Experimental asthma persists in IL-33 receptor knockout mice because of the emergence of thymic stromal lymphopoietin-driven IL-9+ and IL-13+ type 2 innate lymphoid cell subpopulations

NRF2 is a spatiotemporal metabolic hub essential for the polyfunctionality of Th2 cells

Upon encountering allergens, CD4+ T cells differentiate into IL-4-producing Th2 cells in lymph nodes, which later transform into polyfunctional Th2 cells producing IL-5 and IL-13 in inflamed tissues. However, the precise mechanism underlying their polyfunctionality remains elusive. In this study, we elucidate the pivotal role of NRF2 in polyfunctional Th2 cells in murine models of allergic asthma and in human Th2 cells. We found that an increase in reactive oxygen species (ROS) in immune cells infiltrating the lungs is necessary for the development of eosinophilic asthma and polyfunctional Th2 cells in vivo. Deletion of the ROS sensor NRF2 specifically in T cells, but not in dendritic cells, significantly abolished eosinophilia and polyfunctional Th2 cells in the airway. Mechanistically, NRF2 intrinsic to T cells is essential for inducing optimal oxidative phosphorylation and glycolysis capacity, thereby driving Th2 cell polyfunctionality independently of IL-33, partially by inducing PPARγ. Treatment with an NRF2 inhibitor leads to a substantial decrease in polyfunctional Th2 cells and subsequent eosinophilia in mice and a reduction in the production of Th2 cytokines from peripheral blood mononuclear cells in asthmatic patients. These findings highlight the critical role of Nrf2 as a spatial and temporal metabolic hub that is essential for polyfunctional Th2 cells, suggesting potential therapeutic implications for allergic diseases.

TRPM2 exacerbates airway inflammation by regulating oxidized-CaMKⅡ in allergic asthma

Background

Airway epithelial cells play important roles in allergic asthma. Transient receptor potential melastatin-related 2 (TRPM2) and oxidized Ca2+/calmodulin-dependent protein kinase Ⅱ (ox-CaMKⅡ) participate in the airway inflammation. This study aimed to analyze the effects of TRPM2 on ox-CaMKⅡ in the airway epithelial cells during allergic asthma.

Methods

BEAS-2B cells were treated with different dose of IL-13 (0, 5, 10, 20 ng/mL) for 24 h to analyze the changes of TRPM2 and ox-CaMKⅡ protein. Cells expressing different level of TRPM2 were obtained by transfection of TRPM2 siRNA or TRPM2-short cDNA. The transfected cells were treated with 10 ng/mL of IL-13 to analyze the effects of TRPM2 on the ox-CaMKⅡ. A CaMKⅡ inhibitor KN-93 was used to confirm the effects of TRPM2 on levels of ox-CaMKⅡ, p-MEK and p-ERK in the IL-13-treated BEAS-2B cells. Wild-type (WT) mice and TRPM2-knockout (TRPM2-/-) mice were induced by ovalbumin (OVA) to compare the differences of inflammation, levels of ox-CaMKII, p-MEK and p-ERK in airways.

Results

Cell viability was clearly decreased by the 20 ng/mL of IL-13. The levels of TRPM2 and ox-CaMKII protein in cells were increased with increasing doses of IL-13. Transfection of TRPM2 siRNA or TRPM2-short cDNA respectively decreased or increased the levels of ox-CaMKⅡ in the IL-13-stimulated cells. The results of KN-93 treatment were similar to the results of TRPM2 siRNA transfection, that the levels of ox-CaMKⅡ, p-MEK and p-ERK were significantly decreased in the IL-13-treated cells. Compared with the OVA-induced WT mice, levels of inflammation, ox-CaMKⅡ, p-MEK and p-ERK in the airways were significantly weakened in the OVA-induced TRPM2-/- mice.

Conclusions

TRPM2 plays a vital role in regulating ox-CaMKⅡ in airway epithelial cells during allergic asthma.

Angiotensin-(1-7) suppresses airway inflammation and airway remodeling via inhibiting ATG5 in allergic asthma

BACKGROUND

Angiotensin (Ang)-(1-7) can reduce airway inflammation and airway remodeling in allergic asthma. Autophagy-related 5 (ATG5) has attracted wide attentions in asthma. However, the effects of Ang-(1-7) on ATG5-mediated autophagy in allergic asthma are unclear.

METHODS

In this study, human bronchial epithelial cell (BEAS-2B) and human bronchial smooth muscle cell (HBSMC) were treated with different dose of Ang-(1-7) to observe changes of cell viability. Changes of ATG5 protein expression were measured in 10 ng/mL of interleukin (IL)-13-treated cells. Transfection of ATG5 small interference RNA (siRNA) or ATG5 cDNA in cells was used to analyze the effects of ATG5 on secretion of cytokines in the IL-13-treated cells. The effects of Ang-(1-7) were compared to the effects of ATG5 siRNA transfection or ATG5 cDNA transfection in the IL-13-treated cells. In wild-type (WT) mice and ATG5 knockout (ATG5-/-) mice, ovalbumin (OVA)-induced airway inflammation, fibrosis and autophagy were observed. In the OVA-induced WT mice, Ang-(1-7) treatment was performed to observe its effects on airway inflammation, fibrosis and autophagy.

RESULTS

The results showed that ATG5 protein level was decreased with Ang-(1-7) dose administration in the IL-13-treated BEAS-2B and IL13-treated HBSMC. Ang-(1-7) played similar results to ATG5 siRNA that it suppressed the secretion of IL-25 and IL-13 in the IL-13-treated BEAS-2B cells, and inhibited the expression of transforming growth factor (TGF)-β1 and α-smooth muscle actin (α-SMA) protein in the IL-13-treated HBSMC cells. ATG5 cDNA treatment significantly increased the secretion of IL-25 and IL-13 and expression of TGF-β1 and α-SMA protein in IL-13-treated cells. Ang-(1-7) treatment suppressed the effects of ATG5 cDNA in the IL-13-treated cells. In OVA-induced WT mice, Ang-(1-7) treatment suppressed airway inflammation, remodeling and autophagy. ATG5 knockout also suppressed the airway inflammation, remodeling and autophagy.

CONCLUSIONS

Ang-(1-7) treatment suppressed airway inflammation and remodeling in allergic asthma through inhibiting ATG5, providing an underlying mechanism of Ang-(1-7) for allergic asthma treatment.

Regulatory ILC2-Role of IL-10 Producing ILC2 in Asthma

Over the past two decades, a growing body of evidence observations have shown group two innate lymphoid cells (ILC2) to be critical drivers of Type 2 (T2) inflammatory responses associated with allergic inflammatory conditions such as asthma. ILC2 releases copious amounts of pro-inflammatory T2 cytokines-interleukin (IL)-4, IL-5, IL-9, and IL-13. This review provides a comprehensive overview of the newly discovered regulatory subtype of ILC2 described in murine and human mucosal tissue and blood. These KLRG1+ILC2 have the capacity to produce the anti-inflammatory cytokine IL-10. Papers compiled in this review were based on queries of PubMed and Google Scholar for articles published from 2000 to 2023 using keywords "IL-10" and "ILC2". Studies with topical relevance to IL-10 production by ILC2 were included. ILC2 responds to microenvironmental cues, including retinoic acid (RA), IL-2, IL-4, IL-10, and IL-33, as well as neuropeptide mediators such as neuromedin-U (NMU), prompting a shift towards IL-10 and away from T2 cytokine production. In contrast, TGF-β attenuates IL-10 production by ILC2. Immune regulation provided by IL-10+ILC2s holds potential significance for the management of T2 inflammatory conditions. The observation of context-specific cues that alter the phenotype of ILC warrants examining characteristics of ILC subsets to determine the extent of plasticity or whether the current classification of ILCs requires refinement.

NFκB1 inhibits memory formation and supports effector function of ILC2s in memory-driven asthma

Background

ILC2s are capable of generating memory. The mechanism of memory induction and memory-driven effector function (trained immunity) in ILC2s is unknown.

Objective

NFκB1 is preferentially expressed at a high level in ILC2s. We examined the role of NFkB1 in memory induction and memory-driven effector function in a mouse model of asthma.

Methods

Intranasal administration of Alternaria, flexivent, ELISA, histology, real-time PCR, western blot, flow cytometry and immunofluorescence staining.

