Airway epithelial cells activate TH2 cytokine production in mast cells through IL-1 and thymic stromal lymphopoietin

TSLP is localized in and released from human lung macrophages activated by T2-high and T2-low stimuli: relevance in asthma and COPD

BACKGROUND

Macrophages are the predominant immune cells in the human lung and play a central role in airway inflammation, including asthma and chronic obstructive pulmonary disease (COPD). Thymic stromal lymphopoietin (TSLP), a pleiotropic cytokine mainly expressed by bronchial epithelial cells, plays a key role in asthma and COPD pathobiology. TSLP exists in two variants: the long form (lfTSLP) and a shorter TSLP isoform (sfTSLP). We aimed to localize TSLP in human lung macrophages (HLMs) and investigate the mechanisms of its release from these cells. We also evaluated the effects of the two variants of TSLP on the release of angiogenic factor from HLMs.

METHODS

We employed immunofluorescence and Western blot to localize intracellular TSLP in HLMs purified from human lung parenchyma. HLMs were activated by T2-high (IL-4, IL-13) and T2-low (lipopolysaccharide: LPS) immunological stimuli.

RESULTS

TSLP was detected in HLMs and subcellularly localized in the cytoplasm. IL-4 and LPS induced TSLP release from HLMs. Preincubation of macrophages with brefeldin A, known to disrupt the Golgi apparatus, inhibited TSLP release induced by LPS and IL-4. lfTSLP concentration-dependently induced the release of vascular endothelial growth factor-A (VEGF-A), the most potent angiogenic factor, from HLMs. sfTSLP neither activated nor interfered with the activating property of lfTSLP on macrophages.

CONCLUSIONS

Our results highlight a novel immunologic circuit between HLMs and TSLP. Given the central role of macrophages in airway inflammation, this autocrine loop holds potential translational relevance in understanding innovative aspects of the pathobiology of asthma and chronic inflammatory lung disorders.

IL-13 facilitates ferroptotic death in asthmatic epithelial cells via SOCS1-mediated ubiquitinated degradation of SLC7A11

Th2-high asthma is characterized by elevated levels of type 2 cytokines, such as interleukin 13 (IL-13), and its prevalence has been increasing worldwide. Ferroptosis, a recently discovered type of programmed cell death, is involved in the pathological process of Th2-high asthma; however, the underlying mechanisms remain incompletely understood. In this study, we demonstrated that the serum level of malondialdehyde (MDA), an index of lipid peroxidation, positively correlated with IL-13 level and negatively correlated with the predicted forced expiratory volume in 1 s (FEV1%) in asthmatics. Furthermore, we showed that IL-13 facilitates ferroptosis by upregulating of suppressor of cytokine signaling 1 (SOCS1) through analyzing immortalized airway epithelial cells, human airway organoids, and the ovalbumin (OVA)-challenged asthma model. We identified that signal transducer and activator of transcription 6 (STAT6) promotes the transcription of SOCS1 upon IL-13 stimulation. Moreover, SOCS1, an E3 ubiquitin ligase, was found to bind to solute carrier family 7 member 11 (SLC7A11) and catalyze its ubiquitinated degradation, thereby promoting ferroptosis in airway epithelial cells. Last, we found that inhibiting SOCS1 can decrease ferroptosis in airway epithelial cells and alleviate airway hyperresponsiveness (AHR) in OVA-challenged wide-type mice, while SOCS1 overexpression exacerbated the above in OVA-challenged IL-13-knockout mice. Our findings reveal that the IL-13/STAT6/SOCS1/SLC7A11 pathway is a novel molecular mechanism for ferroptosis in Th2-high asthma, confirming that targeting ferroptosis in airway epithelial cells is a potential therapeutic strategy for Th2-high asthma.

