IL-33-responsive lineage- CD25+ CD44(hi) lymphoid cells mediate innate type 2 immunity and allergic inflammation in the lungs

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.

IL-33 is more potent than IL-25 in provoking IL-13-producing nuocytes (type 2 innate lymphoid cells) and airway contraction

BACKGROUND

IL-25 and IL-33 belong to distinct cytokine families, but experimental mouse studies suggest their immunologic functions in type 2 immunity are almost entirely overlapping. However, only polymorphisms in the IL-33 pathway (IL1RL1 and IL33) have been significantly associated with asthma in large-cohort genome-wide association studies.

OBJECTIVE

We sought to identify distinct pathways for IL-25 and IL-33 in the lung that might provide insight into their roles in asthma pathogenesis and potential for therapeutic intervention.

METHODS

IL-25 receptor-deficient (Il17rb(-/-)), IL-33 receptor-deficient (ST2, Il1rl1(-/-)), and double-deficient (Il17rb(-/-)Il1rl1(-/-)) mice were analyzed in models of allergic asthma. Microarrays, an ex vivo lung slice airway contraction model, and Il13(+/eGFP) mice were then used to identify specific effects of IL-25 and IL-33 administration.

RESULTS

Comparison of IL-25 and IL-33 pathway-deficient mice demonstrates that IL-33 signaling plays a more important in vivo role in airways hyperreactivity than IL-25. Furthermore, methacholine-induced airway contraction ex vivo increases after treatment with IL-33 but not IL-25. This is dependent on expression of the IL-33 receptor and type 2 cytokines. Confocal studies with Il13(+/eGFP) mice show that IL-33 more potently induces expansion of IL-13-producing type 2 innate lymphoid cells, correlating with airway contraction. This predominance of IL-33 activity is enforced in vivo because IL-33 is more rapidly expressed and released in comparison with IL-25.

CONCLUSION

Our data demonstrate that IL-33 plays a critical role in the rapid induction of airway contraction by stimulating the prompt expansion of IL-13-producing type 2 innate lymphoid cells, whereas IL-25-induced responses are slower and less potent.

The role of type 2 innate lymphoid cells in asthma

Asthma is a complex and heterogeneous disease with several phenotypes, including an allergic asthma phenotype, characterized by Th2 cytokine production and associated with allergen sensitization and adaptive immunity. Asthma also includes nonallergic asthma phenotypes that require innate rather than adaptive immunity. These innate pathways to asthma involve macrophages, neutrophils, as well as ILCs, newly described cell types that produce a variety of cytokines, including IL-5 and IL-13. We review the recent data regarding ILCs and their role in asthma.

STAT6 and lung inflammation

Lung inflammation has many etiologies, including diseases of Th2-type immunity, such as asthma and anti-parasitic responses. Inflammatory diseases of the lung involve complex interactions among structural cells (airway epithelium, smooth muscle, and fibroblasts) and immune cells (B and T cells, macrophages, dendritic cells, and innate lymphoid cells). Signal transducer and activator of transcription 6 (STAT6) has been demonstrated to regulate many pathologic features of lung inflammatory responses in animal models including airway eosinophilia, epithelial mucus production, smooth muscle changes, Th2 cell differentiation, and IgE production from B cells. Cytokines IL-4 and IL-13 that are upstream of STAT6 are found elevated in human asthma and clinical trials are underway to therapeutically target the IL-4/IL-13/STAT6 pathway. Additionally, recent work suggests that STAT6 may also regulate lung anti-viral responses and contribute to pulmonary fibrosis. This review will focus on the role of STAT6 in lung diseases and mechanisms by which STAT6 controls immune and structural lung cell function.

Essential, dose-dependent role for the transcription factor Gata3 in the development of IL-5+ and IL-13+ type 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s; also called nuocytes, innate helper cells, or natural helper cells) provide protective immunity during helminth infection and play an important role in influenza-induced and allergic airway hyperreactivity. Whereas the transcription factor GATA binding protein 3 (Gata3) is important for the production of IL-5 and -13 by ILC2s in response to IL-33 or -25 stimulation, it is not known whether Gata3 is required for ILC2 development from hematopoietic stem cells. Here, we show that chimeric mice generated with Gata3-deficient fetal liver hematopoietic stem cells fail to develop systemically dispersed ILC2s. In these chimeric mice, in vivo administration of IL-33 or -25 fails to expand ILC2 numbers or to induce characteristic ILC2-dependent IL-5 or -13 production. Moreover, cell-intrinsic Gata3 expression is required for ILC2 development in vitro and in vivo. Using mutant and transgenic mice in which Gata3 gene copy number is altered, we show that ILC2 generation from common lymphoid progenitors, as well as ILC2 homeostasis and cytokine production, is regulated by Gata3 expression levels in a dose-dependent fashion. Collectively, these results identify Gata3 as a critical early regulator of ILC2 development, thereby extending the paradigm of Gata3-dependent control of type 2 immunity to include both innate and adaptive lymphocytes.

Digital quantification of gene expression in sequential breast cancer biopsies reveals activation of an immune response

Advancements in molecular biology have unveiled multiple breast cancer promoting pathways and potential therapeutic targets. Large randomized clinical trials remain the ultimate means of validating therapeutic efficacy, but they require large cohorts of patients and are lengthy and costly. A useful approach is to conduct a window of opportunity study in which patients are exposed to a drug pre-surgically during the interval between the core needle biopsy and the definitive surgery. These are non-therapeutic studies and the end point is not clinical or pathological response but rather evaluation of molecular changes in the tumor specimens that can predict response. However, since the end points of the non-therapeutic studies are biologic, it is critical to first define the biologic changes that occur in the absence of treatment. In this study, we compared the molecular profiles of breast cancer tumors at the time of the diagnostic biopsy versus the definitive surgery in the absence of any intervention using the Nanostring nCounter platform. We found that while the majority of the transcripts did not vary between the two biopsies, there was evidence of activation of immune related genes in response to the first biopsy and further investigations of the immune changes after a biopsy in early breast cancer seem warranted.