Results

NFκB1 was essential for the effector phase of memory-driven asthma. NFκB1 was critical for IL33 production, ILC2 generation, and production of type-2 cytokines, which resulted in eosinophilic inflammation and other features of asthma. NFκB1 induction of type-2 cytokines in ILC2s was independent of GATA3. NFκB1 was important for allergen induction of ILC3s and FoxP3+ Tregs. NFκB1 did not affect Th2 cells or their cytokine production. In contrast to its protagonistic role in the effector phase, NFκB1 had an antagonistic role in the memory phase. NFκB1 inhibited allergen-induced upregulation of memory-associated repressor and preparedness genes in ILC2s. NFκB1 upregulated RUNX1. NFκB1 formed a heterodimer with RUNX1 in ILC2s.

Conclusions

NFκB1 positively regulated the effector phase but inhibited the induction phase of memory. The foregoing pointed to an interdependent antagonism between the memory induction and the memory effector processes. The NFκB1-RUNX1 heterodimer represented a non-canonical transcriptional activator of type-2 cytokines in ILC2s.

L1 cell adhesion molecule may be a protective molecule for atrial fibrillation in patients with valvular heart disease

Background

Atrial fibrillation (AF) is the most prevalent sustained arrhythmia. L1 cell adhesion molecule (L1CAM) served as a crucial regulator of signaling pathways. This research sought to examine the clinical value and functions of soluble L1CAM in the serum of AF patients.

Methods

In total, 118 patients (valvular heart disease patients [VHD, total: n = 93; AF: n = 47; sinus rhythm (SR): n = 46] and healthy controls [n = 25]) were recruited in this retrospective study. Plasma levels of L1CAM were detected by enzyme-linked immunosorbent assays. The Pearson's correlation approach, as applicable, was used for analyzing the correlations. The L1CAM was shown to independently serve as a risk indicator of AF in VHD after being analyzed by the multivariable logistic regression. To examine the specificity and sensitivity of AF, receiver operating characteristic (ROC) curves and the area under the curve (AUC) were used. A nomogram was developed for the visualisation of the model. We further evaluate the prediction model for AF using calibration plot and decision curve analysis.

Results

The plasma level of L1CAM was substantially decreased in AF patients as opposed to healthy control and SR patients (healthy control = 46.79 ± 12.55 pg/ml, SR = 32.86 ± 6.11 pg/ml, AF = 22.48 ± 5.39 pg/ml; SR vs. AF, P < 0.001; control vs. AF, P < 0.001). L1CAM was significantly and negatively correlated with LA and NT-proBNP (LA: r = -0.344, P = 0.002; NT-proBNP: r = -0.380, P = 0.001). Analyses using logistic regression showed a substantial correlation between L1CAM and AF in patients with VHD (For L1CAM, Model 1: OR = 0.704, 95%CI = 0.607-0.814, P < 0.001; Model 2: OR = 0.650, 95% CI = 0.529-0.798, P < 0.001; Model 3: OR = 0.650, 95% CI = 0.529-0.798, P < 0.001). ROC analysis showed that inclusion of L1CAM in the model significantly improved the ability of other clinical indicators to predict AF. The predictive model including L1CAM, LA, NT-proBNP and LVDd had excellent discrimination and a nomogram was developed. The model had good the calibration and clinical utility.

Conclusion

L1CAM was shown to independently serve as a risk indicator for AF in VHD. In AF patients with VHD, the prognostic and predictive effectiveness of models incorporating L1CAM was satisfactory. Collectively, L1CAM may be a protective molecule for atrial fibrillation in patients with valvular heart disease.

Intestinal Microflora Altered by Vancomycin Exposure in Early Life Up-regulates Type 2 Innate Lymphocyte and Aggravates Airway Inflammation in Asthmatic Mice

Allergic asthma is a chronic inflammatory disease primarily mediated by Th2 immune mechanisms. Exposure to antibiotics during early life is associated with an increased risk of allergic asthma, although the exact mechanism is not fully understood. In this study, mice were randomly divided into a normal saline control group (NS group), an OVA-induced asthma group (OVA group), a vancomycin treatment control group (VAN.NS group), and a vancomycin treatment the OVA-induced asthma group (VAN.OVA group). The results showed that vancomycin altered dominant species in experimental mice. The phylum level histogram showed that Bacteroides abundance was increased, and Firmicutes abundance was decreased in the OVA group. Airway inflammation and airway hyperresponsiveness (AHR) were aggravated in the vancomycin-exposed group. Enzyme-linked immunosorbent assay (ELISA) showed that the serum levels of IL-5, IL-13, and IL-33 in the OVA group were higher than those in the NS group, especially in the VAN.OVA group. The expression of GATA binding protein-3(GATA3) and retinoid acid receptor-related orphan receptor alpha (RORa) increased in the OVA group, even more so in the VAN.OVA group. Group 2 innate lymphoid cells (ILC2s) in the lung detected by flow cytometry was increased in OVA mice more than those in control mice, with a more remarkable increase in the VAN.OVA. Our results demonstrated that vancomycin used in early life could alter the intestinal microecology of mice, which, in turn, aggravates airway inflammation and upregulate type 2 innate lymphocytes.

β-sitosterol targets glucocorticoid receptor to reduce airway inflammation and remodeling in allergic asthma

INTRODUCTION

In most asthma patients, symptoms are controlled by treatment with glucocorticoid, but long-term or high-dose use can produce adverse effects. Therefore, it is crucial to find new therapeutic strategies. β-sitosterol could suppress type Ⅱ inflammation in ovalbumin (OVA)-induced mice, but its mechanisms have remained unclear.

METHODS

A binding activity of β-sitosterol with glucocorticoid receptor (GR) was analyzed by molecular docking. Human bronchial epithelial cells (BEAS-2B) and human bronchial smooth muscle cells (HBSMC) were treated with different concentrations (0, 1, 5, 10, 20, and 50 μg/mL) of β-sitosterol for suitable concentration selection. In transforming growth factor (TGF)-β1 treated BEAS-2B and HBSMC, cells were treated with 20 μg/mL β-sitosterol or dexamethasone (Dex) to analyze its possible mechanism. In OVA-induced mice, 2.5 mg/kg β-sitosterol or Dex administration was performed to analyze the therapeutic mechanism of β-sitosterol. A GR antagonist RU486 was used to confirm the mechanism of β-sitosterol in the treatment of asthma.

RESULTS

A good binding of β-sitosterol to GR (score = -8.2 kcal/mol) was found, and the GR expression was upregulated with β-sitosterol dose increase in BEAS-2B and HBSMC. Interleukin (IL)-25 and IL-33 secretion was significantly decreased by β-sitosterol in the TGF-β1-induced BEAS-2B, and the levels of collagen 1A and α-smooth muscle actin (SMA) were reduced in the TGF-β1-induced HBSMC. In the OVA-challenged mice, β-sitosterol treatment improved airway inflammation and remodeling through suppressing type Ⅱ immune response and collagen deposition. The therapeutic effects of β-sitosterol were similar to Dex treatment in vitro and in vivo. RU486 treatment clearly hampered the therapeutic effects of β-sitosterol in the TGF-β1-induced cells and OVA-induced mice.

CONCLUSION

This study identified that β-sitosterol binds GR to perform its functions in asthma treatment. β-sitosterol represent a potential therapeutic drug for allergic asthma.

Aerosol physicochemical determinants of carbon black and ozone inhalation co-exposure induced pulmonary toxicity

Air pollution accounts for more than 7 million premature deaths worldwide. Using ultrafine carbon black (CB) and ozone (O3) as a model for an environmental co-exposure scenario, the dose response relationships in acute pulmonary injury and inflammation were determined by generating, characterizing, and comparing stable concentrations of CB aerosols (2.5, 5.0, 10.0 mg/m3), O3 (0.5, 1.0, 2.0 ppm) with mixture CB + O3 (2.5 + 0.5, 5.0 + 1.0, 10.0 + 2.0). C57BL6 male mice were exposed for 3 h by whole body inhalation and acute toxicity determined after 24 h. CB itself did not cause any alteration, however, a dose response in pulmonary injury/inflammation was observed with O3 and CB + O3. This increase in response with mixtures was not dependent on the uptake but was due to enhanced reactivity of the particles. Benchmark dose modeling showed several-fold increase in potency with CB + O3 compared with CB or O3 alone. Principal component analysis provided insight into response relationships between various doses and treatments. There was a significant correlation in lung responses with charge-based size distribution, total/alveolar deposition, oxidant generation, and antioxidant depletion potential. Lung tissue gene/protein response demonstrated distinct patterns that are better predicted by either particle dose/aerosol responses (interleukin-1β, keratinocyte chemoattractant, transforming growth factor beta) or particle reactivity (thymic stromal lymphopoietin, interleukin-13, interleukin-6). Hierarchical clustering showed a distinct signature with high dose and a similarity in mRNA expression pattern of low and medium doses of CB + O3. In conclusion, we demonstrate that the biological outcomes from CB + O3 co-exposure are significantly greater than individual exposures over a range of aerosol concentrations and aerosol characteristics can predict biological outcome.

