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

Real-World Effectiveness of Anti-IL-5/5R Therapy in Severe Atopic Eosinophilic Asthma with Fungal Sensitization

BACKGROUND

Severe asthma with fungal sensitization (SAFS) is a complex clinical phenotype associated with poorly controlled type 2 inflammation and significant morbidity from both the disease itself and a high steroid burden.

OBJECTIVE

To assess the effectiveness of biologic therapies targeting eosinophilic inflammation in SAFS.

METHODS

We assessed the effectiveness of treatment with mepolizumab or benralizumab in patients with SAFS, and compared outcomes with patients with severe atopic asthma without fungal sensitization and patients with severe nonatopic asthma. Baseline clinical characteristics and clinical outcomes at 48 weeks were evaluated. A subgroup analysis was performed of patients who met the criteria for allergic bronchopulmonary aspergillosis (ABPA) rather than SAFS.

RESULTS

A total of 193 patients treated with mepolizumab (n = 63) or benralizumab (n = 130) were included. Patients with SAFS had higher baseline IgE level compared with patients with severe atopic asthma without fungal sensitization and severe nonatopic asthma (733 ± 837 IU/mL vs 338 ± 494 and 142 ± 171, respectively; both P < .001). There were no other significant baseline differences in clinical characteristics between groups. At 48 weeks, there were significant improvements in 6-item asthma control questionnaire score and exacerbation frequency, and reduction in maintenance oral corticosteroid dose across all groups (all P < .05). No significant between-group differences in outcomes were observed at 48 weeks. Patients with ABPA (n = 9) had a significant reduction in exacerbation frequency (P = .013) with treatment.

CONCLUSIONS

Treatment with eosinophil-targeting biologics led to improvements in exacerbation frequency, oral corticosteroid requirements, and patient-reported outcomes in patients with SAFS, with a reduction in exacerbations in the subgroup of patients with ABPA. These data highlight the potential clinical utility of targeting eosinophilic inflammation in SAFS and ABPA.

Recent advances in our understanding of the allograft response

Organ transplantation is a life-saving treatment for end-stage organ failure. However, despite advances in immunosuppression, donor matching, tissue typing, and organ preservation, many organs are still lost each year to rejection. Ultimately, tolerance in the absence of immunosuppression is the goal, and although this seldom occurs spontaneously, a deeper understanding of alloimmunity may provide avenues for future therapies which aid in its establishment. Here, we highlight the recent key advances in our understanding of the allograft response. On the innate side, recent work has highlighted the previously unrecognised role of innate lymphoid cells as well as natural killer cells in promoting the alloresponse. The two major routes of allorecognition have recently been joined by a third newly identified pathway, semi-direct allorecognition, which is proving to be a key active pathway in transplantation. Through this review, we detail these newly defined areas in the allograft response and highlight areas for potential future therapeutic intervention.

Epithelial IL-33 appropriates exosome trafficking for secretion in chronic airway disease

IL-33 is a key mediator of chronic airway disease driven by type 2 immune pathways, yet the nonclassical secretory mechanism for this cytokine remains undefined. We performed a comprehensive analysis in human airway epithelial cells, which revealed that tonic IL-33 secretion is dependent on the ceramide biosynthetic enzyme neutral sphingomyelinase 2 (nSMase2). IL-33 is cosecreted with exosomes by the nSMase2-regulated multivesicular endosome (MVE) pathway as surface-bound cargo. In support of these findings, human chronic obstructive pulmonary disease (COPD) specimens exhibited increased epithelial expression of the abundantly secreted IL33^Δ34 isoform and augmented nSMase2 expression compared with non-COPD specimens. Using an Alternaria-induced airway disease model, we found that the nSMase2 inhibitor GW4869 abrogated both IL-33 and exosome secretion as well as downstream inflammatory pathways. This work elucidates a potentially novel aspect of IL-33 biology that may be targeted for therapeutic benefit in chronic airway diseases driven by type 2 inflammation.

Cyclic-di-GMP Induces STING-Dependent ILC2 to ILC1 Shift During Innate Type 2 Lung Inflammation

Type 2 inflammation is found in most forms of asthma, which may co-exist with recurrent viral infections, bacterial colonization, and host cell death. These processes drive the accumulation of intracellular cyclic-di-nucleotides such as cyclic-di-GMP (CDG). Group 2 innate lymphoid cells (ILC2s) are critical drivers of type 2 lung inflammation during fungal allergen exposure in mice; however, it is unclear how CDG regulates lung ILC responses during lung inflammation. Here, we show that intranasal CDG induced early airway type 1 interferon (IFN) production and dramatically suppressed CD127+ST2+ ILC2s and type 2 lung inflammation during Alternaria and IL-33 exposure. Further, CD127-ST2-Thy1.2+ lung ILCs, which showed a transcriptomic signature consistent with ILC1s, were expanded and activated by CDG combined with either Alternaria or IL-33. CDG-mediated suppression of type 2 inflammation occurred independent of IL-18R, IL-12, and STAT6 but required the stimulator of interferon genes (STING) and type 1 IFN signaling. Thus, CDG potently suppresses ILC2-driven lung inflammation and promotes ILC1 responses. These results suggest potential therapeutic modulation of STING to suppress type 2 inflammation and/or increase anti-viral responses during respiratory infections.

Group 2 ILC Functional Assays in Allergic Airway Inflammation

ILC2s are a rare innate cell population capable of rapidly producing type 2 cytokines prior to the recruitment and expansion of adaptive type 2 T helper cells. As a result, they are implicated in the pathogenesis of many type-2 immune-mediated diseases, including allergic airway inflammation. Here we describe methods for interrogating and analyzing ILC2 biology in the context of allergic airway inflammation, such as flow cytometric analysis of mouse and human ILC2s as well as live imaging of pulmonary ILC2s.

Modern View of Neutrophilic Asthma Molecular Mechanisms and Therapy

For a long time asthma was commonly considered as a homogeneous disease. However, recent studies provide increasing evidence of its heterogeneity and existence of different phenotypes of the disease. Currently, classification of asthma into several phenotypes is based on clinical and physiological features, anamnesis, and response to therapy. This review describes five most frequently identified asthma phenotypes. Neutrophilic asthma (NA) deserves special attention, since neutrophilic inflammation of the lungs is closely associated with severity of the disease and with the resistance to conventional corticosteroid therapy. This review focuses on molecular mechanisms of neutrophilic asthma pathogenesis and on the role of Th1- and Th17-cells in the development of this type of asthma. In addition, this review presents current knowledge of neutrophil biology. It has been established that human neutrophils are represented by at least three subpopulations with different biological functions. Therefore, total elimination of neutrophils from the lungs can result in negative consequences. Based on the new knowledge of NA pathogenesis and biology of neutrophils, the review summarizes current approaches for treatment of neutrophilic asthma and suggests new promising ways to treat this type of asthma that could be developed in future.

Exploring the origin and regulatory role of mast cells in asthma

PURPOSE OF REVIEW

Mast cells have previously been thought to function solely as effector cells in asthma but more recent studies have indicated that mast cells may play a more central role in propagating and regulating lower airway inflammation in asthma.

RECENT FINDINGS

Initial studies have found increased numbers of mast cell progenitors (MCPs) in the peripheral blood of patients with asthma and these cells could contribute to the increased number of progenitors identified in the airways of patients with asthma. There are unique subpopulations of mast cells within the asthmatic airway, which are characterized by their physical location and distinguished by their expression profile of mast cell proteases. Intraepithelial mast cells are tightly associated with type-2 (T2) inflammation but additional studies have suggested a role for anti-mast cell therapies as a treatment for T2-low asthma. Mast cells have recently been shown to closely communicate with the airway epithelium and airway smooth muscle to regulate lower airway inflammation and airway hyperresponsiveness.

SUMMARY

Recent studies have better illuminated the central role of mast cells in regulating lower airway inflammation and airway hyperresponsiveness.

