Blocking IL-25 signalling protects against gut inflammation in a type-2 model of colitis by suppressing nuocyte and NKT derived IL-13

Tuft cell IL-17RB restrains IL-25 bioavailability and reveals context-dependent ILC2 hypoproliferation

The tuft cell-ILC2 circuit orchestrates rapid type 2 responses upon detecting microbe-derived succinate and luminal helminths. Our findings delineate key mechanistic steps, involving IP3R2 engagement and Ca 2+ flux, governing IL-25 production by tuft cells triggered by succinate detection. While IL-17RB plays a pivotal intrinsic role in ILC2 activation, it exerts a regulatory function in tuft cells. Tuft cells exhibit constitutive Il25 expression, placing them in an anticipatory state that facilitates rapid production of IL-25 protein for ILC2 activation. Tuft cell IL-17RB is crucial for restraining IL-25 bioavailability, preventing excessive tonic ILC2 stimulation due to basal Il25 expression. Suboptimal ILC2 stimulation by IL-25 resulting from tuft cell Il17rb -deficiency or prolonged succinate exposure induces a state of hypoproliferation in ILC2s, also observed in chronic helminth infection. Our study offers critical insights into the regulatory dynamics of IL-25 in this circuit, highlighting the delicate tuning required for responses to diverse luminal states.

Innate Type-2 Cytokines: From Immune Regulation to Therapeutic Targets

The intricate role of innate type-2 cytokines in immune responses is increasingly acknowledged for its dual nature, encompassing both protective and pathogenic dimensions. Ranging from defense against parasitic infections to contributing to inflammatory diseases like asthma, fibrosis, and obesity, these cytokines intricately engage with various innate immune cells. This review meticulously explores the cellular origins of innate type-2 cytokines and their intricate interactions, shedding light on factors that amplify the innate type-2 response, including TSLP, IL-25, and IL-33. Recent advancements in therapeutic strategies, specifically the utilization of biologics targeting pivotal cytokines (IL-4, IL-5, and IL-13), are discussed, offering insights into both challenges and opportunities. Acknowledging the pivotal role of innate type-2 cytokines in orchestrating immune responses positions them as promising therapeutic targets. The evolving landscape of research and development in this field not only propels immunological knowledge forward but also holds the promise of more effective treatments in the future.

Based on Weighted Gene Co-Expression Network Analysis Reveals the Hub Immune Infiltration-Related Genes Associated with Ulcerative Colitis

Purpose

Immune infiltration plays a pivotal role in the pathogenesis of mucosal damage in ulcerative colitis (UC). The objective of this study was to systematically analyze and identify genetic characteristics associated with immune infiltration in UC.

Patients and Methods

Gene expression data from three independent datasets obtained from the Gene Expression Omnibus (GEO) were utilized. By employing the ssGSEA and CIBERSORT algorithms, we estimated the extent of immune cell infiltration in UC samples. Subsequently, Weighted Correlation Network Analysis (WGCNA) was performed to identify gene modules exhibiting significant associations with immune infiltration, and further identification of hub genes associated with immune infiltration was accomplished using least absolute shrinkage and selection operator (LASSO) regression analysis. The relationship between the identified hub genes and clinical information was subsequently investigated.

Results

Our findings revealed significant activation of both innate and adaptive immune cells in UC. Notably, the expression levels of CD44, IL1B, LYN, and ITGA5 displayed strong correlations with immune cell infiltration within the mucosa of UC patients. Immunohistochemical analysis confirmed the significant upregulation of CD44, LYN, and ITGA5 in UC samples, and their expression levels were found to be significantly associated with common inflammatory markers, including the systemic immune inflammation indices, C-reactive protein, and erythrocyte sedimentation rate.

Conclusion

CD44, LYN, and ITGA5 are involved in the immune infiltration pathogenesis of UC and may be potential therapeutic targets for UC.

Role of CD1d and iNKT cells in regulating intestinal inflammation

Invariant natural killer T (iNKT) cells, a subset of unconventional T cells that recognize glycolipid antigens in a CD1d-dependent manner, are crucial in regulating diverse immune responses such as autoimmunity. By engaging with CD1d-expressing non-immune cells (such as intestinal epithelial cells and enterochromaffin cells) and immune cells (such as type 3 innate lymphoid cells, B cells, monocytes and macrophages), iNKT cells contribute to the maintenance of immune homeostasis in the intestine. In this review, we discuss the impact of iNKT cells and CD1d in the regulation of intestinal inflammation, examining both cellular and molecular factors with the potential to influence the functions of iNKT cells in inflammatory bowel diseases such as Crohn's disease and ulcerative colitis.

Disease pathogenesis and barrier functions regulated by group 3 innate lymphoid cells

The mucosal surface is in constant contact with foreign antigens and is regulated by unique mechanisms that are different from immune responses in the peripheral organs. For the last several decades, only adaptive immune cells such as helper T (Th) cells, Th1, Th2, or Th17 were targeted to study a wide variety of immune responses in the mucosal tissues. However, since their discovery, innate lymphoid cells (ILCs) have been attracting attention as a unique subset of immune cells that provide border defense with various functions and tissue specificity. ILCs are classified into different groups based on cell differentiation and functions. Group 3 innate lymphoid cells (ILC3s) are particularly in close proximity to mucosal surfaces and therefore have the opportunity to be exposed to a variety of bacteria including pathogenic bacteria. In recent years, studies have also provided much evidence that ILC3s contribute to disease pathogenesis as well as the defense of mucosal surfaces by rapidly responding to pathogens and coordinating other immune cells. As the counterpart of helper T cells, ILC3s together with other ILC subsets establish the immune balance between adaptive and innate immunity in protecting us from invasion or encounter with non-self-antigens for maintaining a complex homeostasis. In this review, we summarize recent advances in our understanding of ILCs, with a particular focus on the function of ILC3s in their involvement in bacterial infection and disease pathogenesis.

ILC2s control obesity by regulating energy homeostasis and browning of white fat

Innate lymphoid cells (ILCs) have been a hot topic in recent research, they are widely distributed in vivo and play an important role in different tissues. The important role of group 2 innate lymphoid cells (ILC2s) in the conversion of white fat into beige fat has attracted widespread attention. Studies have shown that ILC2s regulate adipocyte differentiation and lipid metabolism. This article reviews the types and functions of ILCs, focusing on the relationship between differentiation, development and function of ILC2s, and elaborates on the relationship between peripheral ILC2s and browning of white fat and body energy homeostasis. This has important implications for the future treatment of obesity and related metabolic diseases.

Innate lymphoid cells and innate-like T cells in cancer - at the crossroads of innate and adaptive immunity

Immunotherapies targeting conventional T cells have revolutionized systemic treatment for many cancers, yet only a subset of patients benefit from these approaches. A better understanding of the complex immune microenvironment of tumours is needed to design the next generation of immunotherapeutics. Innate lymphoid cells (ILCs) and innate-like T cells (ILTCs) are abundant, tissue-resident lymphocytes that have recently been shown to have critical roles in many types of cancers. ILCs and ILTCs rapidly respond to changes in their surrounding environment and act as the first responders to bridge innate and adaptive immunity. This places ILCs and ILTCs as pivotal orchestrators of the final antitumour immune response. In this Review, we outline hallmarks of ILCs and ILTCs and discuss their emerging role in antitumour immunity, as well as the pathophysiological adaptations leading to their pro-tumorigenic function. We explore the pleiotropic, in parts redundant and sometimes opposing, mechanisms that underlie the delicate interplay between the different subsets of ILCs and ILTCs. Finally, we highlight their role in amplifying and complementing conventional T cell functions and summarize immunotherapeutic strategies for targeting ILCs and ILTCs in cancer.