Kaempferol inhibits airway inflammation induced by allergic asthma through NOX4-Mediated autophagy

BACKGROUND

Kaempferol has important medicinal value in the treatment of asthma. However, its mechanism of action has not been fully understood and needs to be explored and studied.

METHODS

A binding activity of kaempferol with nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4) was analyzed by molecular docking. Human bronchial epithelial cells (BEAS-2B) were treated with different concentrations (0, 1, 5, 10, 20, 40 μg/mL) of kaempferol to select its suitable concentration. In the transforming growth factor (TGF)-β1-induced BEAS-2B, cells were treated with 20 μg/mL kaempferol or 20 μM GLX35132 (a NOX4 inhibitor) to analyze its effects on NOX4-mediated autophagy. In the ovalbumin (OVA)-induced mice, 20 mg/kg kaempferol or 3.8 mg/kg GLX351322 administration was performed to analyze the therapeutic effects of kaempferol on NOX4-mediated autophagy. An autophagy activator, rapamycin, was used to confirm the mechanism of kaempferol in treatment of allergic asthma.

RESULTS

A good binding of kaempferol to NOX4 (score = -9.2 kcal/mol) was found. In the TGF-β1-induced BEAS-2B, the NOX4 expression was decreased with kaempferol dose increase. The secretions of IL-25 and IL-33, and the NOX4-mediated autophagy were significantly decreased by kaempferol treatment in the TGF-β1-induced BEAS-2B. In the OVA-challenged mice, kaempferol treatment improved airway inflammation and remodeling through suppressing NOX4-mediated autophagy. The rapamycin treatment clearly hampered the therapeutic effects of kaempferol in the TGF-β1-induced cells and OVA-induced mice.

CONCLUSIONS

This study identifies kaempferol binds NOX4 to perform its functions in the treatment of allergic asthma, providing an effective therapeutic strategy in the further treatment of asthma.

Stem Cell Therapy and Innate Lymphoid Cells

Innate lymphoid cells have the capability to communicate with other immune cell types to coordinate the immune system functioning during homeostasis and inflammation. However, these cells behave differently at the functional level, unlike T cells, these cells do not need antigen receptors for activation because they are activated by the interaction of their receptor ligation. In hematopoietic stem cell transplantation (HSCT), T cells and NK cells have been extensively studied but very few studies are available on ILCs. In this review, an attempt has been made to provide current information related to NK and ILCs cell-based stem cell therapies and role of the stem cells in the regulation of ILCs as well. Also, the latest information on the differentiation of NK cells and ILCs from CD34+ hematopoietic stem cells is covered in the article.

Aspergillus fumigatus-Host Interactions Mediating Airway Wall Remodelling in Asthma

Asthma is a chronic heterogeneous respiratory condition that is mainly associated with sensitivity to airborne agents such as pollen, dust mite products and fungi. Key pathological features include increased airway inflammation and airway wall remodelling. In particular, goblet cell hyperplasia, combined with excess mucus secretion, impairs clearance of the inhaled foreign material. Furthermore, structural changes such as subepithelial fibrosis and increased smooth muscle hypertrophy collectively contribute to deteriorating airway function and possibility of exacerbations. Current pharmacological therapies focused on airway wall remodelling are limited, and as such, are an area of unmet clinical need. Sensitisation to the fungus, Aspergillus fumigatus, is associated with enhanced asthma severity, bronchiectasis, and hospitalisation. How Aspergillus fumigatus may drive airway structural changes is unclear, although recent evidence points to a central role of the airway epithelium. This review provides an overview of the airway pathology in patients with asthma and fungal sensitisation, summarises proposed airway epithelial cell-fungal interactions and discusses the initiation of a tissue remodelling response. Related findings from in vivo animal models are included given the limited analysis of airway pathology in patients. Lastly, an important role for Aspergillus fumigatus-derived proteases in triggering a cascade of damage-repair events through upregulation of airway epithelial-derived factors is proposed.

The Framework for Human Host Immune Responses to Four Types of Parasitic Infections and Relevant Key JAK/STAT Signaling

The human host immune responses to parasitic infections are complex. They can be categorized into four immunological pathways mounted against four types of parasitic infections. For intracellular protozoa, the eradicable host immunological pathway is TH1 immunity involving macrophages (M1), interferon gamma (IFNγ) CD4 T cells, innate lymphoid cells 1 (NKp44+ ILC1), CD8 T cells (Effector-Memory4, EM4), invariant natural killer T cells 1 (iNKT1) cells, and immunoglobulin G3 (IgG3) B cells. For intracellular protozoa, the tolerable host immunological pathway is TH1-like immunity involving macrophages (M2), interferon gamma (IFNγ)/TGFβ CD4 T cells, innate lymphoid cells 1 (NKp44- ILC1), CD8 T cells (EM3), invariant natural killer T 1 (iNKT1) cells, and immunoglobulin A1 (IgA1) B cells. For free-living extracellular protozoa, the eradicable host immunological pathway is TH22 immunity involving neutrophils (N1), interleukin-22 CD4 T cells, innate lymphoid cells 3 (NCR+ ILC3), iNKT17 cells, and IgG2 B cells. For free-living extracellular protozoa, the tolerable host immunological pathway is TH17 immunity involving neutrophils (N2), interleukin-17 CD4 T cells, innate lymphoid cells 3 (NCR- ILC3), iNKT17 cells, and IgA2 B cells. For endoparasites (helminths), the eradicable host immunological pathway is TH2a immunity with inflammatory eosinophils (iEOS), interleukin-5/interleukin-4 CD4 T cells, interleukin-25 induced inflammatory innate lymphoid cells 2 (iILC2), tryptase-positive mast cells (MCt), iNKT2 cells, and IgG4 B cells. For ectoparasites (parasitic insects and arachnids), the eradicable host immunological pathway is TH2b immunity with inflammatory basophils, chymase- and tryptase-positive mast cells (MCct), interleukin-3/interleukin-4 CD4 T cells, interleukin-33 induced nature innate lymphoid cells 2 (nILC2), iNKT2 cells, and immunoglobulin E (IgE) B cells. The tolerable host immunity against ectoparasites and endoparasites is TH9 immunity with regulatory eosinophils, regulatory basophils, interleukin-9 mast cells (MMC9), thymic stromal lymphopoietin induced innate lymphoid cells 2, interleukin-9 CD4 T cells, iNKT2 cells, and IgA2 B cells. In addition, specific transcription factors important for specific immune responses were listed. This JAK/STAT signaling is key to controlling or inducing different immunological pathways. In sum, Tfh is related to STAT5β, and BCL6 expression. Treg is related to STAT5α, STAT5β, and FOXP3. TH1 immunity is related to STAT1α, STAT4, and T-bet. TH2a immunity is related to STAT6, STAT1α, GATA1, and GATA3. TH2b immunity is related to STAT6, STAT3, GATA2, and GATA3. TH22 immunity is associated with both STAT3α and AHR. THαβ immunity is related to STAT1α, STAT1β, STAT2, STAT3β, and ISGF. TH1-like immunity is related to STAT1α, STAT4, STAT5α, and STAT5β. TH9 immunity is related to STAT6, STAT5α, STAT5β, and PU.1. TH17 immunity is related to STAT3α, STAT5α, STAT5β, and RORG. TH3 immunity is related to STAT1α, STAT1β, STAT2, STAT3β, STAT5α, STAT5β, and ISGF. This categorization provides a complete framework of immunological pathways against four types of parasitic infections. This framework as well as relevant JAK/STAT signaling can provide useful knowledge to control allergic hypersensitivities and parasitic infections via development of vaccines or drugs in the near future.

