Critical role of p38 and GATA3 in natural helper cell function

Chronic Inflammation in Asthma: Looking Beyond the Th2 Cell

Asthma is a common chronic inflammatory disease of the airways. A substantial number of patients present with severe and therapy-resistant asthma, for which the underlying biological mechanisms remain poorly understood. In most asthma patients, airway inflammation is characterized by chronic activation of type 2 immunity. CD4+ T helper 2 (Th2) cells are the canonical producers of the cytokines that fuel type 2 inflammation: interleukin (IL)-4, IL-5, IL-9, and IL-13. However, more recent findings have shown that other lymphocyte subsets, in particular group 2 innate lymphoid cells (ILC2s) and type 2 CD8+ cytotoxic T (Tc2) cells, can also produce large amounts of type 2 cytokines. Importantly, a substantial number of severe therapy-resistant asthma patients present with chronic type 2 inflammation, despite the high sensitivity of Th2 cells for suppression by corticosteroids-the mainstay drugs for asthma. Emerging evidence indicates that ILC2s and Tc2 cells are more abundant in severe asthma patients and can adopt corticosteroid-resistance states. Moreover, many severe asthma patients do not present with overt type 2 airway inflammation, implicating non-type 2 immunity as a driver of disease. In this review, we will discuss asthma pathophysiology and focus on the roles played by ILC2s, Tc2 cells, and non-type 2 lymphocytes, placing special emphasis on severe disease forms.

Regulation of Airway Epithelial-Derived Alarmins in Asthma: Perspectives for Therapeutic Targets

Asthma is a chronic respiratory condition predominantly driven by a type 2 immune response. Epithelial-derived alarmins such as thymic stromal lymphopoietin (TSLP), interleukin (IL)-33, and IL-25 orchestrate the activation of downstream Th2 cells and group 2 innate lymphoid cells (ILC2s), along with other immune effector cells. While these alarmins are produced in response to inhaled triggers, such as allergens, respiratory pathogens or particulate matter, disproportionate alarmin production by airway epithelial cells can lead to asthma exacerbations. With alarmins produced upstream of the type 2 inflammatory cascade, understanding the pathways by which these alarmins are regulated and expressed is critical to further explore new therapeutics for the treatment of asthmatic patients. This review emphasizes the critical role of airway epithelium and epithelial-derived alarmins in asthma pathogenesis and highlights the potential of targeting alarmins as a promising therapeutic to improve outcomes for asthma patients.

The Relationship between HERV, Interleukin, and Transcription Factor Expression in ZIKV Infected versus Uninfected Trophoblastic Cells

Zika virus (ZIKV) is an arbovirus with maternal, sexual, and TORCH-related transmission capabilities. After 2015, Brazil had the highest number of ZIVK-infected pregnant women who lost their babies or delivered them with Congenital ZIKV Syndrome (CZS). ZIKV triggers an immune defense in the placenta. This immune response counts with the participation of interleukins and transcription factors. Additionally, it has the potential involvement of human endogenous retroviruses (HERVS). Interleukins are immune response regulators that aid immune tolerance and support syncytial structure development in the placenta, where syncytin receptors facilitate vital cell-to-cell fusion events. HERVs are remnants of ancient viral infections that integrate into the genome and produce syncytin proteins crucial for placental development. Since ZIKV can infect trophoblast cells, we analyzed the relationship between ZIKV infection, HERV, interleukin, and transcription factor modulations in the placenta. To investigate the impact of ZIKV on trophoblast cells, we examined two cell types (BeWo and HTR8) infected with ZIKV-MR766 (African) and ZIKV-IEC-Paraíba (Asian-Brazilian) using Taqman and RT2 Profiler PCR Array assays. Our results indicate that early ZIKV infection (24-72 h) does not induce differential interleukins, transcription factors, and HERV expression. However, we show that the expression of a few of these host defense genes appears to be linked independently of ZIKV infection. Future studies involving additional trophoblastic cell lineages and extended infection timelines will illuminate the dynamic interplay between ZIKV, HERVs, interleukins, and transcription factors in the placenta.

Mef2d potentiates type-2 immune responses and allergic lung inflammation

Innate lymphoid cells (ILCs) and adaptive T lymphocytes promote tissue homeostasis and protective immune responses. Their production depends on the transcription factor GATA3, which is further elevated specifically in ILC2s and T helper 2 cells to drive type-2 immunity during tissue repair, allergic disorders, and anti-helminth immunity. The control of this crucial up-regulation is poorly understood. Using CRISPR screens in ILCs we identified previously unappreciated myocyte-specific enhancer factor 2d (Mef2d)-mediated regulation of GATA3-dependent type-2 lymphocyte differentiation. Mef2d-deletion from ILC2s and/or T cells specifically protected against an allergen lung challenge. Mef2d repressed Regnase-1 endonuclease expression to enhance IL-33 receptor production and IL-33 signaling and acted downstream of calcium-mediated signaling to translocate NFAT1 to the nucleus to promote type-2 cytokine-mediated immunity.

TCR signaling and cellular metabolism regulate the capacity of murine epidermal γδ T cells to rapidly produce IL-13 but not IFN-γ

Resident epidermal T cells of murine skin, called dendritic epidermal T cells (DETCs), express an invariant γδ TCR that recognizes an unidentified self-ligand expressed on epidermal keratinocytes. Although their fetal thymic precursors are preprogrammed to produce IFN-γ, DETCs in the adult epidermis rapidly produce IL-13 but not IFN-γ early after activation. Here, we show that preprogrammed IFN-γ-producing DETC precursors differentiate into rapid IL-13 producers in the perinatal epidermis. The addition of various inhibitors of signaling pathways downstream of TCR to the in vitro differentiation model of neonatal DETCs revealed that TCR signaling through the p38 MAPK pathway is essential for the functional differentiation of neonatal DETCs. Constitutive TCR signaling at steady state was also shown to be needed for the maintenance of the rapid IL-13-producing capacity of adult DETCs because in vivo treatment with the p38 MAPK inhibitor decreased adult DETCs with the rapid IL-13-producing capacity. Adult DETCs under steady-state conditions had lower glycolytic capacity than proliferating neonatal DETCs. TCR stimulation of adult DETCs induced high glycolytic capacity and IFN-γ production during the late phase of activation. Inhibition of glycolysis decreased IFN-γ but not IL-13 production by adult DETCs during the late phase of activation. These results demonstrate that TCR signaling promotes the differentiation of IL-13-producing DETCs in the perinatal epidermis and is needed for maintaining the rapid IL-13-producing capacity of adult DETCs. The low glycolytic capacity of adult DETCs at steady state also regulates the rapid IL-13 response and delayed IFN-γ production after activation.

