Innate IL-13-producing nuocytes arise during allergic lung inflammation and contribute to airways hyperreactivity

Innate lymphoid cells at the interface between obesity and asthma

Obesity and asthma prevalence has dramatically and concomitantly increased over the last 25 years, and many epidemiological studies have highlighted obesity as an important risk factor for asthma. Although many studies have been performed, the underlying mechanisms remain poorly understood. Innate mechanisms have been involved in both diseases, in particular through the recently described innate lymphoid cells (ILCs). ILCs are subdivided into three groups that are defined by their cytokine production and by their master transcription factor expression, in sharp correlation with their T helper counterparts. However, unlike T helper cells, ILCs do not express antigen-specific receptors, but respond to damage-induced signals. ILCs have been found in target tissues of both diseases, and data have implicated these cells in the pathogenesis of both diseases. In particular group 2 ILCs (ILC2) are activated in both the adipose and lung tissues under the effect of interleukin-33 and interleukin-25 expression. However, counter-intuitively to the well-known association between obesity and asthma, ILC2 are beneficial for obesity but deleterious for asthma. This review will examine the roles of ILCs in each disease and recent data highlighting ILCs as a putative link between obesity and asthma.

Allergen-induced Increases in Sputum Levels of Group 2 Innate Lymphoid Cells in Subjects with Asthma

RATIONALE

Group 2 innate lymphoid cells (ILC2), a major source of type 2 cytokines, initiate eosinophilic inflammatory responses in murine models of asthma.

OBJECTIVES

To investigate the role of ILC2 in allergen-induced airway eosinophilic responses in subjects with atopy and asthma.

METHODS

Using a diluent-controlled allergen challenge crossover study, where all subjects (n = 10) developed allergen-induced early and late responses, airway eosinophilia, and increased methacholine airway responsiveness, bone marrow, blood, and sputum samples were collected before and after inhalation challenge.

MEASUREMENTS AND MAIN RESULTS

ILC2 (lin^-FcεRI^-CD45⁺CD127⁺ST2⁺) and CD4⁺T lymphocytes were enumerated by flow cytometry, as well as intracellular IL-5 and IL-13 expression. Steroid sensitivity of ILC2 and CD4⁺ T cells was investigated in vitro. A significant increase in total, IL-5⁺, IL-13⁺, and CRTH2⁺ ILC2 was found in sputum, 24 hours after allergen, coincident with a significant decrease in blood ILC2. Total, IL-5⁺, and IL-13⁺, but not CRTH2⁺, CD4⁺ T cells significantly increased at 24 and 48 hours after allergen in sputum. In blood and bone marrow, only CD4⁺ cells demonstrated increased activation after allergen. Airway eosinophilia correlated with IL-5⁺ ILC2 at all time points and allergen-induced changes in IL-5⁺ CD4⁺ cells at 48 hours after allergen. Dexamethasone significantly attenuated IL-2- and IL-33-stimulated IL-5 and IL-13 production by both cell types.

CONCLUSIONS

Innate and adaptive immune cells are increased in the airways associated with allergic asthmatic responses. Total and type 2 cytokine-positive ILC2 are increased only within the airways, whereas CD4⁺ T lymphocytes demonstrated local and systemic increases. Steroid sensitivity of both cells may explain effectiveness of this therapy in those with mild asthma.

Innate lymphoid cells: major players in inflammatory diseases

Recent years have seen a marked increase in our understanding of innate lymphoid cells (ILCs). ILCs can be classified into different groups based on their similarity to T cell subsets in terms of their expression of key transcription factors and cytokine production. Various immunological functions of ILCs have been described, and increasing numbers of studies have implicated these cells in inflammatory disorders. Here, we detail the roles of ILCs in inflammatory diseases; we cover type 2 inflammatory diseases (such as asthma, chronic rhinosinusitis and atopic dermatitis), as well as inflammatory bowel diseases, psoriasis and other systemic or organ-specific inflammatory and autoimmune diseases. Future directions in the field are discussed, together with potential avenues of treatment.

Natural helper cells mediate respiratory syncytial virus-induced airway inflammation by producing type 2 cytokines in an IL-33-dependent manner

AIM

Type 2 cytokine production during respiratory virus infection is considered to be linked with asthma exacerbation. As potent Th2 cytokine producers, natural helper (NH) cells play a key role in influenza virus-induced airway hyper-responsiveness. However, it is unclear whether NH cells contribute to respiratory syncytial virus (RSV)-induced airway inflammation, and how the cytokine profile in NH cells is changed during RSV infection.

METHODS

BALB/c mice were infected intranasally with RSV. The number of NH cells in lungs was detected by flow cytometry. The expression of cytokine mRNAs was performed by real-time RT-PCR. Cytokines levels were determined by ELISA.

RESULTS

Following intranasal infection with RSV, BALB/c mice showed an increase in the expression of mRNAs for Th2-like cytokines in NH cells. Furthermore, adoptive transfer of pulmonary NH cells resulted in a massive infiltration of mononuclear cells, in particular eosinophils and neutrophils in lungs, in parallel with an augmented production of Th2-associated cytokines, such as IL-4, IL-5 and IL-10 in bronchoalveolar lavage fluids, providing convincing evidence that NH cells contribute to RSV-induced lung pathogenesis by producing type 2 cytokines. It should be noted that blocking IL-33 with antibody can diminish the absolute number of pulmonary NH cells and the relative expression of mRNAs for type 2 cytokines in pulmonary NH cells, suggesting that IL-33 is necessary for activating Th2-type NH cells.

CONCLUSION

These results reveal that pulmonary NH cells might participate in RSV-induced airway inflammation by producing large quality of type 2 cytokines in an IL-33-dependent manner.

Alveolar Epithelial Cell-Derived Mediators: Potential Direct Regulators of Large Airway and Vascular Responses

Bronchial epithelial cells and pulmonary endothelial cells are thought to be the primary modulators of conducting airways and vessels, respectively. However, histological examination of both mouse and human lung tissue reveals that alveolar epithelial cells (AECs) line the adventitia of large airways and vessels and thus are also in a position to directly regulate these structures. The primary purpose of this perspective is to highlight the fact that AECs coat the adventitial surface of every vessel and airway in the lung parenchyma. This localization is ideal for transmitting signals that can contribute to physiologic and pathologic responses in vessels and airways. A few examples of mediators produced by AECs that may contribute to vascular and airway responses are provided to illustrate some of the potential effects that AECs may modulate.

Innate lymphoid cells in allergic and nonallergic inflammation

In the last decade, the full picture of the role of innate lymphoid cells (ILCs) has been gradually revealed. ILCs are classified into 3 groups based on their transcription factors and cytokine production patterns, which mirror helper T-cell subsets. Unlike T cells and B cells, ILCs do not have antigen receptors. They promptly respond to multiple tissue-derived factors, such as cytokines and alarmins, and produce multiple proinflammatory and immunoregulatory cytokines. It has been reported that ILC-derived cytokines are important for the induction and regulation of inflammation. Accumulating evidence suggests that ILCs play substantial roles in protection against infection and the pathogenesis of inflammatory diseases, such as allergic diseases and autoimmune diseases. Different ILC subsets localize in distinct tissue/organ niches and receive tissue-derived signals on different types of inflammation, which allows them to acquire diverse phenotypes with specialized effector capacities. In this review we highlight the roles of ILCs in a variety of organs, such as the airway, skin, and gastrointestinal tract, in the context of allergic and nonallergic inflammation.

