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Abstract: Innate lymphoid cells (ILC) represent a group of lymphocytes that lack specific antigen receptors and are relatively rare as compared to adaptive lymphocytes. ILCs play important roles in allergic and nonallergic inflammatory diseases due to their location at barrier surfaces within the airways, gut, and skin, and they respond to cytokines produced by activated cells in their local environment. Innate lymphoid cells contribute to the immune response by the release of cytokines and other mediators, forming a link between innate and adaptive immunity. In recent years, these cells have been extensively characterized and their role in animal models of disease has been investigated. Data to translate the relevance of ILCs in human pathology, and the potential role of ILCs in diagnosis, as biomarkers and/or as future treatment targets are also emerging. This review, produced by a task force of the Immunology Section of the European Academy of Allergy and Clinical Immunology (EAACI), encompassing clinicians and researchers, highlights the role of ILCs in human allergic and nonallergic diseases in the airways, gastrointestinal tract, and skin, with a focus on new insights into clinical implications, therapeutic options, and future research opportunities. [ABSTRACT FROM AUTHOR]

Background & Objectives: Despite the availability of biologics for severe pediatric asthma, real-life studies reporting on drivers behind initiating biologics and their alignment with the Global Initiative for Asthma (GINA) recommendations are lacking., Methods: We performed analysis within the pediatric asthma noninvasive diagnostic approaches study, a prospective cohort of 6- to 17-year-old children with severe asthma. Information was collected on demographic factors, symptom control, treatment, comorbidities, and diagnostic tests from medical records and questionnaires. We divided patients into "starters" or "nonstarters" based on the clinical decision to initiate biologics and performed multivariate logistic regression analysis to identify drivers behind initiating therapy. Additionally, we assessed patient suitability for biologics according to key factors in the GINA recommendations: Type 2 inflammation, frequency of exacerbations, and optimization of treatment adherence., Results: In total, 72 children (mean age 11.5 ± 3.0 years, 65.3% male) were included (13 starters). Initiation of biologics was associated with a higher GINA treatment step (adjusted odds ratio's [aOR] = 5.0, 95%CI 1.33-18.76), steroid toxicity (aOR = 21.1, 95%CI 3.73-119.91), frequency of exacerbations (aOR = 1.6, 95%CI 1.10-2.39), improved therapy adherence (aOR = 1.7, 95%CI 1.10-2.46), Caucasian ethnicity (aOR = 0.20, 95%CI 0.05-0.80), ≥1 allergic sensitization (aOR = 0.06, 95%CI 0.004-0.97), and allergic rhinitis (aOR = 0.13, 95%CI 0.03-0.65). Furthermore, steroid toxicity was identified as an important factor for deviation from the current recommendations on biologic prescription., Conclusions: We identified multiple drivers and inhibitors for initiating biologics, and showed the clinical need for biologics in severe pediatric asthmatics suffering from steroid toxicity. These findings may help refine asthma management guidelines., (© 2024 The Author(s). Pediatric Pulmonology published by Wiley Periodicals LLC.)

Background: Fatigue is a commonly reported clinical symptom, yet research on fatigue in children with severe asthma is missing. We aimed to explore the extent of fatigue in severe pediatric asthma and identify associated factors., Method: This study was conducted within the Pediatric Asthma Non-Invasive Diagnostic Approaches (PANDA), an observational cohort of 6- to 17-year-old Dutch children with severe asthma. The Pediatric Quality of Life Inventory Multidimensional Fatigue Scale (PedsQL™-MFS) was used to measure self-reported fatigue. Fatigue levels were compared with a general pediatric Dutch population using linear regression, and quantifying the prevalence of "fatigued" (-2 < Standard deviations [SD] ≤ -1) and "severely fatigued" (SD ≤ -2) children. Secondly, we performed linear regression analyses to explore whether fatigue levels were independently associated with asthma attacks, comorbidities, medication, pulmonary function, symptom control, and asthma-related quality of life (QoL)., Results: Severe pediatric asthma patients (n = 78, mean age 11.8 ± 3.1 years) reported significantly more fatigue than Dutch peers (n = 328, mean age 11.8 ± 3.2 years) mean difference in z-score: -0.68; 95%CI -0.96, -0.40. In the severe asthma group, 28.2% scored as "fatigued" and 15.4% as "severely fatigued," compared with 14.0% and 3.4% in the general population. In pediatric asthma patients, asthma-related QoL (β = 0.77, p < .01, ΔR 2  = .43), symptom control (β = 0.56, p < .01, ΔR 2  = .24) and a dysfunctional breathing pattern (β = -0.36, p < .01, ΔR 2  = .12) were most strongly associated with fatigue scores., Conclusion: Fatigue is a common symptom in children with severe asthma and is associated with multiple clinical factors and patient-reported outcomes. It should be considered as an important treatment target., (© 2024 The Author(s). Pediatric Allergy and Immunology published by European Academy of Allergy and Clinical Immunology and John Wiley & Sons Ltd.)