Anisakis pegreffii Extract Induces Airway Inflammation with Airway Remodeling in a Murine Model System

Exposure of the respiratory system to the Anisakis pegreffii L3 crude extract (AE) induces airway inflammation; however, the mechanism underlying this inflammatory response remains unknown. AE contains allergens that promote allergic inflammation; exposure to AE may potentially lead to asthma. In this study, we aimed to establish a murine model to assess the effects of AE on characteristic features of chronic asthma, including airway hypersensitivity (AHR), airway inflammation, and airway remodeling. Mice were sensitized for five consecutive days each week for 4 weeks. AHR, lung inflammation, and airway remodeling were evaluated 24 h after the last exposure. Lung inflammation and airway remodeling were assessed from the bronchoalveolar lavage fluid (BALF). To confirm the immune response in the lungs, changes in gene expression in the lung tissue were assessed with reverse transcription-quantitative PCR. The levels of IgE, IgG1, and IgG2a in blood and cytokine levels in the BALF, splenocyte, and lung lymph node (LLN) culture supernatant were measured with ELISA. An increase in AHR was prominently observed in AE-exposed mice. Epithelial proliferation and infiltration of inflammatory cells were observed in the BALF and lung tissue sections. Collagen deposition was detected in lung tissues. AE exposure increased IL-4, IL-5, and IL-13 expression in the lung, as well as the levels of antibodies specific to AE. IL-4, IL-5, and IL-13 were upregulated only in LLN. These findings indicate that an increase in IL-4+ CD4+ T cells in the LLN and splenocyte resulted in increased Th2 response to AE exposure. Exposure of the respiratory system to AE resulted in an increased allergen-induced Th2 inflammatory response and AHR through accumulation of inflammatory and IL-4+ CD4+ T cells and collagen deposition. It was confirmed that A. pegreffii plays an essential role in causing asthma in mouse models and has the potential to cause similar effects in humans.

The molecular and epigenetic mechanisms of innate lymphoid cell (ILC) memory and its relevance for asthma

Repetitive exposure of Rag1^−/− mice to the Alternaria allergen extract generated a form of memory that elicited an asthma-like response upon a subthreshold recall challenge 3–15 wk later. This memory was associated with lung ICOS⁺ST2⁺ ILC2s. Genetic, pharmacologic, and antibody-mediated inhibition and adoptive transfer established an essential role for ILC2s in memory-driven asthma. ATAC-seq demonstrated a distinct epigenetic landscape of memory ILC2s and identified Bach2 and AP1 (JunD and Fosl2) motifs as major drivers of altered gene accessibility. scRNA-seq, gene knockout, and signaling studies suggest that repetitive allergenic stress induces a gene repression program involving Nr4a2, Zeb1, Bach2, and JunD and a preparedness program involving Fhl2, FosB, Stat6, Srebf2, and MPP7 in memory ILC2s. A mutually regulated balance between these two programs establishes and maintains memory. The preparedness program (e.g., Fhl2) can be activated with a subthreshold cognate stimulation, which down-regulates repressors and activates effector pathways to elicit the memory-driven phenotype.

Novel Anti-Cytokine Strategies for Prevention and Treatment of Respiratory Allergic Diseases

Asthma is a heterogeneous inflammatory disease characterized by airflow obstruction, wheezing, eosinophilia and neutrophilia of the airways. Identification of distinct inflammatory patterns characterizing asthma endotypes led to the development of novel therapeutic approaches. Cytokine or cytokine receptor targeting by therapeutic antibodies, such as anti-IL-4 and anti-IL-5, is now approved for severe asthma treatment. However, the complexity of cytokine networks in asthma should not be underestimated. Inhibition of one pro-inflammatory cytokine may lead to perturbed expression of another pro-inflammatory cytokine. Without understanding of the underlying mechanisms and defining the molecular predictors it may be difficult to control cytokine release that accompanies certain disease manifestations. Accumulating evidence suggests that in some cases a combined pharmacological inhibition of pathogenic cytokines, such as simultaneous blockade of IL-4 and IL-13 signaling, or blockade of upstream cytokines, such as TSLP, are more effective than single cytokine targeting. IL-6 and TNF are the important inflammatory mediators in the pathogenesis of asthma. Preliminary data suggests that combined pharmacological inhibition of TNF and IL-6 during asthma may be more efficient as compared to individual neutralization of these cytokines. Here we summarize recent findings in the field of anti-cytokine therapy of asthma and discuss immunological mechanisms by which simultaneous targeting of multiple cytokines as opposed to targeting of a single cytokine may improve disease outcomes.

Roles of innate lymphoid cells (ILCs) in allergic diseases: The 10-year anniversary for ILC2s

In the 12 years since the discovery of innate lymphoid cells (ILCs), our knowledge of their immunobiology has expanded rapidly. Group 2 ILCs (ILC2s) respond rapidly to allergen exposure and environmental insults in mucosal organs, producing type 2 cytokines. Early studies showed that epithelium-derived cytokines activate ILC2s, resulting in eosinophilia, mucus hypersecretion, and remodeling of mucosal tissues. We now know that ILC2s are regulated by other cytokines, eicosanoids, and neuropeptides as well, and interact with both immune and stromal cells. Furthermore, ILC2s exhibit plasticity by adjusting their functions depending on their tissue environment and may consist of several heterogeneous subpopulations. Clinical studies show that ILC2s are involved in asthma, allergic rhinitis, chronic rhinosinusitis, food allergy, and eosinophilic esophagitis. However, much remains unknown about the immunologic mechanisms involved. Beneficial functions of ILCs in maintenance or restoration of tissue well-being and human health also need to be clarified. As our understanding of the crucial functions ILCs play in both homeostasis and disease pathology expands, we are poised to make tremendous strides in diagnostic and therapeutic options for patients with allergic diseases. This review summarizes discoveries in immunobiology of ILCs and their roles in allergic diseases in the past 5 years, discusses controversies and gaps in our knowledge, and suggests future research directions.

Anti-alarmin approaches entering clinical trials

PURPOSE OF REVIEW

The alarmins, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25 and IL-33, are upstream regulators of T2 (type 2) inflammation and found to be expressed at high levels in airway epithelium of patients with T2 asthma. This review will summarize how alarmins regulate the inflamed asthmatic airways through previously described and newly identified mechanisms.

RECENT FINDINGS

Alarmins drive allergic and nonallergic asthma through activation of innate lymphoid cell 2 (ILC2), which are a rich source of cytokines such as IL-5 and IL-13, with resulting effects on eosinophilopoeisis and remodelling, respectively. Findings from bronchial allergen challenges have illustrated widespread expression of alarmins and their receptors across many effector cells in airways, and recent studies have emphasized alarmin regulation of CD4 T lymphocytes, eosinophils and basophils, and their progenitors. Furthermore, a link between alarmins and lipid mediators is being uncovered.

SUMMARY

Alarmins can drive well defined inflammatory pathways through activation of dendritic cells and polarizing T cells to produce type 2 cytokines, as well as they can directly activate many other effector cells that play a central role in allergic and nonallergic asthma. Clinical trials support a central role for TSLP in driving airway inflammation and asthma exacerbations, while ongoing trials blocking IL-33 and IL-25 will help to define their respective role in asthma.

ILC2-derived IL-9 inhibits colorectal cancer progression by activating CD8+ T cells

Group 2 innate lymphoid cells (ILC2s), characterized by secretion of type 2 cytokines, regulate multiple immune responses. ILC2s are found in different tumor tissues, and ILC2-derived interleukin (IL)-4, IL-5, and IL-13 act on the cells in tumor microenvironment to participate in tumor progression. ILC2s are abundant in colorectal cancer (CRC) tissue, but the role of ILC2s in CRC remains unclear. In this study, we found that the percentage of ILC2s was higher in CRC tissue than in the adjacent normal tissue and that these ILC2s were the dominant IL-9-secreting cell-subsets in CRC tissue, as shown by flow cytometry analysis. ILC2s-derived IL-9 could activate CD8⁺ T cells to inhibit tumor growth, while anti-IL-9 reversed this effect. In vivo experiments showed that neutralizing ILC2s promoted tumor growth, while tumor inhibition occurred by intravenous injection of IL-9. In conclusion, our results demonstrated that ILC2-derived IL-9 could activate CD8⁺ T cells to promote anti-tumor effects in CRC.

