased intestinal permeability, as evidenced by elevated levels of fluorescein isothiocyanate (FITC)-dextran, endotoxins, and bacterial translocation. Enhanced cell survival and proliferation of colonic intestinal cells were observed in Tlr13-deficient mice. A transcriptome analysis revealed that Tlr13 deficiency is associated with substantial changes in gene expression profile of colonic tumor tissue. Tlr13-deficient mice were more susceptible to CAC, with increased production of interleukin (IL)-6, IL-12, and TNF-α cytokines and enhanced STAT3, NF-κB, and MAPK signaling in colon tissues. These findings suggest that TLR13 plays a protective role in maintaining intestinal homeostasis and controlling CAC. Our study provides a novel perspective on intestinal health via TLR13-mediated signaling, which is crucial for deciphering the role of host-microbiota interactions in health and disease.

Long-term exposure from perinatal life to food-grade TiO2 alters intestinal homeostasis and predisposes to food allergy in young mice.

BACKGROUND: Food allergy (FA) is an inappropriate immunological response to food proteins resulting from an impaired induction of oral tolerance. Various early environmental factors can affect the establishment of intestinal homeostasis, predisposing to FA in early life. In this context, we aimed to assess the effect of chronic perinatal exposure to food-grade titanium dioxide (fg-TiO2 ), a common food additive. METHODS: Dams were fed a control versus fg-TiO2 -enriched diet from preconception to weaning, and their progeny received the same diet at weaning. A comprehensive analysis of baseline intestinal and systemic homeostasis was performed in offspring 1 week after weaning by assessing gut barrier maturation and microbiota composition, and local and systemic immune system and metabolome. The effect of fg-TiO2 on the susceptibility of progeny to develop oral tolerance versus FA to cow's milk proteins (CMP) was performed starting at the same baseline time-point, using established models. Sensitization to CMP was investigated by measuring ß-lactoglobulin and casein-specific IgG1 and IgE antibodies, and elicitation of the allergic reaction by measuring mouse mast cell protease (mMCP1) in plasma collected after an oral food challenge. RESULTS: Perinatal exposure to fg-TiO2 at realistic human doses led to an increased propensity to develop FA and an impaired induction of oral tolerance only in young males, which could be related to global baseline alterations in intestinal barrier, gut microbiota composition, local and systemic immunity, and metabolism. CONCLUSIONS: Long-term perinatal exposure to fg-TiO2 alters intestinal homeostasis establishment and predisposes to food allergy, with a clear gender effect.

Epithelial CRL4DCAF2 Is Critical for Maintaining Intestinal Homeostasis Against DSS-Induced Colitis by Regulating the Proliferation and Repair of Intestinal Epithelial Cells.

BACKGROUND AND AIMS: Inflammatory bowel disease (IBD) is currently gaining an increasing global interest. Intestinal epithelial barrier dysfunction is crucial toward developing IBD; however, the underlying mechanisms are not yet elucidated. This study is aimed at elucidating the function of CRL4DCAF2, an E3 ligase, toward mediating intestinal homeostasis. METHODS: Colon samples were collected from patients with IBD and healthy individuals to examine the expression of CRL4DCAF2. CRL4DCAF2 conditional knockdown in mouse intestinal epithelial cells (IECs) (DCAF2EKD) were constructed. DCAF2EKD and their littermate control (DCAF2EWT) were treated with dextran sodium sulfate (DSS) to induce acute colitis. Transcriptome analysis was performed on inflamed colon samples obtained from the mice. Cell cycle regulators were evaluated using real-time polymerase chain reaction (PCR), while tight junction and apoptosis proteins were examined via immunofluorescence and western blot. RESULTS: CRL4DCAF2 expression was significantly decreased in the inflamed IBD epithelium, and low expression of CRL4DCAF2 associated with high recurrence risk. Mice with DCAF2 specific knockout in IECs suffer from embryonic death. Multiple genes involved in cell proliferation, immune response, and gap junction were differentially expressed in inflamed colon from DCAF2EKD compared with DCAF2EWT. Furthermore, conditional downregulation of CRL4DCAF2 in the intestinal epithelium induced primarily epithelial damage, increased intestinal permeability, and diminished tight junction protein expression. In vivo and in vitro cell transfection experiments revealed that CRL4DCAF2 enhanced cell proliferation by promoting p21 ubiquitination and degradation, thereby inhibiting G2/M cell cycle. In addition, CRL4DCAF2 can also inhibit IEC apoptosis and promote cell autophagy. CONCLUSIONS: CRL4DCAF2 downregulation in IECs promotes intestinal barrier dysfunction and inhibits IEC proliferation, thus making it more susceptible to inflammation.