Time-dependent cell-state selection identifies transiently expressed genes regulating ILC2 activation

The decision of whether cells are activated or not is controlled through dynamic intracellular molecular networks. However, the low population of cells during the transition state of activation renders the analysis of the transcriptome of this state technically challenging. To address this issue, we have developed the Time-Dependent Cell-State Selection (TDCSS) technique, which employs live-cell imaging of secretion activity to detect an index of the transition state, followed by the simultaneous recovery of indexed cells for subsequent transcriptome analysis. In this study, we used the TDCSS technique to investigate the transition state of group 2 innate lymphoid cells (ILC2s) activation, which is indexed by the onset of interleukin (IL)-13 secretion. The TDCSS approach allowed us to identify time-dependent genes, including transiently induced genes (TIGs). Our findings of IL4 and MIR155HG as TIGs have shown a regulatory function in ILC2s activation.

A tissue-intrinsic IL-33/EGF circuit promotes epithelial regeneration after intestinal injury

Intestinal stem cells (ISCs) maintain the epithelial lining of the intestines, but mechanisms regulating ISCs and their niche after damage remain poorly understood. Utilizing radiation injury to model intestinal pathology, we report here that the Interleukin-33 (IL-33)/ST2 axis, an immunomodulatory pathway monitored clinically as an intestinal injury biomarker, regulates intrinsic epithelial regeneration by inducing production of epidermal growth factor (EGF). Three-dimensional imaging and lineage-specific RiboTag induction within the stem cell compartment indicated that ISCs expressed IL-33 in response to radiation injury. Neighboring Paneth cells responded to IL-33 by augmenting production of EGF, which promoted ISC recovery and epithelial regeneration. These findings reveal an unknown pathway of niche regulation and crypt regeneration whereby the niche responds dynamically upon injury and the stem cells orchestrate regeneration by regulating their niche. This regenerative circuit also highlights the breadth of IL-33 activity beyond immunomodulation and the therapeutic potential of EGF administration for treatment of intestinal injury.

The modulation of pulmonary group 2 innate lymphoid cell function in asthma: from inflammatory mediators to environmental and metabolic factors

A dysregulated type 2 immune response is one of the fundamental causes of allergic asthma. Although Th2 cells are undoubtedly central to the pathogenesis of allergic asthma, the discovery of group 2 innate lymphoid cells (ILC2s) has added another layer of complexity to the etiology of this chronic disease. Through their inherent innate type 2 responses, ILC2s not only contribute to the initiation of airway inflammation but also orchestrate the recruitment and activation of other members of innate and adaptive immunity, further amplifying the inflammatory response. Moreover, ILC2s exhibit substantial cytokine plasticity, as evidenced by their ability to produce type 1- or type 17-associated cytokines under appropriate conditions, underscoring their potential contribution to nonallergic, neutrophilic asthma. Thus, understanding the mechanisms of ILC2 functions is pertinent. In this review, we present an overview of the current knowledge on ILC2s in asthma and the regulatory factors that modulate lung ILC2 functions in various experimental mouse models of asthma and in humans.

Annexin A1 is a cell-intrinsic metalloregulator of zinc in human ILC2s

Group 2 innate lymphoid cells (ILC2s) produce large amounts of type 2 cytokines including interleukin-5 (IL-5) and IL-13 in response to various stimuli, causing allergic and eosinophilic diseases. However, the cell-intrinsic regulatory mechanisms of human ILC2s remain unclear. Here, we analyze human ILC2s derived from different tissues and pathological conditions and identify ANXA1, encoding annexin A1, as a commonly highly expressed gene in non-activated ILC2s. The expression of ANXA1 decreases when ILC2s activate, but it increases autonomously as the activation subsides. Lentiviral vector-based gene transfer experiments show that ANXA1 suppresses the activation of human ILC2s. Mechanistically, ANXA1 regulates the expression of the metallothionein family genes, including MT2A, which modulate intracellular zinc homeostasis. Furthermore, increased intracellular zinc levels play an essential role in the activation of human ILC2s by promoting the mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways and GATA3 expression. Thus, the ANXA1/MT2A/zinc pathway is identified as a cell-intrinsic metalloregulatory mechanism for human ILC2s.

Intermittent fasting protects against food allergy in a murine model via regulating gut microbiota

Background

The prevalence of food allergy (FA) is increasing. Decreases in the diversity of gut microbiota may contribute to the pathogenesis of FA by regulating IgE production of B cells. Intermittent fasting (IF) is a popular diet with the potential to regulate glucose metabolism, boosting immune memory and optimizing gut microbiota. The potential effect of long-term IF on the prevention and treatment of FA is still unknown.

Methods

Two IF protocols (16 h fasting/8 h feeding and 24 h fasting/24 h feeding) were conducted on mice for 56 days, while the control mice were free to intake food (free diet group, FrD). To construct the FA model, all mice were sensitized and intragastrical challenged with ovalbumin (OVA) during the second half of IF (day 28 to day 56). Rectal temperature reduction and diarrhea were recorded to evaluate the symptoms of FA. Levels of serum IgE, IgG1, Th1/Th2 cytokines, mRNA expression of spleen T cell related transcriptional factors, and cytokines were examined. H&E, immunofluorescence, and toluidine blue staining were used to assess the structural changes of ileum villi. The composition and abundance of gut microbiota were analyzed by 16srRNA sequencing in cecum feces.

Results

The diarrhea score and rectal temperature reduction were lower in the two fasting groups compared to the FrD groups. Fasting was associated with lower levels of serum OVA-sIgE, OVA-sIgG1, interleukin (IL)-4 and IL-5, and mRNA expression of IL-4, IL-5, and IL-10 in the spleen. While no significant association was observed in interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-6, IL-2 levels. Less mast cell infiltration in ileum was observed in the 16h/8h fasting group compared to the FrD group. ZO-1 expression in the ileum of the two fasting groups was higher in IF mice. The 24h/24h fasting reshaped the gut microbiota, with a higher abundance of Alistipes and Rikenellaceae strains compared to the other groups.

Conclusion

In an OVA-induced mice FA model, long-term IF may attenuate FA by reducing Th2 inflammation, maintaining the integrity of the intestinal epithelial barrier, and preventing gut dysbiosis.

HIF-PHD inhibitor regulates the function of group2 innate lymphoid cells and polarization of M2 macrophages

Hypoxia-inducible factor-prolyl hydroxylase (HIF-PHD) inhibitors are therapeutic agents for renal anemia that work through HIF2-mediated upregulation of erythropoietin (EPO) and have also been reported to suppress renal fibrosis. Group 2 innate lymphoid cells (ILC2s) have been proven to be involved in the pathogenesis of fibrosis in various organs, including the kidney. However, the relationship between the HIF pathway, renal fibrosis, and kidney ILC2s remains unclear. In the present study, we found that HIF activation by HIF-PHD inhibitors suppressed type 2 cytokine production from kidney ILC2s. The enhanced HIF pathway downregulated the IL-33 receptor ST2L on ILC2s, and phosphorylation of downstream p38 MAPK was attenuated. M2 macrophages that promote renal fibrosis were polarized by ILC2 supernatants, but reduced cytokine production from ILC2s treated with HIF-PHD inhibitors suppressed this polarization. Our findings suggest that HIF-PHD inhibitors are potential therapeutic agents for renal fibrosis that are mediated by the alteration of ILC2 function.