Background: Months after infection with severe acute respiratory syndrome coronavirus 2, at least 10% of patients still experience complaints. Long-COVID (coronavirus disease 2019) is a heterogeneous disease, and clustering efforts revealed multiple phenotypes on a clinical level. However, the molecular pathways underlying long-COVID phenotypes are still poorly understood., Objectives: We sought to cluster patients according to their blood transcriptomes and uncover the pathways underlying their disease., Methods: Blood was collected from 77 patients with long-COVID from the Precision Medicine for more Oxygen (P4O2) COVID-19 study. Unsupervised hierarchical clustering was performed on the whole blood transcriptome. These clusters were analyzed for differences in clinical features, pulmonary function tests, and gene ontology term enrichment., Results: Clustering revealed 2 distinct clusters on a transcriptome level. Compared with cluster 2 (n = 65), patients in cluster 1 (n = 12) showed a higher rate of preexisting cardiovascular disease (58% vs 22%), higher prevalence of gastrointestinal symptoms (58% vs 29%), shorter hospital duration during severe acute respiratory syndrome coronavirus 2 infection (median, 3 vs 8 days), lower FEV 1 /forced vital capacity (72% vs 81%), and lower diffusion capacity of the lung for carbon monoxide (68% vs 85% predicted). Gene ontology term enrichment analysis revealed upregulation of genes involved in the antiviral innate immune response in cluster 1, whereas genes involved with the adaptive immune response were upregulated in cluster 2., Conclusions: This study provides a start in uncovering the pathophysiological mechanisms underlying long-COVID. Further research is required to unravel why the immune response is different in these clusters, and to identify potential therapeutic targets to create an optimized treatment or monitoring strategy for the individual long-COVID patient., Competing Interests: Disclosure statement Disclosure of potential conflict of interest: K. Golebski received funds paid to the institution from the ZonMW grant long COVID; received funds from GlaxoSmithKline (GSK), ALK, and STIMAG; and received consulting fees from GSK. J. W. Duitman has received research funding from Boehringer Ingelheim and Abbvie. M. I. Abdel-Aziz was funded by a full PhD scholarship from the Ministry of Higher Education of the Arab Republic of Egypt during the conduct of the study and received a grant from Stichting Astma Bestrijding. A. H. Maitland-van der Zee received money paid to the institution from the ERANET Systems Medicine and ZonMW grant, another ZonMW grant for COVID-19 research, the Stichting TAAI research grant, the EUROSTARS research grant COPDetect, an unrestricted research grant from Boehringer Ingelheim and GSK, an unrestricted research grant from the Vertex Innovation Award, and the Innovative Health Initiative 3TR research grant; is the (unpaid) chair of the DSMB SOS BPD study; and was the president of the federation of innovative drug research in the Netherlands (FIGON). The rest of the authors declare that they have no relevant conflicts of interest. Data availability: The data are available in the GEO omnibus under accession GSE267625. Also accessible with the link https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE267625., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

ILC2s are key players in type 2 immunity and contribute to maintaining homeostasis. ILC2s are also implicated in the development of type 2 inflammation-mediated chronic disorders like asthma. While memory ILC2s have been identified in mouse, it is unknown whether human ILC2s can acquire immunological memory. Here, we demonstrate the persistence of CD45RO, a marker previously linked to inflammatory ILC2s, in resting ILC2s that have undergone prior activation. A high proportion of these cells concurrently reduce the expression of the canonical ILC marker CD127 in a tissue-specific manner. Upon isolation and in vitro stimulation of CD127-CD45RO+ ILC2s, we observed an augmented ability to proliferate and produce cytokines. CD127-CD45RO+ ILC2s are found in both healthy and inflamed tissues and display a gene signature of cell activation. Similarly, mouse memory ILC2s show reduced expression of CD127. Our findings suggest that human ILC2s can acquire innate immune memory and warrant a revision of the current strategies to identify human ILC2s., (© 2024 Mathä et al.)