The role of peripheral type 2 innate lymphoid cells in bronchiolitis

Our aim was to detect type 2 innate lymphoid cells (ILC2s)-related cytokines of infants with bronchiolitis by using Elisa, Liquidchip technology and RT-PCR and investigated its correlation with bronchiolitis. We recruited 26 infants with bronchiolitis and 20 healthy infants as control from Xiangya Hospital. Compared to the control group, the serum levels of interleukin-5 (IL-5) [41.99 (21.11) vs 25.70 (19.64)], IL-9 [27.04 (37.51) vs 8.30 (0.54)], IL-13 [184.05 (132.81) vs 121.75 (176.13)], IL-33 [83.70 (46.69) vs 11.23 (55.31)] and thymic stromal lymphopoietin (TSLP) [31.42 (5.41) vs 28.76 (2.56)] were significantly increased in infants with bronchiolitis (P < 0.05), while the level of IgE had no significant difference between the two groups [19.05 (14.15) vs 14.85 (20.2), P > 0.05]. The mRNA expression of IL-17RB (9.83 ± 0.35 vs 9.19 ± 0.58), TSLP (16.98 ± 2.12 vs 15.07 ± 2.25), retinoid acid receptor related orphan receptor α (7.18 ± 0.71 vs 5.46 ± 1.09) and trans-acting T-cell-specific transcription factor 3 (4.86 ± 0.66 vs 4.19 ± 0.90) were significantly increased in infants with bronchiolitis versus the control group (P < 0.05), while there was no statistical significance for suppression of tumorigenicity 2 (5.59 ± 0.68 vs 5.41 ± 0.87, P > 0.05). Our findings suggested that ILC2s possibly play a specific role in immunopathology of bronchiolitis.

The impact of fungal allergic sensitization on asthma

PURPOSE OF REVIEW

Fungal sensitization may contribute to the development of asthma as well as asthma severity. The purpose of this review is to summarize existing knowledge about the pathophysiology, diagnosis, and management of fungal sensitization in asthma and highlight unmet needs and target areas for future investigation.

RECENT FINDINGS

Fungal sensitization may occur by a normal or aberrant immune response. Allergic sensitization to fungi is mediated by the adaptive immune response driven by TH2 cells and the innate immune response driven by the innate lymphoid cells group 2. Diagnosis of fungal sensitization can be made by either skin prick testing or measurement of fungal-specific serum IgE. Fungal sensitization in asthma has been associated with worse disease severity, including reduced lung function, increased risk of hospitalizations, and life-threatening asthma. A spectrum of disease related to fungal sensitization has been described in asthma including allergic bronchopulmonary mycosis and severe asthma with fungal sensitization (SAFS). The role of antifungals and targeted biologic therapy in asthma with fungal sensitization need further investigation.

SUMMARY

There is increasing awareness of the contribution of fungal sensitization to asthma severity. However, there are no therapies with proven efficacy. Randomized clinical trials are needed to further investigate the role of biologics.

Mast cell-derived IL-13 downregulates IL-12 production by skin dendritic cells to inhibit the TH1 cell response to cutaneous antigen exposure

BACKGROUND

Atopic dermatitis (AD) is characterized by a skin barrier defect aggravated by mechanical injury inflicted by scratching, a T_H2 cell-dominated immune response, and susceptibility to viral skin infections that are normally restrained by a T_H1 cell response. The signals leading to a T_H2 cell-dominated immune response in AD are not completely understood.

OBJECTIVE

Our aim was to determine the role of IL-13 in initiation of the T_H cell response to cutaneously encountered antigens.

METHODS

Wild-type, Il13^-/-, Il1rl1^-/-, and Il4ra^-/- mice, as well as mice with selective deficiency of IL-13 in mast cells (MCs) were studied; in addition, dendritic cells (DCs) purified from the draining lymph nodes of tape-stripped and ovalbumin (OVA)-sensitized skin were examined for their ability to polarize naive OVA-TCR transgenic CD4⁺ T cells. Cytokine expression was examined by reverse-transcriptase quantitative PCR, intracellular flow cytometry, and ELISA. Contact hypersensitivity to dinitrofluorobenzene was examined.

RESULTS

Tape stripping caused IL-33-driven upregulation of Il13 expression by skin MCs. MC-derived IL-13 acted on DCs from draining lymph nodes of OVA-sensitized skin to selectively suppress their ability to polarize naive OVA-TCR transgenic CD4⁺ T cells into IFN-γ-secreting cells. MC-derived IL-13 inhibited the T_H1 cell response in contact hypersensitivity to dinitrofluorobenzene. IL-13 suppressed IL-12 production by mouse skin-derived DCs in vitro and in vivo. Scratching upregulated IL13 expression in human skin, and IL-13 suppressed the capacity of LPS-stimulated human skin DCs to express IL-12 and promote IFN-γ secretion by CD4⁺ T cells.

CONCLUSION

Release of IL-13 by cutaneous MCs in response to mechanical skin injury inhibits the T_H1 cell response to cutaneous antigen exposure in AD.

The first-in-human study of CNTO 7160, an anti-interleukin-33 receptor monoclonal antibody, in healthy subjects and patients with asthma or atopic dermatitis

AIMS

To assess safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD) and immunogenicity of CNTO 7160, an anti-interleukin-33 receptor (IL-33R) monoclonal antibody, in healthy subjects and patients with asthma or atopic dermatitis (AD).

METHODS

In Part 1 of this Phase I, randomized, double-blind, placebo-controlled study, healthy subjects (n = 68) received single ascending intravenous (IV) CNTO 7160 dose (0.001 to 10 mg/kg) or placebo. In Part 2, patients with mild asthma (n = 24) or mild AD (n = 15) received 3 biweekly IV CNTO 7160 doses (3 or 10 mg/kg) or placebo.

RESULTS

CNTO 7160 was generally well tolerated, with 1 serious adverse event of severe cellulitis reported (AD, CNTO 7160, 3 mg/kg). CNTO 7160 exhibited nonlinear PK (0.01-10 mg/kg). Mean clearance decreased with increasing dose (2.43 to 18.03 mL/d/kg). CNTO 7160 PK was similar between healthy subjects and patients with asthma or AD (3 or 10 mg/kg). Free sIL-33R suppression was rapid and dose dependent. Ex vivo inhibition of p38 phosphorylation of basophils was dose-dependent (1-10 mg/kg) and sustained inhibition (≥75%) was observed at higher doses (3 or 10 mg/kg). PK/PD modelling and simulation suggests that 1 mg/kg IV every 2 weeks provides adequate systemic drug exposure for sustained inhibition of p38 phosphorylation of basophils. Despite confirmation of target engagement, no apparent CNTO 7160 clinical activity was observed in patients (asthma or AD).

CONCLUSION

This first-in-human study provides PK, PD and safety data, supporting further clinical investigation of CNTO 7160 in patients with asthma and AD.

The Fungal Microbiome and Asthma

Asthma is a group of inflammatory conditions that compromises the airways of a continuously increasing number of people around the globe. Its complex etiology comprises both genetic and environmental aspects, with the intestinal and lung microbiomes emerging as newly implicated factors that can drive and aggravate asthma. Longitudinal infant cohort studies combined with mechanistic studies in animal models have identified microbial signatures causally associated with subsequent asthma risk. The recent inclusion of fungi in human microbiome surveys has revealed that microbiome signatures associated with asthma risk are not limited to bacteria, and that fungi are also implicated in asthma development in susceptible individuals. In this review, we examine the unique properties of human-associated and environmental fungi, which confer them the ability to influence immune development and allergic responses. The important contribution of fungi to asthma development and exacerbations prompts for their inclusion in current and future asthma studies in humans and animal models.

