Transcriptional control of innate lymphoid cells

T-BET and EOMES sustain mature human NK cell identity and antitumor function

Since the T-box transcription factors (TFs) T-BET and EOMES are necessary for initiation of NK cell development, their ongoing requirement for mature NK cell homeostasis, function, and molecular programming remains unclear. To address this, T-BET and EOMES were deleted in unexpanded primary human NK cells using CRISPR/Cas9. Deleting these TFs compromised in vivo antitumor response of human NK cells. Mechanistically, T-BET and EOMES were required for normal NK cell proliferation and persistence in vivo. NK cells lacking T-BET and EOMES also exhibited defective responses to cytokine stimulation. Single-cell RNA-Seq revealed a specific T-box transcriptional program in human NK cells, which was rapidly lost following T-BET and EOMES deletion. Further, T-BET- and EOMES-deleted CD56bright NK cells acquired an innate lymphoid cell precursor-like (ILCP-like) profile with increased expression of the ILC-3-associated TFs RORC and AHR, revealing a role for T-box TFs in maintaining mature NK cell phenotypes and an unexpected role of suppressing alternative ILC lineages. Our study reveals the critical importance of sustained EOMES and T-BET expression to orchestrate mature NK cell function and identity.

Modulating AHR function offers exciting therapeutic potential in gut immunity and inflammation

Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a classical exogenous synthetic ligand of AHR that has significant immunotoxic effects. Activation of AHR has beneficial effects on intestinal immune responses, but inactivation or overactivation of AHR can lead to intestinal immune dysregulation and even intestinal diseases. Sustained potent activation of AHR by TCDD results in impairment of the intestinal epithelial barrier. However, currently, AHR research has been more focused on elucidating physiologic AHR function than on dioxin toxicity. The appropriate level of AHR activation plays a role in maintaining gut health and protecting against intestinal inflammation. Therefore, AHR offers a crucial target to modulate intestinal immunity and inflammation. Herein, we summarize our current understanding of the relationship between AHR and intestinal immunity, the ways in which AHR affects intestinal immunity and inflammation, the effects of AHR activity on intestinal immunity and inflammation, and the effect of dietary habits on intestinal health through AHR. Finally, we discuss the therapeutic role of AHR in maintaining gut homeostasis and relieving inflammation.

Insights into the tumor microenvironment of B cell lymphoma

The standard therapies in lymphoma have predominantly focused on targeting tumor cells with less of a focus on the tumor microenvironment (TME), which plays a critical role in favoring tumor growth and survival. Such an approach may result in increasingly refractory disease with progressively reduced responses to subsequent treatments. To overcome this hurdle, targeting the TME has emerged as a new therapeutic strategy. The TME consists of T and B lymphocytes, tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), cancer-associated fibroblasts (CAFs), and other components. Understanding the TME can lead to a comprehensive approach to managing lymphoma, resulting in therapeutic strategies that target not only cancer cells, but also the supportive environment and thereby ultimately improve survival of lymphoma patients. Here, we review the normal function of different components of the TME, the impact of their aberrant behavior in B cell lymphoma and the current TME-direct therapeutic avenues.

T-BET drives the conversion of human type 3 innate lymphoid cells into functional NK cells

Type 3 innate lymphoid cells (ILC3s) are characterized by RORγt expression and they produce IL-22 upon activation. ILC3s play a role in maintenance of barrier integrity in the intestine. Under inflammatory conditions, the ILC composition of the mucosal tissues is altered due to a high degree of plasticity. It has been extensively demonstrated that both murine and human ILC3s convert into ILC1s to mediate appropriate immune responses. However, plasticity between human ILC3s and NK cells is less well documented. As T-BET and EOMES are key transcription factors in NK cell differentiation, we investigated whether ectopic T-BET or EOMES expression converts human ILC3s into NK cells. ILC3s with ectopic T-BET and EOMES expression downregulate RORγt expression, while T-BET-overexpressing ILC3s additionally upregulate EOMES expression. High E ctopic T-BET expression in ILC3s results in transdifferentiation towards CD94⁺ NK cells, whereas ectopic EOMES overexpression results in dedifferentiation of ILC3s into CD94-CD117^-/low cells but is ineffective in NK cell generation. Dedifferentiating ILC3s from both T-BET and EOMES overexpression cultures upregulate NK cell receptors, perforin and granzyme B. Finally, IL-22 secretion is completely blocked in transdifferentiating ILC3s with both T-BET and EOMES ectopic expression, whereas only T-BET overexpression increases IFN-γ secretion and cytotoxicity. Altogether, these findings demonstrate that human ILC3s can convert into functional NK cells, wherein T-BET, and not EOMES, is the main driver.

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.

Unraveling the Role of Innate Lymphoid Cells in AcuteMyeloid Leukemia

Simple Summary

Acute myeloid leukemia (AML) is an aggressive form of cancer found in the blood and bone marrow with poor survival rates. Patients with AML are known to have many defects in their immune system which render immune cells unable to detect and/or kill cancer cells. Natural Killer (NK) cells are innate immune effector cells responsible for surveying the body to eliminate cancer cells as well as alert other immune cells to help clear the cancer cells. NK cells have developmental and functional defects in AML patients. While advances have been made to understand these NK cell defects in the setting of AML, the role of other closely related and recently discovered members of the innate lymphoid cell (ILC) family is much less clear. The ILC family is comprised of NK cells, ILC1s, ILC2s, and ILC3s, and due in part to their recent discovery, non-NK ILCs are just now beginning to be investigated in the setting of AML. By better understanding how AML alters the normal function of these cell types, and how the alteration regulates AML growth, we may be able to target and tailor new forms of therapy for patients.

Abstract

Over the past 50 years, few therapeutic advances have been made in treating acute myeloid leukemia (AML), an aggressive form of blood cancer, despite vast improvements in our ability to classify the disease. Emerging evidence suggests the immune system is important in controlling AML progression and in determining prognosis. Natural killer (NK) cells are important cytotoxic effector cells of the innate lymphoid cell (ILC) family that have been shown to have potent anti-leukemic functions. Recent studies are now revealing impairment or dysregulation of other ILCs in various types of cancers, including AML, which limits the effectiveness of NK cells in controlling cancer progression. NK cell development and function are inhibited in AML patients, which results in worse clinical outcomes; however, the specific roles of other ILC populations in AML are just now beginning to be unraveled. In this review, we summarize what is known about the role of ILC populations in AML.