Maternal dietary exposure to mycotoxin aflatoxin B1 promotes intestinal immune alterations and microbiota modifications increasing infection susceptibility in mouse offspring

Mycotoxins are secondary metabolites produced by fungi occurring in food that are toxic to animals and humans. Early-life mycotoxins exposure has been linked to diverse pathologies. However, how maternal exposure to mycotoxins impacts on the intestinal barrier function of progeny has not been explored. Here, exposure of pregnant and lactating C57Bl/6J female mice to aflatoxin B₁ (AFB₁; 400 μg/kg body weight/day; 3 times a week) in gelatine pellets, from embryonic day (E)11.5 until weaning (postnatal day 21), led to gut immunological changes in progeny. The results showed an overall increase of lymphocyte number in intestine, a reduction of expression of epithelial genes related to microbial defence, as well as a decrease in cytokine production by intestinal type 2 innate lymphoid cells (ILC2). While susceptibility to chemically induced colitis was not worsened, immune alterations were associated with changes in gut microbiota and with a higher vulnerability to infection by the protozoan Eimeria vermiformis at early-life. Together these results show that maternal dietary exposure to AFB₁ can dampen intestinal barrier homeostasis in offspring decreasing their capability to tackle intestinal pathogens. These data provide insights to understand AFB₁ potential harmfulness in early-life health in the context of intestinal infections.

Could IL-25 be a potential therapeutic target for intestinal inflammatory diseases?

As a member of the IL-17 cytokine family, IL-25 (also called IL-17E) induces and sustains type 2 immunity. IL-25, which is mainly produced by intestinal epithelial cells, has been gradually investigated in recent years for its function in intestinal inflammation but is not yet fully understood. This review summarizes the expression and function of IL-25 in the intestine, especially the progression of its regulatory role on type 2 immunity-related cells. Finally, we discuss the dual role of IL-25 based on inflammatory bowel disease to inform research on targeting IL-25 for the treatment of intestinal inflammatory diseases.

Interleukin 25 and its biological features and function in intestinal diseases

Interleukin 25 (IL-25), also known as IL-17E, is a member of the IL-17 cytokine family and an important regulator of the type 2 immune response. Accumulating evidence suggests that IL-25 interacts with diverse immune as well as non-immune cells and plays a rather complicated role in different backgrounds of multiple organs. IL-25 has been studied in the physiology and pathology of the intestine to some extent. With epithelial cells being an important source in the intestine, IL-25 plays a key role in intestinal immune responses and is associated with inappropriate allergic reactions, autoimmune diseases, and cancer tumorigenesis. In this review, we discuss the emerging comprehension of the biology of IL-25, as well as its cellular sources, targets, and signaling transduction. In particular, we discuss how IL-25 participates in the development of intestinal diseases including helminth infection, inflammatory bowel diseases, food allergy and colorectal cancer, as well as its underlying role in future therapy.

Development of Adaptive Immunity and Its Role in Lung Remodeling

Asthma is characterized by airflow limitations resulting from bronchial closure, which can be either reversible or fixed due to changes in airway tissue composition and structure, also known as remodeling. Airway remodeling is defined as increased presence of mucins-producing epithelial cells, increased thickness of airway smooth muscle cells, angiogenesis, increased number and activation state of fibroblasts, and extracellular matrix (ECM) deposition. Airway inflammation is believed to be the main cause of the development of airway remodeling in asthma. In this chapter, we will review the development of the adaptive immune response and the impact of its mediators and cells on the elements defining airway remodeling in asthma.

TSLP, IL-33, and IL-25: Not just for allergy and helminth infection

The release of cytokines from epithelial and stromal cells is critical for the initiation and maintenance of tissue immunity. Three such cytokines, thymic stromal lymphopoietin, IL-33, and IL-25, are important regulators of type 2 immune responses triggered by parasitic worms and allergens. In particular, these cytokines activate group 2 innate lymphoid cells, TH2 cells, and myeloid cells, which drive hallmarks of type 2 immunity. However, emerging data indicate that these tissue-associated cytokines are not only involved in canonical type 2 responses but are also important in the context of viral infections, cancer, and even homeostasis. Here, we provide a brief review of the roles of thymic stromal lymphopoietin, IL-33, and IL-25 in diverse immune contexts, while highlighting their relative contributions in tissue-specific responses. We also emphasize a biologically motivated framework for thinking about the integration of multiple immune signals, including the 3 featured in this review.

A pathogenic integrated view explaining the different endotypes of asthma and allergic disorders

The inflammation of allergic diseases is characterized by a complex interaction between type 2 and type 3 immune responses, explaining clinical symptoms and histopathological patterns. Airborne stimuli activate the mucosal epithelium to release a number of molecules impacting the activity of resident immune and environmental cells. Signals from the mucosal barrier, regulatory cells, and the inflamed tissue are crucial conditions able to modify innate and adaptive effector cells providing the selective homing of eosinophils or neutrophils. The high plasticity of resident T- and innate lymphoid cells responding to external signals is the prerequisite to explain the multiplicity of endotypes of allergic diseases. This notion paved the way for the huge use of specific biologic drugs interfering with pathogenic mechanisms of inflammation. Based on the response of the epithelial barrier, the activity of resident regulatory cells, and functions of structural non-lymphoid environmental cells, this review proposes some immunopathogenic scenarios characterizing the principal endotypes which can be associated with a precise phenotype of asthma. Recent literature indicates that similar concepts can also be applied to the inflammation of other non-respiratory allergic disorders. The next challenges will consist in defining specific biomarker(s) of each endotype allowing for a quick diagnosis and the most effective personalized therapy.

Enrichment of type I interferon signaling in colonic group 2 innate lymphoid cells in experimental colitis

Group 2 innate lymphoid cells (ILC2s) serve as frontline defenses against parasites. However, excluding helminth infections, it is poorly understood how ILC2s function in intestinal inflammation, including inflammatory bowel disease. Here, we analyzed the global gene expression of ILC2s in healthy and colitic conditions and revealed that type I interferon (T1IFN)-stimulated genes were up-regulated in ILC2s in dextran sodium sulfate (DSS)-induced colitis. The enhancement of T1IFN signaling in ILC2s in DSS-induced colitis was correlated with the downregulation of cytokine production by ILC2s, such as interleukin-5. Blocking T1IFN signaling during colitis resulted in exaggeration of colitis in both wild-type and Rag2-deficient mice. The exacerbation of colitis induced by neutralization of T1IFN signaling was accompanied by reduction of amphiregulin (AREG) in ILC2s and was partially rescued by exogenous AREG treatment. Collectively, these findings show the potential roles of T1IFN in ILC2s that contribute to colitis manifestation.