Bronchial asthma is a heterogeneous respiratory condition characterized by chronic airway inflammation, airway hyperresponsiveness and airway structural changes (known as remodeling). The clinical symptoms can be evoked by (non)specific triggers, and their intensity varies over time. In the past, treatment was mainly focusing on symptoms' alleviation; in contrast modern treatment strategies target the underlying inflammation, even during asymptomatic periods. Components of airway remodeling include epithelial cell shedding and dysfunction, goblet cell hyperplasia, subepithelial matrix protein deposition, fibrosis, neoangiogenesis, airway smooth muscle cell hypertrophy and hyperplasia. Among the other important, and frequently forgotten aspects of airway remodeling, also loss of epithelial barrier integrity, immune defects in anti-infectious defence and mucociliary clearance (MCC) dysfunction should be pointed out. Mucociliary clearance represents one of the most important defence airway mechanisms. Several studies in asthmatics demonstrated various dysfunctions in MCC - e.g., ciliated cells displaying intracellular disorientation, abnormal cilia and cytoplasmic blebs. Moreover, excessive mucus production and persistent cough are one of the well-recognized features of severe asthma and are also associated with defects in MCC. Damaged airway epithelium and impaired function of the ciliary cells leads to MCC dysfunction resulting in higher susceptibility to infection and inflammation. Therefore, new strategies aimed on restoring the remodeling changes and MCC dysfunction could present a new therapeutic approach for the management of asthma and other chronic respiratory diseases., Competing Interests: Declaration of competing interest No conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Severe asthma in children and adolescents exerts a substantial health, financial, and societal burden. Severe asthma is a heterogeneous condition with multiple clinical phenotypes and underlying inflammatory patterns that might be different in individual patients. Various add-on treatments have been developed to treat severe asthma, including monoclonal antibodies (biologics) targeting inflammatory mediators. Biologics that are currently approved to treat children (≥ 6 years of age) or adolescents (≥ 12 years of age) with severe asthma include: anti-immunoglobulin E (omalizumab), anti-interleukin (IL)-5 (mepolizumab), anti-IL5 receptor (benralizumab), anti-IL4/IL13 receptor (dupilumab), and antithymic stromal lymphopoietin (TSLP) (tezepelumab). However, access to these targeted treatments varies across countries and relies on few and crude indicators. There is a need for better treatment stratification to guide which children might benefit from these treatments. In this narrative review we will assess the most recent developments in the treatment of severe pediatric asthma, as well as potential biomarkers to assess treatment efficacy for this patient population., (© 2023. The Author(s).)

Introduction : The coronavirus disease 2019 (COVID-19) pandemic has led to the death of almost 7 million people, however, with a cumulative incidence of 0.76 billion, most people survive COVID-19. Several studies indicate that the acute phase of COVID-19 may be followed by persistent symptoms including fatigue, dyspnea, headache, musculoskeletal symptoms, and pulmonary functional-and radiological abnormalities. However, the impact of COVID-19 on long-term health outcomes remains to be elucidated. Aims : The Precision Medicine for more Oxygen (P4O2) consortium COVID-19 extension aims to identify long COVID patients that are at risk for developing chronic lung disease and furthermore, to identify treatable traits and innovative personalized therapeutic strategies for prevention and treatment. This study aims to describe the study design and first results of the P4O2 COVID-19 cohort. Methods : The P4O2 COVID-19 study is a prospective multicenter cohort study that includes nested personalized counseling intervention trial. Patients, aged 40-65 years, were recruited from outpatient post-COVID clinics from five hospitals in The Netherlands. During study visits at 3-6 and 12-18 months post-COVID-19, data from medical records, pulmonary function tests, chest computed tomography scans and biological samples were collected and questionnaires were administered. Furthermore, exposome data was collected at the patient's home and state-of-the-art imaging techniques as well as multi-omics analyses will be performed on collected data. Results : 95 long COVID patients were enrolled between May 2021 and September 2022. The current study showed persistence of clinical symptoms and signs of pulmonary function test/radiological abnormalities in post-COVID patients at 3-6 months post-COVID. The most commonly reported symptoms included respiratory symptoms (78.9%), neurological symptoms (68.4%) and fatigue (67.4%). Female sex and infection with the Delta, compared with the Beta, SARS-CoV-2 variant were significantly associated with more persisting symptom categories. Conclusions : The P4O2 COVID-19 study contributes to our understanding of the long-term health impacts of COVID-19. Furthermore, P4O2 COVID-19 can lead to the identification of different phenotypes of long COVID patients, for example those that are at risk for developing chronic lung disease. Understanding the mechanisms behind the different phenotypes and identifying these patients at an early stage can help to develop and optimize prevention and treatment strategies.