Eosinophils: multifunctional and distinctive properties

The eosinophil is a granulocyte prominent in allergic diseases and inflammatory responses against helminthic parasites. The eosinophil was named by Paul Ehrlich in 1879, and derives from the intense staining of its granules with the acidic dye eosin. It has been the subject of extensive investigation ever since. It is strongly associated with human diseases involving mucosal surfaces, such as allergic asthma, atopic dermatitis and gastrointestinal disorders. Eosinophils are likely involved in tissue homeostasis, modulation of adaptive immune responses, innate immunity to certain microbes and pathological changes in allergic disorders. Thus, the eosinophil is considered a multifunctional leukocyte that contributes to a wide variety of physiological and pathological processes, depending on its location and activation status. Further studies will be necessary to better understand the biology of this extraordinary leukocyte and to reveal the importance of the cell in human health and disease.

Lung type 2 innate lymphoid cells express cysteinyl leukotriene receptor 1, which regulates TH2 cytokine production

BACKGROUND

Cysteinyl leukotrienes (CysLTs) contribute to asthma pathogenesis, in part through cysteinyl leukotriene receptor 1 (CysLT1R). Recently discovered lineage-negative type 2 innate lymphoid cells (ILC2s) potently produce IL-5 and IL-13.

OBJECTIVES

We hypothesized that lung ILC2s might be activated by leukotrienes through CysLT1R.

METHODS

ILC2s (Thy1.2(+) lineage-negative lymphocytes) and CysLT1R were detected in the lungs of wild-type, signal transducer and activator of transcription 6-deficient (STAT6(-/-)), and recombination-activating gene 2-deficient (RAG2(-/-)) mice by means of flow cytometry. T(H)2 cytokine levels were measured in purified lung ILC2s stimulated with leukotriene D₄ (LTD₄) in the presence or absence of the CysLT1R antagonist montelukast. Calcium influx was measured by using Fluo-4 intensity. Intranasal leukotriene C₄, D₄, and E₄ were administered to naive mice, and levels of ILC2 IL-5 production were determined. Finally, LTD₄ was coadministered with Alternaria species repetitively to RAG2(-/-) mice (with ILC2s) and IL-7 receptor-deficient mice (lack ILC2s), and total ILC2 numbers, proliferation (Ki-67(+)), and bronchoalveolar lavage fluid eosinophil numbers were measured.

RESULTS

CysLT1R was expressed on lung ILC2s from wild-type, RAG2(-/-), and STAT6(-/-) naive and Alternaria species-challenged mice. In vitro LTD₄ induced ILC2s to rapidly generate high levels of IL-5 and IL-13 within 6 hours of stimulation. Interestingly, LTD4, but not IL-33, induced high levels of IL-4 by ILC2s. LTD₄ administered in vivo rapidly induced ILC2 IL-5 production that was significantly reduced by montelukast before treatment. Finally, LTD₄ potentiated Alternaria species-induced eosinophilia, as well as ILC2 accumulation and proliferation.

CONCLUSIONS

We present novel data that CysLT1R is expressed on ILC2s and LTD₄ potently induces CysLT1R-dependent ILC2 production of IL-4, IL-5, and IL-13. Additionally, LTD₄ potentiates Alternaria species-induced eosinophilia and ILC2 proliferation and accumulation.

Interleukin-33: a mediator of inflammation targeting hematopoietic stem and progenitor cells and their progenies

Inflammation is defined as a physiological response initiated by a variety of conditions that cause insult to the body, such as infection and tissue injury. Inflammation is triggered by specialized receptors in the innate immune system, which recognize microbial components known as pathogen-associated molecular patterns or endogenous signals produced by damaged cells (damage-associated molecular patterns). IL-33 is a cytokine that is released predominantly at the epithelial barrier when it is exposed to pathogens, allergens, or injury-inducing stimuli. IL-33 target cells are various, ranging from hematopoietic stem and progenitor cells (HSPCs) and essentially all types of their progeny to many non-hematopoietic cells. The pleiotropic actions of IL-33 suggest that IL-33 is involved in every phase of the inflammatory process. In this review, we discuss recent advances in the understanding of how IL-33 orchestrates inflammatory responses by regulating HSPCs and innate immune cells.

Cytokine targets in airway inflammation

Asthma is an inflammatory disease of the airway wall that leads to bronchial hyper-reactivity and airway obstruction, caused by inflammation, mucus hyper-production and airway wall remodelling. Central to pathogenesis, Th2 and Th17 lymphocytes of the adaptive immune system control many aspects of the disease by producing cytokines such as IL-4, IL-5, IL-13, and IL-17. In addition, many cells of the innate immune system such as mast cells, basophils, neutrophils, eosinophils, dendritic cells (DCs), and innate lymphoid cells (ILCs) play an important role in the initiation or maintenance of disease. Epithelial cells are ever more implicated in disease pathogenesis, as they are able to sense exposure to pathogens via pattern recognition receptors (PRRs) and can activate DCs. This review article will deal with the role of cytokines that are considered essential controllers of the inflammatory, immune and regenerative response to allergens, viruses and environmental pollutants. Emerging Th2 cytokines such as thymic stromal lymphopoietin, GM-CSF, IL-1, IL-33, IL-25 mediate the crosstalk between epithelial cells, DCs, and ILCs. Understanding the crosstalk between structural cells, innate and adaptive immune cells that is mediated by cytokines provides important mechanistic insights into how asthma develops and perpetuates itself. It could also provide the framework on which we will select new therapeutic strategies that prevent exacerbations and alter the natural course of the disease.