Inflammatory Bowel Disease: A Review of Pre-Clinical Murine Models of Human Disease

Crohn’s disease (CD) and ulcerative colitis (UC) are both highly inflammatory diseases of the gastrointestinal tract, collectively known as inflammatory bowel disease (IBD). Although the cause of IBD is still unclear, several experimental IBD murine models have enabled researchers to make great inroads into understanding human IBD pathology. Here, we discuss the current pre-clinical experimental murine models for human IBD, including the chemical-induced trinitrobenzene sulfonic acid (TNBS) model, oxazolone and dextran sulphate sodium (DSS) models, the gene-deficient I-kappa-B kinase gamma (Iκκ-γ) and interleukin(IL)-10 models, and the CD4⁺ T-cell transfer model. We offer a comprehensive review of how these models have been used to dissect the etiopathogenesis of disease, alongside their limitations. Furthermore, the way in which this knowledge has led to the translation of experimental findings into novel clinical therapeutics is also discussed.

Glucocorticoid induced group 2 innate lymphoid cell overactivation exacerbates experimental colitis

Abnormal activation of the innate and adaptive immune systems has been observed in inflammatory bowel disease (IBD) patients. Anxiety and depression increase the risk of IBD by activating the adaptive immune system. However, whether anxiety affects innate immunity and its impact on IBD severity remains elusive. This study investigated the mechanism by which anxiety contributes to IBD development in a murine model of acute wrap restraint stress (WRS). Here, we found that anxiety-induced overactivation of group 2 innate lymphoid cells (ILC2) aggravated colonic inflammation. Overactivation of the hypothalamic–pituitary–adrenal (HPA) axis is a hallmark of the physiological change of anxiety. Corticosterone (CORT), a stress hormone, is a marker of HPA axis activation and is mainly secreted by HPA activation. We hypothesized that the overproduction of CORT stimulated by anxiety exacerbated colonic inflammation due to the abnormally elevated function of ILC2. The results showed that ILC2 secreted more IL-5 and IL-13 in the WRS mice than in the control mice. Meanwhile, WRS mice experienced more body weight loss, shorter colon length, higher concentrations of IL-6 and TNF-α, more severely impaired barrier function, and more severe inflammatory cell infiltration. As expected, the serum corticosterone levels were elevated after restraint stress. Dexamethasone (DEX) was then injected to mimic HPA axis activation induced CORT secretion. DEX injection can also stimulate ILC2 to secrete more type II cytokines and exacerbate oxazolone (OXA) induced colitis. Blocking the IL-13/STAT6 signaling pathway alleviated colitis in WRS and DEX-injected mice. In conclusion, the overactivation of ILC2 induced by CORT contributed to the development of OXA-induced colitis in mice.

Heterogeneity of ILC2s in the Intestine; Homeostasis and Pathology

Group 2 innate lymphoid cells (ILC2s) were identified in 2010 as a novel lymphocyte subset lacking antigen receptors, such as T-cell or B-cell receptors. ILC2s induce local immune responses characterized by producing type 2 cytokines and play essential roles for maintaining tissue homeostasis. ILC2s are distributed across various organs, including the intestine where immune cells are continuously exposed to external antigens. Followed by luminal antigen stimulation, intestinal epithelial cells produce alarmins, such as IL-25, IL-33, and thymic stromal lymphopoietin, and activate ILC2s to expand and produce cytokines. In the context of parasite infection, the tuft cell lining in the epithelium has been revealed as a dominant source of intestinal IL-25 and possesses the capability to regulate ILC2 homeostasis. Neuronal systems also regulate ILC2s through neuropeptides and neurotransmitters, and interact with ILC2s bidirectionally, a process termed “neuro-immune crosstalk”. Activated ILC2s produce type 2 cytokines, which contribute to epithelial barrier function, clearance of luminal antigens and tissue repair, while ILC2s are also involved in chronic inflammation and tissue fibrosis. Recent studies have shed light on the contribution of ILC2s to inflammatory bowel diseases, mainly comprising ulcerative colitis and Crohn’s disease, as defined by chronic immune activation and inflammation. Modern single-cell analysis techniques provide a tissue-specific picture of ILC2s and their roles in regulating homeostasis in each organ. Particularly, single-cell analysis helps our understanding of the uniqueness and commonness of ILC2s across tissues and opens the novel research area of ILC2 heterogeneity. ILC2s are classified into different phenotypes depending on tissue and phase of inflammation, mainly inflammatory and natural ILC2 cells. ILC2s can also switch phenotype to ILC1- or ILC3-like subsets. Hence, recent studies have revealed the heterogeneity and plasticity of ILC2, which indicate dynamicity of inflammation and the immune system. In this review, we describe the regulatory mechanisms, function, and pathological roles of ILC2s in the intestine.

Innate Lymphoid Cells and Intestinal Inflammatory Disorders

Innate lymphoid cells (ILCs) are a population of lymphoid cells that do not express T cell or B cell antigen-specific receptors. They are largely tissue-resident and enriched at mucosal sites to play a protective role against pathogens. ILCs mimic the functions of CD4 T helper (Th) subsets. Type 1 innate lymphoid cells (ILC1s) are defined by the expression of signature cytokine IFN-γ and the master transcription factor T-bet, involving in the type 1 immune response; ILC2s are characterized by the expression of signature cytokine IL-5/IL-13 and the master transcription factor GATA3, participating in the type 2 immune response; ILC3s are RORγt-expressing cells and are capable of producing IL-22 and IL-17 to maintain intestinal homeostasis. The discovery and investigation of ILCs over the past decades extends our knowledge beyond classical adaptive and innate immunology. In this review, we will focus on the roles of ILCs in intestinal inflammation and related disorders.

Update: Innate Lymphoid Cells in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic and nonspecific intestinal inflammatory condition with high relapse rate. Its pathogenesis has been linked to dysbacteriosis, genetic and environmental factors. In recent years, a new type of lymphocytes, termed innate lymphoid cells, has been described and classified into three subtypes of innate lymphoid cells-group 1, group 2 and group 3. An imbalance among these subsets' interaction with gut microbiome, and other immune cells affects intestinal mucosal homeostasis. Understanding the role of innate lymphoid cells may provide ideas for developing novel and targeted approaches for treatment of IBD.

OnabotulinumtoxinA alters inflammatory gene expression and immune cells in chronic headache patients

Occipital headache, the perception of pain in the back of the head, is commonly described by patients diagnosed with migraine, tension-type headache, and occipital neuralgia. The greater and lesser occipital nerves play central role in the pathophysiology of occipital headache. In the clinical setup, such headaches are often treated with onabotulinumtoxinA, a neurotoxin capable of disrupting ability of nociceptors to get activated and/or release proinflammatory neuropeptides. Attempting to understand better onabotulinumtoxinA mechanism of action in reducing headache frequency, we sought to determine its effects on expression of inflammatory genes in injected occipital tissues.

To achieve this goal, we injected 40 units of onabotulinumtoxinA into four muscle groups (occipitalis, splenius capitis, semispinalis capitis, and trapezius muscles—all located on one side of the occiput) of patients with chronic bilateral occipital headache scheduled for occipital nerve decompression surgery 1 month later. At the time of surgery, we collected discarded muscle, fascia and periosteum tissues from respective locations on both sides of the neck and occiput and performed targeted transcriptome analyses to determine expression level of inflammatory genes in onabotulinumtoxinA-injected and onabotulinumA-uninjected tissues.