AIM2 participates in house dust mite (HDM)-induced epithelial dysfunctions and ovalbumin (OVA)-induced allergic asthma in infant mice

Objective: Allergen sensitization and high rates of concomitant allergic diseases are characteristic of severe pediatric asthma. The present study was aimed to explore the mechanism of allergic asthma via bioinformatics and experiment investigation. Methods: The GSE27011 dataset contained the expression profiles of normal and pediatric asthma white blood cells was downloaded for analyzing the different expression genes and function enrichment. The allergic asthma model in infant mice was established by ovalbumin (OVA) stimulation. The cellular model was established by house dust mite (HDM)-stimulation in human bronchial epithelial cells. The absent in melanoma 2 (AIM2) knockdown was achieved by intranasal lentivirus injection or cell infection. The bronchoalveolar lavage fluid (BALF) was collected for cell counting and ELISA assessment of cytokines. Lung tissues were collected for HE staining and immunohistochemical (IHC) staining. Real-time PCR and immunoblotting were used for the determination of key gene expressions in mouse and cell models. Results: upregulation of AIM2 gene expression was observed in pediatric asthma patients based on GSE27011 and OVA-induced infant mouse allergic asthma model. AIM2 knockdown ameliorated OVA caused elevation in airway hyper-responsiveness (AHR), elevation in cell quantities (eosinophils, neutrophils, lymphocytes), and levels of cytokines (IL-4, IL-13, TNF-α, and OVA-specific IgE) in BALF. Moreover, AIM2 knockdown relieved OVA-caused histopathological alterations in mouse lungs, up-regulation of AIM2 levels, and NOD1 and receptor-interacting protein 2 (RIP2) protein levels, as well as p65 phosphorylation. In the cell model, AIM2 knockdown partially ameliorated HDM-induced epithelial dysfunctions by promoting cell viability, down-regulating inflammatory cytokines levels, and decreasing the protein levels of AIM2, NOD1, RIP2, and phosphorylated p65. Conclusion: AIM2 participates in HDM-induced epithelial dysfunctions and OVA-induced allergic asthma progression. AIM2 could be a promising target for pediatric allergic asthma treatment regimens, which warrants further in vivo investigations.

Tezepelumab in patients with allergic and eosinophilic asthma

Asthma is a heterogeneous disease commonly driven by allergic and/or eosinophilic inflammation, both of which may be present in severe disease. Most approved biologics for severe asthma are indicated for specific phenotypes and target individual downstream type 2 components of the inflammatory cascade. Tezepelumab, a human monoclonal antibody (immunoglobulin G2λ), binds specifically to thymic stromal lymphopoietin (TSLP), an epithelial cytokine that initiates and sustains allergic and eosinophilic inflammation in asthma. By blocking TSLP, tezepelumab has demonstrated efficacy across known asthma phenotypes and acts upstream of all current clinically used biomarkers. In a pooled analysis of the phase 2b PATHWAY (NCT02054130) and phase 3 NAVIGATOR (NCT03347279) studies, compared with placebo, tezepelumab reduced the annualized asthma exacerbation rate over 52 weeks by 62% (95% confidence interval [CI]: 53, 70) in patients with perennial aeroallergen sensitization (allergic asthma); by 71% (95% CI: 62, 78) in patients with a baseline blood eosinophil count ≥300 cells/μL; and by 71% (95% CI: 59, 79) in patients with allergic asthma and a baseline blood eosinophil count ≥300 cells/μL. This review examines the efficacy and mode of action of tezepelumab in patients with allergic asthma, eosinophilic asthma and coexisting allergic and eosinophilic phenotypes.

Thymic Stromal Lymphopoietin (TSLP) Is Cleaved by Human Mast Cell Tryptase and Chymase

Thymic stromal lymphopoietin (TSLP), mainly expressed by epithelial cells, plays a central role in asthma. In humans, TSLP exists in two variants: the long form TSLP (lfTSLP) and a shorter TSLP isoform (sfTSLP). Macrophages (HLMs) and mast cells (HLMCs) are in close proximity in the human lung and play key roles in asthma. We evaluated the early proteolytic effects of tryptase and chymase released by HLMCs on TSLP by mass spectrometry. We also investigated whether TSLP and its fragments generated by these enzymes induce angiogenic factor release from HLMs. Mass spectrometry (MS) allowed the identification of TSLP cleavage sites caused by tryptase and chymase. Recombinant human TSLP treated with recombinant tryptase showed the production of 1-97 and 98-132 fragments. Recombinant chymase treatment of TSLP generated two peptides, 1-36 and 37-132. lfTSLP induced the release of VEGF-A, the most potent angiogenic factor, from HLMs. By contrast, the four TSLP fragments generated by tryptase and chymase failed to activate HLMs. Long-term TSLP incubation with furin generated two peptides devoid of activating property on HLMs. These results unveil an intricate interplay between mast cell-derived proteases and TSLP. These findings have potential relevance in understanding novel aspects of asthma pathobiology.