A novel small compound SH-2251 suppresses Th2 cell-dependent airway inflammation through selective modulation of chromatin status at the Il5 gene locus

IL-5 is a key cytokine that plays an important role in the development of pathological conditions in allergic inflammation. Identifying strategies to inhibit IL-5 production is important in order to establish new therapies for treating allergic inflammation. We found that SH-2251, a novel thioamide-related small compound, selectively inhibits the differentiation of IL-5-producing Th2 cells. SH-2251 inhibited the induction of active histone marks at the Il5 gene locus during Th2 cell differentiation. The recruitment of RNA polymerase II, and following expression of the Th2 cell-specific intergenic transcripts around the Il5 gene locus was also inhibited. Furthermore, Th2 cell-dependent airway inflammation in mice was suppressed by the oral administration of SH-2251. Gfi1, a transcriptional repressor, was identified as a downstream target molecule of SH-2251 using a DNA microarray analysis. The Gfi1 expression dramatically decreased in SH-2251-treated Th2 cells, and the SH-2251-mediated inhibition of IL-5-producing Th2 cell differentiation was restored by transduction of Gfi1. Therefore, our study unearthed SH-2251 as a novel therapeutic candidate for allergic inflammation that selectively inhibits active histone marks at the Il5 gene locus.

Development and function of group 2 innate lymphoid cells

The innate lymphoid cell (ILC) family has recently expanded with the discovery of type-2 innate lymphoid cells (ILC2). These cells arise from lymphoid progenitors in the bone marrow and, under the control of the transcriptional regulators RORα and Gata3, they mature to give rise to IL-5, IL-9 and IL-13 producing ILC2. These cells are critical components of the innate immune response to parasitic worm infections and have also been implicated in the pathogenesis of asthma and allergy. Recent advances in our understanding of the molecular regulation of ILC2 development and function now present the opportunity to develop new genetic models to assess ILC2 immune function and to investigate possible therapeutic interventions.

IL-33-mediated innate response and adaptive immune cells contribute to maximum responses of protease allergen-induced allergic airway inflammation

How the innate and adaptive immune systems cooperate in the natural history of allergic diseases has been largely unknown. Plant-derived allergen, papain, and mite allergens, Der f 1 and Der p 1, belong to the same family of cysteine proteases. We examined the role of protease allergens in the induction of Ab production and airway inflammation after repeated intranasal administration without adjuvants and that in basophil/mast cell stimulation in vitro. Papain induced papain-specific IgE/IgG1 and lung eosinophilia. Der f 1 induced Der f 1-specific IgG1 and eosinophilia. Although papain-, Der f 1-, and Der p 1-stimulated basophils expressed allergy-inducing cytokines, including IL-4 in vitro, basophil-depleting Ab and mast cell deficiency did not suppress the papain-induced in vivo responses. Protease inhibitor-treated allergens and a catalytic site mutant did not induce the responses. These results indicate that protease activity is essential to Ab production and eosinophilia in vivo and basophil activation in vitro. IL-33-deficient mice lacked eosinophilia and had reduced papain-specific IgE/IgG1. Coadministration of OVA with papain induced OVA-specific IgE/IgG1, which was reduced in IL-33-deficient mice. We demonstrated IL-33 release, subsequent IL-33-dependent IL-5/IL-13 release, and activation of T1/ST2-expressing lineage(-)CD25(+)CD44(+) innate lymphoid cells in the lung after papain inhalation, suggesting the contribution of the IL-33-type 2 innate lymphoid cell-IL-5/IL-13 axis to the papain-induced airway eosinophilia. Rag2-deficient mice, which lack adaptive immune cells, showed significant, but less severe, eosinophilia. Collectively, these results suggest cooperation of adaptive immune cells and IL-33-responsive innate cells in protease-dependent allergic airway inflammation.

Combination peptide immunotherapy based on T-cell epitope mapping reduces allergen-specific IgE and eosinophilia in allergic airway inflammation

Peptide immunotherapy using soluble peptides containing allergen-derived immunodominant T-cell epitopes holds therapeutic promise for allergic asthma. Previous studies in BALB/c mice using the immunodominant peptide epitope of chicken ovalbumin (p323-339) have been unable to demonstrate therapeutic effects in ovalbumin-induced allergic airway inflammation. We have previously shown that intravenous application of p323-339 can effectively tolerise p323-339-reactive T cells in a non-allergic model in C57BL/6 mice. This study aimed to assess the effects of using p323-339 immunotherapy in a C57BL/6 model of ovalbumin-induced allergic airway inflammation, identify any additional epitopes recognized by the ovalbumin-responsive T-cell repertoire in C57BL/6 mice and assess the effects of combination peptide immunotherapy in this model. Ovalbumin-reactive T-cell lines were generated from ovalbumin-immunized C57BL/6 mice and proliferative responses to a panel of overlapping peptides covering the ovalbumin sequence were assessed. Soluble peptides (singly or combined) were administered intravenously to C57BL/6 mice before the induction of ovalbumin-induced allergic airway inflammation. Peptide immunotherapy using the 323-339 peptide alone did not reduce the severity of allergic airway inflammation. An additional immunodominant T-cell epitope in ovalbumin was identified within the 263-278 sequence. Combination peptide immunotherapy, using the 323-339 and 263-278 peptides together, reduced eosinophilia in the bronchoalveolar lavage and ovalbumin-specific IgE, with apparent reductions in interleukin-5 and interleukin-13. Characterization of the T-cell response to a model allergen has allowed the development of combination peptide immunotherapy with improved efficacy in allergic airway inflammation. This model holds important potential for future mechanistic studies using peptide immunotherapy in allergy.