Innate Lymphoid Cells in Crohn's Disease

Innate lymphoid cells (ILCs) are a large family of cells of the immune system that performs various functions in immune defense, inflammation, and tissue remodeling. As a part of the innate immune system, ILCs are a distinct form of lymphocytes different from T and B cells. ILCs can provide host defense against the source of infection and initiate the repair and remodeling processes to restore and maintain host body homeostasis. The number of patients with Crohn’s disease (CD) worldwide has continued to increase in recent years and this disease has brought sickness and death to many families. Numerous studies have found that ILCs also undergo a series of alternations during the development of CD and contribute to this disease. Despite this, the pathogenesis of CD is still not fully explained. So, we keep researching and exploring. In this review, we have closely linked the latest progress on ILCs and CD, and introduced, in detail, the specific roles of four different types of ILCs in CD. We also describe new progress in the pathogenesis of CD, with particular emphasis on the plasticity of ILC3s in this disease. These new studies and findings may provide new insights and breakthrough points for the treatment of CD.

Innate Lymphoid Cells in the Malignant Melanoma Microenvironment

Simple Summary

Innate lymphoid cells (ILCs) are the innate counterparts of adaptive immune cells. Emerging data indicate that they are also key players in the progression of multiple tumors. In this review we briefly describe ILCs’ functions in the skin, lungs and liver. Next, we analyze the role of ILCs in primary cutaneous melanoma and in its most frequent and deadly metastases, those in liver and lung. We focus on their dual anti– and pro-tumoral functions, depending on the cross-interactions among them and with the surrounding stromal cells that form the tumor microenvironment (TME) in each organ. Next, we detail the role of extracellular vesicles secreted to the TME by ILCs and melanoma on both cell populations. We conclude that the identification of markers and tools to allow the modulation of individual ILC subsets, in addition to the development of standardized protocols, is essential for addressing the therapeutic modulation of ILCs.

Abstract

The role of innate lymphoid cells (ILCs) in cancer progression has been uncovered in recent years. ILCs are classified as Type 1, Type 2, and Type 3 ILCs, which are characterized by the transcription factors necessary for their development and the cytokines and chemokines they produce. ILCs are a highly heterogeneous cell population, showing both anti– and protumoral properties and capable of adapting their phenotypes and functions depending on the signals they receive from their surrounding environment. ILCs are considered the innate counterparts of the adaptive immune cells during physiological and pathological processes, including cancer, and as such, ILC subsets reflect different types of T cells. In cancer, each ILC subset plays a crucial role, not only in innate immunity but also as regulators of the tumor microenvironment. ILCs’ interplay with other immune and stromal cells in the metastatic microenvironment further dictates and influences this dichotomy, further strengthening the seed-and-soil theory and supporting the formation of more suitable and organ-specific metastatic environments. Here, we review the present knowledge on the different ILC subsets, focusing on their interplay with components of the tumor environment during the development of primary melanoma as well as on metastatic progression to organs, such as the liver or lung.

Innate lymphoid cell and adaptive immune cell cross-talk: A talk meant not to forget

Innate lymphoid cells (ILCs) are a relatively new class of innate immune cells with phenotypical characters of lymphocytes but genotypically or functionally behave as typical innate immune cells. They have been classically divided into 3 groups (group 1 ILCs or ILC1s, group 2 ILCs or ILC2s, and group 3 ILCs or ILC3s). They serve as the first line of defense against invading pathogens and allergens at mucosal surfaces. The adaptive immune response works effectively in association with innate immunity as innate immune cells serve as APCs to directly stimulate the adaptive immune cells (various sets of T and B cells). Additionally, innate immune cells also secrete various effector molecules, including cytokines or chemokines impacting the function, differentiation, proliferation, and reprogramming among adaptive immune cells to maintain immune homeostasis. Only superantigens do not require their processing by innate immune cells as they are recognized directly by T cells and B cells. Thus, a major emphasis of the current article is to describe the cross-talk between different ILCs and adaptive immune cells during different conditions varying from normal physiological situations to different infectious diseases to allergic asthma.

Distinct PLZF+CD8αα+ Unconventional T Cells Enriched in Liver Use a Cytotoxic Mechanism to Limit Autoimmunity

Hepatic immune system is uniquely challenged to mount a controlled effector response to pathogens while maintaining tolerance to diet and microbial Ags. We have identified a novel population of innate-like, unconventional CD8αα+TCRαβ+ T cells in naive mice and in human peripheral blood, called CD8αα Tunc, capable of controlling effector T cell responses. They are NK1.1+ (CD161+ in human), express NK-inhibitory receptors, and express the promyelocytic leukemia zinc finger (PLZF) transcription factor that distinguishes them from conventional CD8+ T cells. These cells display a cytotoxic phenotype and use a perforin-dependent mechanism to control Ag-induced or T cell-mediated autoimmune diseases. CD8αα Tunc are dependent upon IL-15/IL-2Rβ signaling and PLZF for their development and/or survival. They are Foxp3-negative and their regulatory activity is associated with a functionally distinct Qa-1b-dependent population coexpressing CD11c and CD244. A polyclonal TCR repertoire, an activated/memory phenotype, and the presence of CD8αα Tunc in NKT- and in MAIT-deficient as well as in germ-free mice indicates that these cells recognize diverse self-protein Ags. Our studies reveal a distinct population of unconventional CD8+ T cells within the natural immune repertoire capable of controlling autoimmunity and also providing a new target for therapeutic intervention.

Shared Transcriptional Control of Innate Lymphoid Cell and Dendritic Cell Development

Innate immunity and adaptive immunity consist of highly specialized immune lineages that depend on transcription factors for both function and development. In this review, we dissect the similarities between two innate lineages, innate lymphoid cells (ILCs) and dendritic cells (DCs), and an adaptive immune lineage, T cells. ILCs, DCs, and T cells make up four functional immune modules and interact in concert to produce a specified immune response. These three immune lineages also share transcriptional networks governing the development of each lineage, and we discuss the similarities between ILCs and DCs in this review.

MicroRNA-146a negatively regulates IL-33 in activated group 2 innate lymphoid cells by inhibiting IRAK1 and TRAF6

Type II innate lymphoid cells (ILC2) play a very important role in the pathogenesis of allergic asthma. This study aims to investigate whether miR-146a inhibition of asthma is related with interleukin (IL)-33 signaling path way in ILC2 and the underlying mechanisms. Asthma mice model was induced by ovalbumin. miRNA146a mimics was administrated to asthma mice or transfected to activated ILC2 purified from asthma mice lung. RT-PCR was used to detect miRNA146a level in lung tissue and ILC2. IL-5 and IL-13 levels in culture supernatant were detected by flow cytometry. Interleukin-1 receptor-associated kinase 1 (IRAK1), TNF receptor-associated factor 6 (TRAF6), signal transducer and activator of transcription 1 (STAT1) protein expression levels were detected by western blot. miR-146a directly inhibited ILC2 function and suppressed ILC2 proliferation both in vivo and in vitro. During stimulation of ILC2, miR-146a expression gradually increased with a decrease of cell proliferation. Modulation of ILC2 function by miR-146a may depend on IL-33/interleukin 1 receptor-like 1 (IL1RL1 or ST2) signaling through inhibiting IRAK1 and TRAF6.miR-146a can inhibit IRAK1 and TRAF6, downstream molecules of ST2 signal pathway, thereby negatively regulate IL-33/ST2-activated ILC2 to inhibit asthma. Targeting miR-146 maybe a novel strategy for the treatment of allergic asthma.