Crossing the valley of death: Toward translational research regarding ILC2

Group 2 innate lymphoid cells (ILC2s) are tissue-resident innate lymphoid cells that express the transcription factor GATA3 as a master regulator, which leads to the production of large amounts of type 2 cytokines, such as IL-5 and IL-13. ILC2s are activated by epithelial cell-derived cytokines, including IL-33 and IL-25, and play a key role in parasite expulsion, allergic responses, tissue repair, and metabolism. In the first five years after the discovery of ILC2s, research mainly focused on their function through cytokine receptors. However, in recent years, their regulatory mechanisms through not only cytokine receptors but also lipids, neuropeptides, and hormones have become a hot topic. For ILC2s that do not recognize foreign antigens, receptor expression of such endogenous factors is important, and the diverse expression patterns create the individuality of ILC2s in each organ. By considering the mechanisms of differentiation and regulation of ILC2s and their role in disease while taking into account spatio-temporal information, it is expected that new therapeutic strategies targeting ILC2s will be developed. Herein, we summarize the current understanding of ILC2s in lung homeostasis and pathology and provide valuable insights that will help to guide the future development of therapeutic methods for ILC2-mediated lung diseases.

A deubiquitination module essential for Treg fitness in the tumor microenvironment

The tumor microenvironment (TME) enhances regulatory T (Treg) cell stability and immunosuppressive functions through up-regulation of lineage transcription factor Foxp3, a phenomenon known as Treg fitness or adaptation. Here, we characterize previously unknown TME-specific cellular and molecular mechanisms underlying Treg fitness. We demonstrate that TME-specific stressors including transforming growth factor-β (TGF-β), hypoxia, and nutrient deprivation selectively induce two Foxp3-specific deubiquitinases, ubiquitin-specific peptidase 22 (Usp22) and Usp21, by regulating TGF-β, HIF, and mTOR signaling, respectively, to maintain Treg fitness. Simultaneous deletion of both USPs in Treg cells largely diminishes TME-induced Foxp3 up-regulation, alters Treg metabolic signatures, impairs Treg-suppressive function, and alleviates Treg suppression on cytotoxic CD8+ T cells. Furthermore, we developed the first Usp22-specific small-molecule inhibitor, which dramatically reduced intratumoral Treg Foxp3 expression and consequently enhanced antitumor immunity. Our findings unveil previously unappreciated mechanisms underlying Treg fitness and identify Usp22 as an antitumor therapeutic target that inhibits Treg adaptability in the TME.

Emerging Effects of IL-33 on COVID-19

Since the start of COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 6 million people have lost their lives worldwide directly or indirectly. Despite intensified efforts to clarify the immunopathology of COVID-19, the key factors and processes that trigger an inflammatory storm and lead to severe clinical outcomes in patients remain unclear. As an inflammatory storm factor, IL-33 is an alarmin cytokine, which plays an important role in cell damage or infection. Recent studies have shown that serum IL-33 is upregulated in COVID-19 patients and is strongly associated with poor outcomes. Increased IL-33 levels in severe infections may result from an inflammatory storm caused by strong interactions between activated immune cells. However, the effects of IL-33 in COVID-19 and the underlying mechanisms remain to be fully elucidated. In this review, we systematically discuss the biological properties of IL-33 under pathophysiological conditions and its regulation of immune cells, including neutrophils, innate lymphocytes (ILCs), dendritic cells, macrophages, CD4⁺ T cells, Th17/Treg cells, and CD8⁺ T cells, in COVID-19 phagocytosis. The aim of this review is to explore the potential value of the IL-33/immune cell pathway as a new target for early diagnosis, monitoring of severe cases, and clinical treatment of COVID-19.

Metabolic features of innate lymphoid cells

Innate and adaptive immune cells are found in distinct tissue niches where they orchestrate immune responses. This requires intrinsic and temporal metabolic adaptability to coordinately activate the immune response cascade. Dysregulation of this program is a key feature of immunosuppression. Direct or indirect metabolic immune cell reprogramming may offer new approaches to modulate immune cells behavior for therapy to overcome dysregulation. In this review, we explored how metabolism regulates lymphocytes beyond the classical T cell subsets. We focus on the innate lymphoid cell (ILC) family, highlighting the distinct metabolic characteristics of these cells, the impact of environmental factors, and the receptors that could alter immune cell functions through manipulation of metabolic pathways to potentially prevent or treat various diseases.

Non-redundant functions of group 2 innate lymphoid cells

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

Dual Immune Regulatory Roles of Interleukin-33 in Pathological Conditions

Interleukin-33 (IL-33), a member of the IL-1 cytokine family and a multifunctional cytokine, plays critical roles in maintaining host homeostasis and in pathological conditions, such as allergy, infectious diseases, and cancer, by acting on multiple types of immune cells and promoting type 1 and 2 immune responses. IL-33 is rapidly released by immune and non-immune cells upon stimulation by stress, acting as an “alarmin” by binding to its receptor, suppression of tumorigenicity 2 (ST2), to trigger downstream signaling pathways and activate inflammatory and immune responses. It has been recognized that IL-33 displays dual-functioning immune regulatory effects in many diseases and has both pro- and anti-tumorigenic effects, likely depending on its primary target cells, IL-33/sST2 expression levels, cellular context, and the cytokine microenvironment. Herein, we summarize our current understanding of the biological functions of IL-33 and its roles in the pathogenesis of various conditions, including inflammatory and autoimmune diseases, infections, cancers, and cases of organ transplantation. We emphasize the nature of context-dependent dual immune regulatory functions of IL-33 in many cells and diseases and review systemic studies to understand the distinct roles of IL-33 in different cells, which is essential to the development of more effective diagnoses and therapeutic approaches for IL-33-related diseases.

RNA-binding protein RBM3 intrinsically suppresses lung innate lymphoid cell activation and inflammation partially through CysLT1R

Innate lymphoid cells (ILC) promote lung inflammation in asthma through cytokine production. RNA-binding proteins (RBPs) are critical post-transcriptional regulators, although less is known about RBPs in ILC biology. Here, we demonstrate that RNA-binding motif 3 (RBM3) is highly expressed in lung ILCs and is further induced by alarmins TSLP and IL-33. Rbm3^-/- and Rbm3^-/-Rag2^-/- mice exposed to asthma-associated Alternaria allergen develop enhanced eosinophilic lung inflammation and ILC activation. IL-33 stimulation studies in vivo and in vitro show that RBM3 suppressed lung ILC responses. Further, Rbm3^-/- ILCs from bone marrow chimeric mice display increased ILC cytokine production suggesting an ILC-intrinsic suppressive function of RBM3. RNA-sequencing of Rbm3^-/- lung ILCs demonstrates increased expression of type 2/17 cytokines and cysteinyl leukotriene 1 receptor (CysLT1R). Finally, Rbm3^-/-Cyslt1r^-/- mice show dependence on CysLT1R for accumulation of ST2⁺IL-17⁺ ILCs. Thus, RBM3 intrinsically regulates lung ILCs during allergen-induced type 2 inflammation that is partially dependent on CysLT1R.