Implications for Interleukin-33 in solid organ transplantation

Interleukin(IL)-33 is a member of the IL-1 cytokine family that has been attributed T helper (Th) type 2 immunity-promoting capacity. However, new studies indicate that IL-33 is a multifunctional protein that acts as transcriptional/signaling repressor, functions as an alarmin alerting the immune system to necrosis, as well as serves as a cytokine that targets cells expressing ST2, the IL-33 receptor. Interestingly, IL-33 is also emerging as a pleiotropic cytokine. Depending on the innate or adaptive immune cells targeted by IL-33, it can not only promote type 2, but also IFN-γ dominated type 1 immunity. In addition, IL-33 expands regulatory T cells. In this review, we assimilate the current knowledge of IL-33 immunobiology and discuss how IL-33 may mediate such diverse roles in the immune response to pathogens and development of immune-mediated pathologies. The function of IL-33 in shaping alloimmune responses to transplanted organs is poorly explored, but a particularly beneficial role of IL-33 in experimental heart transplant models is summarized. Finally, given the implication of IL-33 in pathologies of the lung and intestine, we discuss how IL-33 may contribute to the comparatively poor outcomes following transplantation of these two organs.

Innate lymphoid cells: balancing immunity, inflammation, and tissue repair in the intestine

Innate lymphoid cells (ILCs) are a recently described group of innate immune cells that can regulate immunity, inflammation, and tissue repair in multiple anatomical compartments, particularly the barrier surfaces of the skin, airways, and intestine. Broad categories of ILCs have been defined based on transcription factor expression and the ability to produce distinct patterns of effector molecules. Recent studies have revealed that ILC populations can regulate commensal bacterial communities, contribute to resistance to helminth and bacterial pathogens, promote inflammation, and orchestrate tissue repair and wound healing. This review will examine the phenotype and function of murine and human ILCs and discuss the critical roles these innate immune cells play in health and disease.

Limited anti-inflammatory role for interleukin-1 receptor like 1 (ST2) in the host response to murine postinfluenza pneumococcal pneumonia

Interleukin-1 receptor like 1 (ST2) is a negative regulator of Toll-like receptor (TLR) signaling. TLRs are important for host defense during respiratory tract infections by both influenza and Streptococcus (S.) pneumoniae. Enhanced susceptibility to pneumococcal pneumonia is an important complication following influenza virus infection. We here sought to determine the role of ST2 in primary influenza A infection and secondary pneumococcal pneumonia. ST2 knockout (st2^−/−) and wild-type (WT) mice were intranasally infected with influenza A virus; in some experiments mice were infected 2 weeks later with S. pneumoniae. Both mouse strains cleared the virus similarly during the first 14 days of influenza infection and had recovered their weights equally at day 14. Overall st2^−/− mice tended to have a stronger pulmonary inflammatory response upon infection with influenza; especially 14 days after infection modest but statistically significant elevations were seen in lung IL-6, IL-1β, KC, IL-10, and IL-33 concentrations and myeloperoxidase levels, indicative of enhanced neutrophil activity. Interestingly, bacterial lung loads were higher in st2^−/− mice during the later stages of secondary pneumococcal pneumonia, which was associated with relatively increased lung IFN-γ levels. ST2 deficiency did not impact on gross lung pathology in either influenza or secondary S. pneumoniae pneumonia. These data show that ST2 plays a limited anti-inflammatory role during both primary influenza and postinfluenza pneumococcal pneumonia.

Role of interleukin-33 in innate-type immune cells in allergy

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is preferentially and constitutively expressed in epithelial cells, and it is especially localized in the cells' nucleus. The nuclear IL-33 is released by necrotic cells after tissue injury and/or trauma, and subsequently provokes local inflammation as an alarmin, like high-mobility group box protein-1 (HMGB-1) and IL-1α. IL-33 mainly activates Th2 cells and such innate-type immune cells as mast cells, basophils, eosinophils and natural helper cells that express IL-33R (a heterodimer of IL-1 receptor-like 1 [IL-1RL1; also called ST2, T1, Der4, fit-1] and IL-1 receptor accessory protein [IL-1RAcP]). That activation causes the cells to produce Th2 cytokines, which contribute to host defense against nematodes. On the other hand, excessive and/or inappropriate production of IL-33 is also considered to be involved in the development of such disorders as allergy. In this review, we summarize current knowledge regarding the pathogenic roles of IL-33 in the development of allergic inflammation by focusing on its effects on innate-type immune cells.

Innate lymphoid type 2 cells sustain visceral adipose tissue eosinophils and alternatively activated macrophages

Eosinophils in visceral adipose tissue (VAT) have been implicated in metabolic homeostasis and the maintenance of alternatively activated macrophages (AAMs). The absence of eosinophils can lead to adiposity and systemic insulin resistance in experimental animals, but what maintains eosinophils in adipose tissue is unknown. We show that interleukin-5 (IL-5) deficiency profoundly impairs VAT eosinophil accumulation and results in increased adiposity and insulin resistance when animals are placed on a high-fat diet. Innate lymphoid type 2 cells (ILC2s) are resident in VAT and are the major source of IL-5 and IL-13, which promote the accumulation of eosinophils and AAM. Deletion of ILC2s causes significant reductions in VAT eosinophils and AAMs, and also impairs the expansion of VAT eosinophils after infection with Nippostrongylus brasiliensis, an intestinal parasite associated with increased adipose ILC2 cytokine production and enhanced insulin sensitivity. Further, IL-33, a cytokine previously shown to promote cytokine production by ILC2s, leads to rapid ILC2-dependent increases in VAT eosinophils and AAMs. Thus, ILC2s are resident in VAT and promote eosinophils and AAM implicated in metabolic homeostasis, and this axis is enhanced during Th2-associated immune stimulation.