The Role of the TL1A/DR3 Axis in the Activation of Group 2 Innate Lymphoid Cells in Subjects with Eosinophilic Asthma

Rationale: Group 2 innate lymphoid cells (ILC2s) are critical for type 2 inflammation. In murine models of asthma, some ILC2s remain activated in the absence of epithelial cell-derived cytokine signaling, implicating alternate stimulatory pathways. DR3 (death receptor 3), a member of the tumor necrosis factor receptor superfamily, is expressed on ILC2s. Genome-wide association studies report an association between DR3 ligand, TL1A (tumor necrosis factor-like protein 1A), and chronic inflammatory conditions.Objectives: We investigated the TL1A/DR3 axis in airway ILC2 biology in eosinophilic asthma.Methods: Stable subjects with mild asthma were subject to allergen inhalation challenge, and DR3 expression on sputum cells was assessed. We investigated cytokine regulation of DR3 expression on ILC2s and steroid sensitivity. Airway TL1A was assessed in sputum from subjects with mild asthma and subjects with prednisone-dependent severe eosinophilic asthma.Measurements and Main Results: There was a significant increase in sputum DR3⁺ ILC2s 24 hours after allergen challenge, and DR3 expression on ILC2s was upregulated by IL-2, IL-33, or TSLP in vitro. Stimulation with TL1A significantly increased IL-5 expression by ILC2s and was attenuated by dexamethasone, an effect that was negated in the presence of TSLP. Airway TL1A levels were increased 24 hours after allergen challenge in subjects with mild asthma but were significantly greater in those with severe eosinophilic asthma. The highest levels were detected in subjects with severe asthma with airway autoimmune responses. C1q⁺ immune complexes from the sputa of subjects with severe asthma with high autoantibody levels stimulated TL1A production by monocytes.Conclusions: The TL1A/DR3 axis is a costimulator of ILC2s in asthma, particularly in the airways of patients with a predisposition to autoimmune responses.

Lung fibroblasts produce IL-33 in response to stimulation with retinoblastoma-binding protein 9 via production of prostaglandin E2

Intestinal nematode infection induces pulmonary eosinophilia via IL-33, although the mechanism of pulmonary IL-33 induction remains unclear. Because nematode migration damages lungs, we speculated that lung-derived damage-associated molecular patterns (DAMPs) possess an IL-33-inducing activity (IL33ia). Indeed, intra-nasal administration of a lung extract induced IL-33 production in lungs. Additionally, lung extracts increased Il33 mRNA expression in primary lung fibroblasts. Proteomic analysis identified retinoblastoma-binding protein 9 (RBBP9) as a major DAMP with IL33ia. RBBP9 was originally discovered as a protein that provides cells with resistance to the growth inhibitory effect of transforming growth factor (TGF)-β1. Here, we found that stimulation by RBBP9 induced primary fibroblasts to produce prostaglandin E2 (PGE2) that, in turn, induced fibroblasts to produce IL-33. RBBP9-activated fibroblasts expressed mRNAs of cyclooxygenase-2 (COX-2) and PGE2 synthase-1 that convert arachidonic acid to PGE2. Furthermore, they expressed PGE2 receptors E-prostanoid (EP) 2 and EP4. Thus, treatment with a COX-2 inhibitor or EP2 and/or EP4 receptor antagonists inhibited RBBP9-induced IL-33 production. Nematode infection induced pulmonary Il33 mRNA expression, which was inhibited by the COX-2 inhibitor or EP2 and EP4 antagonists, suggesting that nematode infection induced pulmonary Il33 mRNA via PGE2. RBBP9 was expressed constitutively in the lung in the steady state, which did not increase after nematode infection. Finally, we found that Rbbp9-deficient mice had a significantly diminished capacity to increase pulmonary Il33 mRNA expression following nematode infection. Thus, the PGE2-EP2/EP4 pathway activated by RBBP9 released from damaged lungs is important for pulmonary IL-33 production in nematode-infected animals.

IL-33-ST2 axis regulates myeloid cell differentiation and activation enabling effective club cell regeneration

Evidence points to an indispensable function of macrophages in tissue regeneration, yet the underlying molecular mechanisms remain elusive. Here we demonstrate a protective function for the IL-33-ST2 axis in bronchial epithelial repair, and implicate ST2 in myeloid cell differentiation. ST2 deficiency in mice leads to reduced lung myeloid cell infiltration, abnormal alternatively activated macrophage (AAM) function, and impaired epithelial repair post naphthalene-induced injury. Reconstitution of wild type (WT) AAMs to ST2-deficient mice completely restores bronchial re-epithelialization. Central to this mechanism is the direct effect of IL-33-ST2 signaling on monocyte/macrophage differentiation, self-renewal and repairing ability, as evidenced by the downregulation of key pathways regulating myeloid cell cycle, maturation and regenerative function of the epithelial niche in ST2^−/− mice. Thus, the IL-33-ST2 axis controls epithelial niche regeneration by activating a large multi-cellular circuit, including monocyte differentiation into competent repairing AAMs, as well as group-2 innate lymphoid cell (ILC2)-mediated AAM activation.

Signaling of IL-33 via its receptor, ST2, has been implicated in macrophage function in tissue repair. Here the authors show, using genetic mouse models and single-cell transcriptomic data, that the IL-33/ST2 axis regulates both ILC2-derived IL-13 and macrophage differentiation/reparative function required for club cell regeneration.

Alternaria alternata Accelerates Loss of Alveolar Macrophages and Promotes Lethal Influenza A Infection

Chronic inhalation of fungi and fungal components has been linked to the development of respiratory disorders, although their role with respect to the pathogenesis of acute respiratory virus infection remains unclear. Here, we evaluate inflammatory pathology induced by repetitive administration of a filtrate of the ubiquitous fungus, Alternaria alternata, and its impact on susceptibility to infection with influenza A. We showed previously that A. alternata at the nasal mucosae resulted in increased susceptibility to an otherwise sublethal inoculum of influenza A in wild-type mice. Here we demonstrate that A. alternata-induced potentiation of influenza A infection was not dependent on fungal serine protease or ribonuclease activity. Repetitive challenge with A. alternata prior to virus infection resulted proinflammatory cytokines, neutrophil recruitment, and loss of alveolar macrophages to a degree that substantially exceeded that observed in response to influenza A infection alone. Concomitant administration of immunomodulatory Lactobacillus plantarum, a strategy shown previously to limit virus-induced inflammation in the airways, blocked the exaggerated lethal response. These observations promote an improved understanding of severe influenza infection with potential clinical relevance for individuals subjected to continuous exposure to molds and fungi.

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.

Contributions of IL-33 in Non-hematopoietic Lung Cells to Obstructive Lung Disease

Interleukin (IL)-33 plays important roles in pulmonary immune responses and lung diseases including asthma and chronic obstructive pulmonary disease (COPD). There is substantial interest in identifying and characterizing cellular sources vs. targets of IL-33, and downstream signaling pathways involved in disease pathophysiology. While epithelial and immune cells have largely been the focus, in this review, we summarize current knowledge of expression, induction, and function of IL-33 and its receptor ST2 in non-hematopoietic lung cells in the context of health and disease. Under basal conditions, epithelial cells and endothelial cells are thought to be the primary resident cell types that express high levels of IL-33 and serve as ligand sources compared to mesenchymal cells (smooth muscle cells and fibroblasts). Under inflammatory conditions, IL-33 expression is increased in most non-hematopoietic lung cells, including epithelial, endothelial, and mesenchymal cells. In comparison to its ligand, the receptor ST2 shows low expression levels at baseline but similar to IL-33, ST2 expression is upregulated by inflammation in these non-hematopoietic lung cells which may then participate in chronic inflammation both as sources and autocrine/paracrine targets of IL-33. Downstream effects of IL-33 may occur via direct receptor activation or indirect interactions with the immune system, overall contributing to lung inflammation, airway hyper-responsiveness and remodeling (proliferation and fibrosis). Accordingly from a therapeutic perspective, targeting IL-33 and/or its receptor in non-hematopoietic lung cells becomes relevant.