We found that (i) onabotulinumtoxinA alters expression of inflammatory genes largely in periosteum, minimally in muscle and not at all in fascia; (ii) expression of inflammatory genes in uninjected periosteum and muscle is significantly higher in historical onabotulinumA responders than historical non-responders; (iii) in historical responders’ periosteum, onabotulinumA decreases expression of nearly all significantly altered genes, gene sets that define well recognized inflammatory pathways (e.g. pathways involved in adaptive/innate immune response, lymphocyte activation, and cytokine, chemokine, NF-kB, TNF and interferon signalling), and abundance of 12 different immune cell classes (e.g. neutrophils, macrophages, cytotoxic T-, NK-, Th1-, B- and dendritic-cells), whereas in historical non-responders it increases gene expression but to a level that is nearly identical to the level observed in the uninjected periosteum and muscle of historical responders; and surprisingly (iv) that the anti-inflammatory effects of onabotulinumA are far less apparent in muscles and absent in fascia.

These findings suggest that in historical responders’ periosteum—but not muscle or fascia—inflammation contributes to the pathophysiology of occipital headache, and that further consideration should be given to the possibility that onabotulinumA mechanism of action in migraine prevention could also be achieved through its ability to reduce pre-existing inflammation, likely through localized interaction that lead to reduction in abundance of immune cells in the calvarial periosteum.

Exploring the Early Phase of Crohn's Disease

The development of Crohn's disease (CD) is characterized by a breakdown of homeostatic immune-bacterial communication, which takes place at the intestinal mucosa when environmental triggers impact genetically predisposed individuals. Converging lines of evidence support the hypothesis that this pathogenetic model develops through sequential, although inter-related, steps that indicate failure of mucosal defense mechanisms at various stages. In this context, immunologic phenomena that mediate the initial appearance of inflammatory lesions across the intestinal tissue may differ substantially from those that mediate and perpetuate chronic inflammatory responses. A compromise in the integrity of the epithelial barrier is among the earliest events and leads to accelerated influx of intraluminal antigens and intact microorganisms within the immunologically rich lamina propria. Inadequate clearance of invading microorganisms also may occur as a result of defects in innate immunity, preventing the timely and complete resolution of acute inflammatory responses. The final step is the development of persistent adaptive responses, which also differ between early and late Crohn's disease. Current progress in our ability to delineate single-cell transcriptomics and proteomics has allowed the discovery of cellular and molecular mechanisms that participate in each sequential step of CD development. This not only will advance our understanding of CD pathogenesis, but also facilitate the design of targeted therapeutic approaches.

Early Stress-Response Gene REDD1 Controls Oxazolone-Induced Allergic Contact Dermatitis

REDD1 is an energy sensor and stress-induced mTOR inhibitor. Recently, its novel role in linking metabolism and inflammation/immune responses has emerged. In this study, we assessed the role of REDD1 in murine oxazolone-induced allergic contact dermatitis (ACD), a T cell-dependent model with features of human ACD. A variety of immune indices, including edema, cellular infiltration, inflammatory gene expression, and glucocorticoid response, were compared in Redd1 knockout (KO) and isogenic (C57BL/6 × 129)F1 wild-type mice after sensitization and subsequent ear challenge with oxazolone. Despite relatively normal thymic profiles and similar T cell populations in the lymph nodes of naive Redd1 KO mice, early T cell expansion and cytokine production were profoundly impaired after sensitization. Surprisingly, higher steady-state populations of CD4⁺ and CD8⁺ T cells, as well as macrophages (CD45⁺/Ly-6G^-/CD11b⁺), dendritic cells (CD45⁺/Ly-6G^-/CD11c⁺), neutrophils (CD45⁺/Ly-6G⁺/CD11b⁺), and innate lymphoid cells (CD45⁺/Lineage^-/IL-7Ra⁺/ST2⁺/c-Kit⁺), were observed in the ears of naive Redd1 KO mice. Upon challenge, ear edema, T cell, macrophage, neutrophil, and dendritic cell infiltration into the ear was significantly reduced in Redd1 KO animals. Accordingly, we observed significantly lower induction of IFN-γ, IL-4, and other cytokines as well as proinflammatory factors, including TSLP, IL-33, IL-1β, IL-6, and TNF-α, in challenged ears of Redd1 KO mice. The response to glucocorticoid treatment was also diminished. Taken together, these data establish REDD1 as an essential immune modulator that influences both the initiation of ACD disease, by driving naive T cell activation, and the effector phase, by promoting immune cell trafficking in T cell-mediated skin inflammation.

Innate Lymphoid Cells in Intestinal Homeostasis and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a heterogeneous state of chronic intestinal inflammation of unknown cause encompassing Crohn’s disease (CD) and ulcerative colitis (UC). IBD has been linked to genetic and environmental factors, microbiota dysbiosis, exacerbated innate and adaptive immunity and epithelial intestinal barrier dysfunction. IBD is classically associated with gut accumulation of proinflammatory Th1 and Th17 cells accompanied by insufficient Treg numbers and Tr1 immune suppression. Inflammatory T cells guide innate cells to perpetuate a constant hypersensitivity to microbial antigens, tissue injury and chronic intestinal inflammation. Recent studies of intestinal mucosal homeostasis and IBD suggest involvement of innate lymphoid cells (ILCs). These lymphoid-origin cells are innate counterparts of T cells but lack the antigen receptors expressed on B and T cells. ILCs play important roles in the first line of antimicrobial defense and contribute to organ development, tissue protection and regeneration, and mucosal homeostasis by maintaining the balance between antipathogen immunity and commensal tolerance. Intestinal homeostasis requires strict regulation of the quantity and activity of local ILC subpopulations. Recent studies demonstrated that changes to ILCs during IBD contribute to disease development. A better understanding of ILC behavior in gastrointestinal homeostasis and inflammation will provide valuable insights into new approaches to IBD treatment. This review summarizes recent research into ILCs in intestinal homeostasis and the latest advances in the understanding of the role of ILCs in IBD, with particular emphasis on the interaction between microbiota and ILC populations and functions.

