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

Pulmonary environmental cues drive group 2 innate lymphoid cell dynamics in mice and humans

Group 2 innate lymphoid cells (ILC2s) are enriched in mucosal tissues (e.g., lung) and respond to epithelial cell-derived cytokines initiating type 2 inflammation. During inflammation, ILC2 numbers are increased in the lung. However, the mechanisms controlling ILC2 trafficking and motility within inflamed lungs remain unclear and are crucial for understanding ILC2 function in pulmonary immunity. Using several approaches, including lung intravital microscopy, we demonstrate that pulmonary ILC2s are highly dynamic, exhibit amoeboid-like movement, and aggregate in the lung peribronchial and perivascular spaces. They express distinct chemokine receptors, including CCR8, and actively home to CCL8 deposits located around the airway epithelium. Within lung tissue, ILC2s were particularly motile in extracellular matrix-enriched regions. We show that collagen-I drives ILC2 to markedly change their morphology by remodeling their actin cytoskeleton to promote environmental exploration critical for regulating eosinophilic inflammation. Our study provides previously unappreciated insights into ILC2 migratory patterns during inflammation and highlights the importance of environmental guidance cues in the lung in controlling ILC2 dynamics.

Group 2 Innate Lymphoid Cells in Respiratory Allergic Inflammation

Millions of people worldwide are suffering from allergic inflammatory airway disorders. These conditions are regarded as a consequence of multiple imbalanced immune events resulting in an inadequate response with the exact underlying mechanisms still being a subject of ongoing research. Several cell populations have been proposed to be involved but it is becoming increasingly evident that group 2 innate lymphoid cells (ILC2s) play a key role in the initiation and orchestration of respiratory allergic inflammation. ILC2s are important mediators of inflammation but also tissue remodeling by secreting large amounts of signature cytokines within a short time period. Thereby, ILC2s instruct innate but also adaptive immune responses. Here, we will discuss the recent literature on allergic inflammation of the respiratory tract with a focus on ILC2 biology. Furthermore, we will highlight different therapeutic strategies to treat pulmonary allergic inflammation and their potential influence on ILC2 function as well as discuss the perspective of using human ILC2s for diagnostic purposes.

Similar immune mechanisms control experimental airway eosinophilia elicited by different allergens and treatment protocols

Background

Mouse models have been extremely valuable in identifying the fundamental mechanisms of airway inflammation that underlie human allergic asthma. Several models are commonly used, employing different methods and routes of sensitisation, and allergens of varying clinical relevance. Although all models elicit similar hallmarks of allergic airway inflammation, including airway eosinophilia, goblet cell hyperplasia and cellular infiltration in lung, it is not established whether they do so by involving the same mechanisms.

Results

We compared the impact of inactivation of various innate or adaptive immune genes, as well as sex, in different models of allergic airway inflammation in mice of C57BL/6 background. Chicken ovalbumin (OVA) and house dust mite (HDM) were used as allergens in settings of single or multiple intranasal (i.n.) challenges, after sensitisation in adjuvant or in adjuvant-free conditions. Eosinophil numbers in the broncho-alveolar lavage and lung histopathology were assessed in each model. We found that Major Histocompatibility Complex Class II (MHCII) deficiency and lack of conventional CD4+ T cells had the most profound effect, essentially ablating airway eosinophilia and goblet cell hyperplasia in all models. In contrast, Thymic stromal lymphopoietin receptor (TSLPR) deficiency greatly reduced eosinophilia but had a variable effect on goblet cells. CD1d deficiency and lack of Natural Killer T (NKT) cells moderately impaired inflammation in OVA models but not HDM, whereas sex affected the response to HDM but not OVA. Lastly, defective Toll-like receptor (TLR)4 expression had only a relatively modest overall impact on inflammation.

Conclusion

All the models studied were comparably dependent on adaptive CD4+ T cell responses and TSLP. In contrast, sex, NKT cells and TLR4 appeared to play subtler and more variable roles that were dependent on the type of allergen and mode of immunization and challenge. These results are consistent with clinical data suggesting a key role of CD4+ T cells and TSLP in patients with allergic asthma.

Electronic supplementary material

The online version of this article (10.1186/s12865-019-0295-y) contains supplementary material, which is available to authorized users.

Synergy of Interleukin (IL)-5 and IL-18 in eosinophil mediated pathogenesis of allergic diseases

Eosinophils are circulating granulocytes that have pleiotropic effects in response to inflammatory signals in the body. In response to allergens or pathogens, exposure eosinophils are recruited in various organs that execute pathological immune responses. IL-5 plays a key role in the differentiation, development, and survival of eosinophils. Eosinophils are involved in a variety of allergic diseases including asthma, dermatitis and various gastrointestinal disorders (EGID). IL-5 signal transduction involves JAK-STAT-p38MAPK-NFκB activation and executes extracellular matrix remodeling, EMT transition and immune responses in allergic diseases. IL-18 is a classical cytokine also involved in immune responses and has a critical role in inflammasome pathway. We recently identified the IL-18 role in the generation, transformation, and maturation of (CD101+CD274+) pathogenic eosinophils. In, addition, several other cytokines like IL-2, IL-4, IL-13, IL-21, and IL-33 also contribute in advancing eosinophils associated immune responses in innate and adaptive immunity. This review discusses with a major focus (1) Eosinophils and its constituents, (2) Role of IL-5 and IL-18 in eosinophils development, transformation, maturation, signal transduction of IL-5 and IL-18, (3) The role of eosinophils in allergic disorders and (4) The role of several other associated cytokines in promoting eosinophils mediated allergic diseases.

CCR10+ ILC2s with ILC1-like properties exhibit a protective function in severe allergic asthma

BACKGROUND

We previously showed that patients with severe allergic asthma have high numbers of circulating ILC2s expressing CCR10.

METHOD

Herein, CCR10⁺ ILC2s were further analyzed in the blood of healthy individuals or patients with allergic and non-allergic asthma. Characteristics of human CCR10⁺ and CCR10^- ILC2s were assessed by flow cytometry as well as single-cell multiplex RT-qPCR. The role of CCR10⁺ ILC2s in asthma pathophysiology was studied in allergen-treated mice.

RESULTS

When compared to healthy controls, CCR10⁺ ILC2s are enriched in the blood of both allergic and non-allergic severe asthmatic patients, and these cells are recruited to the lungs. Plasma concentrations of the CCR10 ligand CCL27 are significantly increased in severe asthmatics when compared to non-asthmatic patients. CCR10⁺ ILC2s secrete little T_H 2 cytokines, but exhibit ILC1-like properties, including a capacity to produce IFN-γ. Also, single-cell analysis reveals that the CCR10⁺ ILC2 subset is enriched in cells expressing amphiregulin. CCR10⁺ ILC2 depletion, as well as blocking of IFN-γ activity, exacerbates airway hyperreactivity in allergen-challenged mice, providing evidence for a protective role of these cells in allergic inflammation.

CONCLUSIONS

Frequencies of circulating CCR10⁺ ILC2s and CCL27 plasma concentrations represent candidate markers of asthma severity. The characterization of CCR10⁺ ILC2s in human samples and in mouse asthma models suggests that these cells downregulate allergic inflammation through IFN-γ production.