Orally biomimetic metal-phenolic nanozyme with quadruple safeguards for intestinal homeostasis to ameliorate ulcerative colitis.

BACKGROUND: Ulcerative colitis (UC) is defined by persistent inflammatory processes within the gastrointestinal tract of uncertain etiology. Current therapeutic approaches are limited in their ability to address oxidative stress, inflammation, barrier function restoration, and modulation of gut microbiota in a coordinated manner to maintain intestinal homeostasis. RESULTS: This study involves the construction of a metal-phenolic nanozyme (Cur-Fe) through a ferric ion-mediated oxidative coupling of curcumin. Cur-Fe nanozyme exhibits superoxide dismutase (SOD)-like and •OH scavenging activities, demonstrating significant anti-inflammatory and anti-oxidant properties for maintaining intracellular redox balance in vitro. Drawing inspiration from Escherichia coli Nissle 1917 (EcN), a biomimetic Cur-Fe nanozyme (CF@EM) is subsequently developed by integrating Cur-Fe into the EcN membrane (EM) to improve the in vivo targeting ability and therapeutic effectiveness of the Cur-Fe nanozyme. When orally administered, CF@EM demonstrates a strong ability to colonize the inflamed colon and restore intestinal redox balance and barrier function in DSS-induced colitis models. Importantly, CF@EM influences the gut microbiome towards a beneficial state by enhancing bacterial diversity and shifting the compositional structure toward an anti-inflammatory phenotype. Furthermore, analysis of intestinal microbial metabolites supports the notion that the therapeutic efficacy of CF@EM is closely associated with bile acid metabolism. CONCLUSION: Inspired by gut microbes, we have successfully synthesized a biomimetic Cur-Fe nanozyme with the ability to inhibit inflammation and restore intestinal homeostasis. Collectively, without appreciable systemic toxicity, this work provides an unprecedented opportunity for targeted oral nanomedicine in the treatment of ulcerative colitis.

Involvement of Embryo-Derived and Monocyte-Derived Intestinal Macrophages in the Pathogenesis of Inflammatory Bowel Disease and Their Prospects as Therapeutic Targets.

Inflammatory bowel disease (IBD) is a group of intestinal inflammatory diseases characterized by chronic, recurrent, remitting, or progressive inflammation, which causes the disturbance of the homeostasis between immune cells, such as macrophages, epithelial cells, and microorganisms. Intestinal macrophages (IMs) are the largest population of macrophages in the body, and the abnormal function of IMs is an important cause of IBD. Most IMs come from the replenishment of blood monocytes, while a small part come from embryos and can self-renew. Stimulated by the intestinal inflammatory microenvironment, monocyte-derived IMs can interact with intestinal epithelial cells, intestinal fibroblasts, and intestinal flora, resulting in the increased differentiation of proinflammatory phenotypes and the decreased differentiation of anti-inflammatory phenotypes, releasing a large number of proinflammatory factors and aggravating intestinal inflammation. Based on this mechanism, inhibiting the secretion of IMs' proinflammatory factors and enhancing the differentiation of anti-inflammatory phenotypes can help alleviate intestinal inflammation and promote tissue repair. At present, the clinical medication of IBD mainly includes 5-aminosalicylic acids (5-ASAs), glucocorticoid, immunosuppressants, and TNF-α inhibitors. The general principle of treatment is to control acute attacks, alleviate the condition, reduce recurrence, and prevent complications. Most classical IBD therapies affecting IMs function in a variety of ways, such as inhibiting the inflammatory signaling pathways and inducing IM2-type macrophage differentiation. This review explores the current understanding of the involvement of IMs in the pathogenesis of IBD and their prospects as therapeutic targets.

Effects of Probiotics on Gut Microbiota: An Overview.