Decoding asthma: translating genetic variation in IL33 and IL1RL1 into disease pathophysiology

Asthma is a complex disease that results from the interaction between genetic predisposition and environmental factors. Recently, genome-wide association studies have identified a number of genes that significantly contribute to asthma. Two of these genes, IL33 and IL-1 receptor-like 1 (IL1RL1), act in one signal transduction pathway. IL33 encodes a cytokine released on damage of cells, whereas IL1RL1 encodes part of the IL-33 receptor complex. Recent progress made in functional studies in human subjects and mouse models of allergic airway disease indicate a central role of IL-33 signaling in driving TH2 inflammation, which is central to eosinophilic allergic asthma. Here, IL-33 acts on cells of both the adaptive and innate immune systems. Very recently, a novel population of IL-33-responsive innate immune cells, the type 2 innate lymphoid cells, was found to produce hallmark TH2 cytokines, such as IL-5 and IL-13. The relevance of these cells for asthma is underscored by the identification of retinoic acid-related orphan receptor α(RORA), the gene encoding the transcription factor critical for their differentiation, as another asthma gene in genome-wide association studies. This review describes the mechanisms through which genetic variation at the IL33 and IL1RL1 loci translates into increased susceptibility for asthma. We propose that genetic variation associated with asthma at the IL33 and IL1RL1 loci can be dissected into independent signals with distinct functional consequences for this pathway that is central to asthma pathogenesis.

Innate lymphoid cells--how did we miss them?

Innate lymphoid cells (ILCs) are newly identified members of the lymphoid lineage that have emerging roles in mediating immune responses and in regulating tissue homeostasis and inflammation. Here, we review the developmental relationships between the various ILC lineages that have been identified to date and summarize their functions in protective immunity to infection and their pathological roles in allergic and autoimmune diseases.

ORMDL3 promotes eosinophil trafficking and activation via regulation of integrins and CD48

ORM (yeast)-like protein isoform 3 (ORMDL3) has recently been identified as a candidate gene for susceptibility to asthma; however, the mechanisms by which it contributes to asthma pathogenesis are not well understood. Here we demonstrate a functional role for ORMDL3 in eosinophils in the context of allergic inflammation. Eosinophils recruited to the airways of allergen-challenged mice express ORMDL3. ORMDL3 expression in bone marrow eosinophils is localized in the endoplasmic reticulum and is induced by interleukin-3 and eotaxin-1. Overexpression of ORMDL3 in eosinophils causes increased rolling, distinct cytoskeletal rearrangement, extracellular signal-regulated kinase (1/2) phosphorylation and nuclear translocation of nuclear factor kappa B. Knockdown of ORMDL3 significantly inhibits activation-induced cell shape changes, adhesion and recruitment to sites of inflammation in vivo, combined with reduced expression of CD49d and CD18. In addition, ORMDL3 regulates interleukin-3-induced expression of CD48 and CD48-mediated eosinophil degranulation. These studies show that ORMDL3 regulates eosinophil trafficking, recruitment and degranulation, further elucidating a role for this molecule in allergic asthma and potentially other eosinophilic disorders.

IL-33 citrine reporter mice reveal the temporal and spatial expression of IL-33 during allergic lung inflammation

Interleukin-33 (IL-33) is an IL-1 family cytokine that signals via its receptor T1/ST2, and is a key regulator of inflammation, notably the type-2 response implicated in allergic asthma. Critical to our understanding of the role of IL-33 is the identification of the cellular sources of IL-33. Although progress has been made in this area, the development of a robust live cell reporter of expression would allow the localisation of IL-33 during ongoing immune responses. We have generated a fluorescent reporter mouse line, Il33^Cit/+, to define the expression profile of IL-33 in vivo and demonstrate its temporal and spatial expression during experimental allergic asthma responses. We found that type-2 pneumocytes constitute the major source of IL-33 upon allergic lung inflammation following exposure to OVA, fungal extract or ragweed pollen. Using Il33^Cit/Cit mice (IL-33-deficient), we establish a role for IL-33 early in the initiation of type-2 responses and the induction of nuocytes (ILC2). We also demonstrate a potential mechanism of action by which IL-33 rapidly initiates type-2 immune responses. Il33^Cit/+ mice have enabled new insights into the initiation of type-2 responses and will provide an important tool for further dissection of this important inflammatory pathway in vivo.

The transcription factor GATA3 is essential for the function of human type 2 innate lymphoid cells

Type 2 innate lymphoid cells (ILC2s) are part of a large family of ILCs that are important effectors in innate immunity, lymphoid organogenesis, and tissue remodeling. ILC2s mediate parasite expulsion but also contribute to airway inflammation, emphasizing the functional similarity between these cells and Th2 cells. Consistent with this, we report that the transcription factor GATA3 was highly expressed by human ILC2s. CRTH2(+) ILC2s were enriched in nasal polyps of patients with chronic rhinosinusitis, a typical type 2-mediated disease. Nasal polyp epithelial cells expressed TSLP, which enhanced STAT5 activation, GATA3 expression, and type 2 cytokine production in ILC2s. Ectopic expression of GATA3 in Lin(-)CD127(+)CRTH2(-) cells resulted in induction of CRTH2 and the capacity to produce high amounts of type 2 cytokines in response to TSLP plus IL-33. Hence, we identify GATA3, potently regulated by TSLP, as an essential transcription factor for the function of human ILC2s.