IL-33 Drives Expansion of Type 2 Innate Lymphoid Cells and Regulatory T Cells and Protects Mice From Severe, Acute Colitis

The hallmarks of inflammatory bowel disease are mucosal damage and ulceration, which are known to be high-risk conditions for the development of colorectal cancer. Recently, interleukin (IL)-33 and its receptor ST2 have emerged as critical modulators in inflammatory disorders. Even though several studies highlight the IL-33/ST2 pathway as a key factor in colitis, a detailed mode of action remains elusive. Therefore, we investigated the role of IL-33 during intestinal inflammation and its potential as a novel therapeutic target in colitis. Interestingly, the expression of IL-33, but not its receptor ST2, was significantly increased in biopsies from the inflamed colon of IBD patients compared to non-inflamed colonic tissue. Accordingly, in a mouse model of Dextran Sulfate Sodium (DSS) induced colitis, the secretion of IL-33 significantly accelerated in the colon. Induction of DSS colitis in ST2-/- mice displayed an aggravated colon pathology, which suggested a favorable role of the IL 33/ST2 pathway during colitis. Indeed, injecting rmIL-33 into mice suffering from acute DSS colitis, strongly abrogated epithelial damage, pro-inflammatory cytokine secretion, and loss of barrier integrity, while it induced a strong increase of Th2 associated cytokines (IL-13/IL-5) in the colon. This effect was accompanied by the accumulation of regulatory T cells (Tregs) and type 2 innate lymphoid cells (ILC2s) in the colon. Depletion of Foxp3+ Tregs during IL-33 treatment in DSS colitis ameliorated the positive effect on the intestinal pathology. Finally, IL-33 expanded ILC2s, which were adoptively transferred to DSS treated mice, significantly reduced colonic inflammation compared to DSS control mice. In summary, our results emphasize that the IL-33/ST2 pathway plays a crucial protective role in colitis by modulating ILC2 and Treg numbers.

Out of the shadow of interleukin-17A: the role of interleukin-17F and other interleukin-17 family cytokines in spondyloarthritis

PURPOSE OF REVIEW

The last decade has witnessed tremendous advances in revealing an important role for the interleukin (IL)-17 cytokine family in the pathogenesis of spondyloarthritis (SpA). Although most attention has been focused on IL-17A, a potential role of other IL-17 family members in inflammation and tissue remodelling is emerging. Herein, I review recent studies covering the role of IL-17B-F cytokines in the pathogenesis of SpA.

RECENT FINDINGS

Several recent studies provided new insights into the cellular source, regulation and function of IL-17F. IL-17F/IL-17A expression ratio is higher in psoriatic skin compared to SpA synovitis. IL-17F-expressing T cells produce different proinflammatory mediators than IL-17A-expressing cells, and IL-17F and IL-17A signal through different receptor complex. Dual IL-17A and IL-17F neutralization resulted in greater suppression of downstream inflammatory and tissue remodelling responses. Furthermore, there is additional evidence of IL-23-independent IL-17 production. In contrast to IL-17A, IL-17F and IL-17C, which play proinflammatory roles in skin and joint inflammation, an anti-inflammatory function is proposed for IL-17D. An increase in IL-17E is associated with subclinical gut microbiome alterations after anti-IL-17A therapy in SpA patients.

SUMMARY

IL-17 family cytokines may act as agonists or antagonists to IL-17A contributing in concert to local inflammatory responses. Understanding their function and identifying their cellular sources, and molecular mechanisms driving their expression will be the key to designing rational therapies in SpA.

Crohn's Disease Is Associated With Activation of Circulating Innate Lymphoid Cells

BACKGROUND

Inflammatory bowel disease (IBD) is associated with disturbed mucosal innate lymphoid cell (ILC) composition, which is correlated to the degree of intestinal inflammation. However, it remains unclear whether circulating ILCs are dysregulated in patients with IBD.

METHODS

Blood samples from 53 patients with Crohn's disease (CD), 43 patients with ulcerative colitis (UC), and 45 healthy control subjects (HC) were analyzed by flow cytometry for markers of ILC subsets (ILC1, ILC2, and ILC precursors [ILCp]) and selected IBD-relevant proteins, as predicted by previous genome-wide association studies. A dimensionality reduction approach to analyzing the data was used to characterize circulating ILCs.

RESULTS

The frequency of ILCp expressing the ILC3 activation markers NKp44 and CD56 was increased in CD versus HC and UC (NKp44) or in CD versus HC (CD56), whereas the CD45RA+ ILCp were reduced in CD versus UC. Furthermore, the activation marker HLA-DR was increased on ILC1 and ILC2 in CD versus HC. Interestingly, the IBD-related protein SLAMF1 was upregulated on ILC2 from both CD and UC samples as compared with HC samples. In active CD, SLAMF1+ ILC2 frequency was negatively correlated with disease severity (Harvey-Bradshaw index). The characterization of SLAMF1+ ILC2 revealed a higher expression of the ILC2 markers CRTH2, CD161, and GATA3 as compared with SLAMF1- ILC2.

CONCLUSIONS

In line with the systemic nature of CD inflammation, our findings point toward the activation of ILCs in the blood of patients with CD. Furthermore, in active CD, circulating SLAMF1+ ILC2 are increased in patients with less active disease, introducing SLAMF1+ ILC2 as interesting therapeutic targets deserving further exploration.

IL-25 (IL-17E) in epithelial immunology and pathophysiology

IL-25, also known as IL-17E, is a unique cytokine of the IL-17 family. Indeed, IL-25 exclusively was shown to strongly induce expression of the cytokines associated with type 2 immunity. Although produced by several types of immune cells, such as T cells, dendritic cells, or group 2 innate lymphoid cells, a vast amount of IL-25 derives from epithelial cells. The functions of IL-25 have been actively studied in the context of physiology and pathology of various organs including skin, airways and lungs, gastrointestinal tract, and thymus. Accumulating evidence suggests that IL-25 is a "barrier surface" cytokine whose expression depends on extrinsic environmental factors and when upregulated may lead to inflammatory disorders such as atopic dermatitis, psoriasis, or asthma. This review summarizes the progress of the recent years regarding the effects of IL-25 on the regulation of immune response and the balance between its homeostatic and pathogenic role in various epithelia. We revisit IL-25's general and tissue-specific mechanisms of action, mediated signaling pathways, and transcription factors activated in immune and resident cells. Finally, we discuss perspectives of the IL-25-based therapies for inflammatory disorders and compare them with the mainstream ones that target IL-17A.

[Mechanism and intervention of mucosal immune regulation based on "lung and large intestine being interior-exteriorly related" theory of traditional Chinese medicine]

The "lung and large intestine being interior-exteriorly related" is one of the classical theories in traditional Chinese medicine, which indicates a close correlation between the lung and large intestine in physiology and pathology, and plays a pivotal role in guiding the treatment of the lung and bowel diseases. Modern medicine has revealed some connections between the lung and large intestine in tissue origin and mucosal immunity, and preliminarily illuminated the material basis and possible regulatory mechanism of the theory. Recently, this theory has been applied to guide the treatment of refractory lung and intestine diseases such as COVID-19 and ulcerative colitis and has obtained reliable efficacy. Existing research results show that the anatomical homogeneity of lung and large intestine promotes the correlation between lung-bowel mucosal immunity, and mucosal immunity and migration and homing of innate lymphocytes are one of the physiological and pathological mechanisms for lung and large intestine to share. Under the guidance of this theory, Chinese medicines with heat-clearing and detoxifying or tonic effects are commonly used in the treatment of the lung and intestinal diseases by regulating lung-bowel mucosal immunity and they can be candidate drugs to treat lung/intestinal diseases simultaneously. However, the existing studies on immune regulation are mainly focused on the expression levels of sIgA and cytokines, as well as the changes in the number of immune cells such as innate lymphocytes and B lymphocytes. While the following aspects need further investigation: the airway/intestinal mucous hypersecretion, the functional changes of pulmonary and intestinal mucosal barrier immune cells, the dynamic process of lung/intestinal mucosal immune interaction, the intervention effect of local pulmonary/intestinal microecology, the correlation and biological basis between the heat-clearing and detoxifying effect and the tonic effect, and its regulation of pulmonary/intestinal mucosal immunity. In this paper, we try to analyze the internal relationship between lung and intestine related diseases from the point of view of the common mucosal immune system of lung and intestine, and summarize the characteristics and rules of traditional Chinese medicine compound and its active ingredients, which have regulatory effect on lung and intestine mucosal immune system, so as to further explain the theoretical connotation of "lung and large intestine being interior-exteriorly related" and provide reference for the research and development of drugs for related diseases.