TSLP and IL-33 reciprocally promote each other's lung protein expression and ILC2 receptor expression to enhance innate type-2 airway inflammation

Background

The epithelial cell‐derived danger signal mediators thymic stromal lymphopoietin (TSLP) and IL‐33 are consistently associated with adaptive Th2 immune responses in asthma. In addition, TSLP and IL‐33 synergistically promoted group 2 innate lymphoid cell (ILC2) activation to induce innate allergic inflammation. However, the mechanism of this synergistic ILC2 activation is unknown.

Methods

BALB/c WT and TSLP receptor‐deficient (TSLPR^−/−) mice were challenged intranasally with Alternaria extract (Alt‐Ext) or PBS for 4 consecutive days to evaluate innate airway allergic inflammation. WT mice pre‐administered with rTSLP or vehicle, TSLPR^−/− mice, and IL‐33 receptor‐deficient (ST2^−/−) mice were challenged intranasally with Alt‐Ext or vehicle once or twice to evaluate IL‐33 release and TSLP expression in the lung. TSLPR and ST2 expression on lung ILC2 were measured by flow cytometry after treatment of rTSLP, rIL‐33, rTSLP + rIL‐33, or vehicle.

Results

Thymic stromal lymphopoietin receptor deficient mice had significantly decreased the number of lung ILC2 expressing IL‐5 and IL‐13 following Alt‐Ext‐challenge compared to WT mice. Further, eosinophilia, protein level of lung IL‐4, IL‐5, and IL‐13, and airway mucus score were also significantly decreased in TSLPR^−/− mice compared to WT mice. Endogenous and exogenous TSLP increased Alt‐Ext‐induced IL‐33 release into BALF, and ST2 deficiency decreased Alt‐Ext‐induced TSLP expression in the lung. Further, rTSLP and rIL‐33 treatment reciprocally increased each other's receptor expression on lung ILC2 in vivo and in vitro.

Conclusion

Thymic stromal lymphopoietin and IL‐33 signaling reciprocally enhanced each other's protein release and expression in the lung following Alt‐Ext‐challenge and each other's receptor expression on lung ILC2 to enhance ILC2 activation.

Characterization and pro-inflammatory potential of indoor mold particles

A number of epidemiological studies find an association between indoor air dampness and respiratory health effects. This is often suggested to be linked to enhanced mold growth. However, the role of mold is obviously difficult to disentangle from other dampness-related exposure including microbes as well as non-biological particles and chemical pollutants. The association may partly be due to visible mycelial growth and a characteristic musty smell of mold. Thus, the potential role of mold exposure should be further explored by evaluating information from experimental studies elucidating possible mechanistic links. Such studies show that exposure to spores and hyphal fragments may act as allergens and pro-inflammatory mediators and that they may damage airways by the production of toxins, enzymes, and volatile organic compounds. In the present review, we hypothesize that continuous exposure to mold particles may result in chronic low-grade pro-inflammatory responses contributing to respiratory diseases. We summarize some of the main methods for detection and characterization of fungal aerosols and highlight in vitro research elucidating how molds may induce toxicity and pro-inflammatory reactions in human cell models relevant for airway exposure. Data suggest that the fraction of fungal hyphal fragments in indoor air is much higher than that of airborne spores, and the hyphal fragments often have a higher pro-inflammatory potential. Thus, hyphal fragments of prevalent mold species with strong pro-inflammatory potential may be particularly relevant candidates for respiratory diseases associated with damp/mold-contaminated indoor air. Future studies linking of indoor air dampness with health effects should assess the toxicity and pro-inflammatory potential of indoor air particulate matter and combined this information with a better characterization of biological components including hyphal fragments from both pathogenic and non-pathogenic mold species. Such studies may increase our understanding of the potential role of mold exposure.

A Truncated Form of HpARI Stabilizes IL-33, Amplifying Responses to the Cytokine

The murine intestinal nematode Heligmosomoides polygyrus releases the H. polygyrus Alarmin Release Inhibitor (HpARI) - a protein which binds to IL-33 and to DNA, effectively tethering the cytokine in the nucleus of necrotic cells. Previous work showed that a non-natural truncation consisting of the first 2 domains of HpARI (HpARI_CCP1/2) retains binding to both DNA and IL-33, and inhibited IL-33 release in vivo. Here, we show that the affinity of HpARI_CCP1/2 for IL-33 is significantly lower than that of the full-length protein, and that HpARI_CCP1/2 lacks the ability to prevent interaction of IL-33 with its receptor. When HpARI_CCP1/2 was applied in vivo it potently amplified IL-33-dependent immune responses to Alternaria alternata allergen, Nippostrongylus brasiliensis infection and recombinant IL-33 injection, in direct contrast to the IL-33-suppressive effects of full-length HpARI. Mechanistically, we found that HpARI_CCP1/2 is able to bind to and stabilize IL-33, preventing its degradation and maintaining the cytokine in its active form. This study highlights the importance of IL-33 inactivation, the potential for IL-33 stabilization in vivo, and describes a new tool for IL-33 research.

House Dust Mite Induces Bone Marrow IL-33-Responsive ILC2s and TH Cells

Type 2 innate lymphoid cells (ILC2s) and their adaptive counterpart type 2 T helper (TH2) cells respond to interleukin-33 (IL-33) by producing IL-5, which is a crucial cytokine for eosinophil development in the bone marrow. The aim of this study was to determine if bone marrow ILC2s, TH cells, and eosinophils are locally regulated by IL-33 in terms of number and activation upon exposure to the common aeroallergen house dust mite (HDM). Mice that were sensitized and challenged with HDM by intranasal exposures induced eosinophil development in the bone marrow with an initial increase of IL5Rα+ eosinophil progenitors, following elevated numbers of mature eosinophils and the induction of airway eosinophilia. Bone marrow ILC2s, TH2, and eosinophils all responded to HDM challenge by increased IL-33 receptor (ST2) expression. However, only ILC2s, but not TH cells, revealed increased ST2 expression at the onset of eosinophil development, which significantly correlated with the number of eosinophil progenitors. In summary, our findings suggest that airway allergen challenges with HDM activates IL-33-responsive ILC2s, TH cells, and eosinophils locally in the bone marrow. Targeting the IL-33/ST2 axis in allergic diseases including asthma may be beneficial by decreasing eosinophil production in the bone marrow.

A helminth-derived suppressor of ST2 blocks allergic responses

The IL-33-ST2 pathway is an important initiator of type 2 immune responses. We previously characterised the HpARI protein secreted by the model intestinal nematode Heligmosomoides polygyrus, which binds and blocks IL-33. Here, we identify H. polygyrus Binds Alarmin Receptor and Inhibits (HpBARI) and HpBARI_Hom2, both of which consist of complement control protein (CCP) domains, similarly to the immunomodulatory HpARI and Hp-TGM proteins. HpBARI binds murine ST2, inhibiting cell surface detection of ST2, preventing IL-33-ST2 interactions, and inhibiting IL-33 responses in vitro and in an in vivo mouse model of asthma. In H. polygyrus infection, ST2 detection is abrogated in the peritoneal cavity and lung, consistent with systemic effects of HpBARI. HpBARI_Hom2 also binds human ST2 with high affinity, and effectively blocks human PBMC responses to IL-33. Thus, we show that H. polygyrus blocks the IL-33 pathway via both HpARI which blocks the cytokine, and also HpBARI which blocks the receptor.