Asthma and chronic rhinosinusitis with nasal polyps (CRSwNP) or without (CRSsNP) are chronic respiratory diseases. These two disorders often co-exist based on common anatomical, immunological, histopathological, and pathophysiological basis. Usually, asthma with comorbid CRSwNP is driven by type 2 (T2) inflammation which predisposes to more severe, often intractable, disease. In the past two decades, innovative technologies and detection techniques in combination with newly introduced targeted therapies helped shape our understanding of the immunological pathways underlying inflammatory airway diseases and to further identify several distinct clinical and inflammatory subsets to enhance the development of more effective personalized treatments. Presently, a number of targeted biologics has shown clinical efficacy in patients with refractory T2 airway inflammation, including anti-IgE (omalizumab), anti-IL-5 (mepolizumab, reslizumab)/anti-IL5R (benralizumab), anti-IL-4R-α (anti-IL-4/IL-13, dupilumab), and anti-TSLP (tezepelumab). In non-type-2 endotypes, no targeted biologics have consistently shown clinical efficacy so far. Presently, multiple therapeutical targets are being explored including cytokines, membrane molecules and intracellular signalling pathways to further expand current treatment options for severe asthma with and without comorbid CRSwNP. In this review, we discuss existing biologics, those under development and share some views on new horizons., (© 2023 The Author(s).)

Background: Changes in exhaled volatile organic compounds (VOCs) can be used to discriminate between respiratory diseases, and increased concentrations of hydrocarbons are commonly linked to oxidative stress. However, the VOCs identified are inconsistent between studies, and translational studies are lacking., Methods: In this bench to bedside study, we captured VOCs in the headspace of A549 epithelial cells after exposure to hydrogen peroxide (H 2 O 2 ), to induce oxidative stress, using high-capacity polydimethylsiloxane sorbent fibres. Exposed and unexposed cells were compared using targeted and untargeted analysis. Breath samples of invasively ventilated intensive care unit patients (n=489) were collected on sorbent tubes and associated with the inspiratory oxygen fraction ( F IO 2 ) to reflect pulmonary oxidative stress. Headspace samples and breath samples were analysed using gas chromatography and mass spectrometry., Results: In the cell, headspace octane concentration was decreased after oxidative stress (p=0.0013), while the other VOCs were not affected. 2-ethyl-1-hexanol showed an increased concentration in the headspace of cells undergoing oxidative stress in untargeted analysis (p=0.00014 ) . None of the VOCs that were linked to oxidative stress showed a significant correlation with F IO 2 (R s range: -0.015 to -0.065) or discriminated between patients with F IO 2 ≥0.6 or below (area under the curve range: 0.48 to 0.55)., Conclusion: Despite a comprehensive translational approach, validation of known and novel volatile biomarkers of oxidative stress was not possible in patients at risk of pulmonary oxidative injury. The inconsistencies observed highlight the difficulties faced in VOC biomarker validation, and that caution is warranted in the interpretation of the pathophysiological origin of discovered exhaled breath biomarkers., Competing Interests: Conflict of interest: D. Fenn has nothing to disclose. Conflict of interest: T.A. Lilien has nothing to disclose. Conflict of interest: L.A. Hagens has nothing to disclose. Conflict of interest: M.R. Smit has nothing to disclose. Conflict of interest: N.F.L. Heijnen has nothing to disclose. Conflict of interest: A.M. Tuip-de Boer has nothing to disclose. Conflict of interest: A.H. Neerincx has nothing to disclose. Conflict of interest: K. Golebski has nothing to disclose. Conflict of interest: D.C.J.J. Bergmans has nothing to disclose. Conflict of interest: R.M. Schnabel has nothing to disclose. Conflict of interest: M.J. Schultz has nothing to disclose. Conflict of interest: A.H. Maitland-van der Zee has received research grants outside the submitted work from GSK, Boehringer Ingelheim and Vertex; she is the principal investigator of a P4O2 (Precision Medicine for more Oxygen) public–private partnership sponsored by Health Holland involving many private partners that contribute in cash and/or in kind (Boehringer Ingelheim, Breathomix, Fluidda, Ortec Logiqcare, Philips, Quantib-U, Roche, Smartfish, SODAQ, Thirona, TopMD and Novartis); and she has served in advisory boards for AstraZeneca, GSK and Boehringer Ingelheim, with money paid to her institution. Conflict of interest: P. Brinkman has nothing to disclose. Conflict of interest: L.D.J. Bos reports grants from the Dutch Lung Foundation (Young investigator grant), grants from the Dutch Lung Foundation and Health Holland (Public–Private Partnership grant), grants from the Dutch Lung Foundation (Dirkje Postma Award), grants from IMI COVID19 initiative, and grants from Amsterdam UMC fellowship, outside the submitted work; he has also served in advisory capacity for Santhera and Janssen with money paid to his institution., (Copyright ©The authors 2023.)