Role of innate lymphoid cells in allergic diseases

Background: Over the past decade, there has been increasing interest and research into understanding the type 2 immune responses by the epithelium-derived cytokines interleukin (IL) 33, IL-25, and thymic stromal lymphopoietin. Innate lymphoid cells (ILC) are a unique family of effector immune cells that functionally resemble T cells but lack clonal distributed antigen receptors. Group 2 ILCs, ILC2s, are known for their capability to secrete proallergic cytokines, including IL-5 and IL-13. ILC2s are enriched at mucosal barriers in lung, gut, and skin, and their activation has been associated with a variety of allergic disorders. Objective: To study the role of ILC2 in different allergic disorders, including allergic rhinitis, asthma, atopic dermatitis, and food allergies. Methods: A MEDLINE search was performed for articles that reported on ILC2 in allergic disorders, including allergic rhinitis, asthma, atopic dermatitis, and food allergies. Results: A review of the literature revealed an important role of ILC2 in various allergic disorders. Conclusion: Identification of ILC2s in patients with allergic rhinitis, asthma, and atopic dermatitis indicates that these cells may represent a new therapeutic target. In this review, we discussed the current understanding of ILC2 biology and its function and regulation in various allergic diseases.

Sex Differences in IL-33-Induced STAT6-Dependent Type 2 Airway Inflammation

Sex differences in asthma prevalence are well-documented but poorly understood. Murine models have contributed to our understanding of mechanisms that could regulate this sex disparity, though the majority of these studies have examined responses present after Th2 adaptive immunity is established. We have now investigated how sex influences acute activation of innate cell populations in the lung upon initial exposure to the model antigen, ovalbumin (OVA), in the presence of IL-33 (OVA+IL-33), to prime the lungs for type 2 immunity. We also examined how inflammatory responses induced by OVA+IL-33 were altered in mice lacking the STAT6 transcription factor, which is activated by IL-13, an effector cytokine of IL-33. Our data demonstrate that type 2 inflammation induced by OVA+IL-33 was more severe in female mice compared to males. Females exhibited greater cytokine and chemokine production, eosinophil influx and activation, macrophage polarization to the alternatively activated phenotype, and expansion of group 2 innate lymphoid cells (ILC2s). While increases in ILC2s and eosinophils were largely independent of STAT6 in both males and females, many other responses were STAT6-dependent only in female mice. Our findings indicate that a subset of type 2 inflammatory responses induced by OVA+IL-33 require STAT6 in both males and females and that enhanced type 2 inflammation in females, compared to males, is associated with greater IL-13 protein production. Our findings suggest blunted IL-13 production in males may protect against type 2 inflammation initiated by OVA+IL-33 delivery to the lung.

Critical role of interleukin-23 in development of asthma promoted by cigarette smoke

It has been recently reported that cigarette smoke exposure during allergen sensitization facilitates the development of allergic asthma; however, the underlying mechanisms remain elusive. We evaluated the role of interleukin (IL-23) in a cigarette smoke extract (CSE)-induced Dermatophagoides pteronyssinus (Dp)-allergic asthma mouse model. BALB/c mice were exposed to CSE during allergen sensitization period. Anti-IL-23p19 or IL-23R antibody was administered during the sensitization period. And we evaluated several immunological responses. The expression of IL-23 and IL-23 receptor (IL-23R) was examined in lung tissue. IL-23 and IL-23R expression was increased in the airway epithelium of Dp/CSE co-administered mice. CSE administration during the sensitization promoted Dp-allergic sensitization and the development of asthma phenotypes. Additionally, the proportion of innate lymphoid type 2 cells (ILC2) was also increased by CSE and Dp co-instillation. Anti-IL-23 or IL-23R antibody treatment during allergen sensitization significantly diminished phenotypes of allergic asthma and the ILC2 population. The levels of IL-33 and thymic stromal lymphopoietin (TSLP) were also significantly reduced by anti-IL-23 or IL-23R antibody treatment. IL-23 may thus play a significant role in cigarette smoke-induced allergic sensitization and asthma development. Clinically, the increase in allergen sensitization due to cigarette exposure causes onset of asthma, and IL-23 may be important in this mechanism. KEY MESSAGES: IL-23 and IL-23R expression was increased in the lung epithelium of Dp and CSE co-exposed mice during sensitization period. The population of ILC2s was increased in Dp and CSE co-exposed mice during sensitization period. Anti-IL23 or IL-23R antibody treatment with co-administration of CSE and HDM during sensitization period significantly suppresses ILC2. In vitro, IL-23 blockade in Dp and CSE-stimulated epithelial cells suppressed IL-13 expression in ILC2.

Identification of Group 2 Innate Lymphoid Cells in Mouse Lung, Liver, Small Intestine, Bone Marrow, and Mediastinal and Mesenteric Lymph Nodes

Innate lymphoid cells (ILCs) are a heterogeneous family of lymphocytes that populate barrier and non-barrier tissues. ILCs regulate immune responses to pathogens and commensals but also sustain metabolic homeostasis, tissue remodeling after injury and establish dialogue with the nervous system. ILCs rapidly become activated in the absence of adaptive antigen receptors by responding to signaling molecules provided by hematopoietic or non-hematopoietic cells. Here we provide protocols designed for processing the lung, liver, small intestine, bone marrow, mediastinal and mesenteric lymph nodes in order to obtain a purified leukocyte fraction of cells, in which ILC2 enrichment is optimized. In addition, we describe in detail the methodologies used to activate ILC2s and the assays necessary for the detection of their effector cytokines. We highlight the differences in ILC2 characterization within distinct tissues that we have recently identified. © 2019 by John Wiley & Sons, Inc.

T cells in severe childhood asthma

Severe asthma in children is a debilitating condition that accounts for a disproportionately large health and economic burden of asthma. Reasons for the lack of a response to standard anti-inflammatory therapies remain enigmatic. Work in the last decade has shed new light on the heterogeneous nature of asthma, and the varied immunopathologies of severe disease, which are leading to new treatment approaches for the individual patient. However, most studies to date that explored the immune landscape of the inflamed lower airways have focused on adults. T cells are pivotal to the inception and persistence of inflammatory processes in the diseased lungs, despite a contemporary shift in focus to immune events at the epithelial barrier. This article outlines current knowledge on the types of T cells and related cell types that are implicated in severe asthma. The potential for environmental exposures and other inflammatory cues to condition the immune environment of the lung in early life to favour pathogenic T cells and steroid resistance is discussed. The contributions of T cells and their cytokines to inflammatory processes and treatment resistance are also considered, with an emphasis on new observations in children that argue against conventional type 1 and type 2 T cell paradigms. Finally, the ability for new technologies to revolutionize our understanding of T cells in severe childhood asthma, and to guide future treatment strategies that could mitigate this disease, is highlighted.