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.

Current overview of the role of neuropeptides in ILC2s and future directions

The neural and immune systems are closely connected, and recently, their molecular mechanisms and relationships with diseases have attracted substantial attention. Particularly, it has been increasingly reported that ILC2s, which produce type 2 cytokines independent of acquired immunity, are regulated by neuropeptides such as catecholamines, acetylcholine, vasoactive intestinal peptide, neuromedins, and calcitonin gene-related peptide. However, the regulatory mechanisms in this regard are only partially understood, implying that further studies are still needed to clarify the complete mechanisms and processes. In this review, we summarize current reports on the regulatory effect of neuropeptides on ILC2s, some of which have conflicting results, possibly owing to the complexity of G-protein coupled receptors. By summarizing the current evidence, we hope to be able to identify what is currently unknown as well as what needs to be clarified in the future.

The Role of Airway Epithelial Cell Alarmins in Asthma

The airway epithelium is the first line of defense for the lungs, detecting inhaled environmental threats through pattern recognition receptors expressed transmembrane or intracellularly. Activation of pattern recognition receptors triggers the release of alarmin cytokines IL-25, IL-33, and TSLP. These alarmins are important mediators of inflammation, with receptors widely expressed in structural cells as well as innate and adaptive immune cells. Many of the key effector cells in the allergic cascade also produce alarmins, thereby contributing to the airways disease by driving downstream type 2 inflammatory processes. Randomized controlled clinical trials have demonstrated benefit when blockade of TSLP and IL-33 were added to standard of care medications, suggesting these are important new targets for treatment of asthma. With genome-wide association studies demonstrating associations between single-nucleotide polymorphisms of the TSLP and IL-33 gene and risk of asthma, it will be important to understand which subsets of asthma patients will benefit most from anti-alarmin therapy.

TLR3-driven IFN-β antagonizes STAT5-activating cytokines and suppresses innate type 2 response in the lung

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are involved in type 2 immune responses in mucosal organs and are associated with various allergic diseases in humans. Studies are needed to understand the molecules and pathways that control ILC2s.

OBJECTIVE

The aims of this study were to develop a mouse model that limits the innate type 2 immune response in the lung and to investigate the immunologic mechanisms involved in regulation of lung ILC2s.

METHODS

Naive BALB/c mice were administered various Toll-like receptor agonists and exposed intranasally to the fungal allergen Alternaria alternata. The mechanisms were investigated using gene knockout mice as well as cultures of lung cells and isolated lung ILC2s.

RESULTS

Polyinosinic-polycytidylic acid, or poly (I:C), effectively inhibited innate type 2 response to A alternata. Poly (I:C) promoted production of IFNα, -β, and -γ, and its inhibitory effects were dependent on the IFN-α/β receptor pathway. IFN-β was 100 times more potent than IFN-α at inhibiting type 2 cytokine production by lung ILC2s. Signal transducer and activator of transcription 5 (STAT5)-activating cytokines, including IL-2, IL-7, and thymic stromal lymphopoietin, but not IL-33, promoted survival and proliferation of lung ILC2s in vitro, while IFN-β blocked these effects. Expression of the transcription factor GATA3, which is critical for differentiation and maintenance of ILC2s, was inhibited by IFN-β.

CONCLUSIONS

IFN-β blocks the effects of STAT5-activating cytokines on lung ILC2s and inhibits their survival and effector functions. Administration of IFN-β may provide a new strategy to treat diseases involving ILC2s.

MiR-150-5p regulates the functions of type 2 innate lymphoid cells via the ICAM-1/p38 MAPK axis in allergic rhinitis

Type 2 innate lymphoid cells (ILC2s) exert an increasingly important influence on the pathological process of allergic rhinitis (AR), which is affected by microRNAs-mediated post-transcriptional regulation. This study aims to investigate the function of miR-150-5p in AR patients and the mouse model of AR. The mouse model of AR was established using the OVA challenge. The expressions of miR-150-5p, ICAM-1, p-p38 and p-GATA-3 were evaluated via RT-qPCR and western blot analysis. The level of ILC2s was examined with flow cytometry. Concentrations of OVA-specific IgE, IL-13 and IL-5 in serum were evaluated using ELISA. Histopathological examination was conducted through H&E staining. The interplay between ICAM-1 and miR-150-5p was determined through the DLR assay. The decreased miR-150-5p expression and increased ICAM-1, p-p38 and p-GATA-3 expressions and ILC2s levels were detected in AR patients and AR mice compared with controls. Treatment with miR-150-5p lentivirus alleviated AR symptoms (sneezing, rubbing, mucosa inflammation, serum type 2 cytokines and OVA-specific IgE) and lowered the ILC2s level in AR mice. MiR-150-5p was found to directly bind to 3'-UTR of ICAM-1 and downregulate ICAM-1 expression, thereby descending the level of p-p38, p-GATA-3 and suppressing ILC2s function to alleviate AR symptoms. Treatment with Lenti-ICAM-1 counteracted these protective effects of miR-150-5p. Upregulation of miR-150-5p repressed the ICAM-1/p38 axis which was vital to ILC2s development and function, thereby alleviating allergic symptoms of AR.

Posttranscriptional regulation of ILC2 homeostatic function via tristetraprolin

Group 2 innate lymphoid cells (ILC2s) are unique in their ability to produce low levels of type 2 cytokines at steady state, and their production capacity is dramatically increased upon stimulation with IL-33. However, it is unknown how constitutive cytokine production is regulated in the steady state. Here, we found that tristetraprolin (TTP/Zfp36), an RNA-binding protein that induces mRNA degradation, was highly expressed in naive ILC2s and was downregulated following IL-33 stimulation. In ILC2s from Zfp36-/- mice, constitutive IL-5 production was elevated owing to the stabilization of its mRNA and resulted in an increased number of eosinophils in the intestine. Luciferase assay demonstrated that TTP directly regulates Il5 mRNA stability, and overexpression of TTP markedly suppressed IL-5 production by ILC2s, even under IL-33 stimulation. Collectively, TTP-mediated posttranscriptional regulation acts as a deterrent of excessive cytokine production in steady-state ILC2s to maintain body homeostasis, and downregulation of TTP may contribute to massive cytokine production under IL-33 stimulation.