Introduction: The clinical phenotype of severe acute asthma at the pediatric intensive care unit (PICU) is highly heterogeneous. However, current treatment is still based on a 'one-size-fits-all approach'., Areas Covered: We aim to give a comprehensive description of the clinical characteristics of pediatric patients with severe acute asthma admitted to the PICU and available immunological biomarkers, providing the first steps toward precision medicine for this patient population. A literature search was performed using PubMed for relevant studies on severe acute (pediatric) asthma., Expert Opinion: Omics technologies should be used to investigate the relationship between cellular molecules and pathways, and their clinical phenotypes. Inflammatory phenotypes might guide bedside decisions regarding the use of corticosteroids, neutrophil modifiers and/or type of beta-agonist. A next step toward precision medicine should be inclusion of these patients in clinical trials on biologics.

Severe asthma is a heterogeneous disease with different phenotypes based on clinical, functional or inflammatory parameters. In particular, the eosinophilic phenotype is associated with type 2 inflammation and increased levels of interleukin (IL)-4, IL-5 and IL-13). Monoclonal antibodies that target the eosinophilic inflammatory pathways (IL-5R and IL-5), namely mepolizumab, reslizumab, and benralizumab, are effective and safe for severe eosinophilic asthma. Eosinophils threshold represents the most indicative biomarker for response to treatment with all three monoclonal antibodies. Improvement in asthma symptoms scores, lung function, the number of exacerbations, history of late-onset asthma, chronic rhinosinusitis with nasal polyposis, low oral corticosteroids use and low body mass index represent predictive clinical markers of response. Novel Omics studies are emerging with proteomics data and exhaled breath analyses. These may prove useful as biomarkers of response and non-response biologics. Moreover, future biomarker studies need to be undertaken in paediatric patients affected by severe asthma. The choice of appropriate biologic therapy for severe asthma remains challenging. The importance of finding biomarkers that can predict response continuous an open issue that needs to be further explored. This review describes the clinical effects of targeting the IL-5 pathway in severe asthma in adult and paediatric patients, focusing on predictors of response and non-response., (© 2021 The Authors. Clinical & Experimental Allergy published by John Wiley & Sons Ltd.)

Food allergy is an increasingly prevalent disease driven by uncontrolled type 2 immune response. Currently, knowledge about the underlying mechanisms that initiate and promote the immune response to dietary allergens is limited. Patients with food allergy are commonly sensitized through the skin in their early life, later on developing allergy symptoms within the gastrointestinal tract. Food allergy results from a dysregulated type 2 response to food allergens, characterized by enhanced levels of IgE, IL-4, IL-5, and IL-13 with infiltration of mast cells, eosinophils, and basophils. Recent studies raised a possible role for the involvement of innate lymphoid cells (ILCs) in driving food allergy. Unlike lymphocytes, ILCs lack They represent a group of lymphocytes that lack specific antigen receptors. ILCs contribute to immune responses not only by releasing cytokines and other mediators but also by responding to cytokines produced by activated cells in their local microenvironment. Due to their localization at barrier surfaces of the airways, gut, and skin, ILCs form a link between the innate and adaptive immunity. This review summarizes recent evidence on how skin and gastrointestinal mucosal immune system contribute to both homeostasis and the development of food allergy, as well as the involvement of ILCs toward inflammatory processes and regulatory mechanisms., (© 2021 The Authors. Allergy published by European Academy of Allergy and Clinical Immunology and John Wiley & Sons Ltd.)