Unique Phenotypes of Heart Resident Type 2 Innate Lymphoid Cells

Innate lymphoid cells (ILCs), including ILC1s, ILC2s, and ILC3s, play critical roles in regulating immunity, inflammation, and tissue homeostasis. However, limited attention is focused on the unique phenotype of ILCs in the heart tissue. In this study, we analyzed the ILC subsets in the heart by flow cytometry and found that ILC2s were the dominant population of ILCs, while a lower proportion of type 1 ILCs (including ILC1 and NK cells) and merely no ILC3s in the heart tissue of mice. Our results show that ILC2 development kinetically peaked in heart ILC2s at the age of 4 weeks after birth and later than lung ILC2s. By conducting parabiosis experiment, we show that heart ILC2s are tissue resident cells and minimally replaced by circulating cells. Notably, heart ILC2s have unique phenotypes, such as lower expression of ICOS, CD25 (IL-2Rα), and Ki-67, higher expression of Sca-1 and GATA3, and stronger ability to produce IL-4 and IL-13. In doxorubicin-induced myocardial necroptosis model of mouse heart tissue, IL-33 mRNA expression level and ILC2s were remarkably increased. In addition, IL-4 production by heart ILC2s, but not lung ILC2s, was also dramatically increased after doxorubicin treatment. Our results demonstrate that heart-resident ILC2s showed tissue-specific phenotypes and rapidly responded to heart injury. Thus, further studies are warranted to explore the potential for IL-33-elicited ILC2s response as therapeutics for attenuating heart damage.

The Innate Immune Protein S100A9 Protects from T-Helper Cell Type 2-mediated Allergic Airway Inflammation

Calprotectin is a heterodimer of the proteins S100A8 and S100A9, and it is an abundant innate immune protein associated with inflammation. In humans, calprotectin transcription and protein abundance are associated with asthma and disease severity. However, mechanistic studies in experimental asthma models have been inconclusive, identifying both protective and pathogenic effects of calprotectin. To clarify the role of calprotectin in asthma, calprotectin-deficient S100A9^-/- and wild-type (WT) C57BL/6 mice were compared in a murine model of allergic airway inflammation. Mice were intranasally challenged with extracts of the clinically relevant allergen, Alternaria alternata (Alt Ext), or PBS every third day over 9 days. On Day 10, BAL fluid and lung tissue homogenates were harvested and allergic airway inflammation was assessed. Alt Ext challenge induced release of S100A8/S100A9 to the alveolar space and increased protein expression in the alveolar epithelium of WT mice. Compared with WT mice, S100A9^-/- mice displayed significantly enhanced allergic airway inflammation, including production of IL-13, CCL11, CCL24, serum IgE, eosinophil recruitment, and airway resistance and elastance. In response to Alt Ext, S100A9^-/- mice accumulated significantly more IL-13⁺IL-5⁺CD4⁺ T-helper type 2 cells. S100A9^-/- mice also accumulated a significantly lower proportion of CD4⁺ T regulatory (Treg) cells in the lung that had significantly lower expression of CD25. Calprotectin enhanced WT Treg cell suppressive activity in vitro. Therefore, this study identifies a role for the innate immune protein, S100A9, in protection from CD4⁺ T-helper type 2 cell hyperinflammation in response to Alt Ext. This protection is mediated, at least in part, by CD4⁺ Treg cell function.

The allergenic activity and clinical impact of individual IgE-antibody binding molecules from indoor allergen sources

A large number of allergens have been discovered but we know little about their potential to induce inflammation (allergenic activity) and symptoms. Nowadays, the clinical importance of allergens is determined by the frequency and intensity of their IgE antibody binding (allergenicity). This is a rather limited parameter considering the development of experimental allergology in the last 20 years and the criteria that support personalized medicine. Now it is known that some allergens, in addition to their IgE antibody binding properties, can induce inflammation through non IgE mediated pathways, which can increase their allergenic activity. There are several ways to evaluate the allergenic activity, among them the provocation tests, the demonstration of non-IgE mediated pathways of inflammation, case control studies of IgE-binding frequencies, and animal models of respiratory allergy. In this review we have explored the current status of basic and clinical research on allergenic activity of indoor allergens and confirm that, for most of them, this important property has not been investigated. However, during recent years important advances have been made in the field, and we conclude that for at least the following, allergenic activity has been demonstrated: Der p 1, Der p 2, Der p 5 and Blo t 5 from HDMs; Per a 10 from P. americana; Asp f 1, Asp f 2, Asp f 3, Asp f 4 and Asp f 6 from A. fumigatus; Mala s 8 and Mala s 13 from M. sympodialis; Alt a 1 from A. alternata; Pen c 13 from P. chrysogenum; Fel d 1 from cats; Can f 1, Can f 2, Can f 3, Can f 4 and Can f 5 from dogs; Mus m 1 from mice and Bos d 2 from cows. Defining the allergenic activity of other indoor IgE antibody binding molecules is necessary for a precision-medicine-oriented management of allergic diseases.

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

Parasitic infections pose a wide and varying threat globally, impacting over 25% of the global population with many more at risk of infection. These infections are comprised of, but not limited to, toxoplasmosis, malaria, leishmaniasis and any one of a wide variety of helminthic infections. While a great deal is understood about the adaptive immune response to each of these parasites, there remains a need to further elucidate the early innate immune response. Interleukin-33 is being revealed as one of the earliest players in the cytokine milieu responding to parasitic invasion, and as such has been given the name "alarmin." A nuclear cytokine, interleukin-33 is housed primarily within epithelial and fibroblastic tissues and is released upon cellular damage or death. Evidence has shown that interleukin-33 seems to play a crucial role in priming the immune system toward a strong T helper type 2 immune response, necessary in the clearance of some parasites, while disease exacerbating in the context of others. With the possibility of being a double-edged sword, a great deal remains to be seen in how interleukin-33 and its receptor ST2 are involved in the immune response different parasites elicit, and how those parasites may manipulate or evade this host mechanism. In this review article we compile the current cutting-edge research into the interleukin-33 response to toxoplasmosis, malaria, leishmania, and helminthic infection. Furthermore, we provide insight into directions interleukin-33 research may take in the future, potential immunotherapeutic applications of interleukin-33 modulation and how a better clarity of early innate immune system responses involving interleukin-33/ST2 signaling may be applied in development of much needed treatment options against parasitic invaders.

Fungal allergen-induced IL-33 secretion involves cholesterol-dependent, VDAC-1-mediated ATP release from the airway epithelium

KEY POINTS

Alternaria aeroallergens induce the release of ATP from human bronchial epithelial (HBE) cells by activating a conductive pathway involving voltage-dependent anion channel-1 (VDAC-1) and by exocytosis of ATP localized within membrane vesicles. Inhibition of VDAC-1 blocked Alternaria-evoked Ca²⁺ uptake across the plasma membrane of HBE cells and interleukin (IL)-33 release into the extracellular media. Reducing cholesterol content with a cholesterol scavenger (β-methylcyclodextrin) or statin compound (simvastatin) blocked ATP and IL-33 release by lowering the expression of VDAC-1 in the plasma membrane. Pretreatment with simvastatin for 24 h also inhibited the increase in tight junction macromolecule permeability that occurs following Alternaria exposure. These results establish a novel role for VDAC-1 as a mechanism underlying ATP release induced by fungal allergens and suggests a possible therapeutic use for cholesterol lowering compounds in reducing Alternaria-stimulated allergic inflammation.