Deletion of IL-33R (ST2) abrogates resistance to EAE in BALB/C mice by enhancing polarization of APC to inflammatory phenotype

The administration of interleukin 33 and deletion of IL-33 receptor, ST2 molecule, affects the induction of autoimmunity in different experimental models of human autoimmune diseases. The aim of this study was to analyze the effect of ST2 deletion on the induction of experimental autoimmune encephalomyelitis (EAE) in resistant BALB/c mice. Mice were immunized with MOG(35-55) peptide or disease was induced by passive transfer of encephalitogenic singenic cells and EAE was clinically and histologically evaluated. Expression of intracellular inflammatory cytokines, markers of activation and chemokine receptors on lymphoid tissue and CNS infiltrating mononuclear cells was analyzed by flow cytometry. We report here that deletion of ST2(-/-) molecule abrogates resistance of BALB/c mice to EAE induction based on clinical and histopathological findings. Brain and spinal cord infiltrates of ST2(-/-) mice had significantly higher number of CD4(+) T lymphocytes containing inflammatory cytokines compared to BALB/c WT mice. Adoptive transfer of ST2(-/-) primed lymphocytes induced clinical signs of the disease in ST2(-/-) as well as in WT mice. MOG(35-55) restimulated ST2(-/-) CD4(+) cells as well as ex vivo analyzed lymph node cells had higher expression of T-bet and IL-17, IFN-γ, TNF-α and GM-CSF in comparison with WT CD4(+) cells. ST2(-/-) mice had higher percentages of CD4(+) cells expressing chemokine receptors important for migration to CNS in comparison with WT CD4(+) cells. Draining lymph nodes of ST2(-/-) mice contained higher percentage of CD11c(+)CD11b(+)CD8(-) cells containing inflammatory cytokines IL-6 and IL-12 with higher expression of activation markers. Transfer of ST2(-/-) but not WT dendritic cells induced EAE in MOG(35-55) immunized WT mice. Our results indicate that ST2 deficiency attenuates inherent resistance of BALB/c mice to EAE induction by enhancing differentiation of proinflammatory antigen presenting cells and consecutive differentiation of encephalitogenic T cells in the draining lymph node rather than affecting their action in the target tissue.

Cytokine-induced cytokine production by conventional and innate lymphoid cells

Innate immune and differentiated T cells produce signature cytokines in response to cytokine stimulation. Optimal production requires stimulation by an NF-κB inducer, most commonly an interleukin (IL)-1 family member, and a STAT activator. Usually, there is linkage between the IL-1 family member, the activated STAT and the cytokines produced: IFNγ producers respond to the IL-1 family member, IL-18 and IL-12, a STAT4 activator; IL-13 producers respond to IL-33 (although for ILC2 cells this may be replaced by IL-25) and STAT5 activators; for cells producing IL-17A or IL-22, the combination is IL-1 and a STAT3 inducer. Cytokine-induced cytokine production may have broad significance in orchestrating innate responses to distinct infectious agents and in maintaining inflammatory responses after elimination of the inciting antigen.

Differentiation of innate type-2 effector cells

Type-2 immune responses are the underlying cause of many allergic diseases and provide protection against parasitic infection. Effective type-2 immune responses are generated by type-2 helper CD4(+) T cells (Th2) as well as type-2 innate effector cells. While we have learned a great deal about how CD4(+) Th2 cells regulate their Th2 cytokine gene transcription, we still do not know how type-2 innate effector cells acquire their capacity to express Th2 cytokine genes. Furthermore, it remains poorly understood how Th2 cytokines regulate the differentiation of innate type-2 progenitor cells. In this review, we will focus on (1) the long distance interaction between the sites of allergic inflammation and the site of hematopoiesis in the bone marrow, (2) the characteristics of innate type-2 progenitors, and (3) the molecular mechanisms by which innate type-2 effector cells acquire the capacity to produce type-2 cytokines.

IL-13 in asthma and allergic disease: asthma phenotypes and targeted therapies

Decades of research in animal models have provided abundant evidence to show that IL-13 is a key T(H)2 cytokine that directs many of the important features of airway inflammation and remodeling in patients with allergic asthma. Several promising focused therapies for asthma that target the IL-13/IL-4/signal transducer and activator of transcription 6 pathway are in development, including anti-IL-13 mAbs and IL-4 receptor antagonists. The efficacy of these new potential asthma therapies depends on the responsiveness of patients. However, an understanding of how IL-13-directed therapies might benefit asthmatic patients is confounded by the complex heterogeneity of the disease. Recent efforts to classify subphenotypes of asthma have focused on sputum cellular inflammation profiles, as well as cluster analyses of clinical variables and molecular and genetic signatures. Researchers and clinicians can now evaluate biomarkers of T(H)2-driven airway inflammation in asthmatic patients, such as serum IgE levels, sputum eosinophil counts, fraction of exhaled nitric oxide levels, and serum periostin levels, to aid decision making in clinical trials and drug development and to identify subsets of patients who might benefit from therapies. Although it is unlikely that these therapies will benefit all asthmatic patients with this heterogeneous disease, advances in understanding asthma subphenotypes in relation to clinical variables and T(H)2 cytokine responses offer the opportunity to improve the efficacy and safety of proposed therapies for asthma.

STAT6 regulates natural helper cell proliferation during lung inflammation initiated by Alternaria

Asthma exacerbations can be caused by a number of factors, including the fungal allergen Alternaria, which is specifically associated with severe and near-fatal attacks. The mechanisms that trigger lung responses are unclear and might vary between allergens. A comparison between Alternaria, Aspergillus, Candida, and house dust mite, all allergens in humans, showed that only Alternaria promoted immediate innate airway eosinophilia within 12 h of inhalation in nonsensitized mice. Alternaria, but not the other allergens, induced a rapid increase in airway levels of IL-33, accompanied by IL-33 receptor (IL-33R)-positive natural helper cell (NHC) production of IL-5 and IL-13. NHCs in the lung and bone marrow constitutively expressed transcription factors [GATA-3 and E26 transformation-specific sequence-1 (ETS-1)] that could allow for rapid induction of T helper type 2 (Th2) cytokines. Lung NHC numbers and proliferation (%Ki-67), but not IL-5 or GATA-3 expression, were significantly reduced in STAT6-deficient mice 3 days after one challenge with Alternaria. Alternaria induced NHC expression of the EGF receptor ligand amphiregulin (partially dependent on STAT6), as well as EGF receptor signaling in the airway epithelium. Finally, human peripheral blood NHCs (CRTH2(+)CD127(+) lineage-negative lymphocytes) from allergic individuals highly expressed GATA-3 and ETS-1, similar to lung NHCs in mice. In summary, Alternaria-induced lung NHC proliferation and expression of amphiregulin are regulated by STAT6. In addition, NHCs in mouse and humans are primed to express Th2 cytokines through constitutive expression of GATA-3 and ETS-1. Thus several transcription factor pathways (STAT6, GATA-3, and ETS-1) may contribute to NHC proliferation and Th2-type responses in Alternaria-induced asthma.