Patients diagnosed with coronavirus disease 2019 (COVID-19) become critically ill primarily around the time of activation of the adaptive immune response. Here, we provide evidence that antibodies play a role in the worsening of disease at the time of seroconversion. We show that early-phase severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) spike protein-specific immunoglobulin G (IgG) in serum of critically ill COVID-19 patients induces excessive inflammatory responses by human alveolar macrophages. We identified that this excessive inflammatory response is dependent on two antibody features that are specific for patients with severe COVID-19. First, inflammation is driven by high titers of anti-spike IgG, a hallmark of severe disease. Second, we found that anti-spike IgG from patients with severe COVID-19 is intrinsically more proinflammatory because of different glycosylation, particularly low fucosylation, of the antibody Fc tail. Low fucosylation of anti-spike IgG was normalized in a few weeks after initial infection with SARS-CoV-2, indicating that the increased antibody-dependent inflammation mainly occurs at the time of seroconversion. We identified Fcγ receptor (FcγR) IIa and FcγRIII as the two primary IgG receptors that are responsible for the induction of key COVID-19-associated cytokines such as interleukin-6 and tumor necrosis factor. In addition, we show that anti-spike IgG-activated human macrophages can subsequently break pulmonary endothelial barrier integrity and induce microvascular thrombosis in vitro. Last, we demonstrate that the inflammatory response induced by anti-spike IgG can be specifically counteracted by fostamatinib, an FDA- and EMA-approved therapeutic small-molecule inhibitor of Syk kinase., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).)

The role of innate immune cells in allergen immunotherapy that confers immune tolerance to the sensitizing allergen is unclear. Here, we report a role of interleukin-10-producing type 2 innate lymphoid cells (IL-10 + ILC2s) in modulating grass-pollen allergy. We demonstrate that KLRG1 + but not KLRG1 - ILC2 produced IL-10 upon activation with IL-33 and retinoic acid. These cells attenuated Th responses and maintained epithelial cell integrity. IL-10 + KLRG1 + ILC2s were lower in patients with grass-pollen allergy when compared to healthy subjects. In a prospective, double-blind, placebo-controlled trial, we demonstrated that the competence of ILC2 to produce IL-10 was restored in patients who received grass-pollen sublingual immunotherapy. The underpinning mechanisms were associated with the modification of retinol metabolic pathway, cytokine-cytokine receptor interaction, and JAK-STAT signaling pathways in the ILCs. Altogether, our findings underscore the contribution of IL-10 + ILC2s in the disease-modifying effect by allergen immunotherapy., Competing Interests: Declaration of interests K.G., J.A.L., U.S., M.M.L., R.C.Y.L., S.M.B., B.A.H., G.V.-N., O.H., G.M., F.Q.H., O.F., M.L.A., S.J.H.V., A.-H.M.v.d.Z., C.M.v.D., and W.F. report no conflicts of interest. E.H.S.-K. has received travel grants from ALK-Abello. Stephen Durham has received lecture fees and research funds from ALK, Denmark, manufacturer of grass allergen tablets used for sublingual immunotherapy. M.O. is a consultant for Hycor Biomedical and a co-founder of Tolerogenics SARL. Unrelated intellectual property of M.O. and the Luxembourg Institute of Health has been licensed to Tolerogenics. H.S. is a consultant for GSK for which he receives an honorarium. M.H.S. reports research grants from Immune Tolerance Network, Medical Research Council, Allergy Therapeutics, and LETI Laboratorios and lecture fees from Allergy Therapeutics and ALK., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Group 2 innate lymphoid cells (ILC2s) orchestrate protective type 2 immunity and have been implicated in various immune disorders. In the mouse, circulatory inflammatory ILC2s (iILC2s) were identified as a major source of type 2 cytokines. The human equivalent of the iILC2 subset remains unknown. Here, we identify a human inflammatory ILC2 population that resides in inflamed mucosal tissue and is specifically marked by surface CD45RO expression. CD45RO + ILC2s are derived from resting CD45RA + ILC2s upon activation by epithelial alarmins such as IL-33 and TSLP, which is tightly linked to STAT5 activation and up-regulation of the IRF4/BATF transcription factors. Transcriptome analysis reveals marked similarities between human CD45RO + ILC2s and mouse iILC2s. Frequencies of CD45RO + inflammatory ILC2 are increased in inflamed mucosal tissue and in the circulation of patients with chronic rhinosinusitis or asthma, correlating with disease severity and resistance to corticosteroid therapy. CD45RA-to-CD45RO ILC2 conversion is suppressed by corticosteroids via induction of differentiation toward an immunomodulatory ILC2 phenotype characterized by low type 2 cytokine and high amphiregulin expression. Once converted, however, CD45RO + ILC2s are resistant to corticosteroids, which is associated with metabolic reprogramming resulting in the activation of detoxification pathways. Our combined data identify CD45RO + inflammatory ILC2s as a human analog of mouse iILC2s linked to severe type 2 inflammatory disease and therapy resistance., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Innate lymphoid cells (ILCs) are important for tissue homeostasis and for the initiation of immune responses. Based on their transcriptional regulation and cytokine profiles, ILCs can be categorized into five subsets with defined phenotypes and functional profiles, but they also have the ability to adapt to local environmental cues by changing these profiles. This plasticity raises the question of the extent to which the cytokine production profiles of ILCs are pre-programmed or are a reflection of the tissue microenvironment. Here, we review recent advances in research on ILCs, with a focus on the plasticity of these cells. We highlight the ability of ILCs to communicate with the surrounding microenvironment and discuss the possible consequences of ILC plasticity for our understanding of the biological roles of these cells. Finally, we discuss how we might use this knowledge of ILC plasticity to develop or improve options for the treatment of inflammatory diseases.