Female and male mouse lung group 2 innate lymphoid cells differ in gene expression profiles and cytokine production

Epidemiological studies have shown sex differences in prevalence of non-allergic asthma. Recent reports demonstrated negative effects of androgen signaling on group 2 innate lymphoid cells (ILC2s), explaining a potential mechanism behind sex bias in asthma prevalence. To further understand sex-related differences in ILC2 functions and ILC2 intrinsic or lung environmental mechanisms behind it, we have investigated the effects of sex and age on lung ILC2 function, the amounts of ILC2-activating cytokines in the lung and gene expression profiles of male and female ILC2s. Flow cytometric analyses of naive male and female mouse lung ILC2s showed no difference in their numbers. However, upon three daily intranasal IL-33 injections, lung ILC2s in postpubertal female mice expanded to a greater degree than male counterpart. In line with in vivo results, purified female mouse lung ILC2s produced more cytokines than male ILC2s upon in vitro stimulation. Gene expression profiles of purified naïve male and female ILC2s differed in 4% of the genes, and gene set enrichment analysis showed that female ILC2s are enriched for gene signatures of memory T cells. We did not observe similar degree of differences between female and male ILC2s after IL-33 stimulation. ILC2-activating cytokines including IL-33, IL-7 and TSLP were more highly expressed in whole lung homogenate samples prepared from naïve post pubertal female mouse lung than male mouse lung. Moreover, the differences in responsiveness of male and female ILC2s to IL-33 were not affected in IL-33-deficient mice. These results suggest that female ILC2s are more readily activated than male ILC2s due to their gene expression at the naïve state, which is potentially influenced by the lung environment.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Elevated levels of interleukin-33 are associated with allergic and eosinophilic asthma

IL-33 is a recently discovered cytokine which plays an important role in asthma pathogenesis.

AIM

To evaluate serum IL-33 in patients with asthma and healthy controls, and to evaluate the association of IL-33 with different asthma phenotypes.

METHODS

Patients with asthma (n = 115) and healthy subjects (n = 85) were included in the study. Subjects with asthma were divided into groups according to their phenotype: allergic/non-allergic, eosinophilic/non-eosinophilic, obese/non-obese and severity according to GINA (mild, moderate and severe). The concentration of IL-33 in serum was measured by standardized enzyme-linked immunosorbent assay.

RESULTS

The level of IL-33 was significantly higher in patients with asthma when compared to healthy subjects (672.73 ± 104.47 pg/mL vs 268.52 ± 27.56 pg/mL, P < 0.05). IL-33 was also higher in the allergic asthma group patients when compared to non-allergic asthmatics (844.61 ± 152.08 pg/mL vs 369.56 ± 77.94 pg/mL, P < 0.05). There was a significantly higher serum IL-33 level in the eosinophilic asthma group when compared to the group of non-eosinophilic asthma patients (1001.10 ± 199.11 pg/mL vs 337.49 ± 72.68 pg/mL, P < 0.01). We did not find a significant difference in serum IL-33 level between different asthma severity groups, obese and non-obese asthmatics.

CONCLUSION

IL-33 is increased in asthma patients, particularly in some phenotypes: allergic asthma and eosinophilic asthma.

Mouse Models of Asthma

Mouse models are critical for delineating the mechanisms that underlie asthma pathogenesis and developing new treatments. In this chapter we describe four different asthma models that offer unique benefits and allow investigators to answer distinct research questions. We also describe key surgical procedures that are necessary for assessing experimental asthma.

BLT1 signaling in epithelial cells mediates allergic sensitization via promotion of IL-33 production

BACKGROUND

Epithelial cells (ECs) play a crucial role in allergic sensitization to inhaled protease allergens by instructing type 2 innate lymphoid cells (ILC2) and dendritic cells (DCs) via release of pro-type 2 cytokines, particularly interleukin-33 (IL-33). Leukotriene B4 (LTB4) is a well-known leukocyte chemoattractant via engagement of its receptor 1 (BLT1). However, the role of LTB4-BLT1 axis in allergic sensitization via activation of ECs is still unknown.

METHODS

We evaluated the effect of LTB4-BLT1 axis on IL-33 expression and ILC2 activation in vivo and in vitro. Chimeric mice were established to evaluate the contribution of BLT1 expression in nonimmune cell to allergic sensitization.

RESULTS

Genetical or pharmacological interruption of LTB4-BLT1 axis during sensitization phase markedly reduced papain-induced IL-33 expression, decreased ILC2 activation and DC migration, thereby impairing the priming of allergic Th2 responses. Furthermore, papain inhalation induced a rapid release of LTB4 preceding IL-33, and intranasal administration of LTB4 to naïve WT mice significantly increased IL-33 expression and ILC2 activation in lung, which was absent in Il33^-/- or Ltb4r1^-/- mice. Furthermore, BLT1 was expressed in primary mouse ECs or normal human bronchial ECs (NHBE), and papain induced LTB4 release by NHBE, which in turn amplified IL-33 production dependent on Akt activation via BLT1. Consequently, bone marrow chimeric mice lacking BLT1 in radio-resistant structural cells failed to develop allergic lung inflammation to papain.

CONCLUSION

Our study reveals a functional role of LTB4-BLT1 axis in nonimmune cells, most likely lung ECs, in controlling allergic sensitization as an upstream regulator of IL-33.

Group 2 Innate Lymphoid Cells in Human Respiratory Disorders

Recent studies using animal models have generated profound insight into the functions of various subsets of innate lymphoid cells (ILCs). The group 2 ILC subset (ILC2) has been implicated in tissue homeostasis, defense responses against parasites, tissue repair, and immunopathology associated with type-2 immunity. In addition, progress has also been made in translating these findings from animal studies into a context of human immunity. Importantly, recent observations strongly support a role for ILC2s in several diseases of the human respiratory system. However, many aspects of human ILC2 biology are still unclear, including how these cells develop and which signals control their activity. As a result, the exact role played by ILCs in human health and disease remains poorly understood. Here, we summarize our current understanding of human ILC2 biology and focus on their potential involvement in various human respiratory disorders.

ncRNAs in Inflammatory and Infectious Diseases

Inflammatory and infectious diseases are among the main causes of morbidity and mortality worldwide. Inflammation is central to maintenance of organismal homeostasis upon infection, tissue damage, and malignancy. It occurs transiently in response to diverse stimuli (e.g., physical, radioactive, infective, pro-allergenic, or toxic), and in some cases may manifest itself in chronic diseases. To limit the potentially deleterious effects of acute or chronic inflammatory responses, complex transcriptional and posttranscriptional regulatory networks have evolved, often involving nonprotein-coding RNAs (ncRNA). MicroRNAs (miRNAs) are a class of posttranscriptional regulators that control mRNA translation and stability. Long ncRNAs (lncRNAs) are a very diverse group of transcripts >200 nt, functioning among others as scaffolds or decoys both in the nucleus and the cytoplasm. By now, it is well established that miRNAs and lncRNAs are implicated in all major cellular processes including control of cell death, proliferation, or metabolism. Extensive research over the last years furthermore revealed a fundamental role of ncRNAs in pathogen recognition and inflammatory responses. This chapter reviews and summarizes the current knowledge on regulatory ncRNA networks in infection and inflammation.

Which Factors Associated With Activated Eosinophils Contribute to the Pathogenesis of Aspirin-Exacerbated Respiratory Disease?

Eosinophils have long been recognized as a central effector cell in the lungs of asthmatic patients. They contribute to airway inflammation and remodeling through releasing several molecules such as cytokines, granule proteins, lipid mediators and extracellular traps/vesicles. Repeated evidence reveals that intense eosinophil infiltration in upper and lower airway mucosae contributes to the pathogenesis of aspirin-exacerbated respiratory disease (AERD). Persistent eosinophilia is found to be associated with type 2 immune responses, cysteinyl leukotriene overproduction and eosinophil-epithelium interactions. This review highlights recent findings about key mechanisms of eosinophil activation in the airway inflammation of AERD. In addition, current biologics (targeting type 2 immune responses) were suggested to control eosinophilic inflammation for AERD patients.