Induction of CCL2 (MCP-1) BY IL-33 in Human Umbelical Cord Blood Mast Cells

Mast cells, which derive from a bone marrow progenitor and mature in tissues, are important for allergic reactions, but also in inflammation, autoimmunity, and T-cell-mediated immune responses. The addition of certain cytokines to human umbilical cord blood-derived cultured mast cells have been shown to augment IgE-induced production of distinct cytokines, without histamine secretion. CCL2/MCP-1 is a beta chemokine capable of attracting and activating lymphocytes, macrophages, memory T cells and basophilic cells, but not neutrophils. CCL2/MCP-1 regulates the recruitment of inflammatory cells into tissue during inflammation and allergy. IL-33 belongs to the IL-1 family and binds to the ST2 receptor which has high homology to IL-1 receptor and has biological activities. IL-33, causes allergic inflammation and exerts significant biological effects both in vivo and in vitro. IL-33 induces expression of several cytokines and chemokines, resulting in severe inflammatory and allergic diseases. However, our knowledge regarding the effects of these cytokines on human mast cell functions is limited. Here, using human umbilical cord blood mast cells (HUCBMCs) as a valid model, we found that IL-33 induces CCL2/MCP-1 release in HUCBMCs. The release was higher at 24 h incubation compared with 12 h. This study documents the ability of IL-33 to directly stimulate Human umbilical cord blood mast cells (UCBMCs) to produce CCL2/MCP-1. We show that IL-33 is a strong activator of human mast cells capable of inducing CCL2/MCP-1 released at translational level. The present data describe an additional biological activity of IL-33, suggesting that this cytokine may have an important effect on the recruitment of inflammatory cells in allergic diseases.

Type 2 innate lymphoid cells-new members of the "type 2 franchise" that mediate allergic airway inflammation

Type 2 innate lymphoid cells (ILC2s) are members of an ILC family, which contains NK cells and Rorγt(+) ILCs, the latter including lymphoid tissue inducer (LTi) cells and ILCs producing IL-17 and IL-22. ILC2s are dedicated to the production of IL-5 and IL-13 and, as such, ILC2s provide an early and important source of type 2 cytokines critical for helminth expulsion in the gut. Several studies have also demonstrated a role for ILC2s in airway inflammation. In this issue of the European Journal of Immunology, Klein Wolterink et al. [Eur. J. Immunol. 2012. 42: 1106-1116] show that ILC2s are instrumental in several models of experimental asthma where they significantly contribute to production of IL-5 and IL-13, key cytokines in airway inflammation. This study sheds light over the relative contribution of ILC2s versus T helper type 2 cells (Th2) in type 2 mediated allergen-specific inflammation in the airways as discussed in this commentary.

IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung

Allergic asthma is a chronic inflammatory disorder of the airway associated with bronchial obstruction, airway hyper-reactivity (AHR), and mucus production. The epithelium may direct and propagate asthmatic-like responses. Central to this theory is the observation that viruses, air pollution, and allergens promote epithelial damage and trigger the generation of IL-25, IL-33, and TSLP via innate pathways such as TLRs and purinergic receptors. Similarly, engineered nanomaterials promote a Th2-associated pathophysiology. In this study, we tested the hypothesis that instillation of multi-walled carbon nanotubes (MWCNT) impair pulmonary function in C57Bl/6 mice due to the development of IL-33-dependent Th2-associated inflammation. MWCNT exposure resulted in elevated levels of IL-33 in the lavage fluid (likely originating from airway epithelial cells), enhanced AHR, eosinophil recruitment, and production of Th2-associated cytokines and chemokines. Moreover, these events were dependent on IL-13 signaling and the IL-33/ST2 axis, but independent of T and B cells. Finally, MWCNT exposure resulted in the recruitment of innate lymphoid cells. Collectively, our data suggest that MWCNT induce epithelial damage that results in release of IL-33, which in turn promotes innate lymphoid cell recruitment and the development of IL-13-dependent inflammatory response.

IL-33 induces innate lymphoid cell-mediated airway inflammation by activating mammalian target of rapamycin

BACKGROUND

The IL-1 family cytokine IL-33 is involved in the induction of airway inflammation in allergic patients and after viral infection. Several cell types, including CD4(+) T(H)2 cells and the recently described type 2 innate lymphoid cells (ILCs), are targets for IL-33, yet the mechanisms by which this cytokine modulates their activation are not clear.

OBJECTIVES

Our goal was to investigate a role for mammalian target of rapamycin (mTOR) signaling in the activation of T(H)2 and ILC responses and the induction of airway inflammation by IL-33.

METHODS

We biochemically determined the effect of IL-33 on mTOR activation in T(H)2 cells and ILCs and examined the effect of this signaling pathway in vivo using a murine model of IL-33-induced lung inflammation.