Purpose of Review: Childhood asthma is a heterogeneous inflammatory disease comprising different phenotypes and endotypes and, particularly in its severe forms, has a large impact on the quality-of-life of patients and caregivers. The application of advanced omics technologies provides useful insights into underlying asthma endotypes and may provide potential clinical biomarkers to guide treatment and move towards a precision medicine approach., Recent Findings: The current article addresses how novel omics approaches have shaped our current understanding of childhood asthma and highlights recent findings from (pharmaco)genomics, epigenomics, transcriptomics, and metabolomics studies on childhood asthma and their potential clinical implications to guide treatment in severe asthmatics., Summary: Until now, omics studies have largely expanded our view on asthma heterogeneity, helped understand cellular processes underlying asthma, and brought us closer towards identifying (bio)markers that will allow the prediction of treatment responsiveness and disease progression. There is a clinical need for biomarkers that will guide treatment at the individual level, particularly in the field of biologicals. The integration of multiomics data together with clinical data could be the next promising step towards development individual risk prediction models to guide treatment. However, this requires large-scale collaboration in a multidisciplinary setting.

Recently, human ILCs that express CD117 and CD127 but lack CRTH2 and NKp44 have been shown to contain precursors of ILC1, ILC2, and ILC3. However, these ILCs have not been extensively characterized. We performed an unbiased hierarchical stochastic neighbor embedding (HSNE) analysis of the phenotype of peripheral blood CD117 + ILCs, which revealed the presence of three major subsets: the first expressed NKp46, the second expressed both NKp46 and CD56, and the third expressed KLRG1, but not NKp46 or CD56. Analysis of their cytokine production profiles and transcriptome revealed that NKp46 + ILCs predominantly develop into ILC3s; some of them can differentiate into ILC1/NK-like cells, but they are unable to develop into ILC2s. In contrast, KLRG1 + ILCs predominantly differentiate into ILC2s. Single-cell cultures demonstrate that KLRG1 + ILCs can also differentiate into other ILC subsets depending on the signals they receive. Epigenetic profiling of KLRG1 + ILCs is consistent with the broad differentiation potential of these cells., (© 2019 Nagasawa et al.)

Innate lymphoid cells (ILCs) are crucial for the immune surveillance at mucosal sites. ILCs coordinate early eradication of pathogens and contribute to tissue healing and remodeling, features that are dysfunctional in patients with cystic fibrosis (CF). The mechanisms by which ILCs contribute to CF-immunopathology are ill-defined. Here, we show that group 2 ILCs (ILC2s) transdifferentiated into IL-17-secreting cells in the presence of the epithelial-derived cytokines IL-1β, IL-23 and TGF-β. This conversion is abrogated by IL-4 or vitamin D3. IL-17 producing ILC2s induce IL-8 secretion by epithelial cells and their presence in nasal polyps of CF patients is associated with neutrophilia. Our data suggest that ILC2s undergo transdifferentiation in CF nasal polyps in response to local cytokines, which are induced by infectious agents.