Isolation and Identification of Innate Lymphoid Cells (ILCs) for Immunotoxicity Testing

Innate lymphoid cells (ILCs) comprise a family of innate immune cells that orchestrate mucosal immune responses: initiating, sustaining, and even curbing immune responses. ILCs are relatively rare (≤1% of lymphocytes in mucosal tissues), lack classical cell-surface markers, and can be divided into three subsets (type 1-3 ILCs) based on differences in cytokine production, phenotype, and developmental pathway. Because ILCs can only be identified by combinations of cell-surface markers and cytokine production, multicolor flow cytometry is the most reliable method to purify, characterize, and assess the functionality of ILCs. Here, we describe the methods for cell preparation, flow cytometric analysis, and purification of murine ILCs from the lung.

What Cytokines Can Tell Us About the Pathogenesis of Breast Implant-Associated Anaplastic Large Cell Lymphoma (BIA-ALCL)

Cytokines, their receptors, and downstream signaling partners, especially JAK1/2 and STAT3, are key biomarkers in lymphoproliferative disorders including systemic anaplastic large cell lymphoma (ALCL). Here we review their role in breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). Early results suggest that, in addition to CD30, IL-9, IL-10, and IL-13 can distinguish malignant from benign seromas. IL-6 is increased in both benign and malignant seromas. IFNγ may identify a subset of BIA-ALCL with a different clinical course. Immunohistochemical detection of nuclear transcription factors-which regulate cytokine signaling-and phosphorylated janus kinases/signal transducers and activators of transcription can inform the identification and malignant potential of CD30+ cells. The innate immune response is the first line of defense against microbes suspected to initiate BIA-ALCL. Innate lymphoid cells are grouped according to the cytokines they produce and could potentially be identified as precursors to BIA-ALCL. Cytokines modulate the tumor microenvironment and hence the pathology of BIA-ALCL such as the influx of eosinophils and capsular fibrosis mediated by IL-13. The plasticity of T cells and innate immune cells theoretically can enable therapeutic manipulations toward a less aggressive phenotype. Cytokine receptors targeted in clinical trials of inflammatory and autoimmune disorders could afford opportunities for immunotherapy of BIA-ALCL.

A systematic review of gut-immune-brain mechanisms in Autism Spectrum Disorder

Despite decades of research, the etiological origins of Autism Spectrum Disorder (ASD) remain elusive. Recently, the mechanisms of ASD have encompassed emerging theories involving the gastrointestinal, immune, and nervous systems. While each of these perspectives presents its own set of supporting evidence, the field requires an integration of these modular concepts and an overarching view of how these subsystems intersect. In this systematic review, we have synthesized relevant evidences from the existing literature, evaluating them in an interdependent manner and in doing so, outlining their possible connections. Specifically, we first discussed gastrointestinal and immuno-inflammation pathways in-depth, exploring the relationships between microbial composition, bacterial metabolites, gut mucosa, and immune system constituents. Accounting for temporal differences in the mechanisms involved in neurodevelopment, prenatal and postnatal phases were further elucidated, where the former focused on maternal immune activation (MIA) and fetal development, while the latter addressed the role of immune dysregulation in contributing to atypical neurodevelopment. As autism remains, foremost, a neurodevelopmental disorder, this review presents an integration of disparate modules into a "Gut-Immune-Brain" paradigm. Existing gaps in the literature have been highlighted, and possible avenues for future research with an integrated physiological perspective underlying ASD have also been suggested.

Testosterone Attenuates Group 2 Innate Lymphoid Cell-Mediated Airway Inflammation

Sex hormones regulate many autoimmune and inflammatory diseases, including asthma. As adults, asthma prevalence is 2-fold greater in women compared to men. The number of group 2 innate lymphoid cells (ILC2) is increased in patients with asthma, and we investigate how testosterone attenuates ILC2 function. In patients with moderate to severe asthma, we determine that women have an increased number of circulating ILC2 compared to men. ILC2 from adult female mice have increased IL-2-mediated ILC2 proliferation versus ILC2 from adult male mice, as well as pre-pubescent females and males. Further, 5α-dihydrotestosterone, a hormone downstream of testosterone, decreases lung ILC2 numbers and IL-5 and IL-13 expression from ILC2. In vivo, testosterone attenuated Alternaria-extract-induced IL-5+ and IL-13+ ILC2 numbers and lung eosinophils by intrinsically decreasing lung ILC2 numbers, as well as by decreasing expression of IL-33 and thymic stromal lymphopoietin (TSLP), ILC2-stimulating cytokines. Collectively, these findings provide a foundational understanding of sexual dimorphism in ILC2 function.

Towards Targeting the Aryl Hydrocarbon Receptor in Cystic Fibrosis

Tryptophan (trp) metabolism is an important regulatory component of gut mucosal homeostasis and the microbiome. Metabolic pathways targeting the trp can lead to a myriad of metabolites, of both host and microbial origins, some of which act as endogenous low-affinity ligands for the aryl hydrocarbon receptor (AhR), a cytosolic, ligand-operated transcription factor that is involved in many biological processes, including development, cellular differentiation and proliferation, xenobiotic metabolism, and the immune response. Low-level activation of AhR by endogenous ligands is beneficial in the maintenance of immune health and intestinal homeostasis. We have defined a functional node whereby certain bacteria species contribute to host/microbial symbiosis and mucosal homeostasis. A microbial trp metabolic pathway leading to the production of indole-3-aldehyde (3-IAld) by lactobacilli provided epithelial protection while inducing antifungal resistance via the AhR/IL-22 axis. In this review, we highlight the role of AhR in inflammatory lung diseases and discuss the possible therapeutic use of AhR ligands in cystic fibrosis.

Natural killer cells and anti-tumor immunity

Immune checkpoint inhibitors harness the power of the immune system to fight cancer. The clinical success achieved with antibodies against the inhibitory T cell receptors PD-1 and CTLA4 has focused attention on the possibility of manipulating other immune cells, in particular those involved in innate immunity. Here we review the role of innate lymphoid cells (ILCs) and their contribution to tumor immunity. As the prototypical ILC, the natural killer (NK) cell has an intrinsic ability to detect and kill cancer cells. NK cells are dependent on the cytokine interleukin (IL)-15 for their development and effector activity. We discuss the role of the Suppressor of cytokine (SOCS) proteins in negatively regulating IL-15 and NK cell responses and the potential for targeting these small intracellular regulators as new immune checkpoints.

Prostaglandin E2 suppresses human group 2 innate lymphoid cell function

Background

Group 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E₂ is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation.

Objective

We set out to investigate how PGE₂ regulates human ILC2 function.

Methods

The effects of PGE₂ on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE₂ receptor expression.

Results

PGE₂ inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE₂ downregulated the expression of IL-2 receptor α (CD25). In line with this observation, PGE₂ decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s.