Airway innate lymphoid cells in the induction and regulation of allergy

The recent discovery of innate lymphoid cells has revolutionized our understanding of the pathogenesis of immune diseases including allergy and asthma. Innate lymphoid cells (ILCs) are a heterogeneous collection of lymphocytes that lack antigen-specificity (non-T, non-B cells) and potently produce characteristic cytokines of T cell subsets (Th1, Th2, Th17). ILCs are divided into group 1 (ILC1s), group 2 (ILC2s), or group 3 (ILC3s). Similar to Th2 cells, ILC2s produce IL-4, IL-5, and IL-13, among others, and are present in increased numbers in samples from patients with many allergic disorders including asthma and chronic rhinosinusitis (CRS). Animal models have identified that ILC2s contribute to eosinophilic tissue infiltration, airway hyperresponsiveness, mucus production, as well as coordinate adaptive immune responses. Finally, recent studies support regulation of ILC2s by neuro-immune mechanisms as well as demonstrate a significant degree of plasticity between ILC subsets that may impact the immune responses in asthma and allergic airway diseases. Here, we review the current literature on ILC2s in human asthma and allergic airway diseases, as well as highlight some recent mechanistic insights into ILC2 function from in vitro studies and in vivo animal models.

Innate Immune Cell Suppression and the Link With Secondary Lung Bacterial Pneumonia

Secondary infections arise as a consequence of previous or concurrent conditions and occur in the community or in the hospital setting. The events allowing secondary infections to gain a foothold have been studied for many years and include poor nutrition, anxiety, mental health issues, underlying chronic diseases, resolution of acute inflammation, primary immune deficiencies, and immune suppression by infection or medication. Children, the elderly and the ill are particularly susceptible. This review is concerned with secondary bacterial infections of the lung that occur following viral infection. Using influenza virus infection as an example, with comparisons to rhinovirus and respiratory syncytial virus infection, we will update and review defective bacterial innate immunity and also highlight areas for potential new investigation. It is currently estimated that one in 16 National Health Service (NHS) hospital patients develop an infection, the most common being pneumonia, lower respiratory tract infections, urinary tract infections and infection of surgical sites. The continued drive to understand the mechanisms of why secondary infections arise is therefore of key importance.

Social Networking of Group Two Innate Lymphoid Cells in Allergy and Asthma

Allergic diseases including asthma, chronic rhinosinusitis, and atopic dermatitis are common conditions worldwide. While type 2 immune responses induced by T-cells significantly cause allergic inflammation, the recently identified group two innate lymphoid cells (ILC2s) are emerging as critical players in the development of allergy. Upon allergen exposure, ILC2s are rapidly activated by cytokines released by epithelial cells. Activated ILC2s release various effector cytokines altogether contributing to the pathogenesis of allergy and can even cause inflammation in the absence of T-cells, as observed in asthma. Although the factors inducing ILC2 activation have been identified, evidence suggests that multiple factors can enhance or repress ILC2 proliferation, trafficking, or secretion of effector cytokines upon allergic inflammation. In this review, we discuss the recent findings that influence ILC2 activation and the resulting effects on the pathogenesis of allergy. A better understanding of how ILC2s are modulated will open the door to the development of new therapeutic strategies against allergic diseases.

IL-33 Released in the Liver Inhibits Tumor Growth via Promotion of CD4+ and CD8+ T Cell Responses in Hepatocellular Carcinoma

IL-33 released by epithelial cells and immune cells functions as an alarmin and can induce both type 1 and type 2 immune responses. However, the role of IL-33 release in tumor development is still not clear. In this study, we examined the function of released IL-33 in murine hepatocellular carcinoma (HCC) models by hydrodynamically injecting either IL-33-expressing tumor cells or IL-33-expressing plasmids into the liver of tumor-bearing mice. Tumor growth was greatly inhibited by IL-33 release. This antitumor effect of IL-33 was dependent on suppression of tumorigenicity 2 (ST2) because it was diminished in ST2^-/- mice. Moreover, HCC patients with high IL-33 expression have prolonged overall survival compared with the patients with low IL-33 expression. Further study showed that there were increased percentages and numbers of activated and effector CD4⁺ and CD8⁺ T cells in both spleen and liver in IL-33-expressing tumor-bearing mice. Moreover, IFN-γ production of the CD4⁺ and CD8⁺ T cells was upregulated in both spleen and liver by IL-33. The cytotoxicity of CTLs from IL-33-expressing mice was also enhanced. In vitro rIL-33 treatment could preferentially expand CD8⁺ T cells and promote CD4⁺ and CD8⁺ T cell activation and IFN-γ production. Depletion of CD4⁺ and CD8⁺ T cells diminished the antitumor activity of IL-33, suggesting that the antitumor function of released IL-33 was mediated by both CD4⁺ and CD8⁺ T cells. Taken together, we demonstrated in murine HCC models that IL-33 release could inhibit tumor development through its interaction with ST2 to promote antitumor CD4⁺ and CD8⁺ T cell responses.

The Pleiotropic Immunomodulatory Functions of IL-33 and Its Implications in Tumor Immunity

Interleukin-33 (IL-33) is a IL-1 family member of cytokines exerting pleiotropic activities. In the steady-state, IL-33 is expressed in the nucleus of epithelial, endothelial, and fibroblast-like cells acting as a nuclear protein. In response to tissue damage, infections or necrosis IL-33 is released in the extracellular space, where it functions as an alarmin for the immune system. Its specific receptor ST2 is expressed by a variety of immune cell types, resulting in the stimulation of a wide range of immune reactions. Recent evidences suggest that different IL-33 isoforms exist, in virtue of proteolytic cleavage or alternative mRNA splicing, with potentially different biological activity and functions. Although initially studied in the context of allergy, infection, and inflammation, over the past decade IL-33 has gained much attention in cancer immunology. Increasing evidences indicate that IL-33 may have opposing functions, promoting, or dampening tumor immunity, depending on the tumor type, site of expression, and local concentration. In this review we will cover the biological functions of IL-33 on various immune cell subsets (e.g., T cells, NK, Treg cells, ILC2, eosinophils, neutrophils, basophils, mast cells, DCs, and macrophages) that affect anti-tumor immune responses in experimental and clinical cancers. We will also discuss the possible implications of diverse IL-33 mutations and isoforms in the anti-tumor activity of the cytokine and as possible clinical biomarkers.

C3a is required for ILC2 function in allergic airway inflammation

Aberrant type 2 responses underlie the pathologies in allergic diseases like asthma, yet, our understanding of the mechanisms that drive them remains limited. Recent evidence suggests that dysregulated innate immune factors can perpetuate asthma pathogenesis. In susceptible individuals, allergen exposure triggers the activation of complement, a major arm of innate immunity, leading to the aberrant generation of the C3a anaphylatoxin. C3 and C3a have been shown to be important for the development of Th2 responses, yet remarkably, the mechanisms by which C3a regulates type 2 immunity are relatively unknown. We demonstrate a central role for C3a in driving type 2 innate lymphoid cells (ILC2)-mediated inflammation in response to allergen and IL-33. Our data suggests that ILC2 recruitment is C3a-dependent. Further, we show that ILC2s directly respond to C3a, promoting type 2 responses by specifically: (1) inducing IL-13 and granulocyte-macrophage colony-stimulating factor, whereas inhibiting IL-10 production from ILC2; and (2) enhancing their antigen-presenting capability during ILC-T-cell cross-talk. In summary, we identify a novel mechanism by which C3a can mediate aberrant type 2 responses to aeroallergen exposure, which involves a yet unrecognized cross-talk between two major innate immune components-complement and group 2 innate lymphoid cells.