Mechanisms Driving Gender Differences in Asthma

PURPOSE OF REVIEW

Many phenotypes of asthma exist, ranging from mild asthma with onset during childhood to severe asthma with later onset, making asthma a broad disease with different pathologies. A gender disparity exists in asthma prevalence. As adults, women have an increased asthma prevalence compared to men. Further, women are more likely to have severe asthma and a later onset of asthma compared to men. Here, we review clinical and animal studies that have defined the role of sex hormones in airway inflammation, smooth muscle contraction, mucus production, and airway mechanics associated with asthma pathogenesis.

RECENT FINDINGS

Clinical evidence shows that increased asthma symptoms occur in females starting at puberty compared to those in boys. However, after puberty, the role for sex hormones in regulating asthma symptoms during menstruation, pregnancy, and menopause is not as clear. Animal studies have shown that estrogen increases and testosterone decreases Th2-mediated airway inflammation, and that females have increased IL-17A-mediated airway inflammation compared to males. Further, females had increased DC and Mϕ function compared to males. However, the mechanisms driving the types of allergic inflammation are not fully elucidated. Overall, ovarian hormones increased and testosterone decreased airway inflammation in asthma, but the mechanisms remain unclear. Delineating these pathways using animal models as well as women and men with various phenotypes of asthma will help determine if women with asthma should take (or avoid) hormonal contraceptives as well as predict changes in asthma symptoms during life phases, including pregnancy and menopause, when sex hormones are dramatically changing.

The Innate Cytokines IL-25, IL-33, and TSLP Cooperate in the Induction of Type 2 Innate Lymphoid Cell Expansion and Mucous Metaplasia in Rhinovirus-Infected Immature Mice

Early-life respiratory viral infection is a risk factor for asthma development. Rhinovirus (RV) infection of 6-d-old mice, but not mature mice, causes mucous metaplasia and airway hyperresponsiveness that are associated with the expansion of lung type 2 innate lymphoid cells (ILC2s) and are dependent on IL-13 and the innate cytokine IL-25. However, contributions of the other innate cytokines, IL-33 and thymic stromal lymphopoietin (TSLP), to the observed asthma-like phenotype have not been examined. We reasoned that IL-33 and TSLP expression are also induced by RV infection in immature mice and are required for maximum ILC2 expansion and mucous metaplasia. We inoculated 6-d-old BALB/c (wild-type) and TSLP receptor-knockout mice with sham HeLa cell lysate or RV. Selected mice were treated with neutralizing Abs to IL-33 or recombinant IL-33, IL-25, or TSLP. ILC2s were isolated from RV-infected immature mice and treated with innate cytokines ex vivo. RV infection of 6-d-old mice increased IL-33 and TSLP protein abundance. TSLP expression was localized to the airway epithelium, whereas IL-33 was expressed in epithelial and subepithelial cells. RV-induced mucous metaplasia, ILC2 expansion, airway hyperresponsiveness, and epithelial cell IL-25 expression were attenuated by anti-IL-33 treatment and in TSLP receptor-knockout mice. Administration of intranasal IL-33 and TSLP was sufficient for mucous metaplasia. Finally, TSLP was required for maximal ILC2 gene expression in response to IL-25 and IL-33. The generation of mucous metaplasia in immature RV-infected mice involves a complex interplay among the innate cytokines IL-25, IL-33, and TSLP.

IFN-γ Blocks Development of an Asthma Phenotype in Rhinovirus-Infected Baby Mice by Inhibiting Type 2 Innate Lymphoid Cells

Early-life wheezing-associated infections with rhinovirus (RV) have been associated with asthma development in children. We have shown that RV infection of 6-day-old mice induces mucous metaplasia and airways hyperresponsiveness, which is dependent on IL-13, IL-25, and type 2 innate lymphoid cells (ILC2s). Infection of immature mice fails to induce lung IFN-γ expression, in contrast to mature 8-week-old mice with a robust IFN-γ response, consistent with the notion that deficient IFN-γ production in immature mice permits RV-induced type 2 immune responses. We therefore examined the effects of intranasal IFN-γ administration on RV-induced ILC2 expansion and IL-13 expression in 6-day-old BALB/c and IL-13 reporter mice. Airway responses were assessed by histology, immunofluorescence microscopy, quantitative polymerase chain reaction, ELISA, and flow cytometry. Lung ILC2s were also treated with IFN-γ ex vivo. We found that, compared with untreated RV-infected immature mice, IFN-γ treatment attenuated RV-induced IL-13 and Muc5ac mRNA expression and mucous metaplasia. IFN-γ also reduced ILC2 expansion and the percentage of IL-13-secreting ILC2s. IFN-γ had no effect on the mRNA or protein expression of IL-25, IL-33, or thymic stromal lymphoprotein. Finally, IFN-γ treatment of sorted ILC2s reduced IL-5, IL-13, IL-17RB, ST2, and GATA-3 mRNA expression. We conclude that, in immature mice, IFN-γ inhibits ILC2 expansion and IL-13 expression in vivo and ex vivo, thereby attenuating RV-induced mucous metaplasia. These findings demonstrate the antagonistic function of IFN-γ on ILC2 expansion and gene expression, the absence of which may contribute to the development of an asthma-like phenotype after early-life RV infection.

IL-13+ Type 2 Innate Lymphoid Cells Correlate with Asthma Control Status and Treatment Response

Type 2 innate lymphoid cells (ILC2s) have been shown to produce large amounts of type 2 cytokines in a non-antigen-specific manner. These cytokines act upstream and downstream of ILC2 and are increasingly common in asthma drug development, thus warranting a closer investigation of the mechanism-related clinical manifestations of ILC2 in the selection of patients with asthma. We hypothesized that IL-13⁺ILC2s in the circulation might correlate with asthma control status as a result of persistent T-helper cell type 2 (Th2) inflammation in the lung. Furthermore, we aimed to explore ILC2s' responsiveness to glucocorticoid. The percentages of ILC2s and IL-13⁺ILC2s in different asthma subgroups were checked, and correlation analyses between ILC2s and asthma-related clinical parameters were performed. Dexamethasone treatments in ILC2s and Th2 cells were performed to clarify their response properties. ILC2s were identified as a Lin^-CD45^hiIL-7Rα⁺CRTH2⁺ cell population distinct from human peripheral blood mononuclear cells. Frequencies of ILC2s were increased dramatically in those with asthma (0.04 ± 0.02%) compared with healthy donors (0.025 ± 0.011%). The percentages of IL-13⁺ILC2s were significantly higher in patients in the uncontrolled group (49.7 ± 16.9%) and partly controlled groups (30.8 ± 13.1%) than in those in the well-controlled group (16.7 ± 5.9%) and healthy control subjects (18.7 ± 8.7%). Effective treatment of uncontrolled IL-13⁺ILC2-positive patients with asthma resulted in dynamic modulation of IL-13⁺ILC2 levels back to baseline. ILC2s were more resistant to glucocorticoid than Th2 cells in vitro. ILC2s are strong responders to IL-25/IL-33 stimulation. IL-13⁺ILC2s show a positive correlation with patient asthma control status and are more resistant to glucocorticoid than Th2 cells in humans.