Multifactorial Causes and Consequences of TLSP Production, Function, and Release in the Asthmatic Airway

Disruption of the airway epithelium triggers a defensive immune response that begins with the production and release of alarmin cytokines. These epithelial-derived alarmin cytokines, including thymic stromal lymphopoietin (TSLP), are produced in response to aeroallergens, viruses, and toxic inhalants. An alarmin response disproportionate to the inhaled trigger can exacerbate airway diseases such as asthma. Allergens inhaled into previously sensitized airways are known to drive a T2 inflammatory response through the polarization of T cells by dendritic cells mediated by TSLP. Harmful compounds found within air pollution, microbes, and viruses are also triggers causing airway epithelial cell release of TSLP in asthmatic airways. The release of TSLP leads to the development of inflammation which, when unchecked, can result in asthma exacerbations. Genetic and inheritable factors can contribute to the variable expression of TSLP and the risk and severity of asthma. This paper will review the various triggers and consequences of TSLP release in asthmatic airways.

Use of human airway smooth muscle in vitro and ex vivo to investigate drugs for the treatment of chronic obstructive respiratory disorders

Isolated airway smooth muscle has been extensively investigated since 1840 to understand the pharmacology of airway diseases. There has often been poor predictability from murine experiments to drugs evaluated in patients with asthma or chronic obstructive pulmonary disease (COPD). However, the use of isolated human airways represents a sensible strategy to optimise the development of innovative molecules for the treatment of respiratory diseases. This review aims to provide updated evidence on the current uses of isolated human airways in validated in vitro methods to investigate drugs in development for the treatment of chronic obstructive respiratory disorders. This review also provides historical notes on the pioneering pharmacological research on isolated human airway tissues, the key differences between human and animal airways, as well as the pivotal differences between human medium bronchi and small airways. Experiments carried out with isolated human bronchial tissues in vitro and ex vivo replicate many of the main anatomical, pathophysiological, mechanical and immunological characteristics of patients with asthma or COPD. In vitro models of asthma and COPD using isolated human airways can provide information that is directly translatable into humans with obstructive lung diseases. Regardless of the technique used to investigate drugs for the treatment of chronic obstructive respiratory disorders (i.e., isolated organ bath systems, videomicroscopy and wire myography), the most limiting factors to produce high-quality and repeatable data remain closely tied to the manual skills of the researcher conducting experiments and the availability of suitable tissue.

Endotypic heterogeneity and pathogenesis in chronic rhinosinusitis

PURPOSE OF REVIEW

This review aims to provide updates in realms of endotypic heterogeneity, pathogenesis at the molecular level, potential of biomarkers, and cutting-edge scope of biologics in CRS.

RECENT FINDINGS

High-dimensional analyses, such as transcriptomes, and machine learning, have significantly enhanced CRS endotyping, uncovering diverse pathogenetic mechanisms contributing to its heterogeneity. The dynamic process of epithelial remodeling in CRS pathogenesis has gained more clarity and support as exemplified by IL-13 and oncostatin M (OSM) that are shown intricately linked to epithelial barrier dysfunction. Moreover, anti-dsDNA autoantibody, BAFF, periostin, and cystatin SN show promise as potentials biomarkers, offering diagnostic and prognostic value for CRS.

SUMMARY

The identification of inflammatory molecules involved in endotype specific signaling pathways provides insights into the underlying mechanisms and verifiable biomarkers for diagnosis and prediction of disease severity. More comprehensive clinical studies should be conducted to facilitate biologics from bench to bedside in treating CRS.