Impact of eosinophil-peroxidase (EPX) deficiency on eosinophil structure and function in mouse airways

Eosinophil peroxidase (EPX) is a major constituent of the large cytoplasmic granules of both human and mouse eosinophilic leukocytes. Human EPX deficiency is a rare, autosomal-recessive disorder limited to the eosinophil lineage. Our intent was to explore the impact of EPX gene deletion on eosinophil content, structure, and function. In response to repetitive intranasal challenge with a filtrate of the allergen, Alternaria alternata, we found significantly fewer eosinophils peripherally and in the respiratory tracts of EPX^-/- mice compared to wild-type controls; furthermore, both the major population (Gr1^-/lo ) and the smaller population of Gr1^hi eosinophils from EPX^-/- mice displayed lower median fluorescence intensities (MFIs) for Siglec F. Quantitative evaluation of transmission electron micrographs of lung eosinophils confirmed the relative reduction in granule outer matrix volume in cells from the EPX^-/- mice, a finding analogous to that observed in human EPX deficiency. Despite the reduced size of the granule matrix, the cytokine content of eosinophils isolated from allergen-challenged EPX^{-/ -} and wild-type mice were largely comparable to one another, although the EPX^-/- eosinophils contained reduced concentrations of IL-3. Other distinguishing features of lung eosinophils from allergen-challenged EPX^-/- mice included a reduced fraction of surface TLR4⁺ cells and reduced MFI for NOD1. Interestingly, the EPX gene deletion had no impact on eosinophil-mediated clearance of gram-negative Haemophilus influenzae from the airways. As such, although no clinical findings have been associated with human EPX deficiency, our findings suggest that further evaluation for alterations in eosinophil structure and function may be warranted.

Asthma alleviates obesity in males through regulating metabolism and energy expenditure

Many epidemiological studies suggested a correlation between obesity and asthma. However, little is known about the molecular details explaining this correlation. Here, we show that asthma decreased body weight of asthmatic male mice fed with high fat diet via increasing energy expenditure and insulin sensitivity. The increase of energy expenditure was mainly due to upregulation of pAMPK and Sirt1. The activation of AMPK/Sirt1/PGC1α signaling promoted the expression of the thermogenic genes like ucp1, PRDM16, cidea, Elovl3, PPARα, which occurred in brown adipocyte tissue and subcutaneous white adipose tissue. Besides, by activating IL33/ILC2/AAMac pathway in subcutaneous white adipose tissue, asthma promoted subcutaneous white adipose tissue into beige fat. In addition, insulin sensitivity was improved in the asthmatic male mice by decreasing the expression of G6Pase in the liver, which was recapitulated in HepG2. In human, we found that Body Mass Index (BMI) and waist circumference were significantly lower in males suffering asthma compared with the control in the National Health and Nutrition Examination Survey (NHANES) cohort. These data together suggest asthma in males decreases obesity by improving the metabolism function of brown and subcutaneous adipose tissue, and decreasing insulin resistant in the liver.

Interleukin-33 and ST2 Signaling in Tumor Microenvironment

Interleukin-33 (IL-33) is one of the members of the IL-1 family of cytokines and a ligand of ST2 and IL-1 receptor accessory protein (IL-1RAcP) that is known to affect Th2 inflammatory response with partial effects on Th1 responses. This cytokine is released by epithelial and smooth muscle cells of the airway system during their injury by several environmental stimuli, such as allergens, viruses, helminths, and pollutants. IL-33 is an alarmin that acts as an endogenous danger signal, and it has been known to affect various types of cells, such as mast cells, basophils, eosinophils, T cells, and specific subsets of innate lymphoid cells (ILCs). In recent findings, this cytokine is believed to have a critical role in several types of cancers, such as lung cancer, liver cancer, and head and neck squamous cell cancer. The expression of IL-33/ST2 in cancer tissues shows a close association with tumor growth and tumor progression in several types of cancer, suggesting the IL-33/ST2 pathway as a potential target for therapy.

The Risk G Allele of the Single-Nucleotide Polymorphism rs928413 Creates a CREB1-Binding Site That Activates IL33 Promoter in Lung Epithelial Cells

Cytokine interleukin 33 (IL-33) is constitutively expressed by epithelial barrier cells, and promotes the development of humoral immune responses. Along with other proinflammatory mediators released by the epithelium of airways and lungs, it plays an important role in a number of respiratory pathologies. In particular, IL-33 significantly contributes to pathogenesis of allergy and asthma; genetic variations in the IL33 locus are associated with increased susceptibility to asthma. Large-scale genome-wide association studies have identified minor “G” allele of the single-nucleotide polymorphism rs928413, located in the IL33 promoter area, as a susceptible variant for early childhood and atopic asthma development. Here, we demonstrate that the rs928413(G) allele creates a binding site for the cAMP response element-binding protein 1 (CREB1) transcription factor. In a pulmonary epithelial cell line, activation of CREB1, presumably via the p38 mitogen-activated protein kinases (MAPK) cascade, activates the IL33 promoter containing the rs928413(G) allele specifically and in a CREB1-dependent manner. This mechanism may explain the negative effect of the rs928413 minor “G” allele on asthma development.

IL-33 signalling contributes to pollutant-induced allergic airway inflammation

BACKGROUND

Clinical and experimental studies have identified a crucial role for IL-33 and its receptor ST2 in allergic asthma. Inhalation of traffic-related pollutants, such as diesel exhaust particles (DEP), facilitates the development of asthma and can cause exacerbations of asthma. However, it is unknown whether IL-33/ST2 signalling contributes to the enhancing effects of air pollutants on allergic airway responses.

OBJECTIVE

We aim to investigate the functional role of IL-33/ST2 signalling in DEP-enhanced allergic airway responses, using an established murine model.

METHODS

C57BL/6J mice were exposed to saline, DEP alone, house dust mite (HDM) alone or combined DEP+HDM. To inhibit IL-33 signalling, recombinant soluble ST2 (r-sST2) was given prophylactically (ie, during the whole experimental protocol) or therapeutically (ie, at the end of the experimental protocol). Airway hyperresponsiveness and the airway inflammatory responses were assessed in bronchoalveolar lavage fluid (BALF) and lung.

RESULTS

Combined exposure to DEP+HDM increased IL-33 and ST2 expression in lung, elevated inflammatory responses and bronchial hyperresponsiveness compared to saline, sole DEP or sole HDM exposure. Prophylactic interference with the IL-33/ST2 signalling pathway impaired the DEP-enhanced allergic airway inflammation in the BALF, whereas effects on lung inflammation and airway hyperresponsiveness were minimal. Treatment with r-sST2 at the end of the experimental protocol did not modulate the DEP-enhanced allergic airway responses.

CONCLUSION

Our data suggest that the IL-33/ST2 pathway contributes to the onset of DEP-enhanced allergic airway inflammation.

Serum sST2 levels predict severe exacerbation of asthma

BACKGROUND

Neutrophilic inflammation is associated with poorly controlled asthma. Serum levels of sST2, a soluble IL-33 receptor, increase in neutrophilic lung diseases. We hypothesized that high serum sST2 levels in stable asthmatics are a predictor for exacerbation within a short duration.