The Role of Innate Lymphoid Cells in Immune-Mediated Liver Diseases

Innate lymphoid cells (ILCs) are a recently identified group of innate immune cells lacking antigen-specific receptors that can mediate immune responses and regulate tissue homeostasis and inflammation. ILCs comprise group 1 ILCs, group 2 ILCs, and group 3 ILCs. These ILCs usually localize at mucosal surfaces and combat pathogens by the rapid release of certain cytokines. However, the uncontrolled activation of ILCs can also lead to damaging inflammation, especially in the gut, lung, and skin. Although the physiological and pathogenic roles of ILCs in liver diseases have been attracting increasing attention recently, there has been no systematic review regarding the roles of ILCs in immune-mediated liver diseases. Here, we review the relationships between the ILC subsets and their functions in immune-mediated liver diseases, and discuss their therapeutic potential based on current knowledge about the functional roles of these cells in liver diseases.

Activated plasmacytoid dendritic cells regulate type 2 innate lymphoid cell-mediated airway hyperreactivity

BACKGROUND

Allergic asthma is a prevalent inflammatory disease of the airways caused by dysregulated immune balance in the lungs with incompletely understood pathogenesis. The recently identified type 2 innate lymphoid cells (ILC2s) play significant roles in the pathogenesis of asthma. Although ILC2-activating factors have been identified, the mechanisms that suppress ILC2s remain largely unknown. Plasmacytoid dendritic cells (pDCs) are important in antiviral immunity and in maintaining tolerance to inert antigens.

OBJECTIVE

We sought to address the role of pDCs in regulating ILC2 function and ILC2-mediated airway hyperreactivity (AHR) and lung inflammation.

METHODS

We used several murine models, including BDCA-2-diphtheria toxin receptor (DTR) transgenic and IFN-α receptor 1-deficient mice, as well as purified primary ILC2s, to reach our objective. We extended and validated our findings to human ILC2s.

RESULTS

We show that activation of pDCs through Toll-like receptor 7/8 suppresses ILC2-mediated AHR and airway inflammation and that depletion of pDCs reverses this suppression. We further show that pDCs suppress cytokine production and the proliferation rate while increasing the apoptosis rate of ILC2s through IFN-α production. Transcriptomic analysis of both human and murine ILC2s confirms the activation of regulatory pathways in ILC2s by IFN-α.

CONCLUSION

Activation of pDCs alleviates AHR and airway inflammation by suppressing ILC2 function and survival. Our findings reveal a novel regulatory pathway in ILC2-mediated pulmonary inflammation with important clinical implications.

PD-1 regulates KLRG1+ group 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC-2s) regulate immune responses to pathogens and maintain tissue homeostasis in response to cytokines. Positive regulation of ILC-2s through ICOS has been recently elucidated. We demonstrate here that PD-1 is an important negative regulator of KLRG1⁺ ILC-2 function in both mice and humans. Increase in KLRG1⁺ ILC-2 cell numbers was attributed to an intrinsic defect in PD-1 signaling, which resulted in enhanced STAT5 activation. During Nippostrongylus brasiliensis infection, a significant expansion of KLRG1⁺ ILC-2 subsets occurred in Pdcd1^-/- mice and, upon adoptive transfer, Pdcd1^-/- KLRG1⁺ ILC-2s significantly reduced worm burden. Furthermore, blocking PD-1 with an antibody increased KLRG1⁺ ILC-2 cell number and reduced disease burden. Therefore, PD-1 is required for maintaining the number, and hence function, of KLRG1⁺ ILC-2s.

Innate immunity as the orchestrator of allergic airway inflammation and resolution in asthma

The respiratory system is constantly in direct contact with the environment and, has therefore, developed strong innate and adaptive immune responses to combat pathogens. Unlike adaptive immunity which is mounted later in the course of the immune response and is naive at the outset, innate immunity provides the first line of defense against microbial agents, while also promoting resolution of inflammation. In the airways, innate immune effector cells mainly consist of eosinophils, neutrophils, mast cells, basophils, macrophages/monocytes, dendritic cells and innate lymphoid cells, which attack pathogens directly or indirectly through the release of inflammatory cytokines and antimicrobial peptides, and coordinate T and B cell-mediated adaptive immunity. Airway epithelial cells are also critically involved in shaping both the innate and adaptive arms of the immune response. Chronic allergic airway inflammation and linked asthmatic disease is often considered a result of aberrant activation of type 2 T helper cells (Th2) towards innocuous environmental allergens; however, innate immune cells are increasingly recognized as key players responsible for the initiation and the perpetuation of allergic responses. Moreover, innate cells participate in immune response regulation through the release of anti-inflammatory mediators, and guide tissue repair and the maintenance of airway homeostasis. The scope of this review is to outline existing knowledge on innate immune responses involved in allergic airway inflammation, highlight current gaps in our understanding of the underlying molecular and cellular mechanisms and discuss the potential use of innate effector cells in new therapeutic avenues.

The regulatory dendritic cell marker C1q is a potent inhibitor of allergic inflammation

The complement subunit C1q was recently identified as a marker for monocyte-derived regulatory dendritic cells supporting the differentiation of interleukin (IL)-10-secreting CD4⁺ T cells with a suppressive activity. Furthermore, C1q expression is upregulated in peripheral blood mononuclear cells of allergic patients in the course of successful allergen immunotherapy. Herein, we investigated a potential direct role of C1q in downregulating allergic inflammation. In mice with ovalbumin (OVA) or birch pollen (BP)-induced allergic asthma, C1q is as efficacious as dexamethasone to reduce both airway hyperresponsiveness (AHR), eosinophil, and ILC2 infiltrates in bronchoalveolar lavages, as well as allergen-specific T helper 2 cells in the lungs. Administration of C1q does not expand IL-10⁺/Foxp3⁺ regulatory T cells in the lungs, spleen, or in the blood. Depletion of plasmacytoid dendritic cells (pDCs) abrogates the capacity of C1q to reduce AHR and eosinophilic infiltrates in OVA-sensitized mice. Also C1q treatment inhibits the activation of human and mouse pDCs by CpGs, thereby demonstrating a critical role for pDCs in the anti-inflammatory activity of C1q. We conclude that regulatory dendritic cells can mediate a potent direct anti-inflammatory activity via the expression and/or secretion of molecules such as C1q, independently of their capacity to expand the pool of regulatory T cells.

Addressing unmet needs in understanding asthma mechanisms: From the European Asthma Research and Innovation Partnership (EARIP) Work Package (WP)2 collaborators

Asthma is a heterogeneous, complex disease with clinical phenotypes that incorporate persistent symptoms and acute exacerbations. It affects many millions of Europeans throughout their education and working lives and puts a heavy cost on European productivity. There is a wide spectrum of disease severity and control. Therapeutic advances have been slow despite greater understanding of basic mechanisms and the lack of satisfactory preventative and disease modifying management for asthma constitutes a significant unmet clinical need. Preventing, treating and ultimately curing asthma requires co-ordinated research and innovation across Europe. The European Asthma Research and Innovation Partnership (EARIP) is an FP7-funded programme which has taken a co-ordinated and integrated approach to analysing the future of asthma research and development. This report aims to identify the mechanistic areas in which investment is required to bring about significant improvements in asthma outcomes.

An Update on Lymphocyte Subtypes in Asthma and Airway Disease

Inflammation is a hallmark of many airway diseases. Improved understanding of the cellular and molecular mechanisms of airway disease will facilitate the transition in our understanding from phenotypes to endotypes, thereby improving our ability to target treatments based on pathophysiologic characteristics. For example, allergic asthma has long been considered to be driven by an allergen-specific T helper 2 response. However, clinical and mechanistic studies have begun to shed light on the role of other cell subsets in the pathogenesis and regulation of lung inflammation. In this review, we discuss the importance of different lymphocyte subsets to asthma and other airway diseases, while highlighting the growing evidence that asthma is a syndrome that incorporates many immune phenotypes.