Anti-ST2 Nanoparticle Alleviates Lung Inflammation by Targeting ILC2s-CD4+T Response

Background

Asthma has been regarded as an inflammatory disease, and group 2 innate lymphoid cells (ILC2s) are implicated in asthma pathogenesis. However, no strategy is available to block ILC2s function. Efficiency is also limited due to the use of systemic or subcutaneous routes of administration. The purpose of this study was to investigate the effects of nanoparticles targeting suppression of tumorigenicity 2 (ST2), which is the ILC2 receptor, to alleviate lung inflammation in the murine model of asthma.

Methods

The ultra-small SPIO nanoparticles were firstly synthesized, OVA-induced mice were administered by anti-ST2-conjugated nanoparticles. The inflammatory degree of the lung was investigated by H&E. The percentages of ILC2s and CD4⁺T cells in bronchoalveolar lavage fluid (BALF) and lung tissue were determined by FACS. Th2-cytokine and OVA-IgE levels were detected by real-time PCR and ELISA, respectively.

Results

Treatment with anti-ST2-conjugated nanoparticles significantly alleviated airway inflammation, IL-33 and IL-13 levels and the percentage of CD4⁺T cells. The percentage of ILC2s was increased, whereas the levels of IL-13 and IL-5 expressed by ILC2s were reduced.

Conclusion

In the present study, we demonstrated that anti-ST2-conjugated nanoparticles can efficiently control lung inflammation in OVA-induced mice by reducing the ability of ILC2s to produce IL-5 and IL-13, thereby reducing CD4+T cells. Our study also demonstrated that the nanoparticle delivery system could improve the performance of anti-ST2, which may be used as a strategic tool to expand the current drug market.

Advances and novel developments in mechanisms of allergic inflammation

In the past decade, research in the molecular and cellular underpinnings of basic and clinical immunology has significantly advanced our understanding of allergic disorders, allowing scientists and clinicians to diagnose and treat disorders such as asthma, allergic and nonallergic rhinitis, and food allergy. In this review, we discuss several significant recent developments in basic and clinical research as well as important future research directions in allergic inflammation. Certain key regulatory cytokines, genes and molecules have recently been shown to play key roles in allergic disorders. For example, interleukin-33 (IL-33) plays an important role in refractory disorders such as asthma, allergic rhinitis and food allergy, mainly by inducing T helper (Th) 2 immune responses and clinical trials with IL-33 inhibitors are underway in food allergy. We discuss interleukin 4 receptor pathways, which recently have been shown to play a critical role among the allergic inflammatory pathways that drive allergic disorders and pathogenesis. Further, the cytokine thymic stromal lymphopoietin (TSLP) has recently been shown as a factor in maintaining immune homeostasis and regulating type 2 inflammatory responses at mucosal barriers in allergic inflammation and targeting TSLP-mediated signalling is considered an attractive therapeutic strategy. In addition, new findings establish an important T cell-intrinsic role of mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) proteolytic activity in the suppression of autoimmune responses. We have seen how mutations in the filaggrin gene are a significant risk factor for allergic diseases such as atopic dermatitis, asthma, allergic rhinitis, food allergy, contact allergy, and hand eczema. We are only beginning to understand the mechanisms by which the human microbiota may be regulating the immune system, and how sudden changes in the composition of the microbiota may have profound effects, linked with an increased risk of developing chronic inflammatory disorders, including allergies. New research has shown the important but complex role monocytes play in disorders such as food allergies. Finally, we discuss some of the new directions of research in this area, particularly the important use of biologicals in oral immunotherapy, advances in gene therapy, multifood therapy, novel diagnostics in diagnosing allergic disorders and the central role that omics play in creating molecular signatures and biomarkers of allergic disorders such as food allergy. Such exciting new developments and advances have significantly moved forth our ability to understand the mechanisms underlying allergic diseases for improved patient care.

Crosstalk between the Producers and Immune Targets of IL-9

IL-9 has been reported to play dual roles in the pathogenesis of autoimmune disorders and cancers. The collaboration of IL-9 with microenvironmental factors including the broader cytokine milieu and other cellular components may provide important keys to explain its conflicting effects in chronic conditions. In this review, we summarize recent findings on the cellular sources of, and immunological responders to IL-9, in order to interpret the role of IL-9 in the regulation of immune responses. This knowledge will provide new perspectives to improve clinical benefits and limit adverse effects of IL-9 when treating pathologic conditions.

IL-33/ST2 signaling modulates Afghanistan particulate matter induced airway hyperresponsiveness in mice

Increased symptoms of asthma-like respiratory illnesses have been reported in soldiers returning from tours of duty in Afghanistan. Inhalation of desert particulate matter (PM) may contribute to this deployment-related lung disease (DRLD), but little is known about disease mechanisms. The IL-33 signaling pathway, including its receptor ST2, has been implicated in the pathogenesis of lung diseases including asthma, but its role in PM-mediated airway dysfunction has not been studied. The goal of this study was to investigate whether IL-33/ST2 signaling contributes to airway dysfunction in preclinical models of lung exposure to Afghanistan PM (APM). Wild-type (WT) and ST2 knockout (KO) mice on the BALB/C background were oropharyngeally instilled with a single dose of saline or 50 μg of APM in saline. Airway hyperresponsiveness (AHR) and inflammation were assessed after 24 h. In WT mice, a single APM exposure induced AHR and neutrophilic inflammation. Unlike the WT mice, ST2 KO mice that lack the receptor for IL-33 did not demonstrate AHR although airway neutrophilic inflammation was comparable to the WT mice. Oropharyngeal delivery of a soluble ST2 decoy receptor in APM-exposed WT mice significantly blocked AHR. Additional data in mouse tracheal epithelial cell and lung macrophage cultures demonstrated a role of APM-induced IL-33/ST2 signaling in suppression of regulator of G protein signaling 2 (RGS2), a gene known to protect against bronchoconstriction. We present for the first time that APM may increase AHR, one of the features of asthma, in part through the IL-33/ST2/RGS2 pathway.

Mimicking Antigen-Driven Asthma in Rodent Models-How Close Can We Get?

Asthma is a heterogeneous disease with increasing prevalence worldwide characterized by chronic airway inflammation, increased mucus secretion and bronchial hyperresponsiveness. The phenotypic heterogeneity among asthmatic patients is accompanied by different endotypes, mainly Type 2 or non-Type 2. To investigate the pathomechanism of this complex disease many animal models have been developed, each trying to mimic specific aspects of the human disease. Rodents have classically been employed in animal models of asthma. The present review provides an overview of currently used Type 2 vs. non-Type 2 rodent asthma models, both acute and chronic. It further assesses the methods used to simulate disease development and exacerbations as well as to quantify allergic airway inflammation, including lung physiologic, cellular and molecular immunologic responses. Furthermore, the employment of genetically modified animals, which provide an in-depth understanding of the role of a variety of molecules, signaling pathways and receptors implicated in the development of this disease as well as humanized models of allergic inflammation, which have been recently developed to overcome differences between the rodent and human immune systems, are discussed. Nevertheless, differences between mice and humans should be carefully considered and limits of extrapolation should be wisely taken into account when translating experimental results into clinical use.

The Innate Lymphoid System Is a Critical Player in the Manifestation of Mucoinflammatory Airway Disease in Mice

Innate lymphoid and adaptive immune cells are known to regulate epithelial responses, including mucous cell metaplasia (MCM), but their roles in mucoinflammatory airway diseases, such as cystic fibrosis, remain unknown. Scnn1b transgenic (Scnn1b-Tg⁺) mice, which recapitulate cystic fibrosis-like mucoinflammatory airway disease, deficient in innate lymphoid (Il2rg knockout mice [Il2rg ^KO]), adaptive immune (Rag1 knockout mice [Rag1 ^KO]), or both systems (Il2rg ^KO/Rag1 ^KO), were employed to investigate their respective contributions in the pathogenesis of mucoinflammatory airway disease. As previously reported, immunocompetent Tg⁺ juveniles exhibited spontaneous neonatal bacterial infections with robust mucoinflammatory features, including elevated expression of Th2-associated markers accompanied by MCM, elevated MUC5B expression, and airway mucus obstruction. The bacterial burden was increased in Il2rg ^KO/Tg⁺ juveniles but returned to significantly lower levels in Il2rg ^KO/Rag1 ^KO/Tg⁺ juveniles. Mechanistically, this improvement reflected reduced production of adaptive immunity-derived IL-10 and, in turn, increased activation of macrophages. Although all the mucoinflammatory features were comparable between the immunocompetent Tg⁺ and Rag1 ^KO/Tg⁺ juveniles, the Il2rg ^KO/Tg⁺ and Il2rg ^KO/Rag1 ^KO/Tg⁺ juveniles exhibited suppressed expression levels of Th2 markers, diminished MCM, suppressed MUC5B expression, and reduced mucus obstruction. Collectively, these data indicate that, in the context of airway mucus obstruction, the adaptive immune system suppresses antibacterial macrophage activation, whereas the innate lymphoid system contributes to MCM, mucin production, and mucus obstruction.