Group 2 innate lymphoid cells (ILC2s) are the most well defined group of ILCs. ILC2 development is controlled by the GATA-3 transcription factor and these cells produce archetypal type 2 cytokines, such as IL-5 and IL-13. These cytokines mediate parasite expulsion and tissue repair, but also contribute to type 2 inflammatory diseases, including allergy, asthma and chronic rhinosinusitis with nasal polyps. In response to tightly regulated local environmental cues ILCs can generate characteristics of other subtypes, a process known as plasticity. Recent advances in the ILC2 field has led to the discovery that ILC2s can promptly shift to functional IFN-γ-producing ILC1s or IL-17-producing ILC3s, depending on the cytokines and chemokines produced by antigen presenting cells or epithelial cells. Due to yet unknown triggers, this complex network of signals may become dysregulated. In this review, we will discuss general ILC characteristic, ILC2 development, plasticity, memory function, and implications in disease., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose of Review: Innate lymphoid cells (ILCs) act as early orchestrators of the immune response, tissue repair, and maintenance of barrier homeostasis. This review summarizes recent findings of the role of ILCs in airway disease and highlights ongoing developments in clinical applications and treatment options., Recent Findings: On the basis of the transcription factors required for their development and cytokine profiles, ILCs have been classified into three subsets that resemble those of T-helper subtypes. ILCs produce multiple cytokines in response to signals from activated cells in their local environment. Recent studies in both humans and mice showed that ILCs are located at barrier surfaces and play critical roles in inflammatory diseases of the upper and lower airways., Summary: The discovery of ILCs and their characterization in homeostatic and diseased conditions, have brought new insights into innate and adaptive immune responses at mucosal barrier surfaces. The recent progress in understanding the role of ILCs in airway inflammation directs translation of fundamental studies into clinical applications. This knowledge can be useful for future clinical practice.

Group 2 innate lymphoid cells (ILC2s) secrete type 2 cytokines, which protect against parasites but can also contribute to a variety of inflammatory airway diseases. We report here that interleukin 1β (IL-1β) directly activated human ILC2s and that IL-12 induced the conversion of these activated ILC2s into interferon-γ (IFN-γ)-producing ILC1s, which was reversed by IL-4. The plasticity of ILCs was manifested in diseased tissues of patients with severe chronic obstructive pulmonary disease (COPD) or chronic rhinosinusitis with nasal polyps (CRSwNP), which displayed IL-12 or IL-4 signatures and the accumulation of ILC1s or ILC2s, respectively. Eosinophils were a major cellular source of IL-4, which revealed cross-talk between IL-5-producing ILC2s and IL-4-producing eosinophils. We propose that IL-12 and IL-4 govern ILC2 functional identity and that their imbalance results in the perpetuation of type 1 or type 2 inflammation.

Introduction: Chronic rhinosinusitis with nasal polyposis is an inflammatory disease that, although not directly linked to allergy, often displays a Th2-skewed inflammation characterized by elevated local IgE and IL-5 levels. The nasal cavity is constantly exposed to bacteria and viruses that may trigger epithelial inflammatory responses. To gain more insight into mechanisms by which such a biased inflammation might arise, we have investigated the epithelial expression of the Th2 skewing mediators (TSLP, IL-25, and IL-33) in relationship to disease and microbial triggers., Methods: Epithelial cells were obtained from polyp tissues of nasal polyposis patients and from inferior turbinates of non-diseased controls. Cells were exposed to various TLR-specific triggers to study the effect on mRNA and protein expression level of TSLP, IL-25, and IL-33 and the potential regulatory mechanisms through the expression profile the transcription factors ATF-3, DUSP-1, EGR-1, and NFKB-1., Results: The TLR3 agonist and viral analogue poly(I:C) induced TSLP mRNA 13.0 ± 3.1 fold (p < 0.05) and protein expression by 12.1 ± 2.3-fold (p < 0.05) higher in epithelium isolated from nasal polyposis patients than in epithelium form healthy controls. This enhanced induction of TSLP may be a consequence of a down-regulated expression of DUSP-1 in polyp epithelium., Conclusion: The TLR3 induced expression of TSLP introduces a mechanism by which the Th2-skewed tissue environment might arise in nasal polyps and invites a further evaluation of the potential contribution of current or past viral infections to polyposis pathogenesis.