Group 2 innate lymphoid cells are elevated and activated in chronic rhinosinusitis with nasal polyps

Background

Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) is characterized by type 2 inflammation with high levels of Th2 cytokines. Although T helper cytokines are released from T cells, innate lymphoid cells (ILC) are also known to produce high levels of the same cytokines. However, the presence of various types of ILC in CRS is poorly understood.

Objective

The objective of this study was to fully characterize the presence of all ILC subsets in CRS and to identify phenotypical differences of group 2 ILC (ILC2) in CRSwNP compared to ILC2 from non‐type 2 inflamed areas.

Methods

We investigated the presence of ILC subsets in peripheral blood mononuclear cells (PBMC) from healthy subjects, tonsil tissue, ethmoid tissue from control subjects and patients with non‐polypoid CRS (CRSsNP) and CRSwNP, as well as nasal polyp (NP) tissue from CRSwNP by flow cytometry. Sorted ILC2 were cultured in the presence and absence of IL‐33 and production of IL‐5 and IL‐13 was assessed by Luminex.

Results

We found that all ILC subsets were present in NP but ILC2 were dominant and significantly elevated compared to PBMC, tonsil, CRSsNP, and normal sinus tissue. We also found that inducible T‐cell co‐stimulator (ICOS) and side scatter were increased and CD127 was down‐regulated in ILC2 from NP compared to blood or tonsil ILC2. Thymic stromal lymphopoietin, IL‐7, and IL‐33 were able to down‐regulate expression of CD127 and increase side scatter in blood ILC2. Furthermore, sorted NP ILC2 but not blood ILC2 spontaneously released type 2 cytokines including IL‐5 and IL‐13.

Conclusions and Clinical Relevance

These results suggest that ILC2 are not only elevated but also activated in CRSwNP in vivo and that ILC2 may play important roles in the type 2 inflammation in CRSwNP.

β2 integrins rather than β1 integrins mediate Alternaria-induced group 2 innate lymphoid cell trafficking to the lung

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) expand in the lungs of mice during type 2 inflammation induced by the fungal allergen Alternaria alternata. The increase in ILC2 numbers in the lung has been largely attributed to local proliferation and whether ILC2s migrate from the circulation to the lung after Alternaria exposure is unknown.

OBJECTIVE

We examined whether human (lung, lymph node, and blood) and mouse lung ILC2s express β₁ and β₂ integrin adhesion molecules and whether these integrins are required for trafficking of ILC2s into the lungs of mice.

METHODS

Human and mouse ILC2s were assessed for surface expression of β₁ and β₂ integrin adhesion molecules by using flow cytometry. The role of β₁ and β₂ integrins in ILC2 trafficking to the lungs was assessed by in vivo blocking of these integrins before airway exposure to Alternaria in mice.

RESULTS

Both human and mouse lung ILC2s express high levels of β₁ and β₂ integrin adhesion receptors. Intranasal administration of Alternaria challenge reduced ILC2 numbers in the bone marrow and concurrently increased blood and lung ILC2 numbers. In vivo blocking of β₂ integrins (CD18) significantly reduced ILC2 numbers in the lungs but did not alter ILC2 proliferation, apoptosis, and function. In contrast, in vivo blocking of β₁ integrins or α₄ integrins did not affect lung ILC2 numbers.

CONCLUSION

ILC2 numbers increase in the mouse lung not only through local proliferation but also through trafficking from the circulation into the lung using β₂ rather than β₁ or α₄ integrins.

Guards at the gate: physiological and pathological roles of tissue-resident innate lymphoid cells in the lung

The lung is an important open organ and the primary site of respiration. Many life-threatening diseases develop in the lung, e.g., pneumonia, asthma, chronic obstructive pulmonary diseases (COPDs), pulmonary fibrosis, and lung cancer. In the lung, innate immunity serves as the frontline in both anti-irritant response and anti-tumor defense and is also critical for mucosal homeostasis; thus, it plays an important role in containing these pulmonary diseases. Innate lymphoid cells (ILCs), characterized by their strict tissue residence and distinct function in the mucosa, are attracting increased attention in innate immunity. Upon sensing the danger signals from damaged epithelium, ILCs activate, proliferate, and release numerous cytokines with specific local functions; they also participate in mucosal immune-surveillance, immune-regulation, and homeostasis. However, when their functions become uncontrolled, ILCs can enhance pathological states and induce diseases. In this review, we discuss the physiological and pathological functions of ILC subsets 1 to 3 in the lung, and how the pathogenic environment affects the function and plasticity of ILCs.

Natural helper cells are associated with the exacerbated airway inflammation seen during RSV reinfection of neonatally primed mice

Infection with respiratory syncytial virus (RSV) in neonatal mice causes more aggressive airway disease when the mice are reinfected with the same virus as adults. However, the underlying mechanisms responsible for this phenomenon are not entirely defined. Natural helper (NH) cells are considered a key factor for virus-induced or exacerbated airway inflammation and airway hyper-responsiveness by producing type 2 cytokines. To confirm whether NH cells are involved in the aggravated lung pathology seen during reinfection, BALB/c mice were initially infected as neonates and reinfected in adulthood. We observed that neonatal RSV infection resulted in an enhanced infiltration of eosinophils and neutrophils in the lungs, in parallel with a significant increase in the levels of IL-5 and IL-13 in bronchoalveolar lavage fluids on day 2 after reinfection. It seems likely that pulmonary NH cells may play a role in the occurrence, since mice first infected at 1wk of age developed an additional increase in the number of NH cells as well as IL-5- and IL-13-producing NH cells in the lungs than those first infected as young adults. In fact, an elevated expression of mRNAs for IL-5 and IL-13 in pulmonary NH cells was detected in mice first infected as neonates. Furthermore, adoptive transfer of NH cells into neonatal mice was able to boost eosinophilic infiltration as well as the production of type 2 cytokines in the lungs after reinfection at adulthood. In contrast, the expression of mRNA for the type 1 cytokine IFN-γ was down-regulated markedly by adoptive transfer of NH cells. Thus, these results suggest that Th2-type NH cells may play a role in the exacerbated airway inflammation seen during RSV reinfection of neonatally primed mice.

IL-9 Production by Nonconventional T helper Cells

IL-9 is a pro-inflammatory cytokine implicated in certain immune-mediated diseases where chronic or acute inflammation of the mucosa plays an important role. Although initially described as being produced by what was then thought to be Th2 cells, it was later described that specialized lymphocyte populations are involved in IL-9 production. In addition to the classical Th9 effector (subset of CD4+ T cells), IL-9 is also produced by nonconventional lymphocytes, namely invariant natural killer T (iNKT) cells and innate lymphoid cells (ILCs). The identification of IL-9-producing cells by flow cytometry and cytokine measurements are pivotal for assigning and defining functional cellular phenotypes. In this chapter we provide methods for the in vitro polarization of IL-9-producing nonconventional lymphocytes and the best conditions for the detection of IL-9 production by intracellular staining.

Role of the IL-33-ST2 axis in sepsis

Sepsis remains a major clinical problem with high morbidity and mortality. As new inflammatory mediators are characterized, it is important to understand their roles in sepsis. Interleukin 33 (IL-33) is a recently described member of the IL-1 family that is widely expressed in cells of barrier tissues. Upon tissue damage, IL-33 is released as an alarmin and activates various types of cells of both the innate and adaptive immune system through binding to the ST2/IL-1 receptor accessory protein complex. IL-33 has apparent pleiotropic functions in many disease models, with its actions strongly shaped by the local microenvironment. Recent studies have established a role for the IL-33-ST2 axis in the initiation and perpetuation of inflammation during endotoxemia, but its roles in sepsis appear to be organism and model dependent. In this review, we focus on the recent advances in understanding the role of the IL-33/ST2 axis in sepsis.