Epithelial-Mesenchymal Transition in Asthma Airway Remodeling Is Regulated by the IL-33/CD146 Axis

Epithelial-mesenchymal transition (EMT) is essential in asthma airway remodeling. IL-33 from epithelial cells is involved in pulmonary fibrosis. CD146 has been extensively explored in cancer-associated EMT. Whether IL-33 regulates CD146 in the EMT process associated with asthma airway remodeling is still largely unknown. We hypothesized that EMT in airway remodeling was regulated by the IL-33/CD146 axis. House dust mite (HDM) extract increased the expression of IL-33 and CD146 in epithelial cells. Increased expression of CD146 in HDM-treated epithelial cells could be blocked with an ST2-neutralizing antibody. Moreover, HDM-induced EMT was dependent on the CD146 and TGF-β/SMAD-3 signaling pathways. IL-33 deficiency decreased CD146 expression and alleviated asthma severity. Similarly, CD146 deficiency mitigated EMT and airway remodeling in a murine model of chronic allergic airway inflammation. Furthermore, CD146 expression was significantly elevated in asthma patients. We concluded that IL-33 from HDM extract-treated alveolar epithelial cells stimulated CD146 expression, promoting EMT in airway remodeling in chronic allergic inflammation.

The origins of allergy from a systems approach

OBJECTIVE

The origins of allergic diseases have traditionally been explained by immunoglobulin E-mediated immune responses to account for asthma, atopic dermatitis, atopic rhinitis, and food allergy. Research insights into disease origins support a broader array of factors that predispose, initiate, or exacerbate altered immunity in allergic diseases, such as (1) inherent epithelial barrier dysfunction; (2) loss of immune tolerance; (3) disturbances in the gut; and (4) organ-specific microbiomes, diet, and age. Here, we discuss these influences that together form a better understanding of allergy as a systems disease.

DATA SOURCES

We summarize recent advances in epithelial dysfunction, environmental influences, inflammation, infection, alterations in the specific microbiome, and inherent genetic predisposition.

STUDY SELECTIONS

We performed a literature search targeting primary and review articles.

RESULTS

We explored microbial-epithelial-immune interactions underlying the early-life origins of allergic disorders and evaluated immune mechanisms suggesting novel disease prevention or intervention strategies. Damage to epithelial surfaces lies at the origin of various manifestations of allergic disease. As a sensor of environmental stimuli, the epithelium of the lungs, gut, and skin is affected by an altered microbiome, air pollution, food allergens in a changed diet, and chemicals in modern detergents. This collectively leads to alterations of lung, skin, or gut epithelial surfaces, driving a type 2 immune response that underlies atopic diseases. Treatment and prevention of allergic diseases include biologics, oral desensitization, targeted gut microbiome alterations, and changes in behavior.

CONCLUSION

Understanding the spectrum of allergy as a systems disease will allow us to better define the mechanisms of allergic disorders and improve their treatment.

Summary of the Keystone Symposium "Origins of allergic disease: Microbial, epithelial and immune interactions," March 24-27, Tahoe City, California

The aims of the Keystone Symposium conference, "Origins of allergic disease: Microbial, epithelial and immune interactions" were to present and discuss potential microbial-epithelial-immune interactions underlying the early-life origins of allergic disorders, as well as immune mechanisms that might suggest novel disease prevention or intervention strategies. Cross-talk and sharing of ideas among participating experts in basic science and clinical aspects of allergic diseases provided substantial insight into the concept of allergic disorders as a systems disease. The overriding message distilled from the discussions was that damage to epithelial surfaces lies at the origin of the various manifestations of allergic disease. The epithelium of the lungs, gut, and skin, which operates as a critical sensor of environmental stimuli, is besieged by an onslaught of contemporary environmental forces including an altered microbiome, air pollution, food allergens in a changed diet, and chemicals in modern detergents. Collectively, this onslaught leads to alterations of lung, skin, or gut epithelial surfaces, driving a type 2 immune response that underlies most, if not all, of the atopic diseases. Possible remedies for treatment and prevention of allergic diseases were discussed, including a precision medicine approach using biologics, oral desensitization, targeted gut microbiome alterations, and behavior alteration.

IL-9 and IL-9-producing cells in tumor immunity

Abstract

Interleukin (IL)-9 belongs to the IL-2Rγc chain family and is a multifunctional cytokine that can regulate the function of many kinds of cells. It was originally identified as a growth factor of T cells and mast cells. In previous studies, IL-9 was mainly involved in the development of allergic diseases, autoimmune diseases and parasite infections. Recently, IL-9, as a double-edged sword in the development of cancers, has attracted extensive attention. Since T-helper 9 (Th9) cell-derived IL-9 was verified to play a powerful antitumor role in solid tumors, an increasing number of researchers have started to pay attention to the role of IL-9-skewed CD8⁺ T (Tc9) cells, mast cells and Vδ2 T cell-derived IL-9 in tumor immunity. Here, we review recent studies on IL-9 and several kinds of IL-9-producing cells in tumor immunity to provide useful insight into tumorigenesis and treatment.

Ablation of IL-33 Suppresses Th2 Responses but Is Accompanied by Sustained Mucus Obstruction in the Scnn1b Transgenic Mouse Model

Cystic fibrosis is characterized by dehydration of the airway surface liquid layer with persistent mucus obstruction. Th2 immune responses are often manifested as increased mucous cell density (mucous cell metaplasia) associated with mucus obstruction. IL-33 is a known inducer of Th2 immune responses, but its roles in mucus obstruction and related phenotypes in a cystic fibrosis-like lung disease model (i.e., Scnn1b-Tg-positive [Tg+]) mouse, remain unclear. Accordingly, IL-33 knockout (IL-33KO) Tg+ mice were examined and compared with IL-33 heterozygous (IL-33HET) Tg+ mice. As compared with IL-33HET/Tg+ mice, IL-33KO/Tg+ mice had complete absence of bronchoalveolar lavage fluid eosinophilia, accompanied with significant reduction in bronchoalveolar lavage fluid concentration of IL-5, a cytokine associated with eosinophil differentiation and recruitment, and IL-4, a major Th2 cytokine. As compared with IL-33HET/Tg+ mice, IL-33KO/Tg+ mice had significantly reduced levels of Th2-associated gene signatures (Slc26a4, Clca1, Retnla, and Chi3l4), along with complete loss of intracellular mucopolysaccharide staining in the airway epithelium. As compared with IL-33HET/Tg+ mice, although the IL-33KO/Tg+ mice had significantly reduced levels of MUC5AC protein expression, they showed no reduction in the degree of mucus obstruction, MUC5B protein expression, bacterial burden, and neonatal mortality. Interestingly, the histological features, including subepithelial airway inflammation and alveolar space enlargement, were somewhat exaggerated in IL-33KO/Tg+ mice compared with IL-33HET/Tg+ mice. Taken together, our data indicate that although IL-33 modulates Th2 inflammatory responses and MUC5AC protein production, mucus obstruction is not dependent on IL-33.

Bcl6 and Blimp1 reciprocally regulate ST2+ Treg-cell development in the context of allergic airway inflammation

BACKGROUND

Bcl6 is required for the development of T follicular helper cells and T follicular regulatory (Tfr) cells that regulate germinal center responses. Bcl6 also affects the function of regulatory T (Treg) cells.

OBJECTIVE

The goal of this study was to define the functions of Bcl6 in Treg cells, including Tfr cells, in the context of allergic airway inflammation.

METHODS

We used a model of house dust mite sensitization to challenge wild-type, Bcl6^fl/fl Foxp3-Cre, and Prdm1 (Blimp1)^fl/fl Foxp3-Cre mice to study the reciprocal roles of Bcl6 and Blimp1 in allergic airway inflammation.