Conclusion

Our findings reveal that PGE₂ limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

γδ T cells represent a major spontaneously cytotoxic cell population in the chicken

Natural killer cells in the chicken are mainly confined to the intestine, while only small frequencies are detectable in spleen, lung and blood. Here, we compared the spontaneous cytotoxicity of lymphocytes isolated from blood, spleen and intestine using a flow cytometric based cytotoxicity assay. There was no spontaneous cytotoxicity detected in chicken blood preparations. In contrast, freshly prepared splenocytes exhibited a spontaneous cytotoxicity of up to 50% and intestinal epithelial lymphocytes of up to 85%. This cytotoxicity was observed against the RP9 but not against the chicken CU24 target cell line. The observed cytotoxicity was MHC unrestricted since B²B² derived effector cells killed RP9 target cells (B²B¹⁵) equally well compared to MHC mismatched 2D8 targets (B¹⁹B¹⁹). The cytotoxicity of splenocytes was enhanced by preincubation with IL-2 or strongly increased with IL-2 plus IL-12. By cell sorting, we identified the CD8⁺γδ T cell subset as the major effectors, whereas both CD8^-γδ T cells and CD8⁺αβ T cells had only low cytolytic potential. Within intestinal lymphocyte CD45⁺cells displayed cytotoxicity as well as sorted γδ T cells and NK cell. In conclusion, the chicken γδ T cells represent a major cytotoxic lymphocyte subset that can lyse target cells in a MHC unrestricted manner.

New concepts in asthma: clinical phenotypes and pathophysiological mechanisms

Asthma is among the most common chronic inflammatory diseases worldwide. Recent evidence indicates that the pathogenesis shows a high degree of heterogeneity. Patient subsets have been identified that exhibit different cellular and molecular patterns of dysregulation. A prominent example is eosinophilic Th2-driven asthma. These unique and molecular patterns are termed endotypes. Characterization of endotypes has broad implications for therapeutic interventions. Although ∼80% of asthmatic patients respond well to standard anti-inflammatory therapies, the remaining subset particularly consisting of severe patients requires a more specialized endotype-specific approach. This interrelationship between clinical phenotypes, molecular endotypes and endotype-specific therapies is the focus of this review.

Transgenic Adipose-specific Expression of the Nuclear Receptor RORα Drives a Striking Shift in Fat Distribution and Impairs Glycemic Control

RORα is a member of the nuclear receptor (NR) superfamily and analysis of the (global) RORα-deficient mouse model revealed this NR has a role in glycemic control and fat deposition. Therefore, we generated an adipose-specific RORα ‘gain of function’ mouse model under the control of the fatty acid binding protein 4 (FABP4) promoter to elucidate the function of RORα in adipose tissue. The Tg-FABP4-RORα4 mice demonstrated a shift in fat distribution to non-adipose tissues when challenged with a high fat diet (HFD). Specifically, we observed a subcutaneous lipodystrophy, accompanied by hepatomegaly (fatty liver/mild portal fibrosis) and splenomegaly; in a background of decreased weight gain and total body fat after HFD. Moreover, we observed significantly higher fasting blood glucose and impaired clearance of glucose in Tg-FABP4-RORα4 mice. Genome wide expression and qPCR profiling analysis identified: (i) subcutaneous adipose specific decreases in the expression of genes involved in fatty acid biosynthesis, lipid droplet expansion and glycemic control, and (ii) the fibrosis pathway as the most significant pathway [including dysregulation of the collagen/extracellular matrix (ECM) pathways] in subcutaneous adipose and liver. The pathology presented in the Tg-FABP4-RORα4 mice is reminiscent of human metabolic disease (associated with aberrant ECM expression) highlighting the therapeutic potential of this NR.

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Adipose-specific expression of RORα is associated with subcutaneous lipodystrophy and hepatomegaly with fibrosis.

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The phenotype is associated with impaired glycemic control and decreased weight gain on a high fat diet.

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Gene expression profiling reveals significant dysregulation of extra cellular matrix signaling.

We have generated a ‘gain of function’ animal model with the nuclear hormone receptor RORα4 to understand the function of this protein in fat. Over expression of the RORα4 gene, was associated with fat deposition in non-adipose tissues on a high fat diet. Moreover, we observed a decrease in fat tissue (located under the skin) accompanied by enlargement of the liver and spleen. In addition, over expression of this receptor was associated with impaired glycemic control. The pathology in this animal model is reminiscent of metabolic disease in humans, highlighting the therapeutic potential of pharmacologically manipulating this nuclear receptor.

In Situ Mapping of Innate Lymphoid Cells in Human Skin: Evidence for Remarkable Differences between Normal and Inflamed Skin

Although innate lymphoid cells (ILCs) have recently been identified also in skin, their role in this organ remains poorly understood. In this study, we aimed at developing a technique to assess ILCs in situ and to determine their topographical distribution in human skin. We collected lesional skin biopsies from patients with atopic dermatitis and psoriasis (both n = 13) and normal human skin from healthy controls. After establishing immunofluorescence ILC in situ stainings, we developed an analysis approach (gating combined with manual validation) to reliably identify ILCs. Topographical mapping was obtained by automated calculations of the distances between ILCs and different cellular/structural elements of the skin. Whereas normal human skin harbored a very scarce ILC population (mostly ILC1s and AHR⁺ILC3s), atopic dermatitis and psoriasis skin was infiltrated by clearly visible ILC subsets. We observed atopic dermatitis skin to contain not only ILC2s but also a prominent AHR⁺ILC3 population. Conversely, we encountered almost equal proportions of ILC1s and RORC⁺ILC3s in psoriasis skin. Distance calculations revealed ILCs to reside near the epidermis and in close proximity to T lymphocytes. ILC mapping in situ will provide valuable information about their likely communication partners in normal and diseased skin and forms the basis for the appropriate mechanistic studies.

The Role of the Microbial Metabolites Including Tryptophan Catabolites and Short Chain Fatty Acids in the Pathophysiology of Immune-Inflammatory and Neuroimmune Disease

There is a growing awareness that gut commensal metabolites play a major role in host physiology and indeed the pathophysiology of several illnesses. The composition of the microbiota largely determines the levels of tryptophan in the systemic circulation and hence, indirectly, the levels of serotonin in the brain. Some microbiota synthesize neurotransmitters directly, e.g., gamma-amino butyric acid, while modulating the synthesis of neurotransmitters, such as dopamine and norepinephrine, and brain-derived neurotropic factor (BDNF). The composition of the microbiota determines the levels and nature of tryptophan catabolites (TRYCATs) which in turn has profound effects on aryl hydrocarbon receptors, thereby influencing epithelial barrier integrity and the presence of an inflammatory or tolerogenic environment in the intestine and beyond. The composition of the microbiota also determines the levels and ratios of short chain fatty acids (SCFAs) such as butyrate and propionate. Butyrate is a key energy source for colonocytes. Dysbiosis leading to reduced levels of SCFAs, notably butyrate, therefore may have adverse effects on epithelial barrier integrity, energy homeostasis, and the T helper 17/regulatory/T cell balance. Moreover, dysbiosis leading to reduced butyrate levels may increase bacterial translocation into the systemic circulation. As examples, we describe the role of microbial metabolites in the pathophysiology of diabetes type 2 and autism.