The emerging role of type 2 inflammation in asthma

Introduction: Bronchial asthma (BA) is a chronic airways inflammatory disease. Based on the biological mechanisms that underline the disease, asthma has been classified as type 2 or non-type 2 phenotype.Areas covered: An emerging role has been identified for group 2 innate lymphoid cells (ILC2s) able to produce the classical type 2 cytokines. The role of Th2 cells and IL-4 is crucial in the pathogenesis of allergic BA as supported by asthma models. IL-13, shares many biological functions with IL-4 such as induction of IgE synthesis and regulation of eosinophil trafficking. However, IL-13 does not induce Th2 cell differentiation. The Authors reviewed evidence on the new concept of type 2 inflammation and the cellular and molecular network behind this process. Literature data in the PubMed were analyzed for peer-reviewed articles published until September 2020.Expert opinion: The current trend is to consider Th2- and ILC2-driven pathways as two separate pathogenic mechanisms, recent data underscore that adaptive Th2- and innate cell responses represent two integrated systems in the production of IL-4, IL-5, and IL-13 leading to the current 'concept' of type 2 inflammation. This review highlights the role of Th2 cells and ILC2 in the recent new concept of type 2 inflammation.

Possible role of microRNA miRNA-IL-25 interaction in mice with ulcerative colitis

Background: The regulatory network of ulcerative colitis (UC)-associated miRNAs is not fully understood. In this study, we aim to investigate the global profile and regulatory network of UC associated miRNAs in the context of dextran sulfate sodium (DSS). Methods: UC was induced in C57BL mice using DSS. Differentially expressed miRNAs were screened by RNA sequencing and subjected to the Kyoto Encyclopedia of Genes and Genomes Pathway enrichment analysis. RT-qPCR was used to verify the differential expression of miRNAs and candidate target mRNA. Luciferase reporter vector bearing a miRNA binding site was constructed to verify the binding site of the miRNA on mRNA. Results:A total of 95 miRNAs (31 were up-regulated and 64 were down regulated) differentially expressed in the colonic tissues of the UC mice. Among the differentially expressed miRNAs, IL-25 pathway genes were enriched. Subsequent RT-qPCR confirmed a decreased expression of IL-25 and a significant up regulation of IL-25 target miRNAs including mmu-miR-135b-5p, mmu-miR-7239-5p and mmu-miR-691 in UC mice. Conclusion: Using the luciferase assay, we verified the biding sites of mmu-miR-135b-5p and mmu-miR-691 to the IL-25 3ʹUTR. In conclusion, mmu-miR-135b-5p:IL-25 and mmu-miR-691:IL-25 interactions are important pathways that may exert a protective role in UC.

Innate Lymphoid Cells of the Lung

Although, as the major organ of gas exchange, the lung is considered a nonlymphoid organ, an interconnected network of lung-resident innate cells, including epithelial cells, dendritic cells, macrophages, and natural killer cells is crucial for its protection. These cells provide defense against a daily assault by airborne bacteria, viruses, and fungi, as well as prevent the development of cancer, allergy, and the outgrowth of commensals. Our understanding of this innate immune environment has recently changed with the discovery of a family of innate lymphoid cells (ILCs): ILC1s, ILC2s, and ILC3s. All lack adaptive antigen receptors but can provide a substantial and rapid source of IFN-γ, IL-5 and IL-13, and IL-17A or IL-22, respectively. Their ability to afford immediate protection to the lung and to influence subsequent adaptive immune responses highlights the importance of understanding ILC-regulated immunity for the design of future therapeutic interventions.

NKT cells and the regulation of intestinal immunity: a two‐way street

The mammalian gastrointestinal compartment is colonised by millions of microorganisms that have a central influence on human health. Intestinal homeostasis requires a continuous dialogue between the commensal bacteria and intestinal immune cells. While interactions between host and commensal bacteria are normally beneficial, allowing training and functional tuning of immune cells, dysregulated immune system-microbiota crosstalk can favour the development of chronic inflammatory diseases, as it is the case for inflammatory bowel disease (IBD). Natural killer T (NKT) cells, which recognise CD1-restricted microbial and self-lipids, contribute to the regulation of mucosal immunity by controlling intestinal homeostasis and participating in the development of IBD. Here, we provide an overview of the recently identified pathways underlying the crosstalk between commensal bacteria and NKT cells and discuss the effect of these interactions in intestinal health and disease.

Characterization of Rat ILCs Reveals ILC2 as the Dominant Intestinal Subset

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes that lack antigen-specific receptors and exhibit innate effector functions such as cytokine production that play an important role in immediate responses to pathogens especially at mucosal sites. Mouse and human ILC subsets have been extensively characterized in various tissues and in blood. In this study, we present the first characterization of ILCs and ILC subsets in rat gut and secondary lymphoid organs using flow cytometry and single cell RNA sequencing. Our results show that phenotype and function of rat ILC subsets are conserved as compared to human and mouse ILCs. However, and in contrast to human and mouse, our study unexpectedly revealed that ILC2 and not ILC3 was the dominant ILC subset in the rat intestinal lamina propria. ILC2 predominance in the gut was independent of rat strain, sex or housing facility. In contrast, ILC3 was the predominant ILC subset in mesenteric lymph nodes and Peyer patches. In conclusion, our study demonstrates that in spite of highly conserved phenotype and function between mice, rat and humans, the distribution of ILC subsets in the intestinal mucosa is dependent on the species likely in response to both genetic and environmental factors.

Dual-Functionalized MSCs that Express CX3CR1 and IL-25 Exhibit Enhanced Therapeutic Effects on Inflammatory Bowel Disease

Mesenchymal stem cells (MSCs) have shown great promise in inflammatory bowel disease (IBD) treatment, owing to their immunosuppressive capabilities, but their therapeutic effectiveness is sometimes thwarted by their low efficiency in entering the inflamed colon and variable immunomodulatory ability in vivo. Here, we demonstrated a new methodology to manipulate MSCs to express CX3C chemokine receptor 1 (CX3CR1) and interleukin-25 (IL-25) to promote their delivery to the inflamed colon and enhance their immunosuppressive capability. Compared to MSCs without treatment, MSCs infected with a lentivirus (LV) encoding CX3CR1 and IL-25 (CX3CR1&IL-25-LV-MSCs) exhibited enhanced targeting to the inflamed colon and could further move into extravascular space of the colon tissues via trans-endothelial migration in dextran sodium sulfate (DSS)-challenged mice after MSC intravenous injection. The administration of the CX3CR1&IL-25-LV-MSCs achieved a better therapeutic effect than that of the untreated MSCs, as indicated by pathological indices and inflammatory markers. Antibody-blocking studies indicated that the enhanced therapeutic effects of dual-functionalized MSCs were dependent on CX3CR1 and IL-25 function. Overall, this strategy, which is based on enhancing the homing and immunosuppressive abilities of MSCs, represents a promising therapeutic approach that may be valuable in IBD therapy.