Thymic stromal lymphopoietin (TSLP) is a substrate for tryptase in patients with mastocytosis

Mastocytosis is a heterogeneous disease associated to uncontrolled proliferation and increased density of mast cells in different organs. This clonal disorder is related to gain-of-function pathogenic variants of the c-kit gene that encodes for KIT (CD117) expressed on mast cell membrane. Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine, which plays a key role in allergic disorders and several cancers. TSLP is a survival and activating factor for human mast cells through the engagement of the TSLP receptor. Activated human mast cells release several preformed mediators, including tryptase. Increased mast cell-derived tryptase is a diagnostic biomarker of mastocytosis. In this study, we found that in these patients serum concentrations of TSLP were lower than healthy donors. There was an inverse correlation between TSLP and tryptase concentrations in mastocytosis. Incubation of human recombinant TSLP with sera from patients with mastocytosis, containing increasing concentrations of tryptase, concentration-dependently decreased TSLP immunoreactivity. Similarly, recombinant β-tryptase reduced the immunoreactivity of recombinant TSLP, inducing the formation of a cleavage product of approximately 10 kDa. Collectively, these results indicate that TSLP is a substrate for human mast cell tryptase and highlight a novel loop involving these mediators in mastocytosis.

Thymic stromal lymphopoietin participates in the host response to intra-amniotic inflammation leading to preterm labor and birth

The aim of this study was to establish the role of thymic stromal lymphopoietin (TSLP) in the intra-amniotic host response of women with spontaneous preterm labor (sPTL) and birth. Amniotic fluid and chorioamniotic membranes (CAM) were collected from women with sPTL who delivered at term (n = 30) or preterm without intra-amniotic inflammation (n = 34), with sterile intra-amniotic inflammation (SIAI, n = 27), or with intra-amniotic infection (IAI, n = 17). Amnion epithelial cells (AEC), Ureaplasma parvum, and Sneathia spp. were also utilized. The expression of TSLP, TSLPR, and IL-7Rα was evaluated in amniotic fluid or CAM by RT-qPCR and/or immunoassays. AEC co-cultured with Ureaplasma parvum or Sneathia spp. were evaluated for TSLP expression by immunofluorescence and/or RT-qPCR. Our data show that TSLP was elevated in amniotic fluid of women with SIAI or IAI and expressed by the CAM. TSLPR and IL-7Rα had detectable gene and protein expression in the CAM; yet, CRLF2 was specifically elevated with IAI. While TSLP localized to all layers of the CAM and increased with SIAI or IAI, TSLPR and IL-7Rα were minimal and became most apparent with IAI. Co-culture experiments indicated that Ureaplasma parvum and Sneathia spp. differentially upregulated TSLP expression in AEC. Together, these findings indicate that TSLP is a central component of the intra-amniotic host response during sPTL.

Severe Asthmatic Responses: The Impact of TSLP

Asthma is a chronic inflammatory disease that affects the lower respiratory system and includes several categories of patients with varying features or phenotypes. Patients with severe asthma (SA) represent a group of asthmatics that are poorly responsive to medium-to-high doses of inhaled corticosteroids and additional controllers, thus leading in some cases to life-threatening disease exacerbations. To elaborate on SA heterogeneity, the concept of asthma endotypes has been developed, with the latter being characterized as T2-high or low, depending on the type of inflammation implicated in disease pathogenesis. As SA patients exhibit curtailed responses to standard-of-care treatment, biologic therapies are prescribed as adjunctive treatments. To date, several biologics that target specific downstream effector molecules involved in disease pathophysiology have displayed superior efficacy only in patients with T2-high, eosinophilic inflammation, suggesting that upstream mediators of the inflammatory cascade could constitute an attractive therapeutic approach for difficult-to-treat asthma. One such appealing therapeutic target is thymic stromal lymphopoietin (TSLP), an epithelial-derived cytokine with critical functions in allergic diseases, including asthma. Numerous studies in both humans and mice have provided major insights pertinent to the role of TSLP in the initiation and propagation of asthmatic responses. Undoubtedly, the magnitude of TSLP in asthma pathogenesis is highlighted by the fact that the FDA recently approved tezepelumab (Tezspire), a human monoclonal antibody that targets TSLP, for SA treatment. Nevertheless, further research focusing on the biology and mode of function of TSLP in SA will considerably advance disease management.

New Concepts in Barrier Dysfunction in CRSwNP and Emerging Roles of Tezepelumab and Dupilumab

BACKGROUND

Epithelial barrier disturbances in CRSwNP patients play an important role in both the innate and adaptive immune responses, contributing to chronic inflammation, olfactory dysfunction, and impairments in quality of life.