The role of probiotics in regulating intestinal flora to enhance host immunity has recently received widespread attention. Altering the human gut microbiota may increase the predisposition to several disease phenotypes such as gut inflammation and metabolic disorders. The intestinal microbiota converts dietary nutrients into metabolites that serve as biologically active molecules in modulating regulatory functions in the host. Probiotics, which are active microorganisms, play a versatile role in restoring the composition of the gut microbiota, helping to improve host immunity and prevent intestinal disease phenotypes. This comprehensive review provides firsthand information on the gut microbiota and their influence on human health, the dietary effects of diet on the gut microbiota, and how probiotics alter the composition and function of the human gut microbiota, along with their corresponding effects on host immunity in building a healthy intestine. We also discuss the implications of probiotics in some of the most important human diseases. In summary, probiotics play a significant role in regulating the gut microbiota, boosting overall immunity, increasing the abundance of beneficial bacteria, and helping ameliorate the symptoms of multiple diseases.

Wuliangye strong aroma baijiu promotes intestinal homeostasis by improving gut microbiota and regulating intestinal stem cell proliferation and differentiation.

BACKGROUND: Wuliangye strong aroma baijiu (hereafter, Wuliangye baijiu) is a traditional Chinese grain liquor containing short-chain fatty acids, ethyl caproate, ethyl lactate, other trace components, and a large proportion of ethanol. The effects of Wuliangye baijiu on intestinal stem cells and intestinal epithelial development have not been elucidated. Here, the role of Wuliangye baijiu in intestinal epithelial regeneration and gut microbiota modulation was investigated by administering a Lieber-DeCarli chronic ethanol liquid diet in a mouse model to mimic long-term (8 weeks') light/moderate alcohol consumption (1.6 g kg-1 day-1) in healthy human adults. RESULTS: Wuliangye baijiu promoted colonic crypt proliferation in mice. According to immunofluorescence and reverse transcription-quantitative polymerase chain reaction analyses, compared with the ethanol-only treatment, Wuliangye baijiu increased the number of intestinal stem cells and goblet cells and the expression of enteroendocrine cell differentiation markers in the mouse colon. Furthermore, gut microbiota analysis showed an increase in the relative abundance of microbiota related to intestinal homeostasis following Wuliangye baijiu administration. Notably, increased abundance of Bacteroidota, Faecalibaculum, Lachnospiraceae, and Blautia may play an essential role in promoting stem-cell-mediated intestinal epithelial development and maintaining intestinal homeostasis. CONCLUSIONS: In summary, these findings suggest that Wuliangye baijiu can be used to regulate intestinal stem cell proliferation and differentiation in mice and to alter gut microbiota distributions, thereby promoting intestinal homeostasis. This research elucidates the mechanism by which Wuliangye baijiu promotes intestinal health. © 2024 Society of Chemical Industry.

GPR120 Inhibits Colitis Through Regulation of CD4+ T Cell Interleukin 10 Production.

BACKGROUND & AIMS: G protein-coupled receptor (GPR) 120 has been implicated in regulating metabolic syndromes with anti-inflammatory function. However, the role of GPR120 in intestinal inflammation is unknown. Here, we investigated whether and how GPR120 regulates CD4+ T cell function to inhibit colitis development. METHODS: Dextran sodium sulfate (DSS)-induced colitis model, Citrobacter rodentium infection model, and CD4+ T cell adoptive transfer model were used to analyze the role of GPR120 in regulating colitis development. The effect of GPR120 on CD4+ T cell functions was analyzed by RNA sequencing, flow cytometry, and Seahorse metabolic assays. Mice were administered GPR120 agonist for investigating the potential of GPR120 agonist in preventing and treating colitis. RESULTS: Deficiency of GPR120 in CD4+ T cells resulted in more severe colitis in mice upon dextran sodium sulfate insult and enteric infection. Transfer of GPR120-deficient CD4+CD45Rbhi T cells induced more severe colitis in Rag-/- mice with lower intestinal interleukin (IL) 10+CD4+ T cells. Treatment with the GPR120 agonist CpdA promoted CD4+ T cell production of IL10 by up-regulating Blimp1 and enhancing glycolysis, which was regulated by mTOR. GPR120 agonist-treated wild-type, but not IL10-deficient and Blimp1-deficient, T helper 1 cells induced less severe colitis. Furthermore, oral administration of GPR120 agonist protected mice from intestinal inflammation in both prevention and treatment schemes. Gpr120 expression was positively correlated with Il10 expression in the human colonic mucosa, including patients with inflammatory bowel diseases. CONCLUSIONS: Our findings show the role of GPR120 in regulating intestinal CD4+ T cell production of IL10 to inhibit colitis development, which identifies GPR120 as a potential therapeutic target for treating inflammatory bowel diseases.