RESULTS

In the house dust mite model, Tfr cells repress the production of IgE and Bcl6⁺ Treg cells suppress the generation of type 2 cytokine-producing cells in the lungs. In mice with Bcl6-deficient Treg cells, twice as many ST2⁺ (IL-33R⁺) Treg cells develop as are observed in wild-type mice. ST2⁺ Treg cells in the context of allergic airway inflammation are Blimp1 dependent, express type 2 cytokines, and share features of visceral adipose tissue Treg cells. Bcl6-deficient Treg cells are more susceptible, and Blimp1-deficient Treg cells are resistant, to acquiring the ST2⁺ Treg-cell phenotype in vitro and in vivo in response to IL-33. Bcl6-deficient ST2⁺ Treg cells, but not Bcl6-deficient ST2⁺ conventional T cells, strongly promote allergic airway inflammation when transferred into recipient mice. Lastly, ST2 is required for the exacerbated allergic airway inflammation in Bcl6^fl/fl Foxp3-Cre mice.

CONCLUSIONS

During allergic airway inflammation, Bcl6 and Blimp1 play dual roles in regulating Tfr-cell activity in the germinal center and in the development of ST2⁺ Treg cells that promote type 2 cytokine responses.

HMGB1-induced ILC2s activate dendritic cells by producing IL-9 in asthmatic mouse model

Asthma is a disease of the respiratory system that is commonly considered a T-helper 2 (Th2) cell-associated inflammatory disease. Group 2 innate lymphoid cells (ILC2s) promote the inflammatory responses in asthma by secreting type 2 cytokines. Interleukin (IL)-9 also serves as a promoting factor in asthma and it is well known that ILC2s have an autocrine effect of IL-9 to sustain their survival and proliferation. However, the specific role of ILC2-derived IL-9 in asthma remains unclear. HMGB1 (High-Mobility Group Box-1) is a nuclear protein, and Previous studies have shown that HMGB1 can regulate the differentiation of T-helper cells and participate in the development of asthma. But whether HMGB1 can regulate the innate lymphocytes in the pathological process of asthma is unknown. In this study we have shown increased presence of HMGB1 protein in the lung of mice with asthma, which was associated with increased secretion of IL-9 by ILC2s. This led to the activation of dendritic cells (DCs) that can accelerate the differentiation of Th2 cells and worsen the severity of asthma. Taken together, our study provides a complementary understanding of the asthma development and highlights a novel inflammatory pathway in the pathogenesis of asthma.

Optimal identification of human conventional and nonconventional (CRTH2-IL7Rα-) ILC2s using additional surface markers

BACKGROUND

Human type 2 innate lymphoid cells (ILC2s) are identified by coupled detection of CRTH2 and IL7Rα on lineage negative (Lin^-) cells. Type 2 cytokine production by CRTH2^-IL7Rα^- innate lymphoid cells (ILCs) is unknown.

OBJECTIVE

We sought to identify CRTH2^-IL7Rα^- type 2 cytokine-producing ILCs and their disease relevance.

METHODS

We studied human blood and lung ILCs from asthmatic and control subjects by flow cytometry, ELISA, RNA sequencing, quantitative PCR, adoptive transfer to mice, and measurement of airway hyperreactivity by Flexivent.

RESULTS

We found that IL-5 and IL-13 were expressed not only by CRTH2⁺ but also by CRTH2^-IL7Rα⁺ and CRTH2^-IL7Rα^- (double-negative [DN]) human blood and lung cells. All 3 ILC populations expressed type 2 genes and induced airway hyperreactivity when adoptively transferred to mice. The frequency of type 2 cytokine-positive IL7Rα and DN ILCs were similar to that of CRTH2 ILCs in the blood and lung. Their frequency was higher in asthmatic patients than in disease controls. Transcriptomic analysis of CRTH2, IL7Rα, and DN ILCs confirmed the expression of mRNA for type 2 transcription factors in all 3 populations. Unexpectedly, the mRNA for GATA3 and IL-5 correlated better with mRNA for CD30, TNFR2, ICOS, CCR4, and CD200R1 than for CRTH2. By using a combination of these surface markers, especially CD30/TNFR2, we identified a previously unrecognized ILC2 population.

CONCLUSIONS

The commonly used surface markers for human ILC2s leave a majority of type 2 cytokine-producing ILC2s unaccounted for. We identified top GATA3-correlated cell surface-expressed genes in human ILCs by RNA sequencing. These new surface markers, such as CD30 and TNFR2, identified a previously unrecognized human ILC2 population. This ILC2 population is likely to contribute to asthma.

IL-33 in Chronic Respiratory Disease: From Preclinical to Clinical Studies

IL-33 has been deorphanized as a member of the IL-1 family and has key roles as an alarmin and cytokine with potent capacity to drive type 2 inflammation. This has led to a plethora of studies surrounding its role in chronic diseases with a type 2 inflammatory component. Here, we review the roles of IL-33 in two chronic respiratory diseases, asthma and chronic obstructive pulmonary disease (COPD). We discuss the hallmark and paradigm-shifting studies that have contributed to our understanding of IL-33 biology. We cover animal studies that have elucidated the mechanisms of IL-33 and assessed the role of anti-IL-33 treatment and immunization against IL-33. We highlight key clinical evidence for the potential of targeting increased IL-33 in respiratory diseases including exacerbations, and we outline current clinical trials using an anti-IL-33 monoclonal antibody in asthma patients. Finally, we discuss some of the challenges that have arisen in IL-33 biology and highlight potential future directions in targeting this cytokine in chronic respiratory diseases.

The Intriguing Role of Interleukin 13 in the Pathophysiology of Asthma

Approximately 5–10% of asthmatic patients worldwide suffer from severe asthma. Experimental and clinical studies have demonstrated that IL-13 is an important cytokine in chronic airways inflammation. IL-13 is involved in Th2 inflammation and has been identified as a possible therapeutic target in the treatment of asthma. Two different human monoclonal antibodies (mAbs) anti-IL-13 (tralokinumab and lebrikizumab) block binding and signaling of IL-13 to its receptors, IL-13Rα1 and IL-13Rα2. Several randomized, double-blind, placebo-controlled multicenter studies have evaluated the safety and efficacy of tralokinumab and lebrikizumab in the treatment of adult patients with severe asthma, but all have failed to meet their primary endpoints. No serious adverse events related to the treatment with these anti-IL-13 mAbs have been reported in these studies. These negative clinical results contrast with positive findings from blocking IL-13 signaling in experimental models of asthma, raising doubts about the transferrable value of some models. Interestingly, dupilumab, a mAb which blocks both IL-4 and IL-13 signaling reduces exacerbation rates and improves lung function in severe asthmatics. These results suggest that IL-4 and IL-13 share some, but not all functional activities in airway inflammation. Tralokinumab might show efficacy in a highly selected cohort of asthmatics characterized by overexpression of IL-13.

The Cytokines of Asthma

Asthma is a chronic inflammatory airway disease associated with type 2 cytokines interleukin-4 (IL-4), IL-5, and IL-13, which promote airway eosinophilia, mucus overproduction, bronchial hyperresponsiveness (BHR), and immunogloubulin E (IgE) synthesis. However, only half of asthma patients exhibit signs of an exacerbated Type 2 response. "Type 2-low" asthma has different immune features: airway neutrophilia, obesity-related systemic inflammation, or in some cases, few signs of immune activation. Here, we review the cytokine networks driving asthma, placing these in cellular context and incorporating insights from cytokine-targeting therapies in the clinic. We discuss established and emerging paradigms in the context of the growing appreciation of disease heterogeneity and argue that the development of new and improved therapeutics will require understanding the diverse mechanisms underlying the spectrum of asthma pathologies.

The Interplay between Host Immunity and Respiratory Viral Infection in Asthma Exacerbation

Asthma is one of the most common and chronic diseases characterized by multidimensional immune responses along with poor prognosis and severity. The heterogeneous nature of asthma may be attributed to a complex interplay between risk factors (either intrinsic or extrinsic) and specific pathogens such as respiratory viruses, and even bacteria. The intrinsic risk factors are highly correlated with asthma exacerbation in host, which may be mediated via genetic polymorphisms, enhanced airway epithelial lysis, apoptosis, and exaggerated viral replication in infected cells, resulting in reduced innate immune response and concomitant reduction of interferon (types I, II, and III) synthesis. The canonical features of allergic asthma include strong Th2-related inflammation, sensitivity to non-steroidal anti-inflammatory drugs (NSAIDs), eosinophilia, enhanced levels of Th2 cytokines, goblet cell hyperplasia, airway hyper-responsiveness, and airway remodeling. However, the NSAID-resistant non-Th2 asthma shows a characteristic neutrophilic influx, Th1/Th17 or even mixed (Th17-Th2) immune response and concurrent cytokine streams. Moreover, inhaled corticosteroid-resistant asthma may be associated with multifactorial innate and adaptive responses. In this review, we will discuss the findings of various in vivo and ex vivo models to establish the critical heterogenic asthmatic etiologies, host-pathogen relationships, humoral and cell-mediated immune responses, and subsequent mechanisms underlying asthma exacerbation triggered by respiratory viral infections.