Vitamin A Controls the Presence of RORγ+ Innate Lymphoid Cells and Lymphoid Tissue in the Small Intestine

Changes in diet and microbiota have determining effects on the function of the mucosal immune system. For example, the active metabolite of vitamin A, retinoic acid (RA), has been described to maintain homeostasis in the intestine by its influence on both lymphocytes and myeloid cells. Additionally, innate lymphoid cells (ILCs), important producers of cytokines necessary for intestinal homeostasis, are also influenced by vitamin A in the small intestines. In this study, we show a reduction of both NCR(-) and NCR(+) ILC3 subsets in the small intestine of mice raised on a vitamin A-deficient diet. Additionally, the percentages of IL-22-producing ILCs were reduced in the absence of dietary vitamin A. Conversely, mice receiving additional RA had a specific increase in the NCR(-) ILC3 subset, which contains the lymphoid tissue inducer cells. The dependence of lymphoid tissue inducer cells on vitamin A was furthermore illustrated by impaired development of enteric lymphoid tissues in vitamin A-deficient mice. These effects were a direct consequence of ILC-intrinsic RA signaling, because retinoic acid-related orphan receptor γt-Cre × RARα-DN mice had reduced numbers of NCR(-) and NCR(+) ILC3 subsets within the small intestine. However, lymphoid tissue inducer cells were not affected in these mice nor was the formation of enteric lymphoid tissue, demonstrating that the onset of RA signaling might take place before retinoic acid-related orphan receptor γt is expressed on lymphoid tissue inducer cells. Taken together, our data show an important role for vitamin A in controlling innate lymphoid cells and, consequently, postnatal formed lymphoid tissues within the small intestines.

Prostaglandin I2 Signaling and Inhibition of Group 2 Innate Lymphoid Cell Responses

RATIONALE

Group 2 innate lymphoid cells (ILC2s) robustly produce IL-5 and IL-13, cytokines central to the asthma phenotype; however, the effect of prostaglandin (PG) I2 on ILC2 function is unknown.

OBJECTIVES

To determine the effect of PGI2 on mouse and human ILC2 cytokine expression in vitro and the effect of endogenous PGI2 and the PGI2 analog cicaprost on lung ILC2s in vivo.

METHODS

Flow-sorted bone marrow ILC2s of wild-type (WT) and PGI2 receptor-deficient (IP(-/-)) mice were cultured with IL-33 and treated with the PGI2 analog cicaprost. WT and IP(-/-) mice were challenged intranasally with Alternaria alternata extract for 4 consecutive days to induce ILC2 responses, and these were quantified. Prior to A. alternata extract, challenged WT mice were treated with cicaprost. Human flow-sorted peripheral blood ILC2s were cultured with IL-33 and IL-2 and treated with the PGI2 analog cicaprost.

MEASUREMENT AND MAIN RESULTS

We demonstrate that PGI2 inhibits IL-5 and IL-13 protein expression by IL-33-stimulated ILC2s purified from mouse bone marrow in a manner that was dependent on signaling through the PGI2 receptor IP. In a mouse model of 4 consecutive days of airway challenge with an extract of A. alternata, a fungal aeroallergen associated with severe asthma exacerbations, endogenous PGI2 signaling significantly inhibited lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s, as well as the mean fluorescence intensity of IL-5 and IL-13 staining. In addition, exogenous administration of a PGI2 analog inhibited Alternaria extract-induced lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s and the mean fluorescence intensity of IL-5 and IL-13 staining. Finally, a PGI2 analog inhibited IL-5 and IL-13 expression by human ILC2s that were stimulated with IL-2 and IL-33.

CONCLUSIONS

These results suggest that PGI2 may be a potential therapy to reduce the ILC2 response to protease-containing aeroallergens, such as Alternaria.

IL-25 and CD4(+) TH2 cells enhance type 2 innate lymphoid cell-derived IL-13 production, which promotes IgE-mediated experimental food allergy

BACKGROUND

Food-mediated allergic reactions have emerged as a major health problem. The underlying mechanisms that promote uncontrolled type 2 immune responses to dietary allergens in the gastrointestinal tract remain elusive.

OBJECTIVE

We investigated whether altering IL-25 signaling enhances or attenuates allergic responses to food allergens.

METHODS

Mice of an IL-25 transgenic mouse line (iIL-25Tg mice), which constitutively overexpress intestinal IL-25, and Il17rb(-/-) mice, in which Il17rb gene expression is disrupted, were sensitized and gavage fed with ovalbumin (OVA). We assessed symptomatic characteristics of experimental food allergy, including incidence of diarrhea, incidence of hypothermia, intestinal TH2 immune response, and serum OVA-specific IgE and mast cell protease 1 production.

RESULTS

Rapid induction of Il25 expression in the intestinal epithelium preceded onset of the anaphylactic response to ingested OVA antigen. iIL-25Tg mice were more prone and Il17rb(-/-) mice were more resistant to experimental food allergy. Resident intestinal type 2 innate lymphoid cells (ILC2s) were identified as the major producers of IL-5 and IL-13 in response to IL-25. Reconstituting irradiated wild-type mice with Rora(-/-) or Il17rb(-/-) bone marrow resulted in a deficiency or dysfunction of the ILC2 compartment, respectively, and resistance to experimental food allergy. Repeated intragastric antigen challenge induced a significant increase in numbers of CD4(+) TH2 cells, which enhance IL-25-stimulated IL-13 production by ILC2s ex vivo and in vivo. Finally, reconstituted IL-13-deficient ILC2s had reduced capability to promote allergic inflammation, resulting in increased resistance to experimental food allergy.

CONCLUSION

IL-25 and CD4(+) TH2 cells induced by ingested antigens enhance ILC2-derived IL-13 production, thereby promoting IgE-mediated experimental food allergy.

Innate lymphoid cells in intestinal immunity and inflammation

Innate lymphoid cells (ILCs) are a new and distinct family of innate immune cells that play an important role in immunity and inflammation. In this review, we focus on the role of ILCs in mucosal tissues, especially in the gut, in health and disease. ILCs support intestinal homeostasis by protecting the intestine from pathogens, contributing to the development of gut lymphoid tissue, and helping to repair injuries. By cooperating with epithelial cells and other innate and adaptive immune cells, ILCs participate in the control of pathogens and tolerance of commensal bacteria. The development and maintenance of ILCs are influenced by nutrients and metabolites sourced from diet and/or gut bacteria. ILCs have been shown to be involved in host metabolism and to participate in various diseases of the intestine including infectious and chronic inflammatory diseases, and cancer. Thus, the elucidation of ILC biology provides an exciting potential for development of novel therapeutic means to modulate immune responses in various disease settings.