A RAS inhibitor reduces allergic airway remodeling via regulating IL-33-derived type 2 innate lymphoid cells

Purpose: IL-33 is known to induce corticosteroid-resistant eosinophilic inflammation and airway remodeling by activating type 2 innate lymphoid cells (ILC2s). Although the RAS signal pathway plays an important role in IL-33-induced ILC2s activation and airway remodeling, it is not known if RAS inhibitors are effective against refractory asthma. We examined the effects of the RAS inhibitor XRP44X in refractory asthma. Methods: RAS activity were examined by BAL fluid and T-cells isolated from spleen cells in Dermatophagoides pteronyssinus (Dp)-sensitized/challenged acute allergic airway inflammation model. A chronic allergic airway inflammation mouse model was generated by challenged with Dp. XRP44X and/or fluticasone were administrated nasally to different experimental groups. The effects of nasal simultaneous administration of XRP44X or fluticasone were assessed in mice administrated with IL-33 or Dp. Results: RAS activity in CD4⁺ T cells stimulated by Dp were suppressed by XRP44X. Although fluticasone and XRP44X only improved allergic airway inflammation in mice, XRP44X in combination with fluticasone produced further improvement in not only eosinophilic inflammation but also bronchial subepithelial thickness. XRP44X suppressed IL-5 and IL-13 production from ILC2s, although this effect was not suppressed by fluticasone. IL-33-induced airway inflammation resistant to fluticasone was ameliorated by XRP44X via regulating the accumulation of lung ILC2s. Conclusion: The RAS signal pathway plays a crucial role in allergen-induced airway remodeling associated with ILC2s. XRP44X may have therapeutic potential for refractory asthma.

A Gata3 enhancer necessary for ILC2 development and function

The type 2 helper effector program is driven by the master transcription factor GATA3 and can be expressed by subsets of both innate lymphoid cells (ILCs) and adaptive CD4+ T helper (Th) cells. While ILC2s and Th2 cells acquire their type 2 differentiation program under very different contexts, the distinct regulatory mechanisms governing this common program are only partially understood. Here we show that the differentiation of ILC2s, and their concomitant high level of GATA3 expression, are controlled by a Gata3 enhancer, Gata3 +674/762, that plays only a minimal role in Th2 cell differentiation. Mice lacking this enhancer exhibited defects in several but not all type 2 inflammatory responses, depending on the respective degree of ILC2 and Th2 cell involvement. Our study provides molecular insights into the different gene regulatory pathways leading to the acquisition of the GATA3-driven type 2 helper effector program in innate and adaptive lymphocytes.

Stage-specific action of Runx1 and GATA3 controls silencing of PU.1 expression in mouse pro-T cells

PU.1 (encoded by Spi1), an ETS-family transcription factor with many hematopoietic roles, is highly expressed in the earliest intrathymic T cell progenitors but must be down-regulated during T lineage commitment. The transcription factors Runx1 and GATA3 have been implicated in this Spi1 repression, but the basis of the timing was unknown. We show that increasing Runx1 and/or GATA3 down-regulates Spi1 expression in pro-T cells, while deletion of these factors after Spi1 down-regulation reactivates its expression. Leveraging the stage specificities of repression and transcription factor binding revealed an unconventional but functional site in Spi1 intron 2. Acute Cas9-mediated deletion or disruption of the Runx and GATA motifs in this element reactivates silenced Spi1 expression in a pro-T cell line, substantially more than disruption of other candidate elements, and counteracts the repression of Spi1 in primary pro-T cells during commitment. Thus, Runx1 and GATA3 work stage specifically through an intronic silencing element in mouse Spi1 to control strength and maintenance of Spi1 repression during T lineage commitment.

Synergistic role of retinoic acid signaling and Gata3 during primitive choanae formation

Developmental defects of primitive choanae, an anatomical path to connect the embryonic nasal and oral cavity, result in disorders called choanal atresia, which are associated with many congenital diseases and require immediate clinical intervention after birth. Previous studies revealed that reduced retinoid signaling underlies the etiology of choanal atresia. In the present study, by using multiple mouse models which conditionally deleted Rdh10 and Gata3 during embryogenesis, we showed that Gata3 expression is regulated by retinoid signaling during embryonic craniofacial development and plays crucial roles for development of the primitive choanae. Interestingly, Gata3 loss of function is known to cause hypoparathyroidism, sensorineural deafness and renal disease (HDR) syndrome, which exhibits choanal atresia as one of the phenotypes in humans. Our model partially phenocopies HDR syndrome with choanal atresia, and is thus a useful tool for investigating the molecular and cellular mechanisms of HDR syndrome. We further uncovered critical synergy of Gata3 and retinoid signaling during embryonic development, which will shed light on novel molecular and cellular etiology of congenital defects in primitive choanae formation.

Serum free culture for the expansion and study of type 2 innate lymphoid cells

Type 2 innate lymphoid cells (ILC2s) were discovered approximately ten years ago and their clinical relevance is gaining greater importance. However, their successful isolation from mammalian tissues and in vitro culture and expansion continues to pose challenges. This is partly due to their scarcity compared to other leukocyte populations, but also because our current knowledge of ILC2 biology is incomplete. This study is focused on ST2⁺ IL-25R^lo lung resident ILC2s and demonstrate for the first time a methodology allowing mouse type 2 innate lymphoid cells to be cultured, and their numbers expanded in serum-free medium supplemented with Interleukins IL-33, IL-2, IL-7 and TSLP. The procedures described methods to isolate ILC2s and support their growth for up to a week while maintaining their phenotype. During this time, they significantly expand from low to high cell concentrations. Furthermore, for the first time, sub-cultures of primary ILC2 purifications in larger 24- and 6-well plates were undertaken in order to compare their growth in other media. In culture, ILC2s had doubling times of 21 h, a growth rate of 0.032 h⁻¹ and could be sub-cultured in early or late phases of exponential growth. These studies form the basis for expanding ILC2 populations that will facilitate the study and potential applications of these rare cells under defined, serum-free conditions.

Systematic identification of the cancer pathways and molecules related with breast cancer immunogenicity

To identify molecular features related to immunogenic activity in breast cancer (BC) and provide new targets and directions for BC immunotherapy, we firstly used ESTIMATE to evaluate the degree of immune cell infiltration of the BC patients in TCGA and METABRIC, and explore the relationship between the degree of immune cell infiltration and prognosis of BC patients. Then, we identified the cancer pathways, proteins and miRNAs related to BC immunogenicity, predicted the target genes of these miRNAs, and identified the pathways related to these target genes with KEGG pathway enrichment analysis. We also explored the correlation between PD-L1 expression level and cancer pathways and found that PD-L1 expression showed a positive association with cancer-related pathways. In this article we have successfully identified several cancer-related pathways, proteins, miRNAs, and their target genes, which provided promising new targets for BC immunotherapy. And PD-L1 blockade therapy may be more effective in BC patients with the activation of some cancer-related pathways.