METHODS

This prospective observational study evaluated the serum sST2 levels of 104 asthmatic patients who were treated by a lung disease specialist with follow-ups for 3 months.

RESULTS

High serum sST2 levels (> 18 ng/ml) predicted severe asthma exacerbation within 3 months. Serum sST2 levels correlated positively with asthma severity (treatment step), airway H2O2 levels, and serum IL-8 levels. High serum sST2 levels and blood neutrophilia (> 6000 /μl) were independent predictors of exacerbation. We defined a post-hoc exacerbation-risk score combining high serum sST2 level and blood neutrophilia, which stratified patients into four groups. The score predicted exacerbation-risk with an area under curve of 0.91 in the receiver operating characteristic curve analysis. Patients with the highest scores had the most severe phenotype, with 85.7% showing exacerbation, airflow limitation, and corticosteroid-insensitivity.

CONCLUSIONS

High serum sST2 levels predicted exacerbation within the general asthmatic population and, when combined with blood neutrophil levels, provided an exacerbation-risk score that was an accurate predictor of exacerbation occurring within 3 months.

Long-Term Clinical Outcomes of High-Dose Mepolizumab Treatment for Hypereosinophilic Syndrome

BACKGROUND

Conventional therapies for hypereosinophilic syndromes (HES) have variable efficacy and carry significant long-term toxicities. Anti-IL-5 (mepolizumab) therapy has a glucocorticoid (GC)-sparing effect in GC-sensitive HES, but the efficacy of mepolizumab in treatment-refractory HES patients with severe disease has not been examined to date.

OBJECTIVE

To identify predictors of response to mepolizumab in subjects with severe treatment-refractory HES and compare long-term outcomes in these subjects with HES subjects treated with conventional therapies.

METHODS

Retrospective analysis of clinical and laboratory data from 35 HES subjects treated with mepolizumab and 55 HES subjects on conventional therapy, all followed at a single center, was performed.

RESULTS

Peak eosinophilia, GC sensitivity, pulmonary involvement, HES clinical subtype, and pretreatment serum IL-5 were correlated with mepolizumab response. Despite evidence of more severe disease at baseline, mepolizumab-treated subjects had comparable long-term clinical outcomes to HES subjects treated with conventional therapies and reported improvements in therapy-related comorbidities. Subjects managed with mepolizumab monotherapy had fewer disease flares than HES subjects on conventional therapies or mepolizumab-treated HES subjects requiring additional HES therapies.

CONCLUSIONS

This study confirms that mepolizumab is an effective and well-tolerated therapy for HES, but suggests that response is more likely in GC-responsive subjects with idiopathic or overlap forms of HES. A primary benefit of treatment is the reduction of comorbidity due to discontinuation or the reduction of conventional HES therapies. Although subjects who completely discontinued GC had the most benefit, high-dose mepolizumab was a safe and effective salvage therapy for severe, treatment-refractory HES.

ILC2 frequency and activity are inhibited by glucocorticoid treatment via STAT pathway in patients with asthma

Background

Group 2 innate lymphoid cells (ILC2s) were closely associated with asthma. However, there were no perspective studies about the effects of glucocorticoid on ILC2s in asthma patients. Our objective was to perform a perspective study and evaluate the ILC2 activity after glucocorticoid therapy in asthma patients.

Methods

The asthma and asthma with allergic rhinitis patients were treated with glucocorticoid for 3 months. The circulating ILC2 levels were evaluated. The effects of glucocorticoid on ILC2s and possible signalling pathways were investigated in vitro.

Results

The patients were well‐controlled, and the high ILC2 levels were significantly decreased at 1 and 3 months after treatment. Peripheral blood monocytes from allergic patients produced dramatic IL‐5, IL‐13 and IL‐9 in response to IL‐25, IL‐33 plus IL‐2, and glucocorticoid significantly decreased their levels. Moreover, ILC2s were identified to be the predominant source of IL‐5, IL‐13 and IL‐9, and glucocorticoid treatment was able to reverse their high levels. STAT3, STAT5, STAT6, JAK3 and MEK signalling pathways were proved to be involved in regulating ILC2 activity under the glucocorticoid treatment.

Conclusion

The data suggested that glucocorticoid administration could be effective in treating asthma by regulating ILC2s via MEK/JAK‐STAT signalling pathways. This provides a new understanding of glucocorticoid application in regard to allergic diseases.

Monocyte chemotactic protein-induced protein 1 controls allergic airway inflammation by suppressing IL-5-producing TH2 cells through the Notch/Gata3 pathway

BACKGROUND

Asthmatic and allergic inflammation is mediated by TH2 cytokines (IL-4, IL-5, and IL-13). Although we have learned much about how TH2 cells are differentiated, the TH2 checkpoint mechanisms remain elusive.

OBJECTIVES

In this study we investigate how monocyte chemotactic protein-induced protein 1 (MCPIP1; encoded by the Zc3h12a gene) regulates IL-5-producing TH2 cell differentiation and TH2-mediated inflammation.

METHODS

The functions of Zc3h12a-/- CD4 T cells were evaluated by checking the expression of TH2 cytokines and transcription factors in vivo and in vitro. Allergic airway inflammation of Zc3h12a-/- mice was examined with murine asthma models. In addition, antigen-specific CD4 T cells deficient in MCPIP1 were transferred to wild-type recipient mice, challenged with ovalbumin (OVA) or house dust mite (HDM), and accessed for TH2 inflammation.

RESULTS

Zc3h12a-/- mice have spontaneous severe lung inflammation, with an increase in mainly IL-5- and IL-13-producing but not IL-4-producing TH2 cells in the lung. Mechanistically, differentiation of IL-5-producing Zc3h12a-/- TH2 cells is mediated through Notch signaling and Gata3 independent of IL-4. Gata3 mRNA is stabilized in Zc3h12a-/- TH2 cells. MCPIP1 promotes Gata3 mRNA decay through the RNase domain. Furthermore, deletion of MCPIP1 in OVA- or HDM-specific T cells leads to significantly increased TH2-mediated airway inflammation in OVA or HDM murine models of asthma.

CONCLUSIONS

Our study reveals that MCPIP1 regulates the development and function of IL-5-producing TH2 cells through the Notch/Gata3 pathway. MCPIP1 represents a new and promising target for the treatment of asthma and other TH2-mediated diseases.

Innate and adaptive immune responses to fungi in the airway

Fungi are ubiquitous outdoors and indoors. Exposure, sensitization, or both to fungi are strongly associated with development of asthma and allergic airway diseases. Furthermore, global climate change will likely increase the prevalence of fungi and enhance their antigenicity. Major progress has been made during the past several years regarding our understanding of antifungal immunity. Fungi contain cell-wall molecules, such as β-glucan and chitin, and secrete biologically active proteases and glycosidases. Airway epithelial cells and innate immune cells, such as dendritic cells, are equipped with cell-surface molecules that react to these fungal products, resulting in production of cytokines and proinflammatory mediators. As a result, the adaptive arm of antifungal immunity, including TH1-, TH2-, and TH17-type CD4+ T cells, is established, reinforcing protection against fungal infection and causing detrimental immunopathology in certain subjects. We are only in the beginning stages of understanding the complex biology of fungi and detailed mechanisms of how they activate the immune response that can protect against or drive diseases in human subjects. Here we describe our current understanding with an emphasis on airway allergic immune responses. The gaps in our knowledge and desirable future directions are also discussed.