OBJECTIVE

To evaluate the role of the sinonasal epithelium in disease and health, review the pathophysiology of epithelial barrier dysfunction in CRSwNP, and the immunologic targets for treatment.

METHODS

Literature review.

RESULTS

Blockade of cytokines such as thymic stromal lymphopoietin (TSLP), IL-4, and IL-13 have shown promise in barrier restoration and IL-13, specifically may be central to olfactory dysfunction.

CONCLUSION

The sinonasal epithelium plays a crucial role in the health and function of the mucosa and immune response. Increased understanding of the local immunologic dysfunction has led to several therapeutics that can potentially restore epithelial barrier function and olfaction. Real world and comparative effectiveness studies are needed.

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.

Biologics and airway remodeling in severe asthma

Asthma is a chronic inflammatory airway disease resulting in airflow obstruction, which in part can become irreversible to conventional therapies, defining the concept of airway remodeling. The introduction of biologics in severe asthma has led in some patients to the complete normalization of previously considered irreversible airflow obstruction. This highlights the need to distinguish a "fixed" airflow obstruction due to structural changes unresponsive to current therapies, from a "reversible" one as demonstrated by lung function normalization during biological therapies not previously obtained even with high-dose systemic glucocorticoids. The mechanisms by which exposure to environmental factors initiates the inflammatory responses that trigger airway remodeling are still incompletely understood. Alarmins represent epithelial-derived cytokines that initiate immunologic events leading to inflammatory airway remodeling. Biological therapies can improve airflow obstruction by addressing these airway inflammatory changes. In addition, biologics might prevent and possibly even revert "fixed" remodeling due to structural changes. Hence, it appears clinically important to separate the therapeutic effects (early and late) of biologics as a new paradigm to evaluate the effects of these drugs and future treatments on airway remodeling in severe asthma.

Sargassum horneri extract containing polyphenol alleviates DNCB-induced atopic dermatitis in NC/Nga mice through restoring skin barrier function

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by skin barrier dysfunction. Sargassum horneri (S. horneri) is a brown alga that has been widely used in traditional medicine of eastern Asian countries. Recent studies proved that a brown alga S. horneri has anti-inflammatory activity. In this study, we investigated the effect of S. horneri ethanol extract (SHE) against AD in 2,4-dinitrobenzene (DNCB) induced AD in NC/Nga mice. We observed that SHE treatment decreased the epidermal thickness and epidermal hyperplasia that had been worsened through DNCB application. Moreover, SHE significantly inhibited the proliferation of mast cells and decreased the expression of IL-13 on CD4⁺ cells prompted by elevated thymic stromal lymphopoietin (TSLP) expression in DNCB-induced AD in mice. We also demonstrated that SHE directly inhibited the expression of keratinocyte-produced TSLP known to exacerbate skin barrier impairment. Especially, the decrease of filaggrin, an integral component of proper skin barrier function through a function in aggregating keratin filaments, observed in DNCB-induced AD mice was significantly improved when treated with SHE. More importantly, we proved that SHE was able to decrease the serum levels of IgG₁ and IgG₂ₐ, two crucial factors of AD, indicating the protective effect of SHE. Taken together, our findings suggest that SHE may protect NC/Nga mice against DNCB-induced AD via promoting skin barrier function.

Angiogenesis, Lymphangiogenesis, and Inflammation in Chronic Obstructive Pulmonary Disease (COPD): Few Certainties and Many Outstanding Questions

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, predominantly affecting the lung parenchyma and peripheral airways, that results in progressive and irreversible airflow obstruction. COPD development is promoted by persistent pulmonary inflammation in response to several stimuli (e.g., cigarette smoke, bacterial and viral infections, air pollution, etc.). Angiogenesis, the formation of new blood vessels, and lymphangiogenesis, the formation of new lymphatic vessels, are features of airway inflammation in COPD. There is compelling evidence that effector cells of inflammation (lung-resident macrophages and mast cells and infiltrating neutrophils, eosinophils, basophils, lymphocytes, etc.) are major sources of a vast array of angiogenic (e.g., vascular endothelial growth factor-A (VEGF-A), angiopoietins) and/or lymphangiogenic factors (VEGF-C, -D). Further, structural cells, including bronchial and alveolar epithelial cells, endothelial cells, fibroblasts/myofibroblasts, and airway smooth muscle cells, can contribute to inflammation and angiogenesis in COPD. Although there is evidence that alterations of angiogenesis and, to a lesser extent, lymphangiogenesis, are associated with COPD, there are still many unanswered questions.