Leukotrienes provide an NFAT-dependent signal that synergizes with IL-33 to activate ILC2s

von Moltke et al. demonstrate that optimal cytokine induction in group 2 innate lymphocytes results from synergy between NFAT-dependent leukotriene signaling and IL-33 signaling. This integration of signaling pathways may represent an innate substitute for the T cell receptor.

Group 2 innate lymphoid cells (ILC2s) and type 2 helper T cells (Th2 cells) are the primary source of interleukin 5 (IL-5) and IL-13 during type 2 (allergic) inflammation in the lung. In Th2 cells, T cell receptor (TCR) signaling activates the transcription factors nuclear factor of activated T cells (NFAT), nuclear factor κB (NF-κB), and activator protein 1 (AP-1) to induce type 2 cytokines. ILC2s lack a TCR and respond instead to locally produced cytokines such as IL-33. Although IL-33 induces AP-1 and NF-κB, NFAT signaling has not been described in ILC2s. In this study, we report a nonredundant NFAT-dependent role for lipid-derived leukotrienes (LTs) in the activation of lung ILC2s. Using cytokine reporter and LT-deficient mice, we find that complete disruption of LT signaling markedly diminishes ILC2 activation and downstream responses during type 2 inflammation. Type 2 responses are equivalently attenuated in IL-33– and LT-deficient mice, and optimal ILC2 activation reflects potent synergy between these pathways. These findings expand our understanding of ILC2 regulation and may have important implications for the treatment of airways disease.

Grass pollen immunotherapy: where are we now

During allergen immunotherapy (AIT), the allergic patient is exposed to the disease-inducing antigens (allergens) in order to induce clinical and immunological tolerance and obtain disease modification. Large trials of grass AIT with highly standardized subcutaneous and sublingual tablet vaccines have been conducted to document the clinical effect. Induction of blocking antibodies as well as changes in the balance between T-cell phenotypes, including induction of regulatory T-cell subtypes, have been demonstrated for both treatment types. These observations increase the understanding of the immunological mechanism behind the clinical effect and may make it possible to use the immunological changes as biomarkers of clinical effect. The current review describes the recent mechanistic findings for subcutaneous immunotherapy and sublingual immunotherapy/tablet treatment and discusses how the observed immunological changes translate into a scientific foundation for the observed clinical effects of grass pollen immunotherapy and lead to new treatment strategies for grass AIT.

IL-33 regulates the IgA-microbiota axis to restrain IL-1α-dependent colitis and tumorigenesis

Inflammatory bowel diseases (IBD) affect over 5 million individuals in the industrialized world, with an increasing incidence rate worldwide. IBD also predisposes affected individuals to development of colorectal cancer, which is a leading cause of cancer-related deaths in adults. Mutations in genes encoding molecules in the IL-33 signaling pathway are associated with colitis and colitis-associated cancer (CAC), but how IL-33 modulates gut homeostasis is unclear. Here, we have shown that Il33-deficient mice are highly susceptible to colitis and CAC. Mechanistically, we observed that IL-33 promoted IgA production from B cells, which is important for maintaining microbial homeostasis in the intestine. Il33-deficient mice developed a dysbiotic microbiota that was characterized by increased levels of mucolytic and colitogenic bacteria. In response to chemically induced colitis, this microbial landscape promoted the release of IL-1α, which acted as a critical driver of colitis and CAC. Consequently, reconstitution of symbiotic microbiota or IL-1α ablation markedly ameliorated colitis susceptibility in Il33-deficient animals. Our results demonstrate that IL-33 promotes IgA production to maintain gut microbial homoeostasis and restrain IL-1α-dependent colitis and CAC. This study therefore highlights modulation of IL-33, IgA, IL-1α, and the microbiota as a potential therapeutic approach in the treatment of IBD and CAC.

Th9 and other IL-9-producing cells in allergic asthma

Allergic asthma is a worldwide increasing chronic disease of the airways which affects more than 300 million people. It is associated with increased IgE, mast cell activation, airway hyperresponsiveness (AHR), mucus overproduction and remodeling of the airways. Previously, this pathological trait has been associated with T helper type 2 (Th2) cells. Recently, different CD4⁺ T cell subsets (Th17, Th9) as well as cells of innate immunity, like mast cells and innate lymphoid cells type 2 (ILC2s), which are all capable of producing the rediscovered cytokine IL-9, are known to contribute to this disease. Regarding Th9 cells, it is known that naïve T cells develop into IL-9-producing cells in the presence of interleukin-4 (IL-4) and transforming growth factor beta (TGFβ). Downstream of IL-4, several transcription factors like signal transducer and activator of transcription 6 (STAT6), interferon regulatory factor 4 (IRF4), GATA binding protein 3 (GATA3), basic leucine zipper transcription factor, ATF-like (BATF) and nuclear factor of activated T cells (NFAT) are activated. Additionally, the transcription factor PU.1, which is downstream of TGFβ signaling, also seems to be crucial in the development of Th9 cells. IL-9 is a pleiotropic cytokine that influences various distinct functions of different target cells such as T cells, B cells, mast cells and airway epithelial cells by activating STAT1, STAT3 and STAT5. Because of its pleiotropic functions, IL-9 has been demonstrated to be involved in several diseases, such as cancer, autoimmunity and other pathogen-mediated immune-regulated diseases. In this review, we focus on the role of Th9 and IL-9-producing cells in allergic asthma.

Protein kinase Cθ controls type 2 innate lymphoid cell and TH2 responses to house dust mite allergen

BACKGROUND

Protein kinase C (PKC) θ, a serine/threonine kinase, is involved in T_H2 cell activation and proliferation. Type 2 innate lymphoid cells (ILC2s) resemble T_H2 cells and produce the T_H2 cytokines IL-5 and IL-13 but lack antigen-specific receptors. The mechanism by which PKC-θ drives innate immune cells to instruct T_H2 responses in patients with allergic lung inflammation remains unknown.

OBJECTIVES

We hypothesized that PKC-θ contributes to ILC2 activation and might be necessary for ILC2s to instruct the T_H2 response.

METHODS

PRKCQ gene expression was assessed in innate lymphoid cell subsets purified from human PBMCs and mouse lung ILC2s. ILC2 activation and eosinophil recruitment, T_H2-related cytokine and chemokine production, lung histopathology, interferon regulatory factor 4 (IRF4) mRNA expression, and nuclear factor of activated T cells (NFAT1) protein expression were determined. Adoptive transfer of ILC2s from wild-type mice was performed in wild-type and PKC-θ-deficient (PKC-θ^-/-) mice.

RESULTS

Here we report that PKC-θ is expressed in both human and mouse ILC2s. Mice lacking PKC-θ had reduced ILC2 numbers, T_H2 cell numbers and activation, airway hyperresponsiveness, and expression of the transcription factors IRF4 and NFAT1. Importantly, adoptive transfer of ILC2s restored eosinophil influx and IL-4, IL-5 and IL-13 production in lung tissue, as well as T_H2 cell activation. The pharmacologic PKC-θ inhibitor (Compound 20) administered during allergen challenge reduced ILC2 numbers and activation, as well as airway inflammation and IRF4 and NFAT1 expression.