Innate lymphoid cells in organ fibrosis

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

Respiratory syncytial virus prevents the subsequent development of ovalbumin-induced allergic responses by inhibiting ILC2 via the IL-33/ST2 pathway

AIM

How respiratory syncytial virus (RSV) influences the development of ovalbumin (OVA)-induced asthma remains elusive. As potent T helper (Th)2 cytokine producers, group 2 innate lymphoid cells (ILC2s) are known to serve important functions in the pathogenesis of allergic inflammation. However, how RSV infection affects innate immunity, especially with regard to the function of ILC2s in OVA-induced allergic airway inflammation, is largely unknown.

MATERIALS & METHODS

RSV was used to infect adult BALB/c mice intranasally prior to sensitization and subsequent challenge with OVA. ILC2 frequencies and Th2 cytokine production by ILC2s were assessed by flow cytometry. Cytokine levels were detected both by real-time PCR and ELISA.

RESULTS

Previous infection with RSV attenuated airway inflammation and decreased Th2 cytokine production in mice sensitized and challenged with OVA. Furthermore, previous infection with RSV inhibited the influx of ILC2s into the lung, and constrained their Th2 cytokine production. Adoptive transfer of ILC2s increased asthma-associated airway inflammation in mice previously infected with RSV. These results indicate that previous infection with RSV prevents OVA-induced asthma development via inhibition of ILC2s. Previous infection with RSV attenuated IL-33 production in lung tissue and reduced relative ST2L expression in lung ILC2s, meaning that previous infection with RSV may alter ILC2 function via the IL-33/ST2 signaling pathway.

CONCLUSION

These results demonstrate that previous infection with RSV attenuates OVA-induced airway inflammation by inhibiting the recruitment and Th2 cytokine production of ILC2s via the IL-33/ST2 pathway.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

Chinese Society of Allergy Guidelines for Diagnosis and Treatment of Allergic Rhinitis

Allergic rhinitis (AR) is a global health problem that causes major illnesses and disabilities worldwide. Epidemiologic studies have demonstrated that the prevalence of AR has increased progressively over the last few decades in more developed countries and currently affects up to 40% of the population worldwide. Likewise, a rising trend of AR has also been observed over the last 2-3 decades in developing countries including China, with the prevalence of AR varying widely in these countries. A survey of self-reported AR over a 6-year period in the general Chinese adult population reported that the standardized prevalence of adult AR increased from 11.1% in 2005 to 17.6% in 2011. An increasing number of Journal Articles and imporclinical trials on the epidemiology, pathophysiologic mechanisms, diagnosis, management and comorbidities of AR in Chinese subjects have been published in international peer-reviewed journals over the past 2 decades, and substantially added to our understanding of this disease as a global problem. Although guidelines for the diagnosis and treatment of AR in Chinese subjects have also been published, they have not been translated into English and therefore not generally accessible for reference to non-Chinese speaking international medical communities. Moreover, methods for the diagnosis and treatment of AR in China have not been standardized entirely and some patients are still treated according to regional preferences. Thus, the present guidelines have been developed by the Chinese Society of Allergy to be accessible to both national and international medical communities involved in the management of AR patients. These guidelines have been prepared in line with existing international guidelines to provide evidence-based recommendations for the diagnosis and management of AR in China.

Modeling asthma: Pitfalls, promises, and the road ahead

Asthma is a chronic, heterogeneous, and recurring inflammatory disease of the lower airways, with exacerbations that feature airway inflammation and bronchial hyperresponsiveness. Asthma has been modeled extensively via disease induction in both wild-type and genetically manipulated laboratory mice (Mus musculus). Antigen sensitization and challenge strategies have reproduced numerous important features of airway inflammation characteristic of human asthma, notably the critical roles of type 2 T helper cell cytokines. Recent models of disease induction have advanced to include physiologic aeroallergens with prolonged respiratory challenge without systemic sensitization; others incorporate tobacco, respiratory viruses, or bacteria as exacerbants. Nonetheless, differences in lung size, structure, and physiologic responses limit the degree to which airway dynamics measured in mice can be compared to human subjects. Other rodent allergic airways models, including those featuring the guinea pig (Cavia porcellus) might be considered for lung function studies. Finally, domestic cats (Feline catus) and horses (Equus caballus) develop spontaneous obstructive airway disorders with clinical and pathologic features that parallel human asthma. Information on pathogenesis and treatment of these disorders is an important resource.

Small Molecule Mimetics of α-Helical Domain of IRAK2 Attenuate the Proinflammatory Effects of IL-33 in Asthma-like Mouse Models

IL-33 and its receptor ST2 play important roles in airway inflammation and contribute to asthma onset and exacerbation. The IL-33/ST2 signaling pathway recruits adapter protein myeloid differentiation primary response 88 (MyD88) to transduce intracellular signaling. MyD88 forms a complex with IL-R-associated kinases (IRAKs), IRAK4 and IRAK2, called the Myddosome (MyD88-IRAK4-IRAK2). The myddosome subsequently activates downstream NF-κB and MAPKs p38 and JNK. We established an asthma-like mouse model by intratracheal administration of IL-33. The IL-33 model has a very similar phenotype compared with the OVA-induced mouse asthma model. The importance of MyD88 in the IL-33/ST2 signaling transduction was demonstrated by the MyD88 knockout mice, which were protected from the IL-33-induced asthma. We synthesized small molecule mimetics of the α-helical domain of IRAK2 with drug-like characteristics based on the recent advances in the designing of α-helix compounds. The mimetics can competitively interfere in the protein-protein interaction between IRAK2 and IRAK4, leading to disruption of Myddosome formation. A series of small molecules were screened using an NF-κB promoter assay in vitro. The lead compound, 7004, was further studied in the IL-33-induced and OVA-induced asthma mouse models in vivo. Compound 7004 can inhibit the IL-33-induced NF-κB activity, disrupt Myddosome formation, and attenuate the proinflammatory effects in asthma-like models. Our data indicate that the Myddosome may represent a novel intracellular therapeutic target for diseases in which IL-33/ST2 plays important roles, such as asthma and other inflammatory diseases.

T cells and ILC2s are major effector cells in influenza-induced exacerbation of allergic airway inflammation in mice

Influenza virus infection is an important cause of severe asthma exacerbations, but it remains unclear how a Th1‐mediated antiviral response triggers a prototypical Th2 disease. We investigated CD4⁺ T cells and group 2 innate lymphoid cells (ILC2s) in influenza virus‐infected mice. We found that ILC2s accumulated in the lung rapidly after influenza virus infection, but the induction of IL‐5 and IL‐13 secretion was delayed and concomitant with T cell activation. In an influenza‐induced exacerbation of allergic airway inflammation model we noticed an initial reduction of ILC2 numbers and cytokine production in broncho‐alveolar lavage compared to chronic house dust mite (HDM)‐mediated airway inflammation alone. ILC2s phenotype was characterized by low T1/ST2, ICOS, KLRG1, and CD25 expression, resembling naïve ILC2s. The contribution of ILC2s to type 2 cytokine production in the early stage of the influenza‐induced exacerbation was limited. In contrast, T cells showed increased IL‐4 and IL‐5 production when exposed to both HDM and influenza virus. Upon virus clearance, ILC2s regained an activated T1/ST2^highICOS^highKLRG1^highCD25^high phenotype paired with cytokine production and were major contributors to the type 2 cytokine milieu. Collectively, our data indicate that both T cells and ILC2s contribute to influenza‐induced exacerbation of allergic airway inflammation, but with different kinetics.