ABSTRACT

Human bronchial epithelial (HBE) cells exposed to allergens derived from the common saprophytic fungus, Alternaria alternata release ATP, which in turn stimulates P2X₇ receptor-mediated Ca²⁺ uptake across the plasma membrane. The subsequent increase in intracellular calcium concentration induces proteolytic processing and secretion of interleukin (IL)-33, a critical cytokine involved in the initiation of allergic airway inflammation. A major objective of the present study was to identify the mechanism responsible for conductive ATP release. The results show that pretreatment of HBE cells with inhibitors of the voltage-dependent anion channel-1 (VDAC-1) or treatment with a VDAC-1 selective blocking antibody or silencing mRNA expression of the channel by RNA interference, inhibit Alternaria-evoked ATP release. Moreover, inhibition of VDAC-1 channel activity or reducing protein expression blocked the secretion of IL-33. Similarly, reducing the cholesterol content of HBE cells with simvastatin or the cholesterol scavenger β-methylcyclodextrin also blocked ATP release and IL-33 secretion by decreasing the level of VDAC-1 expression in the plasma membrane. In addition, simvastatin inhibited the increase in tight junction macromolecule permeability that was previously observed after Alternaria exposure. These results demonstrate a novel function for VDAC-1 as the conductive mechanism responsible for Alternaria-induced ATP release, an essential early step in the processing, mobilization and secretion of IL-33 by the airway epithelium. Furthermore, the simvastatin-evoked reduction of VDAC-1 expression in the plasma membrane, suggests the possibility that cholesterol lowering compounds may be beneficial in alleviating allergic airway inflammation induced by fungal allergens.

Regnase-1 degradation is crucial for IL-33- and IL-25-mediated ILC2 activation

Group 2 innate lymphoid cells (ILC2s) are a critical innate source of type 2 cytokines in allergic inflammation. Although ILC2s are recognized as a critical cell population in the allergic inflammation, the regulatory mechanism(s) of ILC2s are less well understood. Here, we show that Regnase-1, an immune regulatory RNAse that degrades inflammatory mRNAs, negatively regulates ILC2 function and that IκB kinase (IKK) complex-mediated Regnase-1 degradation is essential for IL-33- and IL-25-induced ILC2 activation. ILC2s from Regnase-1AA/AA mice expressing a Regnase-1 S435A/S439A mutant resistant to IKK complex-mediated degradation accumulated Regnase-1 protein in response to IL-33 and IL-25. IL-33- and IL-25-stimulated Regnase-1AA/AA ILC2s showed reduced cell proliferation and type 2 cytokine (IL-5, IL-9, and IL-13) production and increased cell death. In addition, Il2ra and Il1rl1, but not Il5, Il9, or Il13, mRNAs were destabilized in IL-33-stimulated Regnase-1AA/AA ILC2s. In vivo, Regnase-1AA/AA mice showed attenuated acute type 2 pulmonary inflammation induced by the instillation of IL-33, IL-25, or papain. Furthermore, the expulsion of Nippostrongylus brasiliensis was significantly delayed in Regnase-1AA/AA mice. These results demonstrate that IKK complex-mediated Regnase-1 degradation is essential for ILC2-mediated type 2 responses both in vitro and in vivo. Therefore, controlling Regnase-1 degradation is a potential therapeutic target for ILC2-contributed allergic disorders.

p38 MAPK signalling regulates cytokine production in IL-33 stimulated Type 2 Innate Lymphoid cells

Type 2 Innate lymphoid cells (ILC2s) are implicated in helminth infections and asthma where they play a role in the production of Th2-type cytokines. ILC2s express the IL-33 receptor and are a major cell type thought to mediate the effects of this cytokine in vivo. To study the signalling pathways that mediate IL-33 induced cytokine production, a culture system was set up to obtain pure populations of ILC2s from mice. Inhibitors of the p38α/β and ERK1/2 MAPK pathways reduced the production of IL-5, IL-6, IL-9, IL-13 and GM-CSF by ILC2 in response to IL-33, with inhibition of p38 having the greatest effect. MK2 and 3 are kinases activated by p38α; MK2/3 inhibitors or knockout of MK2/3 in mice reduced the production of IL-6 and IL-13 (two cytokines implicated in asthma) but not IL-5, IL-9 or GM-CSF in response to IL-33. MK2/3 inhibition also suppressed IL-6 and IL-13 production by human ILC2s. MK2/3 were required for maximal S6 phosphorylation, suggesting an input from the p38α-MK2/3 pathway to mTOR1 activation in ILC2s. The mTORC1 inhibitor rapamycin also reduced IL-6 and IL-13 production, which would be consistent with a model in which MK2/3 regulate IL-6 and IL-13 via mTORC1 activation in ILC2s.

Current Concepts in the Management of Allergic Fungal Rhinosinusitis

Allergic fungal rhinosinusitis (AFRS) represents a subtype of chronic rhinosinusitis with nasal polyposis that exhibits a unique, often striking clinical presentation. Since its initial description more than a quarter century ago, a more sophisticated understanding of the pathophysiology of AFRS has been achieved and significant advancements in improving clinical outcomes made. This review focuses on the latest developments involving the pathophysiology and clinical management of this fascinating disease.

Proinflammatory Pathways in the Pathogenesis of Asthma

There are multiple proinflammatory pathways in the pathogenesis of asthma. These include both innate and adaptive inflammation, in addition to inflammatory and physiologic responses mediated by eicosanoids. An important component of the innate allergic immune response is ILC2 activated by interleukin (IL)-33, thymic stromal lymphopoietin, and IL-25 to produce IL-5 and IL-13. In terms of the adaptive T-lymphocyte immunity, CD4+ Th2 and IL-17-producing cells are critical in the inflammatory responses in asthma. Last, eicosanoids involved in asthma pathogenesis include prostaglandin D₂ and the cysteinyl leukotrienes that promote smooth muscle constriction and inflammation that propagate allergic responses.

Airway brush cells generate cysteinyl leukotrienes through the ATP sensor P2Y2

Chemosensory epithelial cells (EpCs) are specialized cells that promote innate type 2 immunity and protective neurally mediated reflexes in the airway. Their effector programs and modes of activation are not fully understood. Here, we define the transcriptional signature of two choline acetyltransferase-expressing nasal EpC populations. They are found in the respiratory and olfactory mucosa and express key chemosensory cell genes including the transcription factor Pou2f3, the cation channel Trpm5, and the cytokine Il25 Moreover, these cells share a core transcriptional signature with chemosensory cells from intestine, trachea and thymus, and cluster with tracheal brush cells (BrCs) independently from other respiratory EpCs, indicating that they are part of the brush/tuft cell family. Both nasal BrC subsets express high levels of transcripts encoding cysteinyl leukotriene (CysLT) biosynthetic enzymes. In response to ionophore, unfractionated nasal BrCs generate CysLTs at levels exceeding that of the adjacent hematopoietic cells isolated from naïve mucosa. Among activating receptors, BrCs express the purinergic receptor P2Y2. Accordingly, the epithelial stress signal ATP and aeroallergens that elicit ATP release trigger BrC CysLT generation, which is mediated by the P2Y2 receptor. ATP- and aeroallergen-elicited CysLT generation in the nasal lavage is reduced in mice lacking Pou2f3, a requisite transcription factor for BrC development. Last, aeroallergen-induced airway eosinophilia is reduced in BrC-deficient mice. These results identify a previously undescribed BrC sensor and effector pathway leading to generation of lipid mediators in response to luminal signals. Further, they suggest that BrC sensing of local damage may provide an important sentinel immune function.

Lung Innate Lymphoid Cell Composition Is Altered in Primary Graft Dysfunction

Rationale: Primary graft dysfunction (PGD) is the leading cause of early morbidity and mortality after lung transplantation, but the immunologic mechanisms are poorly understood. Innate lymphoid cells (ILC) are a heterogeneous family of immune cells regulating pathologic inflammation and beneficial tissue repair. However, whether changes in donor-derived lung ILC populations are associated with PGD development has never been examined.Objectives: To determine whether PGD in chronic obstructive pulmonary disease or interstitial lung disease transplant recipients is associated with alterations in ILC subset composition within the allograft.Methods: We performed a single-center cohort study of lung transplantation patients with surgical biopsies of donor tissue taken before, and immediately after, allograft reperfusion. Donor immune cells from 18 patients were characterized phenotypically by flow cytometry for single-cell resolution of distinct ILC subsets. Changes in the percentage of ILC subsets with reperfusion or PGD (grade 3 within 72 h) were assessed.Measurements and Main Results: Allograft reperfusion resulted in significantly decreased frequencies of natural killer cells and a trend toward reduced ILC populations, regardless of diagnosis (interstitial lung disease or chronic obstructive pulmonary disease). Seven patients developed PGD (38.9%), and PGD development was associated with selective reduction of the ILC2 subset after reperfusion. Conversely, patients without PGD exhibited significantly higher ILC1 frequencies before reperfusion, accompanied by elevated ILC2 frequencies after allograft reperfusion.Conclusions: The composition of donor ILC subsets is altered after allograft reperfusion and is associated with PGD development, suggesting that ILCs may be involved in regulating lung injury in lung transplant recipients.