CONCLUSIONS

Therefore our findings identify PKC-θ as a critical factor for ILC2 activation that contributes to T_H2 cell differentiation, which is associated with IRF4 and NFAT1 expression in allergic lung inflammation.

Respiratory syncytial virus infection activates IL-13-producing group 2 innate lymphoid cells through thymic stromal lymphopoietin

BACKGROUND

Respiratory syncytial virus (RSV) is a major health care burden with a particularly high worldwide morbidity and mortality rate among infants. Data suggest that severe RSV-associated illness is in part caused by immunopathology associated with a robust type 2 response.

OBJECTIVE

We sought to determine the capacity of RSV infection to stimulate group 2 innate lymphoid cells (ILC2s) and the associated mechanism in a murine model.

METHODS

Wild-type (WT) BALB/c, thymic stromal lymphopoietin receptor (TSLPR) knockout (KO), or WT mice receiving an anti-TSLP neutralizing antibody were infected with the RSV strain 01/2-20. During the first 4 to 6 days of infection, lungs were collected for evaluation of viral load, protein concentration, airway mucus, airway reactivity, or ILC2 numbers. Results were confirmed with 2 additional RSV clinical isolates, 12/11-19 and 12/12-6, with known human pathogenic potential.

RESULTS

RSV induced a 3-fold increase in the number of IL-13-producing ILC2s at day 4 after infection, with a concurrent increase in total lung IL-13 levels. Both thymic stromal lymphopoietin (TSLP) and IL-33 levels were increased 12 hours after infection. TSLPR KO mice did not mount an IL-13-producing ILC2 response to RSV infection. Additionally, neutralization of TSLP significantly attenuated the RSV-induced IL-13-producing ILC2 response. TSLPR KO mice displayed reduced lung IL-13 protein levels, decreased airway mucus and reactivity, attenuated weight loss, and similar viral loads as WT mice. Both 12/11-19 and 12/12-6 similarly induced IL-13-producing ILC2s through a TSLP-dependent mechanism.

CONCLUSION

These data demonstrate that multiple pathogenic strains of RSV induce IL-13-producing ILC2 proliferation and activation through a TSLP-dependent mechanism in a murine model and suggest the potential therapeutic targeting of TSLP during severe RSV infection.

The origin and role of innate lymphoid cells in the lung

Innate lymphoid cells (ILCs), a newly identified member of the lymphoid population, play a critical role in the transition from innate to adaptive immunity in host defense. ILCs are important in mucosal barrier immunity, tissue homeostasis, and immune regulation throughout the body. Significant alterations in ILC responses in lung diseases have been observed and reported. Emerging evidence has shown that ILCs are importantly involved in the pathogenesis and development of a variety of lung diseases, i.e., helminth infections, allergic airway inflammation, and airway hyper-responsiveness. However, as a tissue-resident cell population, the role of ILCs in the lung remains poorly characterized. In this review, we discuss the role of ILCs in lung diseases, the mechanisms underlying the ILC-mediated regulation of immunity, and the therapeutic potential of modulating ILC responses.

Serum IL-5 and IL-13 consistently serve as the best predictors for the blood eosinophilia phenotype in adult asthmatics

BACKGROUND

Molecular biomarkers that identify the phenotype of blood eosinophilia were evaluated in adult asthmatics, and their relationship with clinically significant asthma outcomes was assessed. Patients were clustered based on their molecular fingerprint.

METHODS

At inclusion, 64 patients were evaluated for phenotypic traits, sputum and blood eosinophilia, exhaled NO, serum cytokines and chemokines, total serum IgE, lung function (LF), and airway hyper-responsiveness (AHR). Within-patient changes were evaluated in 44 patients 6 weeks later.

RESULTS

Lung function, asthma control, and monocyte chemotactic protein-1 (MCP-1) were identified as the most important distinguisher and blood eosinophilia as second most important identifier in principal component analysis. A robust relationship was observed between blood eosinophilia and IL-5, IL-13, and eosinophil-derived neurotoxin (EDN), which stayed consistent after 6 weeks. Serum IL-5 and IL-13 were the two best, followed by EDN as separators of high vs low blood eosinophilia. Periostin did not identify blood or sputum eosinophilia, even after stratification for total IgE, and did not correlate with IL-5, IL-13, eotaxin, or EDN. IL-5 and IL-13 showed strong correlations with AHR and monocyte chemoattractant protein (MCP)-1 with asthma severity and fast LF decline. The presence of high or low expression of MCP-1, eotaxin, and IL-8 identified two separate blood eosinophilia patient clusters linked to asthma severity.

CONCLUSION

Serum IL-5 and IL-13 are reliable biomarkers for the blood eosinophilia asthma phenotype. High or low expression of MCP-1, eotaxin, and IL-8 discriminates between eosinophilic asthma severity clusters.

Group 2 innate lymphoid cells are increased in nasal polyps in patients with eosinophilic chronic rhinosinusitis

ILC2s represent a critical innate cellular source of type 2 cytokines and may play important roles in various diseases. We examined the role of ILC2s in the pathogenesis of two subgroups of CRSwNP: ECRS and non-ECRS. We analyzed the prevalence of ILC2s in sinonasal tissues and in blood from patients with ECRS, non-ECRS, CRSsNP, and control. The prevalence of ILC2s in nasal tissues was higher in patients with ECRS as compared to those with non-ECRS or CRSsNP. The prevalence of blood ILC2s was not different between patients with ECRS and non-ECRS. The prevalence of blood ILC2s was higher in patients with allergic rhinitis and elevated serum IgE levels. Alternaria-induced IL-33 secretion was increased in nasal epithelial cells derived from patients with ECRS as compared to those from patients with non-ECRS or CRSsNP. ILC2s may be involved in the pathogenesis of CRSwNP, in particular in patients with tissue eosinophilia (i.e., ECRS).

Lipid mediators as regulators of human ILC2 function in allergic diseases

Group 2 innate lymphoid cells (ILC2) are specialized in type 2 immunity. ILC2 are activated early in immune responses and, despite their low abundance, are able to initiate and amplify allergic inflammation by orchestrating other type 2 immune cells. Based on recent discoveries, the spectrum of ILC2 regulating factors has been extended. It is now well established that not only epithelial cell-derived innate cytokines, but also bioactive lipids can regulate ILC2 activity and accumulation. Additionally, ILC2 appear to be susceptible to changes in the cytokine milieu and can acquire an ILC1-like phenotype due to a high degree of cellular plasticity. As ILC2 are fundamentally involved in the pathogenesis of type 2 diseases, they represent a promising therapeutic target for allergic airway and skin diseases. In this review we summarize the current knowledge about ILC2 biology in the allergy context, with a particular focus on the emerging role of lipid mediators in regulating ILC2 function.

Staphylococcal enterotoxin A-activated regulatory T cells promote allergen-specific TH2 response to intratracheal allergen inoculation

BACKGROUND

T_H2 responses are implicated in asthma pathobiology. Epidemiologic studies have found a positive association between asthma and exposure to staphylococcal enterotoxins.

OBJECTIVE

We used a mouse model of asthma to determine whether staphylococcal enterotoxins promote T_H2 differentiation of allergen-specific CD4 conventional T (Tcon) cells and asthma by activating allergen-nonspecific regulatory T (Treg) cells to create a T_H2-polarizing cytokine milieu.