Critical Roles of Balanced Innate Lymphoid Cell Subsets in Intestinal Homeostasis, Chronic Inflammation, and Cancer

Innate lymphoid cells (ILCs) comprise a recently identified subset of innate immune cells that are mainly localized to mucosa-associated tissues. Although they have not yet been fully characterized, they can generally be divided into ILC1s, ILC2s, and ILC3s. ILCs and their corresponding cytokines act as important mediators of the early stages of the immune response during inflammation, tissue repair, and the maintenance of epithelial integrity. Consequently, the dysregulation of ILC subsets might promote inflammation and cancer. Numerous studies have demonstrated that these cells play an important role in maintaining the microecological balance of the small intestine; however, their specific roles in mediating inflammation in this tissue and tumorigenesis remain unclear and controversial. In this review, we focus on recent progress that has helped to gain a better understanding of the role of ILCs in intestinal homeostasis, chronic inflammation, and cancer. Further focused research on the regulation and role of ILCs in intestinal homeostasis and pathology will help to reveal valuable diagnostic and therapeutic targets for the treatment of intestinal diseases.

ILC2 Activation by Protozoan Commensal Microbes

Group 2 innate lymphoid cells (ILC2s) are a member of the ILC family and are involved in protective and pathogenic type 2 responses. Recent research has highlighted their involvement in modulating tissue and immune homeostasis during health and disease and has uncovered critical signaling circuits. While interactions of ILC2s with the bacterial microbiome are rather sparse, other microbial members of our microbiome, including helminths and protozoans, reveal new and exciting mechanisms of tissue regulation by ILC2s. Here we summarize the current field on ILC2 activation by the tissue and immune environment and highlight particularly new intriguing pathways of ILC2 regulation by protozoan commensals in the intestinal tract.

Contribution of Epithelial Cell Dysfunction to the Pathogenesis of Chronic Rhinosinusitis with Nasal Polyps

Background

In the past, the airway epithelium was thought to be primarily an inert physical barrier. We now know that the upper airway epithelium plays a critical role in both innate and adaptive immunity, and that epithelial dysfunction is strongly associated with inflammatory airway disease. The pathogenesis of chronic rhinosinusitis is poorly understood, but growing evidence supports a key role for the airway epithelium in the pathophysiology of the disease.

Objective

The purpose of this study is to explore our current understanding of how dysfunction in human sinonasal epithelial cells (HSNECs) contributes to the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP) and to examine how current and developing therapies affect epithelial cell functions.

Methods

A literature review of papers published in English pertaining to epithelial cell dysfunction in patients with CRSwNP was performed using the PubMed database. The search utilized combinations of the following key words: sinusitis, polyps, epithelium, pathophysiology, barrier function, dendritic cells, eosinophils, T cells, complement, mucociliary clearance, vitamin D, cytokines, chemokines, taste receptors, steroids, saline, and therapy.

Results

HSNEC mucociliary clearance, barrier function, secretion of cytokines, influence on dendritic cells, influence on T-cells, regulation of eosinophils, vitamin D metabolism, complement production, and taste receptor function are altered in patients with CRSwNP and contribute to the pathogenesis of the disease. Current therapies utilized to manage CRSwNP counteract the effects of HSNEC dysfunction and relieve key symptoms of the disease.

Conclusion

HSNECs are key players in both innate and adaptive immunity, and altered epithelial functions are closely intertwined with the pathogenesis of CRSwNP. Our review supports further investigation of altered HSNEC function in patients with CRSwNP and supports development of novel epithelial-targeted therapies for its management.

Group 2 Innate Lymphoid Cells (ILC2): Type 2 Immunity and Helminth Immunity

Group 2 innate lymphoid cells (ILC2) have emerged as a major component of type 2 inflammation in mice and humans. ILC2 secrete large amounts of interleukins 5 and 13, which are largely responsible for host protective immunity against helminth parasites because these cytokines induce profound changes in host physiology that include: goblet cell metaplasia, mucus accumulation, smooth muscle hypercontractility, eosinophil and mast cell recruitment, and alternative macrophage activation (M2). This review covers the initial recognition of ILC2 as a distinct cell lineage, the key studies that established their biological importance, particularly in helminth infection, and the new directions that are likely to be the focus of emerging work that further explores this unique cell population in the context of health and disease.

Innate Lymphoid Cells in Mucosal Immunity

Innate lymphoid cells (ILCs) are innate counterparts of T cells that contribute to immune responses by secreting effector cytokines and regulating the functions of other innate and adaptive immune cells. ILCs carry out some unique functions but share some tasks with T cells. ILCs are present in lymphoid and non-lymphoid organs and are particularly abundant at the mucosal barriers, where they are exposed to allergens, commensal microbes, and pathogens. The impact of ILCs in mucosal immune responses has been extensively investigated in the gastrointestinal and respiratory tracts, as well as in the oral cavity. Here we review the state-of-the-art knowledge of ILC functions in infections, allergy and autoimmune disorders of the mucosal barriers.

Type 2 Innate Lymphoid Cells in Liver and Gut: From Current Knowledge to Future Perspectives

Innate lymphoid cells (ILCs) represent a heterogeneous population of recently discovered immune cells that mirror the functions of adaptive T lymphocytes. However, ILCs are devoid of specific antigen receptors and cellular activation depends on environmental cytokines, rendering them as early regulators of immune responses. Type 2 innate lymphoid cells (ILC2s) respond to alarmins, such as interleukin-25 and -33 and shape Th2-associated immunity by expressing IL-5 and IL-13 in a GATA3-dependent manner. In addition, ILC2s express the epidermal growth factor-like molecule Amphiregulin thereby promoting regeneration of injured tissue during inflammation. The gut and liver confer nutrient metabolism and bidirectional exchange of products, known as the gut-liver axis. Accordingly, both organs are continuously exposed to a large variety of harmless antigens. This requires avoidance of immunity, which is established by a tolerogenic environment in the gut and liver. However, dysregulations within the one organ are assumed to influence vitality of the other and frequently promote chronic inflammatory settings with poor prognosis. Intensive research within the last years has revealed that ILC2s are involved in acute and chronic inflammatory settings of gut and liver. Here, we highlight the roles of ILC2s in intestinal and hepatic inflammation and discuss a regulatory potential.

Innate lymphoid cells in intestinal cancer development

Colorectal cancer (CRC) is a highly prominent cause of cancer-related deaths worldwide. Although the functions of immune cells in the colorectal tumor microenvironment are complex and heterogeneous, dysregulated changes in the composition and activation state of immune cells are believed to represent key events supporting the establishment of pro- or anti-tumorigenic immune states. Recently, innate lymphoid cells (ILCs) emerged as central innate immune mediators during both gastrointestinal homeostasis and inflammatory pathologies. Hence, ILCs might also represent promising targets in the context of cancer therapy and are increasingly recognized as innate immune cells with potent immunomodulatory properties. In this review, we summarize the pleiotropic roles of the different ILC subsets for intestinal homeostasis and discuss the recent evidence on their potential involvement in the development and growth of intestinal cancers.