Pulmonary neuroendocrine cells amplify allergic asthma responses

Pulmonary neuroendocrine cells (PNECs) are rare airway epithelial cells whose function is poorly understood. Here we show that Ascl1-mutant mice that have no PNECs exhibit severely blunted mucosal type 2 response in models of allergic asthma. PNECs reside in close proximity to group 2 innate lymphoid cells (ILC2s) near airway branch points. PNECs act through calcitonin gene-related peptide (CGRP) to stimulate ILC2s and elicit downstream immune responses. In addition, PNECs act through the neurotransmitter γ-aminobutyric acid (GABA) to induce goblet cell hyperplasia. The instillation of a mixture of CGRP and GABA in Ascl1-mutant airways restores both immune and goblet cell responses. In accordance, lungs from human asthmatics show increased PNECs. These findings demonstrate that the PNEC-ILC2 neuroimmunological modules function at airway branch points to amplify allergic asthma responses.

Alternaria alternata challenge at the nasal mucosa results in eosinophilic inflammation and increased susceptibility to influenza virus infection

BACKGROUND

Eosinophils in the nasal mucosa are an elemental feature of allergic rhinitis.

OBJECTIVE

Our objective was to explore eosinophilic inflammation and its impact on respiratory virus infection at the nasal mucosa.

METHODS

Inflammation in the nasal mucosae of mice was evaluated in response to repetitive stimulation with strict intranasal volumes of a filtrate of Alternaria alternata. Mice were then challenged with influenza virus.

RESULTS

Repetitive stimulation with A. alternata resulted in eosinophil recruitment to the nasal passages in association with elevated levels of IL-5, IL-13 and eotaxin-1; eosinophil recruitment was diminished in eotaxin-1-/- mice, and abolished in Rag1-/- mice. A. alternata also resulted in elevated levels of nasal wash IgA in both wild-type and eosinophil-deficient ∆dblGATA mice. Interestingly, A. alternata-treated mice responded to an influenza virus infection with profound weight loss and mortality compared to mice that received diluent alone (0% vs 100% survival, ***P < .001); the lethal response was blunted when A. alternata was heat-inactivated. Minimal differences in virus titre were detected, and eosinophils present in the nasal passages at the time of virus inoculation provided no protection against the lethal sequelae. Interestingly, nasal wash fluids from mice treated with A. alternata included more neutrophils and higher levels of pro-inflammatory mediators in response to virus challenge, among these, IL-6, a biomarker for disease severity in human influenza.

CONCLUSIONS AND CLINICAL RELEVANCE

Repetitive administration of A. alternata resulted in inflammation of the nasal mucosae and unanticipated morbidity and mortality in response to subsequent challenge with influenza virus. Interestingly, and in contrast to findings in the lower airways, eosinophils recruited to the nasal passages provided no protection against lethal infection. As increased susceptibility to influenza virus among individuals with rhinitis has been the subject of several clinical reports, this model may be used for further exploration of these observations.

All along the watchtower: group 2 innate lymphoid cells in allergic responses

Group 2 innate lymphoid cells (ILC2) are a subset of innate lymphocytes that responds to local, tissue-derived signals and initiates allergic immune responses. ILC2 activation promotes the recruitment of eosinophils, polarization of alternatively activated macrophages, and tissue-remodeling, processes associated with the 'weep and sweep' response to helminthic worm colonization and infection. ILC2s also coordinate both physiologic and pathologic type 2 allergic immune responses, including promoting normal tissue development and remodeling and driving allergic pathology such as atopic dermatitis and allergic asthma. In this review we summarize recent advances in ILC2 biology, particularly focusing on how local cells and signals coordinately regulate ILC2s, how this may influence physiologic processes, and how ILC2 cooperate with adaptive T helper type 2 cells to drive pathologic allergic inflammation.

Interleukin-33 Receptor (ST2) Deficiency Improves the Outcome of Staphylococcus aureus-Induced Septic Arthritis

The ST2 receptor is a member of the Toll/IL-1R superfamily and interleukin-33 (IL-33) is its agonist. Recently, it has been demonstrated that IL-33/ST2 axis plays key roles in inflammation and immune mediated diseases. Here, we investigated the effect of ST2 deficiency in Staphylococcus aureus-induced septic arthritis physiopathology. Synovial fluid samples from septic arthritis and osteoarthritis individuals were assessed regarding IL-33 and soluble (s) ST2 levels. The IL-33 levels in samples from synovial fluid were significantly increased, whereas no sST2 levels were detected in patients with septic arthritis when compared with osteoarthritis individuals. The intra-articular injection of 1 × 10⁷ colony-forming unity/10 μl of S. aureus American Type Culture Collection 6538 in wild-type (WT) mice induced IL-33 and sST2 production with a profile resembling the observation in the synovial fluid of septic arthritis patients. Data using WT, and ST2 deficient (^−/−) and interferon-γ (IFN-γ)^−/− mice showed that ST2 deficiency shifts the immune balance toward a type 1 immune response that contributes to eliminating the infection due to enhanced microbicide effect via NO production by neutrophils and macrophages. In fact, the treatment of ST2^−/− bone marrow-derived macrophage cells with anti-IFN-γ abrogates the beneficial phenotype in the absence of ST2, which confirms that ST2 deficiency leads to IFN-γ expression and boosts the bacterial killing activity of macrophages against S. aureus. In agreement, WT cells achieved similar immune response to ST2 deficiency by IFN-γ treatment. The present results unveil a previously unrecognized beneficial effect of ST2 deficiency in S. aureus-induced septic arthritis.

Macrophages regulate lung ILC2 activation via Pla2g5-dependent mechanisms

Group V phospholipase A₂ (Pla2g5) is a lipid-generating enzyme necessary for macrophage effector functions in pulmonary inflammation. However, the lipid mediators involved and their cellular targets have not been identified. Mice lacking Pla2g5 showed markedly reduced lung ILC2 activation and eosinophilia following repetitive Alternaria Alternata inhalation. While Pla2g5-null mice had Wt levels of immediate IL-33 release after one Alternaria dose, they failed to upregulate IL-33 in macrophages following repeated Alternaria administration. Unexpectedly, while adoptive transfer of bone marrow-derived (BM)-macrophages restored ILC2 activation and eosinophilia in Alternaria-exposed Pla2g5-null mice, exogenous IL-33 did not. Conversely, transfers of Pla2g5-null BM-macrophages reduced inflammation in Alternaria-exposed Wt mice. Mass spectrometry analysis of free fatty acids (FFAs) demonstrated significantly reduced FFAs (including linoleic acid (LA) and oleic acid (OA)) in lung and BM-macrophages lacking Pla2g5. Exogenous administration of LA or LA+OA to Wt mice sharply potentiated IL-33-induced lung eosinophilia and ILC2 expansion in vitro and in vivo. In contrast, OA potentiated IL-33-induced inflammation and ILC2 expansion in Pla2g5-null mice, but LA was inactive both in vivo and in vitro. Notably, Pla2g5-null ILC2s showed significantly reduced expression of the FFA-receptor-1 compared to Wt ILC2s. Thus, macrophage-associated Pla2g5 contributes significantly to type-2 immunity through regulation of IL-33 induction and FFA-driven ILC2 activation.