Tryptophan and the innate intestinal immunity: Crosstalk between metabolites, host innate immune cells, and microbiota.

The intestinal mucosal barrier is critical for the absorption of nutrients and the health of both humans and animals. Recent publications from clinical and experimental studies have shown the importance of the nutrients-bacteria-host interaction for the intestinal homeostasis. Dysfunction of these interactions has been reported to be associated with metabolic disorders and development of intestinal diseases such as the irritable bowel syndrome and inflammatory bowel diseases. Tryptophan and its metabolites, including kynurenine, kynurenic acid, and 5-hydroxytrptamine, can influence the proliferation of enterocytes, intestinal integrity, and immune response, as well as intestinal microbiota, therefore, regulating and contributing to the intestinal health. In this review, we highlight recent findings on the effect of tryptophan and its metabolites on the mucosal barrier and intestinal homeostasis and its regulation of innate immune response. Moreover, we present the signaling pathways related to Trp metabolism, such as mammalian target of rapamycin, aryl hydrocarbon receptor, and pregnane X receptor, which contribute to the intestinal homeostasis and discuss future perspectives on spontaneous interference in host tryptophan metabolism as potential clinical strategies of intestinal diseases.

Microplastics perturb colonic epithelial homeostasis associated with intestinal overproliferation, exacerbating the severity of colitis.

A great amount of the population died due to living or working in an unhealthy environment, highlighting the critical role of environmental pollutants in inducing diseases. Microplastics are widespread environmental pollutants and have been found in various tissues of human beings, yet the risk of microplastics in the occurrence of disease, especially environmentally-related colitis, is unclear. This study focused on the effects of microplastics exposure on intestinal homeostasis and the initiation of colitis. We noticed that microplastics exposure had a limited impact on mice, as verified by no difference observed in bodyweight change, IL-1ß and IL-6 levels in jejunum and liver. Nevertheless, in the colon, the IL-1ß and IL-6 levels were slightly increased and the goblet cell number was decreased. Interestingly, we observed that crypt number and depth, the levels of intestinal stem cell markers, combined with the expression of proliferating cell nuclear antigen and proto-oncogene c-Myc were all significantly increased with microplastics treatment, indicating the overproliferation of colonic mucosa. The effect of microplastics on proliferation and differentiation of crypt was further demonstrated to be regulated by the overactivation of the Notch signaling pathway in intestinal organoids. Furthermore, microplastics exposure accelerated the development of colitis with severe bodyweight loss, diarrhea and bloody stools, macroscopic and pathological damage, and inflammation levels. Worsened liver pathological damage and inflammation in mice with colitis under microplastics exposure also were found. These results suggested that microplastics disrupted the balance between colonic epithelium self-renewal and differentiation, exacerbating the colitis, and might be an environmental-related disease risk factor.

Functions and regulation of T cell-derived interleukin-10.

Interleukin (IL)-10 is an essential anti-inflammatory cytokine and functions as a negative regulator of immune responses to microbial antigens. IL-10 is particularly important in maintaining the intestinal microbe-immune homeostasis. Loss of IL-10 promotes the development of inflammatory bowel disease (IBD) as a consequence of an excessive immune response to the gut microbiota. IL-10 also functions more generally to prevent excessive inflammation during the course of infection. Although IL-10 can be produced by virtually all cells of the innate and adaptive immune system, T cells constitute a non-redundant source for IL-10 in many cases. The various roles of T cell-derived IL-10 will be discussed in this review. Given that IL-10 is at the center of maintaining the delicate balance between effective immunity and tissue protection, it is not surprising that IL-10 expression is highly dynamic and tightly regulated. We summarize the environmental signals and molecular pathways that regulate IL-10 expression. While numerous studies have provided us with a deep understanding of IL-10 biology, the majority of findings have been made in murine models, prompting us to highlight gaps in our knowledge about T cell-derived IL-10 in the human system.