Innate Lymphoid Cells: A Link between the Nervous System and Microbiota in Intestinal Networks

Innate lymphoid cells (ILCs) are a novel family of innate immune cells that act as key coordinators of intestinal mucosal surface immune defense and are essential for maintaining intestinal homeostasis and barrier integrity by responding to locally produced effector cytokines or direct recognition of exogenous or endogenous danger patterns. ILCs are also involved in the pathogenesis of inflammatory bowel disease (IBD). Many studies have demonstrated the occurrence of crosstalk between ILCs and intestinal microbiota, and ILCs have recently been shown to be connected to the enteric nervous system (ENS). Thus, ILCs may act as a key link between the nervous system and microbiota in intestinal networks. In this review, we briefly summarize the role of the ILCs in the intestinal tract (particularly in the context of IBD) and discuss the relationship between ILCs and the microbiota/ENS.

Anti-Inflammatory Effect of IL-37-Producing T-Cell Population in DSS-Induced Chronic Inflammatory Bowel Disease in Mice

Inflammatory bowel disease (IBD) is a chronic inflammatory disease that is thought to arise in part from abnormal adaptive immune responses against intestinal microbiota. T lymphocytes play significant roles in triggering mucosal inflammation and/or maintaining gut immune homeostasis. It has been demonstrated that IL-37 expresses in a variety of cells and exerts a protective function involved in both innate immunity and adaptive immunity. In the present study, a population of IL-37-producing T-cells was detected in the spleen and mesenteric lymph nodes (MLNs) in IL-37^+/+ mice after dextran sodium sulfate (DSS) induction. Adoptive transfer of the T-cells from the spleen of IL-37^+/+ mice following DSS treatment partly recovered the body weight, improved the disease activity index (DAI) and macroscopic damage score, and attenuated the intestinal inflammation. In addition, colon shortening, an indirect marker of inflammation, was decreased, consistent with the decreased IFN-γ level and the increased IL-10 level in the colonic tissue. Collectively, our data uncovered a subset of T-lymphocytes expressing IL-37, which represents a potent regulation of immunity and serves as the protective role in chronic IBD.

Roles for Interleukin 17 and Adaptive Immunity in Pathogenesis of Colorectal Cancer

Sporadic colorectal cancer is one of the most common and lethal cancers worldwide. The locations and functions of immune cells in the colorectal tumor microenvironment are complex and heterogeneous. T-helper (Th)1 cell-mediated responses against established colorectal tumors are associated with better outcomes of patients (time of relapse-free or overall survival), whereas Th17 cell-mediated responses and production of interleukin 17A (IL17A) have been associated with worse outcomes of patients. Tumors that develop in mouse models of colorectal cancer are rarely invasive and differ in many ways from human colorectal tumors. However, these mice have been used to study the mechanisms by which Th17 cells and IL17A promote colorectal tumor initiation and growth, which appear to involve their direct effects on colon epithelial cells. Specific members of the colonic microbiota may promote IL17A production and IL17A-producing cell functions in the colonic mucosa to promote carcinogenesis. Increasing our understanding of the interactions between the colonic microbiota and the mucosal immune response, the roles of Th17 cells and IL17 in these interactions, and how these processes are altered during colon carcinogenesis, could lead to new strategies for preventing or treating colorectal cancer.

Targeting IL-13 as a Host-Directed Therapy Against Ulcerative Colitis

The role of interleukin-13 in mediating ulcerative colitis remains under scrutiny. Compelling evidence from both man and mouse suggests that IL-13 not only contributes to the pathology associated with disease but is also involved in mediating the inflammatory response. These studies have led to the approach of targeting IL-13 as a promising treatment strategy in alleviating ulcerative colitis disease. Despite this evidence, recent clinical trial data suggests that specifically blocking the receptor through which IL-13 signals, IL-4 receptor-alpha (IL-4Rα) in ulcerative colitis patients, is insufficient in protecting them from disease outcome. This challenges the importance of IL-13 as a therapeutic target. This review describes the role of IL-13 in ulcerative colitis and current treatment strategies that target IL-13. The potential role of IL-13 signaling independently of IL-4Rα in mediating ulcerative colitis is highlighted as an important consideration when targeting the signaling mechanisms of IL-13 for therapeutic approaches.

Natural killer T cells and ulcerative colitis

Ulcerative colitis (UC) is one of the two major forms of inflammatory bowel disease (IBD). Both innate immunity and adaptive immunity are aberrant in IBD. The pathogenesis of UC includes abnormal inflammation and immune responses of the digestive tract. Natural killer T (NKT) cells participate in the innate and adaptive immune responses, together with a vast array of cytokines. Recent studies suggested that IL-13, IL5 and IL-4 are involved in the occurrence and the development of UC. Manipulating NKT cells may be a potential strategy to reconstruct the abnormal immune responses in UC. In this review, we explore the roles of NKT cells and cytokines in UC. Additionally, neutralizing antibodies and inhibitors of cytokines produced by NKT cells or their receptors are also discussed as novel therapeutic choices for UC.

Invariant Natural Killer T and Mucosal-Associated Invariant T Cells in Asthmatic Patients

Recent studies have highlighted the heterogeneity of asthma. Distinct patient phenotypes (symptoms, age at onset, atopy, and lung function) may result from different pathogenic mechanisms, including airway inflammation, remodeling, and immune and metabolic pathways in a specific microbial environment. These features, which define the asthma endotype, may have significant consequences for the development and progression of the disease. Asthma is generally associated with Th2 cells, which produce a panel of cytokines (IL-4, IL-5, IL-13) that act in synergy to drive lung inflammatory responses, mucus secretion, IgE production, and fibrosis, causing the characteristic symptoms of asthma. In addition to conventional CD4⁺ T lymphocytes, other T-cell types can produce Th2 or Th17 cytokines rapidly. Promising candidate cells for studies of the mechanisms underlying the pathophysiology of asthma are unconventional T lymphocytes, such as invariant natural killer T (iNKT) and mucosal-associated invariant T (MAIT) cells. This review provides an overview of our current understanding of the impact of iNKT and MAIT cells on asthmatic inflammation, focusing particularly on pediatric asthma.

Innate lymphoid cells in organ fibrosis

Innate lymphoid cells (ILCs) are a recently identified family of lymphoid effector cells. ILCs are mainly clustered into 3 groups based on their unique cytokine profiles and transcription factors typically attributed to the subsets of T helper cells. ILCs have a critical role in the mucosal immune response through promptly responding to pathogens and producing large amount of effector cytokines of type 1, 2, or 3 responses. In addition to the role of early immune responses against infections, ILCs, particularly group 2 ILCs (ILC2), have recently gained attention for modulating remodeling and fibrosis especially in the mucosal tissues. Herein, we overview the current knowledge in this area, highlighting roles of ILCs on fibrosis in the mucosal tissues, especially focusing on the gut and lung. We also discuss some new directions for future research by extrapolating from knowledge derived from studies on Th cells.