NK cell and ILC heterogeneity in colorectal cancer. New perspectives from high dimensional data

Innate lymphoid cells (ILCs) and tissue-resident natural killer (NK) cells ensure immunity at environmental interfaces and help maintain barrier integrity of the intestinal tract. This wide range of innate lymphocytes is able to provide fast and potent inflammatory responses that, when deregulated, have been associated with pathogenesis of inflammatory bowel disease (IBD) and colorectal cancer (CRC). While the presence of tumor-infiltrating NK cells is generally associated with a favorable outcome in CRC patients, emerging evidence reveals distinct roles for ILCs in regulating CRC pathogenesis and progression. Advances in next generation sequencing technology, and in particular of single-cell RNA-seq approaches, along with multidimensional flow cytometry analysis, have helped to deconvolute the complexity and heterogeneity of the ILC system both in homeostatic and pathological contexts. In this review, we discuss the protective and detrimental roles of NK cells and ILCs in the pathogenesis of CRC, focusing on the phenotypic and transcriptional modifications these cells undergo during CRC development and progression.

The Fate of Activated Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) reside in both mucosal and non-mucosal tissues and play critical roles in the first line of defense against parasites and irritants such as allergens. Upon activation by cytokines released from epithelial and stromal cells during tissue damage or stimulation, ILC2s produce copious amounts of IL-5 and IL-13, leading to type 2 inflammation. Over the past 10 years, ILC2 involvement in a variety of human diseases has been unveiled. However, questions remain as to the fate of ILC2s after activation and how that might impact their role in chronic inflammatory diseases such as asthma and fibrosis. Here, we review studies that have revealed novel properties of post-activation ILC2s including the generation of immunological memory, exhausted-like phenotype, transdifferentiation and activation-induced migration.

Tumor-Derived Lactic Acid Contributes to the Paucity of Intratumoral ILC2s

Group 2 innate lymphoid cells (ILC2s) are abundant in non-lymphoid tissues and increase following infectious and inflammatory insults. In solid tumors, however, ILC2s constitute a relatively small proportion of immune cells. Here, we show, using melanoma as a model, that while the IL-33/IL C2/eosinophil axis suppresses tumor growth, tumor-derived lactate attenuates the function and survival of ILC2s. Melanomas with reduced lactate production (LDHA^low) are growth delayed and typified by an increased number of ILC2s compared with control tumors. Upon IL-33 stimulation, ILC2s accompanied by eosinophils more effectively restrain the growth of LDHA^low tumors than control melanomas. Furthermore, database analysis reveals a negative correlation between the expression of LDHA and markers associated with ILC2s and the association of high expression of IL33 and an eosinophil marker SIGLEC8 with better overall survival in human cutaneous melanoma patients. This work demonstrates that the balance between the IL-33/ILC2/eosinophil axis and lactate production by tumor cells regulates melanoma growth.

How transcription factors drive choice of the T cell fate

Recent evidence has elucidated how multipotent blood progenitors transform their identities in the thymus and undergo commitment to become T cells. Together with environmental signals, a core group of transcription factors have essential roles in this process by directly activating and repressing specific genes. Many of these transcription factors also function in later T cell development, but control different genes. Here, we review how these transcription factors work to change the activities of specific genomic loci during early intrathymic development to establish T cell lineage identity. We introduce the key regulators and highlight newly emergent insights into the rules that govern their actions. Whole-genome deep sequencing-based analysis has revealed unexpectedly rich relationships between inherited epigenetic states, transcription factor-DNA binding affinity thresholds and influences of given transcription factors on the activities of other factors in the same cells. Together, these mechanisms determine T cell identity and make the lineage choice irreversible.

NK cells and ILCs in tumor immunotherapy

Cells of the innate immunity play an important role in tumor immunotherapy. Thus, NK cells can control tumor growth and metastatic spread. Thanks to their strong cytolytic activity against tumors, different approaches have been developed for exploiting/harnessing their function in patients with leukemia or solid tumors. Pioneering trials were based on the adoptive transfer of autologous NK cell-enriched cell populations that were expanded in vitro and co-infused with IL-2. Although relevant results were obtained in patients with advanced melanoma, the effect was mostly limited to certain metastatic localizations, particularly to the lung. In addition, the severe IL-2-related toxicity and the preferential IL-2-induced expansion of Treg limited this type of approach. This limitation may be overcome by the use of IL-15, particularly of modified IL-15 molecules to improve its half-life and optimize the biological effects. Other approaches to harness NK cell function include stimulation via TLR, the use of bi- and tri-specific NK cell engagers (BiKE and TriKE) linking activating NK receptors (e.g. CD16) to tumor-associated antigens and even incorporating an IL-15 moiety (TriKE). As recently shown, in tumor patients, NK cells may also express inhibitory checkpoints, primarily PD-1. Accordingly, the therapeutic use of checkpoint inhibitors may unleash NK cells against PD-L1⁺ tumors. This effect may be predominant and crucial in tumors that have lost HLA cl-I expression, thus resulting "invisible" to T lymphocytes. Additional approaches in which NK cells may represent an important tool for cancer therapy, are to exploit the unique properties of the "adaptive" NK cells. These CD57⁺ NKG2C⁺ cells, despite their mature stage and a potent cytolytic activity, maintain a strong proliferating capacity. This property revealed to be crucial in hematopoietic stem cell transplantation (HSCT), particularly in the haplo-HSCT setting, to cure high-risk leukemias. T depleted haplo-HSCT (e.g. from one of the parents) allowed to save the life of thousands of patients lacking a HLA-compatible donor. In this setting, NK cells have been shown to play an essential role against leukemia cells and infections. Another major advance is represented by chimeric antigen receptor (CAR)-engineered NK cells. CAR-NK, different from CAR-T cells, may be obtained from allogeneic donors since they do not cause GvHD. Accordingly, they may represent "off-the-shelf" products to promptly treat tumor patients, with affordable costs. Different from NK cells, helper ILC (ILC1, ILC2 and ILC3), the innate counterpart of T helper cell subsets, remain rather ambiguous with respect to their anti-tumor activity. A possible exception is represented by a subset of ILC3: their frequency in peri-tumoral tissues in patients with NSCLC directly correlates with a better prognosis, possibly reflecting their ability to contribute to the organization of tertiary lymphoid structures, an important site of T cell-mediated anti-tumor responses. It is conceivable that innate immunity may significantly contribute to the major advances that immunotherapy has ensured and will continue to ensure to the cure of cancer.