Expansion of inflammatory innate lymphoid cells in patients with common variable immune deficiency

BACKGROUND

Common variable immunodeficiency (CVID) is an antibody deficiency treated with immunoglobulin; however, patients can have noninfectious inflammatory conditions that lead to heightened morbidity and mortality.

OBJECTIVES

Modular analyses of RNA transcripts in whole blood previously identified an upregulation of many interferon-responsive genes. In this study we sought the cell populations leading to this signature.

METHODS

Lymphoid cells were measured in peripheral blood of 55 patients with CVID (31 with and 24 without inflammatory/autoimmune complications) by using mass cytometry and flow cytometry. Surface markers, cytokines, and transcriptional characteristics of sorted innate lymphoid cells (ILCs) were defined by using quantitative PCR. Gastrointestinal and lung biopsy specimens of subjects with inflammatory disease were stained to seek ILCs in tissues.

RESULTS

The linage-negative, CD127(+), CD161(+) lymphoid population containing T-box transcription factor, retinoic acid-related orphan receptor (ROR) γt, IFN-γ, IL-17A, and IL-22, all hallmarks of type 3 innate lymphoid cells, were expanded in the blood of patients with CVID with inflammatory conditions (mean, 3.7% of PBMCs). ILCs contained detectable amounts of the transcription factors inhibitor of DNA binding 2, T-box transcription factor, and RORγt and increased mRNA transcripts for IL-23 receptor (IL-23R) and IL-26, demonstrating inflammatory potential. In gastrointestinal and lung biopsy tissues of patients with CVID, numerous IFN-γ(+)RORγt(+)CD3(-) cells were identified, suggesting a role in these mucosal inflammatory states.

CONCLUSIONS

An expansion of this highly inflammatory ILC population is a characteristic of patients with CVID with inflammatory disease; ILCs and the interferon signature are markers for the uncontrolled inflammatory state in these patients.

Forging T-Lymphocyte Identity: Intersecting Networks of Transcriptional Control

T-lymphocyte development branches off from other lymphoid developmental programs through its requirement for sustained environmental signals through the Notch pathway. In the thymus, Notch signaling induces a succession of T-lineage regulatory factors that collectively create the T-cell identity through distinct steps. This process involves both the staged activation of T-cell identity genes and the staged repression of progenitor-cell-inherited regulatory genes once their roles in self-renewal and population expansion are no longer needed. With the recent characterization of innate lymphoid cells (ILCs) that share transcriptional regulation programs extensively with T-cell subsets, T-cell identity can increasingly be seen as defined in modular terms, as the processes selecting and actuating effector function are potentially detachable from the processes generating and selecting clonally unique T-cell receptor structures. The developmental pathways of different classes of T cells and ILCs are distinguished by the numbers of prerequisites of gene rearrangement, selection, and antigen contact before the cells gain access to nearly common regulatory mechanisms for choosing effector function. Here, the major classes of transcription factors that interact with Notch signals during T-lineage specification are discussed in terms of their roles in these programs, the evidence for their spectra of target genes at different stages, and their cross-regulatory and cooperative actions with each other. Specific topics include Notch modulation of PU.1 and GATA-3, PU.1-Notch competition, the relationship between PU.1 and GATA-3, and the roles of E proteins, Bcl11b, and GATA-3 in guiding acquisition of T-cell identity while avoiding redirection to an ILC fate.

Innate lymphoid cells facilitate NK cell development through a lymphotoxin-mediated stromal microenvironment

Lymphotoxin expressed by RORγt⁺ innate lymphoid cells is critical for natural killer cell development.

Natural killer (NK) cell development relies on signals provided from the bone marrow (BM) microenvironment. It is thought that lymphotoxin (LT) α₁β₂ expressed by the NK cell lineage interacts with BM stromal cells to promote NK cell development. However, we now report that a small number of RORγt⁺ innate lymphoid cells (ILCs), and not CD3⁻NK1.1⁺ cells, express LT to drive NK development. Similar to LT^−/− or RORγt^−/− mice, the mice conditionally lacking LTα₁β₂ on RORγt⁺ ILCs experience a developmental arrest at the immature NK stages, between stages of NK development to the mature NK cell stage. This developmental block results in a functional deficiency in the clearance of NK-sensitive tumor cells. Reconstitution of Thy1⁺ ILCs from BM or purified RORγt⁺ ILCs from lamina propria lymphocytes into LT-deficient RORγt⁺ BM cultures rescues NK cell development. These data highlight a previously undiscovered role of RORγt⁺ ILCs for NK cell development and define LT from ILCs as an essential molecule for the stromal microenvironment supporting NK cell development.

Mechanisms of innate lymphoid cell and natural killer T cell activation during mucosal inflammation

Mucosal surfaces in the airways and the gastrointestinal tract are critical for the interactions of the host with its environment. Due to their abundance at mucosal tissue sites and their powerful immunomodulatory capacities, the role of innate lymphoid cells (ILCs) and natural killer T (NKT) cells in the maintenance of mucosal tolerance has recently moved into the focus of attention. While NKT cells as well as ILCs utilize distinct transcription factors for their development and lineage diversification, both cell populations can be further divided into three polarized subpopulations reflecting the distinction into Th1, Th2, and Th17 cells in the adaptive immune system. While bystander activation through cytokines mediates the induction of ILC and NKT cell responses, NKT cells become activated also through the engagement of their canonical T cell receptors (TCRs) by (glyco)lipid antigens (cognate recognition) presented by the atypical MHC I like molecule CD1d on antigen presenting cells (APCs). As both innate lymphocyte populations influence inflammatory responses due to the explosive release of copious amounts of different cytokines, they might represent interesting targets for clinical intervention. Thus, we will provide an outlook on pathways that might be interesting to evaluate in this context.

Transcriptional control of early T and B cell developmental choices

T and B cells share a common somatic gene rearrangement mechanism for assembling the genes that code for their antigen receptors; they also have developmental pathways with many parallels. Shared usage of basic helix-loop-helix E proteins as transcriptional drivers underlies these common features. However, the transcription factor networks in which these E proteins are embedded are different both in membership and in architecture for T and B cell gene regulatory programs. These differences permit lineage commitment decisions to be made in different hierarchical orders. Furthermore, in contrast to B cell gene networks, the T cell gene network architecture for effector differentiation is sufficiently modular so that E protein inputs can be removed. Complete T cell-like effector differentiation can proceed without T cell receptor rearrangement or selection when E proteins are neutralized, yielding natural killer and other innate lymphoid cells.