RESULTS

We found that IL-33 induces mTOR activation through p110δ phosphoinositide 3-kinase and that blockade of the mTOR pathway inhibited IL-33-induced IL-5 and IL-13 production by T(H)2 cells and ILCs. Furthermore, use of a ribosomal protein S6 kinase 1 inhibitor implicated a role for ribosomal protein S6 kinase 1 in IL-33-induced mTOR-dependent cytokine production. Intranasal administration of IL-33 to wild-type mice induced airway inflammation, whereas adoptive transfer of wild-type ILCs to IL-33 receptor-deficient (St2(-/-)) mice recapitulated this response. Importantly, coadministration of the mTOR inhibitor rapamycin reduced IL-33-dependent ILC, macrophage, and eosinophil accumulation; cytokine secretion; and mucus deposition in the airways.

CONCLUSION

These data reveal a hitherto unrecognized role of mTOR signaling in IL-33-driven, ILC-dependent inflammation in vivo and suggest that manipulation of this pathway might represent a target for therapeutic intervention for airway inflammation.

Innate lymphoid cells in the airways

The airways, similar to other mucosal surfaces, are continuously exposed to the outside environment and a barrage of antigens, allergens, and microorganisms. Of critical importance therefore is the ability to mount rapid and effective immune responses to control commensal and pathogenic microbes, while simultaneously limiting the extent of these responses to prevent immune pathology and chronic inflammation. The function of the adaptive immune response in controlling these processes at mucosal surfaces has been well documented but the important role of the innate immune system, particularly the recently identified family of innate lymphoid cells, has only lately become apparent. In this review, we give an overview of the innate lymphoid cells that exist in the airways and examine the evidence pertaining to their emerging roles in airways immunity, inflammation, and homeostasis.

Interleukin-33 and the function of innate lymphoid cells

Interleukin (IL)-33 is a member of the IL-1 cytokine family that has been shown to play an important role in the induction and effector phases of type 2 immune responses. Both innate and adaptive immunity are regulated by IL-33, and many studies have shown disease-associated functions for this cytokine. Recently, IL-33 has been implicated in the function of novel innate lymphocyte populations that regulate both protective responses in parasitic infections and allergic airway inflammation. Here, we discuss recent data highlighting the dual roles of IL-33 in protective and deleterious immune responses.

Role of innate lymphocytes in infection and inflammation

Cooperation between the innate and adaptive immune responses is critical for enabling protective immunity against various invading microbes. Distinct types of effector T cells have different functions in adaptive immune responses. Th1 cells play important roles in the control of intracellular bacteria by producing IFN-γ to activate macrophages and in anti-viral immunity by producing IFN-γ and activating cytotoxic T lymphocytes. Th2 cell-derived cytokines are important in activating mast cells, eosinophils, and goblet cells in anti-helminth immunity. Th17 cells are pivotal for the inflammatory response mediated by neutrophils, which resists extracellular bacterial infection. In all cases, it is critical that the innate immune responses limit the growth and expansion of invading microbes until antigen-specific adaptive immune responses are established. Recent studies have identified multiple subsets in innate lymphocytes corresponding to previously defined Th subsets. Classical natural killer cells, RORγ⁺ lymphoid tissue inducer-related cells, and Th2-type innate lymphocytes play distinct roles in innate immune responses by producing Th1, Th17, and Th2 cytokines, respectively. Cooperation between innate lymphocytes and antigen-specific T and B cells are likely important in protective immunity against distinct types of microbes. The most recently identified subset is the RORγ-independent Lin⁻Thy-1⁺IL-7R⁺GATA3⁺ innate lymphocyte subset such as natural helper (NH) cell, which is Id2- and IL-7-dependent. This population produces Th2 cytokines, most notably IL-5 and IL-13, and plays a major role in innate immune responses during anti-helminth immunity. In addition, these cells are likely involved in the pathophysiology of some types of allergic diseases. We summarize here current knowledge regarding various innate lymphocyte subsets. In particular, we focus on the Th2-type innate lymphocyte subset.

Allergic host defences

Allergies are generally thought to be a detrimental outcome of a mistargeted immune response that evolved to provide immunity to macroparasites. Here we present arguments to suggest that allergic immunity has an important role in host defence against noxious environmental substances, including venoms, haematophagous fluids, environmental xenobiotics and irritants. We argue that appropriately targeted allergic reactions are beneficial, although they can become detrimental when excessive. Furthermore, we suggest that allergic hypersensitivity evolved to elicit anticipatory responses and to promote avoidance of suboptimal environments.

Innate lymphoid cells: critical regulators of allergic inflammation and tissue repair in the lung

Maintenance of epithelial barrier function in the skin, respiratory tract and intestine is critical to limit exposure to commensal and pathogenic microbes and to maintain tissue homeostasis. Innate lymphoid cells (ILCs) are a recently recognized innate immune cell population that plays critical roles in host defense, regulation of inflammation and promotion of wound healing and tissue repair at barrier surfaces. In this review we discuss recent advances in the understanding of how ILC populations in the respiratory tract impact allergic airway inflammation and lung epithelial repair.

Dynamic role of epithelium-derived cytokines in asthma

Asthma is an inflammatory disorder of the airways, characterized by infiltration of mast cells, eosinophils, and Th2-type CD4+ T cells in the airway wall. Airway epithelium constitutes the first line of interaction with our atmospheric environment. The protective barrier function of the airway epithelium is likely impaired in asthma. Furthermore, recent studies suggest critical immunogenic and immunomodulatory functions of airway epithelium. In particular, a triad of cytokines, including IL-25, IL-33 and TSLP, is produced and released by airway epithelial cells in response to various environmental and microbial stimuli or by cellular damage. These cytokines induce and promote Th2-type airway inflammation and cause remodeling and pathological changes in the airway walls, suggesting their pivotal roles in the pathophysiology of asthma. Thus, the airway epithelium can no longer be regarded as a mere structural barrier, but must be considered an active player in the pathogenesis of asthma and other allergic disorders.