METHODS

Ovalbumin (OVA)-specific, staphylococcal enterotoxin A (SEA)-nonreactive naive CD4 Tcon cells were cocultured with SEA-reactive allergen-nonspecific Treg or CD4 Tcon cells in the presence of OVA and SEA. The OVA-specific CD4 T cells were then analyzed for IL-13 and IFN-γ expression. SEA-activated Treg cells were analyzed for the expression of the T_H2-polarizing cytokine IL-4 and the T-cell activation markers CD69 and CD62L. For asthma induction, mice were intratracheally sensitized with OVA or cat dander extract (CDE) alone or together with SEA and then challenged with OVA or CDE. Mice were also subject to transient Treg cell depletion before sensitization with OVA plus SEA. Asthma features and T_H2 differentiation in these mice were analyzed.

RESULTS

SEA-activated Treg cells induced IL-13 but suppressed IFN-γ expression in OVA-specific CD4 Tcon cells. SEA-activated Treg cells expressed IL-4, upregulated CD69, and downregulated CD62L. Sensitization with OVA plus SEA but not OVA alone induced asthma, and SEA exacerbated asthma induced by CDE. Depletion of Treg cells abolished these effects of SEA and IL-13 expression in OVA-specific T cells.

CONCLUSION

SEA promoted T_H2 responses of allergen-specific T cells and asthma pathogenesis by activating Treg cells.

Interleukin-33, friend and foe in type-2 immune responses

IL-33 is the most recent addition to the IL-1 cytokine family, identified in 2005 as the ligand of T1/ST2 and inducer of type-2 immune responses. IL-33 has been implicated in a wide range of disease settings, in anti-inflammatory responses and homeostasis, and thus signalling must be strictly regulated. Altered gene expression, post-translational modification, decoy receptor, and receptor signalling are all modulatory mechanisms used to control the IL-33 pathway. Understanding both the genetic and post-translational factors influencing IL-33 activity will be critical for provision of safe effective treatment of type-2 disorders.

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.

Advances in the treatment of virus-induced asthma

Viral exacerbations continue to represent the major burden in terms of morbidity, mortality and health care costs associated with asthma. Those at greatest risk for acute asthma are those with more severe airways disease and poor asthma control. It is this group with established asthma in whom acute exacerbations triggered by virus infections remain a serious cause of increased morbidity. A range of novel therapies are emerging to treat asthma and in particular target this group with poor disease control, and in most cases their efficacy is now being judged by their ability to reduce the frequency of acute exacerbations. Critical for the development of new treatment approaches is an improved understanding of virus-host interaction in the context of the asthmatic airway. This requires research into the virology of the disease in physiological models in conjunction with detailed phenotypic characterisation of asthma patients to identify targets amenable to therapeutic intervention.

NFATc1 deletion in T lymphocytes inhibits the allergic trait in a murine model of asthma

BACKGROUND

NFATc1 isoforms are highly regulated in peripheral T cells where they contribute to the effector function and cell homeostasis.

OBJECTIVE

Here, we investigated the role of NFATc1 in asthma and in T cells.

METHODS

In a murine model of allergic asthma, we analysed differences in T-cell development in this allergic disease model, between wild-type and NFATc1 conditional knockout mice. Thus, we performed quantitative real-time PCR to investigate the mRNA expression of Th2-associated genes as well as genes that are involved in IgE immunoglobulin class-switch. Additionally, we used ELISA, Western blot and flow cytometry (FACS) to analyse protein concentrations of Th1-, Th2- and Th17-specific transcription factors and cytokines and the Th2 chemokine, thymus and activation-regulated chemokine/chemokine ligand 17 (TARC/CCL17) by ELISA.

RESULTS

Mice lacking NFATc1 in CD4(+) T cells display a significant reduction in lung Th2 and Th17 as well as an increase of Th1 cells in an experimental asthma model. Additionally, Batf gene, a recently described transcription factor of the Th2 and Th17 cell differentiation as well as a key T and B transcription factor involved in the IgE immunoglobulin class-switch, was found decreased in the lungs of these mice. As a consequence, serum OVA-specific IgE and IgG1 levels were found significantly decreased after allergen exposure and in the absence of NFATc1 in T cells in experimental allergic asthma.

CONCLUSIONS AND CLINICAL RELEVANCE

Targeting NFATc1 in T lymphocytes ameliorated the allergic trait in the airways of NFATc1(fl/fl) xCD4Cre mice. NFATc1 emerges as a novel target for anti-allergy intervention.

Innate lymphoid cells contribute to allergic airway disease exacerbation by obesity

BACKGROUND

Epidemiologic and clinical observations identify obesity as an important risk factor for asthma exacerbation, but the underlying mechanisms remain poorly understood. Type 2 innate lymphoid cells (ILC2s) and type 3 innate lymphoid cells (ILC3s) have been implicated, respectively, in asthma and adipose tissue homeostasis and in obesity-associated airway hyperresponsiveness (AHR).

OBJECTIVE

We sought to determine the potential involvement of innate lymphoid cells (ILCs) in allergic airway disease exacerbation caused by high-fat diet (HFD)-induced obesity.

METHODS

Obesity was induced by means of HFD feeding, and allergic airway inflammation was subsequently induced by means of intranasal administration of house dust mite (HDM) extract. AHR, lung and visceral adipose tissue inflammation, humoral response, cytokines, and innate and adaptive lymphoid populations were analyzed in the presence or absence of ILCs.

RESULTS

HFD feeding exacerbated allergic airway disease features, including humoral response, airway and tissue eosinophilia, AHR, and T_H2 and T_H17 pulmonary profiles. Notably, nonsensitized obese mice already exhibited increased lung ILC counts and tissue eosinophil infiltration compared with values in lean mice in the absence of AHR. The numbers of total and cytokine-expressing lung ILC2s and ILC3s further increased in HDM-challenged obese mice compared with those in HDM-challenged lean mice, and this was accompanied by high IL-33 and IL-1β levels and decreased ILC markers in visceral adipose tissue. Furthermore, depletion of ILCs with an anti-CD90 antibody, followed by T-cell reconstitution, led to a profound decrease in allergic airway inflammatory features in obese mice, including T_H2 and T_H17 infiltration.

CONCLUSION

These results indicate that HFD-induced obesity might exacerbate allergic airway inflammation through mechanisms involving ILC2s and ILC3s.

Arginase 1 is an innate lymphoid-cell-intrinsic metabolic checkpoint controlling type 2 inflammation

Group 2 innate lymphoid cells (ILC2s) regulate tissue inflammation and repair following activation by cell-extrinsic factors including host-derived cytokines. However, the cell-intrinsic metabolic pathways that control ILC2 function are undefined. Here we demonstrate that expression of the enzyme Arginase 1 (Arg1) is a conserved trait of murine and human ILC2s during acute or chronic lung inflammation. Deletion of murine ILC-intrinsic Arg1 abrogated type 2 lung inflammation by restraining ILC2 proliferation and dampening cytokine production. Mechanistically, inhibition of Arg1 enzymatic activity disrupted multiple components of ILC2 metabolic programming by altering arginine catabolism, impairing polyamine biosynthesis and reducing aerobic glycolysis. These data identify Arg1 as a key regulator of ILC2 bioenergetics, controlling proliferative capacity and pro-inflammatory functions that promote type 2 inflammation.

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.

Potential Therapeutic Aspects of Alarmin Cytokine Interleukin 33 or Its Inhibitors in Various Diseases

PURPOSE

The purpose of this review was to examine the comprehensively accumulated data regarding potential therapeutic aspects of exogenous administration of interleukin 33 (IL-33) or its antagonists in allergic, cancerous, infectious, and inflammatory diseases.