The Fungal Microbiome and Asthma

Asthma is a group of inflammatory conditions that compromises the airways of a continuously increasing number of people around the globe. Its complex etiology comprises both genetic and environmental aspects, with the intestinal and lung microbiomes emerging as newly implicated factors that can drive and aggravate asthma. Longitudinal infant cohort studies combined with mechanistic studies in animal models have identified microbial signatures causally associated with subsequent asthma risk. The recent inclusion of fungi in human microbiome surveys has revealed that microbiome signatures associated with asthma risk are not limited to bacteria, and that fungi are also implicated in asthma development in susceptible individuals. In this review, we examine the unique properties of human-associated and environmental fungi, which confer them the ability to influence immune development and allergic responses. The important contribution of fungi to asthma development and exacerbations prompts for their inclusion in current and future asthma studies in humans and animal models.

TNFR2 Signaling Enhances ILC2 Survival, Function, and Induction of Airway Hyperreactivity

Group 2 innate lymphoid cells (ILC2s) can initiate pathologic inflammation in allergic asthma by secreting copious amounts of type 2 cytokines, promoting lung eosinophilia and airway hyperreactivity (AHR), a cardinal feature of asthma. We discovered that the TNF/TNFR2 axis is a central immune checkpoint in murine and human ILC2s. ILC2s selectively express TNFR2, and blocking the TNF/TNFR2 axis inhibits survival and cytokine production and reduces ILC2-dependent AHR. The mechanism of action of TNFR2 in ILC2s is through the non-canonical NF-κB pathway as an NF-κB-inducing kinase (NIK) inhibitor blocks the costimulatory effect of TNF-α. Similarly, human ILC2s selectively express TNFR2, and using hILC2s, we show that TNFR2 engagement promotes AHR through a NIK-dependent pathway in alymphoid murine recipients. These findings highlight the role of the TNF/TNFR2 axis in pulmonary ILC2s, suggesting that targeting TNFR2 or relevant signaling is a different strategy for treating patients with ILC2-dependent asthma.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Autophagy is critical for group 2 innate lymphoid cell metabolic homeostasis and effector function

BACKGROUND

Allergic asthma is a chronic inflammatory disorder characterized by airway hyperreactivity (AHR) and driven by T_H2 cytokine production. Group 2 innate lymphoid cells (ILC2s) secrete high amounts of T_H2 cytokines and contribute to the development of AHR. Autophagy is a cellular degradation pathway that recycles cytoplasmic content. However, the role of autophagy in ILC2s remains to be fully elucidated.

OBJECTIVE

We characterized the effects of autophagy deficiency on ILC2 effector functions and metabolic balance.

METHODS

ILC2s from autophagy-deficient mice were isolated to evaluate proliferation, apoptosis, cytokine secretion, gene expression and cell metabolism. Also, autophagy-deficient ILC2s were adoptively transferred into Rag^-/-GC^-/- mice, which were then challenged with IL-33 and assessed for AHR and lung inflammation.

RESULTS

We demonstrate that autophagy is extensively used by activated ILC2s to maintain their homeostasis and effector functions. Deletion of the critical autophagy gene autophagy-related 5 (Atg5) resulted in decreased cytokine secretion and increased apoptosis. Moreover, lack of autophagy among ILC2s impaired their ability to use fatty acid oxidation and strikingly promoted glycolysis, as evidenced by our transcriptomic and metabolite analyses. This shift of fuel dependency led to impaired homeostasis and T_H2 cytokine production, thus inhibiting the development of ILC2-mediated AHR. Notably, this metabolic reprogramming was also associated with an accumulation of dysfunctional mitochondria, producing excessive reactive oxygen species.

CONCLUSION

These findings provide new insights into the metabolic profile of ILC2s and suggest that modulation of fuel dependency by autophagy is a potentially new therapeutic approach to target ILC2-dependent inflammation.

Immunologic mechanisms in asthma

Asthma is a chronic airway disease, which affects more than 300 million people. The pathogenesis of asthma exhibits marked heterogeneity with many phenotypes defining visible characteristics and endotypes defining molecular mechanisms. With the evolution of novel biological therapies, patients, who do not-respond to conventional asthma therapy require novel biologic medications, such as anti-IgE, anti-IL-5 and anti-IL4/IL13 to control asthma symptoms. It is increasingly important for physicians to understand immunopathology of asthma and to characterize asthma phenotypes. Asthma is associated with immune system activation, airway hyperresponsiveness (AHR), epithelial cell activation, mucus overproduction and airway remodeling. Both innate and adaptive immunity play roles in immunologic mechanisms of asthma. Type 2 asthma with eosinophilia is a common phenotype in asthma. It occurs with and without visible allergy. The type 2 endotype comprises; T helper type 2 (Th2) cells, type 2 innate lymphoid cells (ILC2), IgE-secreting B cells and eosinophils. Eosinophilic nonallergic asthma is ILC2 predominated, which produces IL-5 to recruit eosinophil into the mucosal airway. The second major subgroup of asthma is non-type 2 asthma, which contains heterogeneous group of endoypes and phenotypes, such as exercise-induced asthma, obesity induced asthma, etc. Neutrophilic asthma is not induced by allergens but can be induced by infections, cigarette smoke and pollution. IL-17 which is produced by Th17 cells and type 3 ILCs, can stimulate neutrophilic airway inflammation. Macrophages, dendritic cells and NKT cells are all capable of producing cytokines that are known to contribute in allergic and nonallergic asthma. Bronchial epithelial cell activation and release of cytokines, such as IL-33, IL-25 and TSLP play a major role in asthma. Especially, allergens or environmental exposure to toxic agents, such as pollutants, diesel exhaust, detergents may affect the epithelial barrier leading to asthma development. In this review, we focus on the immunologic mechanism of heterogenous asthma phenotypes.

Macrophage Migration Inhibitory Factor (MIF) Is Essential for Type 2 Effector Cell Immunity to an Intestinal Helminth Parasite

Immunity to intestinal helminths is known to require both innate and adaptive components of the immune system activated along the Type 2 IL-4R/STAT6-dependent pathway. We have found that macrophage migration inhibitory factor (MIF) is essential for the development of effective immunity to the intestinal helminth Heligmosomoides polygyrus, even following vaccination which induces sterile immunity in wild-type mice. A chemical inhibitor of MIF, 4-IPP, was similarly found to compromise anti-parasite immunity. Cellular analyses found that the adaptive arm of the immune response, including IgG1 antibody responses and Th2-derived cytokines, was intact and that Foxp3+ T regulatory cell responses were unaltered in the absence of MIF. However, MIF was found to be an essential cytokine for innate cells, with ablated eosinophilia and ILC2 responses, and delayed recruitment and activation of macrophages to the M2 phenotype (expressing Arginase 1, Chil3, and RELM-α) upon infection of MIF-deficient mice; a macrophage deficit was also seen in wild-type BALB/c mice exposed to 4-IPP. Gene expression analysis of intestinal and lymph node tissues from MIF-deficient and -sufficient infected mice indicated significantly reduced levels of Arl2bp, encoding a factor involved in nuclear localization of STAT3. We further found that STAT3-deficient macrophages expressed less Arginase-1, and that mice lacking STAT3 in the myeloid compartment (LysMCrexSTAT3fl/fl) were unable to reject a secondary infection with H. polygyrus. We thus conclude that in the context of a Type 2 infection, MIF plays a critical role in polarizing macrophages into the protective alternatively-activated phenotype, and that STAT3 signaling may make a previously unrecognized contribution to immunity to helminths.