Enforced expression of Gata3 in T cells and group 2 innate lymphoid cells increases susceptibility to allergic airway inflammation in mice

Airway inflammation in allergic asthma reflects a threshold response of the innate immune system, including group 2 innate lymphoid cells (ILC2), followed by an adaptive Th2 cell-mediated response. Transcription factor Gata3 is essential for differentiation of both Th2 cells and ILC2. We investigated the effects of enforced Gata3 expression in T cells and ILC2 on the susceptibility of mice to allergic airway inflammation (AAI). We used CD2-Gata3 transgenic (Tg) mice with enforced Gata3 expression driven by the CD2 promoter, which is active both in T cells and during ILC2 development. CD2-Gata3 Tg mice and wild-type (WT) littermates were analyzed in mild models of AAI without adjuvants. Whereas OVA allergen exposure did not induce inflammation in WT controls, CD2-Gata3 Tg mice showed clear AAI and enhanced levels of IL-5 and IL-13 in bronchoalveolar lavage. Likewise, in house dust mite-driven asthma, CD2-Gata3 Tg mice were significantly more susceptible to AAI than WT littermates, whereby both ILC2 and Th2 cells were important cellular sources of IL-5 and IL-13 in bronchoalveolar lavage and lung tissue. Compared with WT littermates, CD2-Gata3 Tg mice contained increased numbers of ILC2, which expressed high levels of IL-33R and contributed significantly to early production of IL-4, IL-5, and IL-13. CD2-Gata3 Tg mice also had a unique population of IL-33-responsive non-B/non-T lymphoid cells expressing IFN-γ. Enforced Gata3 expression is therefore sufficient to enhance Th2 and ILC2 activity, and leads to increased susceptibility to AAI after mild exposure to inhaled harmless Ags that otherwise induce Ag tolerance.

Toward understanding the role of aryl hydrocarbon receptor in the immune system: current progress and future trends

The immune system is regulated by distinct signaling pathways that control the development and function of the immune cells. Accumulating evidence suggest that ligation of aryl hydrocarbon receptor (Ahr), an environmentally responsive transcription factor, results in multiple cross talks that are capable of modulating these pathways and their downstream responsive genes. Most of the immune cells respond to such modulation, and many inflammatory response-related genes contain multiple xenobiotic-responsive elements (XREs) boxes upstream. Active research efforts have investigated the physiological role of Ahr in inflammation and autoimmunity using different animal models. Recently formed paradigm has shown that activation of Ahr by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 3,3′-diindolylmethane (DIM) prompts the differentiation of CD4⁺Foxp3⁺ regulatory T cells (Tregs) and inhibits T helper (Th)-17 suggesting that Ahr is an innovative therapeutic strategy for autoimmune inflammation. These promising findings generate a basis for future clinical practices in humans. This review addresses the current knowledge on the role of Ahr in different immune cell compartments, with a particular focus on inflammation and autoimmunity.

Prostaglandin D2 activates group 2 innate lymphoid cells through chemoattractant receptor-homologous molecule expressed on TH2 cells

Background

Activation of the group 2 innate lymphoid cell (ILC2) population leads to production of the classical type 2 cytokines, thus promoting type 2 immunity. Chemoattractant receptor-homologous molecule expressed on T_H2 cells (CRTH2), a receptor for prostaglandin D₂ (PGD₂), is expressed by human ILC2s. However, the function of CRTH2 in these cells is unclear.

Objectives

We sought to determine the role of PGD₂ and CRTH2 in human ILC2s and compare it with that of the established ILC2 activators IL-25 and IL-33.

Methods

The effects of PGD₂, IL-25, and IL-33 on the cell migration, cytokine production, gene regulation, and receptor expression of ILC2s were measured with chemotaxis, ELISA, Luminex, flow cytometry, quantitative RT-PCR, and QuantiGene assays. The effects of PGD₂ under physiologic conditions were evaluated by using the supernatant from activated mast cells.

Results

PGD₂ binding to CRTH2 induced ILC2 migration and production of type 2 cytokines and many other cytokines. ILC2 activation through CRTH2 also upregulated the expression of IL-33 and IL-25 receptor subunits (ST2 and IL-17RA). The effects of PGD₂ on ILC2s could be mimicked by the supernatant from activated human mast cells and inhibited by a CRTH2 antagonist.

Conclusions

PGD₂ is an important and potent activator of ILC2s through CRTH2 mediating strong proallergic inflammatory responses. Through IgE-mediated mast cell degranulation, these innate cells can also contribute to adaptive type 2 immunity; thus CRTH2 bridges the innate and adaptive pathways in human ILC2s.

Emerging Role of Interleukin 22 in Hepatitis B Virus Infection: a Double-edged Sword

Hepatitis B virus (HBV) infection remains a worldwide health problem, and is the major cause of hepatitis, liver cirrhosis, and hepatocellular carcinoma. The innate and adaptive immune responses of the HBV-infected host contribute greatly to the development and pathogenesis of chronic HBV infection, and often affect the efficacy of anti-HBV drugs. Interleukin (IL)-22 is a newly identified cytokine that is involved in the pathogenesis of liver disease, but its role in liver inflammation in patients with HBV infection remains controversial. In this report, we summarize the production and function of IL-22 in inflammatory environments, and review the current research into IL-22 biology in HBV infection. A better understanding of the intrahepatic microenvironments that directly influence the activity of IL-22 will be important for the development of new immunotherapeutic approaches that target IL-22-producing cells or IL-22 itself.

Innate lymphoid cells in homeostasis, infection, chronic inflammation and tumors of the gastrointestinal tract

PURPOSE OF REVIEW

To highlight the functions of a recently discovered group of immune cells known as innate lymphoid cells (ILCs) during homeostasis and infections of the gastrointestinal tract.

RECENT FINDINGS

ILCs are lymphocytes that lack specific antigen receptors. They are found in the mucosae and mucosal-associated lymphoid tissues, where they promptly initiate cytokine responses to pathogens upon initial exposure. ILCs have been classified into distinct groups based on their cytokine secretion: ILC1 produce IFN-γ, ILC2 secrete IL-5 and IL-13, and ILC3 produce IL-22 and IL-17. Recent studies have discovered the heterogeneity of ILC1 and ILC3 in the gastrointestinal tract. ILC1 subsets may contribute to the inflammatory bowel disease. ILC3 subsets may be beneficial in the defense against gastrointestinal infections, but their sustained activation may lead to cancer.

SUMMARY

ILCs may provide a target for new avenues of therapeutic intervention in inflammatory bowel disease and gastrointestinal cancer.

Role of the aryl hydrocarbon receptor (AhR) in lung inflammation

Millions of individuals worldwide are afflicted with acute and chronic respiratory diseases, causing temporary and permanent disabilities and even death. Oftentimes, these diseases occur as a result of altered immune responses. The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acts as a regulator of mucosal barrier function and may influence immune responsiveness in the lungs through changes in gene expression, cell-cell adhesion, mucin production, and cytokine expression. This review updates the basic immunobiology of the AhR signaling pathway with regards to inflammatory lung diseases such as asthma, chronic obstructive pulmonary disease, and silicosis following data in rodent models and humans. Finally, we address the therapeutic potential of targeting the AhR in regulating inflammation during acute and chronic respiratory diseases.