METHODS

A selected review was undertaken of publications that examined the protective and exacerbating effects of IL-33 or its inhibitors in different diseases. Mechanisms of action are summarized to examine the putative role of IL-33 in various diseases.

FINDINGS

IL-33 promoted antibacterial, antiviral, anti-inflammatory, and vaccine adjuvant functions. However, in TH2-biased respiratory, allergic, parasitic, and inflammatory conditions, IL-33 exhibited disease-sensitizing effects. The alarmin cytokine IL-33 induced protective effects in diseases via recruitment of regulatory T cells; antiviral CD8(+) cells, natural killer cells, γδ T cells, and nuocytes; antibacterial and antifungal neutrophils or macrophages; vaccine-associated B/T cells; and inhibition of nuclear factor-κB-mediated gene transcription. In contrast, IL-33 exacerbated the disease process by increasing TH2 cytokines, IgE and eosinophilic immune responses, and inhibition of leukocyte recruitment in various diseases.

IMPLICATIONS

The protective or exacerbated aspects of use of IL-33 or its inhibitors are dependent on the type of infection or inflammatory condition, duration of disease (acute or chronic), organ involved, cytokine microenvironment, dose or kinetics of IL-33, and genetic predisposition. The alarmin cytokine IL-33 acts at cellular, molecular, and transcriptional levels to mediate pluripotent functions in various diseases and has potential therapeutic value to mitigate the disease process.

Innate lymphoid cells in asthma: Will they take your breath away?

Asthma is a complex and heterogeneous disease that is characterized by airway hyper-reactivity (AHR) and airway inflammation. Although asthma was long thought to be driven by allergen-reactive TH 2 cells, it has recently become clear that the pathogenesis of asthma is more complicated and associated with multiple pathways and cell types. A very exciting recent development was the discovery of innate lymphoid cells (ILCs) as key players in the pathogenesis of asthma. ILCs do not express antigen receptors but react promptly to "danger signals" from inflamed tissue and produce an array of cytokines that direct the ensuing immune response. The roles of ILCs may differ in distinct asthma phenotypes. ILC2s may be critical for initiation of adaptive immune responses in inhaled allergen-driven AHR, but may also function independently of adaptive immunity, mediating influenza-induced AHR. ILC2s also contribute to resolution of lung inflammation through their production of amphiregulin. Obesity-induced asthma is associated with expansion of IL-17A-producing ILC3s in the lungs. Furthermore, ILCs may also contribute to steroid-resistant asthma. Although the precise roles of ILCs in different types of asthma are still under investigation, it is clear that inhibition of ILC function represents a potential target that could provide novel treatments for asthma.

Type 2 innate lymphoid cells: at the cross-roads in allergic asthma

Allergic asthma is a chronic inflammatory disease of the lower airways that affects millions of people worldwide. Allergic asthma is a T helper 2 cell (Th2)-mediated disease, in which Th2 cytokines interleukin (IL)-4, IL-5, and IL-13 are closely associated with the symptoms. IL-4 is needed by B cells to switch toward an IgE response, IL-5 recruits and activates eosinophils while IL-13 increases mucus production. The identification of type 2 innate lymphoid cells (ILC2), which are able to rapidly produce large amounts of IL-5 and IL-13 in response to epithelial derived cytokines, implicated a new key player besides Th2 cells. ILCs constitute a family of innate lymphocytes distinct from T and B cells. ILC2s are located in various epithelial compartments in mice and human, including the lung. The recent finding of increased numbers of ILC2s in the airways of severe asthma patients prompts further research to clarify their immunological function. Murine studies have shown that ILC2s are an early innate source of IL-5 and IL-13 after allergen exposure, which induce airway eosinophilic infiltration, mucus hyperproduction, and airway hyperresponsiveness but not allergen-specific IgE production. ILC2s contribute to the initiation as well as to the maintenance of the adaptive type 2 immune response. Here, we review the recent progress on our understanding of the role of ILC2s in the immunopathology of allergic asthma, in particular by studies using murine models which have elucidated fundamental mechanisms by which ILC2s act.

Characterization and Quantification of Innate Lymphoid Cell Subsets in Human Lung

BACKGROUND

Innate lymphoid cells (ILC) are a new family of innate immune cells that have emerged as important regulators of tissue homeostasis and inflammation. However, limited data are available concerning the relative abundance and characteristics of ILC in the human lung.

METHODS

The aim of this study was to characterize and enumerate the different ILC subsets in human lung by multi-color flow cytometry.

RESULTS

Within the CD45+ Lin- CD127+ pulmonary ILC population, we identified group 1 (ILC1), group 2 (ILC2) and group 3 (ILC3) innate lymphoid cells using specific surface markers (i.e. IL12Rβ2, CRTH2 and CD117 respectively) and key transcription factors (i.e. T-bet, GATA-3 and RORγT respectively). Based on the presence of NKp44, ILC3 were further subdivided in natural cytotoxicity receptor (NCR)+ and NCR- ILC3. In addition, we demonstrated the production of signature cytokines IFN-γ, IL-5, IL-17A, IL-22 and GM-CSF in the pulmonary ILC population. Interestingly, we observed a tendency to a higher frequency of NCR- ILC3 in lungs of patients with chronic obstructive pulmonary disease (COPD) compared with controls.

CONCLUSIONS

We show that the three main ILC subsets are present in human lung. Importantly, the relative abundance of ILC subsets tended to change in COPD patients in comparison to control individuals.

Biologics in asthma--the next step toward personalized treatment

Asthma is a multifaceted disease and is associated with significant impairment and risk, and a therapeutic response that is highly variable. Although current treatments are usually effective for patients with mild-to-moderate disease, patients with more severe asthma are often unresponsive to current efforts, and there remains a need for agents with properties that may achieve control in these individuals. There is ongoing research to identify bioactive molecules that contribute to the pathophysiology of asthma, and many of these have been identified as potential therapeutic targets to improve control of this disease. As a consequence of these efforts, monoclonal antibodies have been developed and tested as to their effectiveness in the treatment of asthma. The assessment of these new treatments has identified particular pathways that, in selected patients, have shown benefit. The following review will discuss the current and future use of biological agents for the treatment of asthma, their efficacy, and how certain patient phenotypes and endotypes may be associated with biomarkers that may be used to select treatments to achieve greatest effectiveness of their use. As knowledge of the effects of these biological agents in asthma emerges, as well as the patients in whom they are most beneficial, the movement toward personalized treatment will follow.

Innate immunity is a key factor for the resolution of inflammation in asthma

The resolution of inflammation is an integral and natural part of the physiological response to tissue injury, infection and allergens or other noxious stimuli. Resolution is now recognised as an active process with highly regulated cellular and biochemical events. Recent discoveries have highlighted that innate inflammatory cells have bimodal effector functions during the inflammatory response, including active roles during the resolution process. Several mediators displaying potent pro-resolving actions have recently been uncovered. Lipoxin A4, the lead member of this new class of pro-resolving mediators, has anti-inflammatory actions on type 2 innate lymphoid cells and pro-resolving actions through natural killer cells in asthma immunobiology. Eosinophils are also able to control crucial aspects of resolution through the generation of pro-resolving mediators. Uncontrolled asthma has been associated with a defect in the generation of specialised pro-resolving mediators, including lipoxin A4 and protectin D1. Thus, bioactive stable analogue mimetics of these mediators that can harness endogenous resolution mechanisms for inflammation may offer new therapeutic strategies for asthma and airway inflammation associated diseases.