Post-Translational Modifications of Transcription Factors Harnessing the Etiology and Pathophysiology in Colonic Diseases

Defects in mucosal immune balance can lead to colonic diseases such as inflammatory bowel diseases and colorectal cancer. With the advancement of understanding for the immunological and molecular basis of colonic disease, therapies targeting transcription factors have become a potential approach for the treatment of colonic disease. To date, the biomedical significance of unique post-translational modifications on transcription factors has been identified, including phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. This review focuses on our current understanding and the emerging evidence of how post-translational regulations modify transcription factors involved in the etiology and pathophysiology of colonic disease as well as the implications of these findings for new therapeutic approaches in these disorders.

p38 MAPK signalling regulates cytokine production in IL-33 stimulated Type 2 Innate Lymphoid cells

Type 2 Innate lymphoid cells (ILC2s) are implicated in helminth infections and asthma where they play a role in the production of Th2-type cytokines. ILC2s express the IL-33 receptor and are a major cell type thought to mediate the effects of this cytokine in vivo. To study the signalling pathways that mediate IL-33 induced cytokine production, a culture system was set up to obtain pure populations of ILC2s from mice. Inhibitors of the p38α/β and ERK1/2 MAPK pathways reduced the production of IL-5, IL-6, IL-9, IL-13 and GM-CSF by ILC2 in response to IL-33, with inhibition of p38 having the greatest effect. MK2 and 3 are kinases activated by p38α; MK2/3 inhibitors or knockout of MK2/3 in mice reduced the production of IL-6 and IL-13 (two cytokines implicated in asthma) but not IL-5, IL-9 or GM-CSF in response to IL-33. MK2/3 inhibition also suppressed IL-6 and IL-13 production by human ILC2s. MK2/3 were required for maximal S6 phosphorylation, suggesting an input from the p38α-MK2/3 pathway to mTOR1 activation in ILC2s. The mTORC1 inhibitor rapamycin also reduced IL-6 and IL-13 production, which would be consistent with a model in which MK2/3 regulate IL-6 and IL-13 via mTORC1 activation in ILC2s.

Differential Expression of the Transcription Factor GATA3 Specifies Lineage and Functions of Innate Lymphoid Cells

Lymphoid tissue inducer (LTi) cells are regarded as a subset of innate lymphoid cells (ILCs). However, these cells are not derived from the ILC common progenitor, which generates other ILC subsets and is defined by the expression of the transcription factor PLZF. Here, we examined transcription factor(s) determining the fate of LTi progenitors versus non-LTi ILC progenitors. Conditional deletion of Gata3 resulted in the loss of PLZF+ non-LTi progenitors but not the LTi progenitors that expressed the transcription factor RORγt. Consistently, PLZF+ non-LTi progenitors expressed high amounts of GATA3, whereas GATA3 expression was low in RORγt+ LTi progenitors. The generation of both progenitors required the transcriptional regulator Id2, which defines the common helper-like innate lymphoid progenitor (ChILP), but not cytokine signaling. Nevertheless, low GATA3 expression was necessary for the generation of functionally mature LTi cells. Thus, differential expression of GATA3 determines the fates and functions of distinct ILC progenitors.

Tissue-resident NK cells and other innate lymphoid cells

Natural killer (NK) cells are important innate effectors for their defense against pathogens and tumors without the need of prior sensitization. Along with the growing understanding of basic NK cell biology, it has been widely accepted that NK cells are a heterogeneous population of innate lymphoid cell (ILC) family. Apart from the conventional NK cell (cNK) subset that circulates throughout the body, some non-lymphoid tissues contain tissue-resident NK (trNK) cell subsets, and the composition of NK cell subsets varies greatly with different locations. Except for cNK cells, other ILCs are known as tissue-resident cells. In this review, we summarize the unique properties of trNK cells, discuss their lineage relationship with other ILCs, and highlight recent advances in our understanding of the functions of trNK cells and other ILCs.

The Transcription Factor RORα Preserves ILC3 Lineage Identity and Function during Chronic Intestinal Infection

Innate lymphoid cells (ILCs) are critical for host defense and tissue repair but can also contribute to chronic inflammatory diseases. The transcription factor RORα is required for ILC2 development but is also highly expressed by other ILC subsets where its function remains poorly defined. We previously reported that Rora^sg/sg bone marrow chimeric mice (C57BL/6J) were protected from Salmonella-induced intestinal fibrosis due to defective ILC3 responses. In this study, single-cell RNA analysis of ILCs isolated from inflamed tissues indicates that RORα perturbation led to a reduction in ILC3 lineages. Furthermore, residual Rora^sg/sg ILC3s have decreased expression of key signature genes, including Rorc and activating cytokine receptors. Collectively, our data suggest that RORα plays a key role in preserving functional ILC3s by modulating their ability to integrate environmental cues to efficiently produce cytokines.

Type 2 innate lymphoid cells participate in IL-33-stimulated Th2-associated immune response in chronic obstructive pulmonary disease

The aim of the present study was to investigate the roles of type 2 innate lymphoid cells (ILC2s) and interleukin-33 (IL-33) in chronic obstructive pulmonary disease (COPD). Serum and peripheral blood mononuclear cells (PBMCs) were isolated from healthy controls and COPD patients. ILC2 cells from the peripheral blood of COPD patients were stimulated with IL-33 or neutralizing ST2 antibody+IL-33 in vitro. The cell viability was assessed using a Cell Counting Kit-8 assay. ELISA was used to detect serum IL-33 and the levels of IL-4, IL-5, IL-6, IL-13 and soluble ST2 (sST2) in the culture supernatant. The percentage of ILC2 cells was measured by flow cytometry. The mRNA expression levels of GATA binding protein 3 (GATA3), RAR-related orphan receptor (ROR)α, ST2 and prostaglandin D2 receptor 2 (CRTH2) were detected by reverse transcription-quantitative PCR. It was revealed that IL-33, IL-5, IL-6 and IL-13 were significantly elevated in peripheral blood of patients with COPD. The proportion of ILC2s in peripheral blood of COPD patients was significantly increased, and the expression of RORA and CRTH2 was increased. The proportion of ST2⁺ ILC2 cells was significantly increased. After 48 h of IL-33 stimulation in vitro, the ratio of linage^-CD45⁺CD127⁺CRTH2⁺ cells reached a maximum. In addition, the viability of ILC2 cells, the expression levels of RORA, GATA3, ST2 and CRTH2 mRNA and the cytokines IL-4, IL-6, IL-5, IL-13 and sST2 were significantly increased. These effects were abrogated by treatment with anti-ST2. In conclusion, IL-33 is upregulated in the serum of patients with COPD and the proportion of ILC2s among the PBMCs is increased. IL-33 may promote the proliferation of ILC2 cells and secrete type 2 T-helper cell cytokines to participate in the immune response in COPD.

Neuropeptide CGRP Limits Group 2 Innate Lymphoid Cell Responses and Constrains Type 2 Inflammation

Innate lymphocytes maintain tissue homeostasis at mucosal barriers, with group 2 innate lymphoid cells (ILC2s) producing type 2 cytokines and controlling helminth infection. While the molecular understanding of ILC2 responses has advanced, the complexity of microenvironmental factors impacting ILC2s is becoming increasingly apparent. Herein, we used single-cell analysis to explore the diversity of gene expression among lung lymphocytes during helminth infection. Following infection, we identified a subset of ILC2s that preferentially expressed Il5-encoding interleukin (IL)-5, together with Calca-encoding calcitonin gene-related peptide (CGRP) and its cognate receptor components. CGRP in concert with IL-33 and neuromedin U (NMU) supported IL-5 but constrained IL-13 expression and ILC2 proliferation. Without CGRP signaling, ILC2 responses and worm expulsion were enhanced. Collectively, these data point to CGRP as a context-dependent negative regulatory factor that shapes innate lymphocyte responses to alarmins and neuropeptides during type 2 innate immune responses.