Mucosal innate immune cells regulate both gut homeostasis and intestinal inflammation

Continuous exposure of intestinal mucosal surfaces to diverse microorganisms and their metabolites reflects the biological necessity for a multifaceted, integrated epithelial and immune cell-mediated regulatory system. The development and function of the host cells responsible for the barrier function of the intestinal surface (e.g., M cells, Paneth cells, goblet cells, and columnar epithelial cells) are strictly regulated through both positive and negative stimulation by the luminal microbiota. Stimulation by damage-associated molecular patterns and commensal bacteria-derived microbe-associated molecular patterns provokes the assembly of inflammasomes, which are involved in maintaining the integrity of the intestinal epithelium. Mucosal immune cells located beneath the epithelium play critical roles in regulating both the mucosal barrier and the relative composition of the luminal microbiota. Innate lymphoid cells and mast cells, in particular, orchestrate the mucosal regulatory system to create a mutually beneficial environment for both the host and the microbiota. Disruption of mucosal homeostasis causes intestinal inflammation such as that seen in inflammatory bowel disease. Here, we review the recent research on the biological interplay among the luminal microbiota, epithelial cells, and mucosal innate immune cells in both healthy and pathological conditions.

Helix-loop-helix factor inhibitor of differentiation 3 regulates interleukin-5 expression and B-1a B cell proliferation

OBJECTIVE

Natural immunity is emerging as an important mediator of protection from atherogenesis. Natural IgM antibodies that recognize oxidation-specific epitopes on low-density lipoprotein or phospholipids and the B-1a B cells that produce them attenuate atherosclerosis. We previously demonstrated that Apoe(-/-) mice globally deficient in the helix-loop-helix protein inhibitor of differentiation 3 (Id3) develop early diet-induced atherosclerosis. Furthermore, B cell-mediated attenuation of atherosclerosis in B cell-deficient mice was dependent on Id3. Here, we sought to determine whether Id3 regulates B-1a B cells and the natural antibodies that they produce and identify mechanisms mediating these effects.

APPROACH AND RESULTS

Mice lacking Id3 had significantly fewer B-1a B cells in the spleen and peritoneal cavity and reduced serum levels of the natural antibody E06. B cell-specific deletion of Id3 revealed that this effect was not because of the loss of Id3 in B cells. Interleukin (IL)-33 induced abundant, Id3-dependent IL-5 production in the recently identified innate lymphoid cell, the natural helper (NH) cell, but not Th2 or mast cells. In addition, delivery of IL-5 to Id3-deficient mice restored B-1a B cell proliferation. B-1a B cells were present in aortic samples also containing NH cells. Aortic NH cells produced IL-5, a B-1a B cell mitogen in response to IL-33 stimulation.

CONCLUSIONS

These studies are the first to identify NH and B-1a B cells in the aorta and provide evidence that Id3 is a key regulator of NH cell IL-5 production and B-1a B cell homeostasis.

Tissue-specific effector functions of innate lymphoid cells

Innate lymphoid cells (ILCs) is the collective term for a group of related innate lymphocytes, including natural killer (NK) cells and the more recently discovered non-NK ILCs, which all lack rearranged antigen receptors such as those expressed by T and B cells. Similar to NK cells, the newly discovered ILCs depend on the transcription factor Id2 and the common γ-chain of the interleukin-2 receptor for development. However, in contrast to NK cells, non-NK ILCs also require interleukin-7. In addition to the cytotoxic functions of NK cells, assuring protection against tumour development and viruses, new data indicate that ILCs contribute to a wide range of homeostatic and pathophysiological conditions in various organs via specialized cytokine production capabilities. Here we summarize current knowledge on ILCs with a particular emphasis on their tissue-specific effector functions, in the gut, liver, lungs and uterus. When possible, we try to highlight the role that these cells play in humans.

Th1- and Th2-like subsets of innate lymphoid cells

Innate lymphoid cells (ILCs) constitute a family of effectors in innate immunity and regulators of tissue remodeling that have a cytokine and transcription factor expression pattern that parallels that of the T-helper (Th) cell family. Here, we discuss how ILCs can be categorized and summarize the current knowledge of Th1- and Th2-like ILCs with regard to the molecular mechanisms of development, effector functions, and their interplay with other cell types.

Type 2 innate lymphocytes in allergic airway inflammation

CD4(+) T helper-2 (Th2) cells, which produce a unique profile of IL-4, IL-5 and IL-13 pro-inflammatory cytokines, are thought to be central in the orchestration and amplification of allergic asthma. However, a novel non-T/non-B lymphoid cell population, named type 2 innate lymphocytes (ILC2s), that produces high amounts of IL-5 and IL-13 was recently discovered. Unlike Th2 cells, these ILC2s are not antigen-restricted and are activated by epithelial cell-derived cytokines IL-25 and IL-33. In this review, we will focus on recent studies, mainly involving allergen-based mouse models, that have provided evidence for a significant contribution of ILC2 to allergic airway information.

Human type 1 innate lymphoid cells accumulate in inflamed mucosal tissues

Innate lymphoid cells (ILCs) are effectors of innate immunity and regulators of tissue modeling. Recently identified ILC populations have a cytokine expression pattern that resembles that of the helper T cell subsets T(H)2, T(H)17 and T(H)22. Here we describe a distinct ILC subset similar to T(H)1 cells, which we call 'ILC1'. ILC1 cells expressed the transcription factor T-bet and responded to interleukin 12 (IL-12) by producing interferon-γ (IFN-γ). ILC1 cells were distinct from natural killer (NK) cells as they lacked perforin, granzyme B and the NK cell markers CD56, CD16 and CD94, and could develop from RORγt(+) ILC3 under the influence of IL-12. The frequency of the ILC1 subset was much higher in inflamed intestine of people with Crohn's disease, which indicated a role for these IFN-γ-producing ILC1 cells in the pathogenesis of gut mucosal inflammation.

Type 2 innate lymphoid cells: friends or foes-role in airway allergic inflammation and asthma

Innate-like lymphocytes (ILLs) and innate lymphoid cells (ILCs) are two newly characterized families of lymphocytes with limited and no rearranged antigen receptors, respectively. These soldiers provide a first line of defense against foreign insults by triggering a prompt innate immune response and bridging the gap of innate and adaptive immunity. Type 2 innate lymphoid cells (ILCs2) are newly identified members of the ILC family that play a key role in type 2 immune responses by prompt production of type 2 cytokines (especially IL-5 and IL-13) in response to antigen-induced IL-25/33 and by recruiting type 2 “immune franchise.” Regarding the two different roles of type 2 cytokines, helminth expulsion and type 2-related diseases, here we review the latest advances in ILC2 biology and examine the pivotal role of resident ILCs2 in allergen-specific airway inflammation and asthma.