Advances in asthma, asthma-COPD overlap, and related biologics in 2018

Over the past year, numerous important advances in our understanding of multiple aspects of asthma, ranging from disease pathogenesis to epidemiology to therapeutics, have been reported. This review is a compilation of highlights from articles published largely in the Journal of Allergy and Clinical Immunology and supplemented by articles published elsewhere that have substantially advanced the fields of asthma, chronic obstructive pulmonary disease (COPD), and asthma-COPD overlap and biologic therapies for these disorders. The intention of this article is not to provide a comprehensive review but rather to focus on several areas that have developed quickly and/or received extensive attention from our readers.

Interleukin 1 Receptor-Like 1 (IL1RL1) Promotes Airway Bacterial and Viral Infection and Inflammation

Interleukin 1 receptor-like 1 (IL1RL1), also known as suppression of tumorigenicity 2 (ST2), is the receptor for interleukin 33 (IL-33) and has been increasingly studied in type 2 inflammation. An increase in airway IL-33/ST2 signaling in asthma has been associated with eosinophilic inflammation, but little is known about the role of ST2 in neutrophilic inflammation. Airway Mycoplasma pneumoniae and human rhinovirus (HRV) infections are linked to neutrophilic inflammation during acute exacerbations of asthma. However, whether ST2 contributes to M. pneumoniae- and HRV-mediated airway inflammation is poorly understood. The current study sought to determine the functions of ST2 during airway M. pneumoniae or HRV infection. In cultured normal human primary airway epithelial cells, ST2 overexpression (OE) increased the production of neutrophilic chemoattractant IL-8 in the absence or presence of M. pneumoniae or HRV1B infection. ST2 OE also enhanced HRV1B-induced IP-10, a chemokine involved in asthma exacerbations. In the M. pneumoniae-infected mouse model, ST2 deficiency, in contrast to sufficiency, significantly reduced the levels of neutrophils following acute (≤24 h) infection, while in the HRV1B-infected mouse model, ST2 deficiency significantly reduced the levels of proinflammatory cytokines KC, IP-10, and IL-33 in bronchoalveolar lavage (BAL) fluid. Overall, ST2 overexpression in human epithelial cells and ST2 sufficiency in mice increased the M. pneumoniae and HRV loads in cell supernatants and BAL fluid. After pathogen infection, ST2-deficient mice showed a higher level of the host defense protein lactotransferrin in BAL fluid. Our data suggest that ST2 promotes proinflammatory responses (e.g., neutrophils) to airway bacterial and viral infection and that blocking ST2 signaling may broadly attenuate airway infection and inflammation.

Epithelial cell-derived cytokines: more than just signaling the alarm

The epithelial cell-derived cytokines thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 are central regulators of type 2 immunity, which drives a broad array of allergic responses. Often characterized as "alarmins" that are released by the barrier epithelium in response to external insults, these epithelial cell-derived cytokines were initially thought to act only early in allergic inflammation. Indeed, TSLP can condition dendritic cells to initiate type 2 responses, and IL-33 may influence susceptibility to asthma through its role in establishing the immune environment in the perinatal lungs. However, TSLP, IL-33, and IL-25 all regulate a broad spectrum of innate immune cell populations and are particularly potent in eliciting and activating type 2 innate lymphoid cells (ILC2s) that may act throughout allergic inflammation. Recent data suggest that a TSLP/ILC axis may mediate steroid resistance in asthma. Recent identification of memory Th2 cell subsets that are characterized by high receptor expression for TSLP, IL-33, and IL-25 further supports a role for these cytokines in allergic exacerbations. There is therefore growing interest in developing biologics that target TSLP, IL-33, and IL-25. This Review provides an overview of TSLP, IL-33, and IL-25 and the development of blocking antibodies that target these epithelial cell-derived cytokines.

Pleiotropic Effects of IL-33 on CD4+ T Cell Differentiation and Effector Functions

IL-33, a member of the IL-1 family of cytokines, was originally described in 2005 as a promoter of type 2 immune responses. However, recent evidence reveals a more complex picture. This cytokine is released locally as an alarmin upon cellular damage where innate cell types respond to IL-33 by modulating their differentiation and influencing the polarizing signals they provide to T cells at the time of antigen presentation. Moreover, the prominent expression of the IL-33 receptor, ST2, on GATA3⁺ T helper 2 cells (T_H2) demonstrated that IL-33 could have a direct impact on T cells. Recent observations reveal that T-bet⁺ T_H1 cells and Foxp3⁺ regulatory T (T_REG) cells can also express the ST2 receptor, either transiently or permanently. As such, IL-33 can have a direct effect on the dynamics of T cell populations. As IL-33 release was shown to play both an inflammatory and a suppressive role, understanding the complex effect of this cytokine on T cell homeostasis is paramount. In this review, we will focus on the factors that modulate ST2 expression on T cells, the effect of IL-33 on helper T cell responses and the role of IL-33 on T_REG cell function.

Sex-associated TSLP-induced immune alterations following early-life RSV infection leads to enhanced allergic disease

Many studies have linked severe RSV infection during early-life with an enhanced likelihood of developing childhood asthma, showing a greater susceptibility in boys. Our studies show that early-life RSV infection leads to differential long-term effects based upon the sex of the neonate; leaving male mice prone to exacerbation upon secondary allergen exposure while overall protecting female mice. During initial viral infection, we observed better viral control in the female mice with correlative expression of interferon-β that was not observed in male mice. Additionally, we observed persistent immune alterations in male mice at 4 weeks post infection. These alterations include Th2 and Th17-skewing, innate cytokine expression (Tslp and Il33), and infiltration of innate immune cells (DC and ILC2). Upon exposure to allergen, beginning at 4 weeks following early-life RSV-infection, male mice show severe allergic exacerbation while female mice appear to be protected. Due to persistent expression of TSLP following early-life RSV infection in male mice, genetically modified TSLPR-/- mice were evaluated and demonstrated an abrogation of allergen exacerbation in male mice. These data indicate that TSLP is involved in the altered immune environment following neonatal RSV-infection that leads to more severe responses in males during allergy exposure, later in life. Thus, TSLP may be a clinically relevant therapeutic target early in life.

Bronchial Allergen Challenge of Patients with Atopic Asthma Triggers an Alarmin (IL-33, TSLP, and IL-25) Response in the Airways Epithelium and Submucosa

The alarmin cytokines IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) play a critical role in asthma pathogenesis by inducing mucosal Th2-type cytokine production. Although environmental exposure to aeroallergens has been proposed as an alarmin trigger in asthma, there has been no systematic parallel study of the effects of allergen exposure on the expression of these cytokines in the airways of human asthmatics. Using single and sequential double immunohistochemistry, we evaluated the numbers and phenotypes of IL-25-, IL-33-, and TSLP-immunoreactive cells in sections of bronchial biopsies from mild atopic asthmatics (n = 16) before and 24 h after allergen inhalational challenge. Allergen challenge highly increased expression of baseline immunoreactivity for IL-25, IL-33, and TSLP, both in the bronchial epithelium and submucosa (p < 0.001), to a degree that correlated with the extent of the late phase of airway obstruction. Aside from epithelial cells, the principal source of immunoreactivity for all three alarmins, TSLP, and IL-33 immunoreactivity colocalized principally with endothelial cells and mast cells, neutrophils, and fibroblasts, whereas IL-25 immunoreactivity colocalized principally with eosinophils as well as endothelial cells, mast cells, and fibroblasts. The data implicate that allergen challenge directly increases airway alarmin expression in atopic asthmatics to a degree correlating with increase late-phase airway obstruction, affirming these molecules as potential molecular targets for the inhibition of allergen-induced airway inflammation and obstruction.

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.