The ST2/Interleukin-33 Axis in Hematologic Malignancies: The IL-33 Paradox

Interleukin (IL)-33 is a chromatin-related nuclear interleukin that is a component of IL-1 family. IL-33 production augments the course of inflammation after cell damage or death. It is discharged into the extracellular space. IL-33 is regarded as an “alarmin” able to stimulate several effectors of the immune system, regulating numerous immune responses comprising cancer immune reactions. IL-33 has been demonstrated to influence tumorigenesis. However, as far as this cytokine is concerned, we are faced with what has sometimes been defined as the IL-33 paradox. Several studies have demonstrated a relevant role of IL-33 to numerous malignancies, where it may have pro- and—less frequently—antitumorigenic actions. In the field of hematological malignancies, the role of IL-33 seems even more complex. Although we can affirm the existence of a negative role of IL-33 in Chronic myelogenos leukemia (CML) and in lymphoproliferative diseases and a positive role in pathologies such as Acute myeloid leukemia (AML), the action of IL-33 seems to be multiple and sometimes contradictory within the same pathology. In the future, we will have to learn to govern the negative aspects of activating the IL-33/ST2 axis and exploit the positive ones.

The cysteinyl leukotriene 3 receptor regulates expansion of IL-25-producing airway brush cells leading to type 2 inflammation

Respiratory epithelial cells (EpCs) orchestrate airway mucosal inflammation in response to diverse environmental stimuli, but how distinct EpC programs are regulated remains poorly understood. Here, we report that inhalation of aeroallergens leads to expansion of airway brush cells (BrCs), specialized chemosensory EpCs and the dominant epithelial source of interleukin-25 (IL-25). BrC expansion was attenuated in mice lacking either LTC₄ synthase, the biosynthetic enzyme required for cysteinyl leukotriene (CysLT) generation, or the EpC receptor for leukotriene E₄ (LTE₄), CysLT₃R. LTE₄ inhalation was sufficient to elicit CysLT₃R-dependent BrC expansion in the murine airway through an IL-25-dependent but STAT6-independent signaling pathway. Last, blockade of IL-25 attenuated both aeroallergen and LTE₄-elicited CysLT₃R-dependent type 2 lung inflammation. These results demonstrate that CysLT₃R senses the endogenously generated lipid ligand LTE₄ and regulates airway BrC number and function.

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.

Essential role of CD4+ T cells for the activation of group 2 innate lymphoid cells during respiratory syncytial virus infection in mice

Aim: To investigate whether and how CD4⁺ T cells contribute to ILC2 activation during respiratory syncytial virus (RSV) infection. Methods: The methods of flow cytometry, quantitative PCR and ELISA were used in the present study. Results: Depletion of CD4⁺ T cells diminished the numbers of lung ILC2s as well as their ability to produce type 2 cytokines. CD4⁺ T cell-mediated ILC2 activation is related to IL-2. The main cellular source of IL-2 was CD4⁺ T cells. Depletion of CD4⁺ T cells decreased IL-2 levels in the lungs of RSV-infected mice. IL-2 can directly stimulate ILC2 proliferation and promote ILC2s to produce cytokines. Treatment of mice with neutralizing anti-IL-2 monoclonal antibodies diminished ILC2 activation. Conclusion: These results suggest that CD4⁺ T cells contribute to RSV-induced ILC2 activation partly via producing IL-2.

Asthma from immune pathogenesis to precision medicine

Asthma is characterized by multiple immunological mechanisms (endotypes) determining variable clinical presentations (phenotypes). The identification of endotypic mechanisms is crucial to better characterize patients and to identify tailored therapeutic approaches with novel biological agents targeting specific immunological pathways. This review focused on summarizing the major immunological mechanisms involved in the pathogenesis of asthma, as well as on discussing the emergence of phenotypic features of the disease. Novel biological agents and other drugs targeting specific endotypes are discussed, as their use represent a precision medicine approach to the disease that is nowadays mandatory particularly for treating more severe patients.

Immunopathology of Airway Surface Liquid Dehydration Disease

The primary purpose of pulmonary ventilation is to supply oxygen (O₂) for sustained aerobic respiration in multicellular organisms. However, a plethora of abiotic insults and airborne pathogens present in the environment are occasionally introduced into the airspaces during inhalation, which could be detrimental to the structural integrity and functioning of the respiratory system. Multiple layers of host defense act in concert to eliminate unwanted constituents from the airspaces. In particular, the mucociliary escalator provides an effective mechanism for the continuous removal of inhaled insults including pathogens. Defects in the functioning of the mucociliary escalator compromise the mucociliary clearance (MCC) of inhaled pathogens, which favors microbial lung infection. Defective MCC is often associated with airway mucoobstruction, increased occurrence of respiratory infections, and progressive decrease in lung function in mucoobstructive lung diseases including cystic fibrosis (CF). In this disease, a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene results in dehydration of the airway surface liquid (ASL) layer. Several mice models of Cftr mutation have been developed; however, none of these models recapitulate human CF-like mucoobstructive lung disease. As an alternative, the Scnn1b transgenic (Scnn1b-Tg+) mouse model overexpressing a transgene encoding sodium channel nonvoltage-gated 1, beta subunit (Scnn1b) in airway club cells is available. The Scnn1b-Tg+ mouse model exhibits airway surface liquid (ASL) dehydration, impaired MCC, increased mucus production, and early spontaneous pulmonary bacterial infections. High morbidity and mortality among mucoobstructive disease patients, high economic and health burden, and lack of scientific understanding of the progression of mucoobstruction warrants in-depth investigation of the cause of mucoobstruction in mucoobstructive disease models. In this review, we will summarize published literature on the Scnn1b-Tg+ mouse and analyze various unanswered questions on the initiation and progression of mucobstruction and bacterial infections.

The airway epithelium in asthma

Asthma is a genetically and phenotypically complex disease that has a major impact on global health. Signs and symptoms of asthma are caused by the obstruction of airflow through the airways. The epithelium that lines the airways plays a major role in maintaining airway patency and in host defense. The epithelium initiates responses to inhaled or aspirated substances, including allergens, viruses, and bacteria, and epithelial-derived cytokines are important in the recruitment and activation of immune cells in the airway. Changes in the structure and function of the airway epithelium are a prominent feature of asthma. Approximately half of individuals with asthma have evidence of active type 2 immune responses in the airway. In these individuals, epithelial cytokines promote type 2 responses, and responses to type 2 cytokines result in increased epithelial mucus production and other effects that cause airway obstruction. Recent work also implicates other epithelial responses, including interleukin-17, interferon and ER stress responses, that may contribute to asthma pathogenesis and provide new targets for therapy.

Type 2 innate lymphoid cells in the induction and resolution of tissue inflammation

Type 2 immunity against pathogens is tightly regulated to ensure appropriate inflammatory responses that clear infection and prevent excessive tissue damage. Recent research has shown that type 2 innate lymphoid cells (ILC2s) contribute to steady-state tissue integrity and exert tissue-specific functions. However, upon exposure to inflammatory stimuli, they also initiate and amplify type 2 inflammation by inducing mucus production, eosinophilia, and Th2 differentiation. In this review, we discuss the regulation of ILC2 activation by transcription factors and metabolic pathways, as well as by extrinsic signals such as cytokines, lipid mediators, hormones, and neuropeptides. We also review recent discoveries about ILC2 plasticity and heterogeneity in different tissues, as revealed partly through single-cell RNA sequencing of transcriptional responses to various stimuli. Understanding the tissue-specific pathways that regulate ILC2 diversity and function is a critical step in the development of potential therapies for allergic diseases.