Innate lymphoid cells, mediators of tissue homeostasis, adaptation and disease tolerance

Innate lymphoid cells (ILC) are a recently identified group of tissue-resident innate lymphocytes. Available data support the view that ILC or their progenitors are deposited and retained in tissues early during ontogeny. Thereby, ILC become an integral cellular component of tissues and organs. Here, we will review the intriguing relationships between ILC and basic developmental and homeostatic processes within tissues. Studying ILC has already led to the appreciation of the integral roles of immune cells in tissue homeostasis, morphogenesis, metabolism, regeneration, and growth. This area of immunology has not yet been studied in-depth but is likely to reveal important networks contributing to disease tolerance and may be harnessed for future therapeutic approaches.

The group 2 innate lymphoid cell (ILC2) regulatory network and its underlying mechanisms

Group 2 innate lymphoid cells (ILC2s) play critical roles in the induction of type 2 inflammation, response to parasite infection, metabolic homeostasis, and tissue repair. These multifunctional roles of ILC2s are tightly controlled by complex regulatory systems in the local microenvironment, the disruption of which may cause various health problems. This review summarizes up-to-date knowledge regarding positive and negative regulators for ILC2s based on their function and signaling pathways, including activating cytokines (IL-33, IL-25; MAPK, NF-κB pathways), co-stimulatory cytokines (IL-2, IL-7, IL-9, TSLP; STAT5, IL-4; STAT6, TNF superfamily; MAPK, NF-κB pathways), suppressive cytokines (type1 IFNs, IFN-γ, IL-27; STAT1, IL-10, TGF-β), transdifferentiation cytokines (IL-12; STAT4, IL-1β, IL-18), lipid mediators (LTC4, LTD4, LTE4, PGD2; Ca²⁺ -NFAT pathways, PGE2, PGI2; AC/cAMP/PKA pathways, LXA4, LTB4), neuropeptides (NMU; Ca²⁺ -NFAT, MAPK pathways, VIP, CGRP, catecholamine, acetylcholine), sex hormones (androgen, estrogen), nutrients (butyrate; HDAC inhibitors, vitamins), and cell-to-cell interactions (ICOSL-ICOS; STAT5, B7-H6-NKp30, E-cadherin-KLRG1). This comprehensive review affords a better understanding of the regulatory network system for ILC2s, providing impetus to develop new treatment strategies for ILC2-related health problems.

Innate Lymphoid Cells: 10 Years On

Innate lymphoid cells (ILCs) are lymphocytes that do not express the type of diversified antigen receptors expressed on T cells and B cells. ILCs are largely tissue-resident cells and are deeply integrated into the fabric of tissues. The discovery and investigation of ILCs over the past decade has changed our perception of immune regulation and how the immune system contributes to the maintenance of tissue homeostasis. We now know that cytokine-producing ILCs contribute to multiple immune pathways by, for example, sustaining appropriate immune responses to commensals and pathogens at mucosal barriers, potentiating adaptive immunity, and regulating tissue inflammation. Critically, the biology of ILCs also extends beyond classical immunology to metabolic homeostasis, tissue remodeling, and dialog with the nervous system. The last 10 years have also contributed to our greater understanding of the transcriptional networks that regulate lymphocyte commitment and delineation. This, in conjunction with the recent advances in our understanding of the influence of local tissue microenvironments on the plasticity and function of ILCs, has led to a re-evaluation of their existing categorization. In this review, we distill the advances in ILC biology over the past decade to refine the nomenclature of ILCs and highlight the importance of ILCs in tissue homeostasis, morphogenesis, metabolism, repair, and regeneration.

Toll-like receptor 9-dependent interferon production prevents group 2 innate lymphoid cell-driven airway hyperreactivity

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are important mediators of allergic asthma. Bacterial components, such as unmethylated CpG DNA, a Toll-like receptor (TLR) 9 agonist, are known to possess beneficial immunomodulatory effects in patients with T cell-mediated chronic asthma. However, their roles in regulating ILC2s remain unclear.

OBJECTIVE

We sought to determine the role of TLR9 activation in regulating ILC2 function and to evaluate the therapeutic utility of an immunomodulatory microparticle containing natural TLR9 ligand (MIS416).

METHODS

We evaluated the immunomodulatory effects of CpG A in IL-33-induced airway hyperreactivity (AHR) and airway inflammation. The roles of interferons were examined in vivo and in vitro by using signal transducer and activator of transcription 1 (Stat1)^-/- mice and neutralizing antibodies against IFN-γ and IFN-α/β receptor subunit 1, and their cellular sources were identified. The therapeutic utility of MIS416 was investigated in the Alternaria alternata model of allergic asthma and in humanized NSG mice.

RESULTS

We show that TLR9 activation by CpG A suppresses IL-33-mediated AHR and airway inflammation through inhibition of ILC2s. Activation of TLR9 leads to production of IFN-α, which drives IFN-γ production by natural killer cells. Importantly, IFN-γ is essential for TLR9-driven suppression, and IFN-α cannot compensate for impaired IFN-γ signaling. We further show that IFN-γ directly inhibits ILC2 function through a STAT1-dependent mechanism. Finally, we demonstrate the therapeutic potential of MIS416 in A alternata-induced airway inflammation and validated these findings in human subjects.

CONCLUSION

TLR9 activation alleviates ILC2-driven AHR and airway inflammation through direct suppression of cell function. Microparticle-based delivery of TLR9 ligands might serve as a therapeutic strategy for asthma treatment.

T-bet controls intestinal mucosa immune responses via repression of type 2 innate lymphoid cell function

Innate lymphoid cells (ILCs) play an important role in regulating immune responses at mucosal surfaces. The transcription factor T-bet is crucial for the function of ILC1s and NCR⁺ ILC3s and constitutive deletion of T-bet prevents the development of these subsets. Lack of T-bet in the absence of an adaptive immune system causes microbiota-dependent colitis to occur due to aberrant ILC3 responses. Thus, T-bet expression in the innate immune system has been considered to dampen pathogenic immune responses. Here, we show that T-bet plays an unexpected role in negatively regulating innate type 2 responses, in the context of an otherwise intact immune system. Selective loss of T-bet in ILCs leads to the expansion and increased activity of ILC2s, which has a functionally important impact on mucosal immunity, including enhanced protection from Trichinella spiralis infection and inflammatory colitis. Mechanistically, we show that T-bet controls the intestinal ILC pool through regulation of IL-7 receptor signalling. These data demonstrate that T-bet expression in ILCs acts as the key transcriptional checkpoint in regulating pathogenic vs. protective mucosal immune responses, which has significant implications for the understanding of the pathogenesis of inflammatory bowel diseases and intestinal infections.