Mechanisms and pathogenesis of chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a heterogeneous disease characterized by local inflammation of the upper airways and is historically divided into 2 main phenotypes: CRS with nasal polyps and CRS without nasal polyps. Inflammation in CRS is mainly characterized by 3 endotypes based on elevation of canonical lymphocyte cytokines: type (T) 1 (T1) by TH1 cytokine IFN-γ, T2 by TH2 cutokines IL-4, IL-5, and IL-13, and T3 by TH17 cytokines including IL-17. Inflammation in both CRS without nasal polyps and CRS with nasal polyps is highly heterogeneous, and the frequency of various endotypes varies geographically around the world. This finding complicates establishment of a unified understanding of the mechanisms of pathogenesis in CRS. Sinonasal epithelium acts as a passive barrier, and epithelial barrier dysfunction is a common feature in CRS induced by endotype-specific cytokines directly and indirectly. The sinonasal epithelium also participates in both innate immunity via recognition by innate pattern-recognition receptors and promotes and regulates adaptive immunity via release of chemokines and innate cytokines including thymic stromal lymphopoietin. The purpose of this review was to discuss the contribution of the epithelium to CRS pathogenesis and to update the field regarding endotypic heterogeneity and various mechanisms for understanding pathogenesis in CRS.

Epithelial immune regulation of inflammatory airway diseases: Chronic rhinosinusitis with nasal polyps (CRSwNP)

BACKGROUND

The epithelial immune regulation is an essential and protective feature of the barrier function of the mucous membranes of the airways. Damage to the epithelial barrier can result in chronic inflammatory diseases, such as chronic rhinosinusitis (CRS) or bronchial asthma. Thymic stromal lymphopoietin (TSLP) is a central regulator in the epithelial barrier function and is associated with type 2 (T2) and non-T2 inflammation.

MATERIALS AND METHODS

The immunology of chronic rhinosinusitis with polyposis nasi (CRSwNP) was analyzed in a literature search, and the existing evidence was determined through searches in Medline, Pubmed as well as the national and international study and guideline registers and the Cochrane Library. Human studies or studies on human cells that were published between 2010 and 2020 and in which the immune mechanisms of TSLP in T2 and non-T2 inflammation were examined were considered.

RESULTS

TSLP is an epithelial cytokine (alarmin) and a central regulator of the immune reaction, especially in the case of chronic airway inflammation. Induction of TSLP is implicated in the pathogenesis of many diseases like CRS and triggers a cascade of subsequent inflammatory reactions.

CONCLUSION

Treatment with TSLP-blocking monoclonal antibodies could therefore open up interesting therapeutic options. The long-term safety and effectiveness of TSLP blockade has yet to be investigated.

Atopic dermatitis: molecular, cellular, and clinical aspects

Atopic dermatitis (AD) is a complicated, inflammatory skin disease, which numerous genetic and environmental factors play roles in its development. AD is categorized into different phenotypes and stages, although they are mostly similar in their pathophysiological aspects. Immune response alterations and structural distortions of the skin-barrier layer are evident in AD patients. Genetic makeup, lifestyle, and environment are also significantly involved in contextual factors. Genes involved in AD-susceptibility, including filaggrin and natural moisturizing, cause considerable structural modifications in the skin's lipid bilayer and cornified envelope. Additionally, the skin's decreased integrity and altered structure are accompanied by biochemical changes in the normal skin microflora's dysbiosis. The dynamic immunological responses, genetic susceptibilities, and structural modifications associated with AD's pathophysiology will be extensively discussed in this review, each according to the latest achievements and findings.

Effect of Angiotensin-Converting-Enzyme Inhibitor and Angiotensin II Receptor Antagonist Treatment on ACE2 Expression and SARS-CoV-2 Replication in Primary Airway Epithelial Cells

Rationale: SARS-CoV-2 gains entrance to airway epithelial cells (AECs) through binding of the viral spike protein to the angiotensin-converting enzyme 2 (ACE2) on the cell surface. However, ACE2 also converts angiotensin II into angiotensin-(1-7) and counterbalances the renin-angiotensin-aldosterone system, with resultant protective effects in the cardiovascular system. Some data suggest that two common antihypertension medications (angiotensin II receptor antagonists, ARBs; and angiotensin-converting-enzyme inhibitors, ACEIs) may increase ACE2 expression in heart and kidney cells, fueling debate about how these widely used medications may modulate SARS-CoV-2 infectivity and risk of COVID-19. Aim: Determine whether exposure of bronchial AECs to the ARB losartan or the ACEI captopril modulate expression of ACE2 by AECs, SARS CoV2 replication, or expression of proinflammatory cytokines and type I and III interferon (IFN) responses. Methods: Primary bronchial AECs from children and adults (n = 19; Ages 8-75 yrs) were differentiated ex vivo at an air-liquid interface to generate organotypic cultures. Cultures were treated with captopril (1 μM) or losartan (2 μM) with culture media changes starting 72 h before infection with SARS-CoV-2. In a biosafety level 3 (BSL-3) facility, cultures were infected with SARS-CoV-2 isolate USA-WA1/2020 at a multiplicity of infection (MOI) of 0.5. At 96 h following infection, RNA and protein were isolated. SARS-CoV-2 replication in cultures was assessed with quantitative PCR (qPCR). ACE2, IL-6, IL-1B, IFNB1, and IFNL2 expression were assessed by qPCR. Results: Neither captopril nor losartan treatment significantly changed ACE2, IL-6, IL-1B, IFNB1, or IFNL2 expression by AECs as compared to SARS-CoV-2 infected AEC cultures without captopril or losartan treatment. At 96 h following infection, SARS-CoV-2 copy number/ng RNA was not significantly different between untreated AEC cultures, cultures treated with captopril, or cultures treated with losartan. Conclusion: These findings suggest that at the level of the airway epithelium neither the ACEI captopril or ARB losartan significantly modify expression of the SARS-CoV-2 entry factor ACE2, nor does either medication increase replication SARS-CoV-2 replication. This ex vivo data is reassuring and is consistent with evolving clinical data suggesting ACEIs and ARBs do not increase the risk for poor prognosis with COVID-19 and may actually reduce the risk of COVID-19 disease.

Monoclonal Antibodies Targeting Alarmins: A New Perspective for Biological Therapies of Severe Asthma

Alarmins are innate cytokines, including thymic stromal lymphopoietin (TSLP), interleukin-33 (IL-33), and interleukin-25 (IL-25), which are mainly produced by airway epithelium and exert a prominent role in asthma pathobiology. In particular, several environmental factors such as allergens, cigarette smoking, airborne pollutants, and infectious agents trigger the release of alarmins, which in turn act as upstream activators of pro-inflammatory pathways underlying type 2 (T2-high) asthma. Indeed, alarmins directly activate group 2 innate lymphoid cells (ILC2), eosinophils, basophils, and mast cells and also stimulate dendritic cells to drive the commitment of naïve T helper (Th) cells towards the Th2 immunophenotype. Therefore, TSLP, IL-33, and IL-25 represent suitable targets for add-on therapies of severe asthma. Within this context, the fully human anti-TSLP monoclonal antibody tezepelumab has been evaluated in very promising randomized clinical trials. Tezepelumab and other anti-alarmins are thus likely to become, in the near future, valuable therapeutic options for the biological treatment of uncontrolled severe asthma.

Human Lung-Resident Macrophages Express and Are Targets of Thymic Stromal Lymphopoietin in the Tumor Microenvironment

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine highly expressed by epithelial cells and several innate and adaptive immune cells. TSLP exerts its biological effects by binding to a heterodimeric complex composed of TSLP receptor (TSLPR) and IL-7Rα. In humans, there are two TSLP isoforms: the short form (sfTSLP), constitutively expressed, and the long form (lfTSLP), which is upregulated in inflammation. TSLP has been implicated in the induction and progression of several experimental and human cancers. Primary human lung macrophages (HLMs), monocyte-derived macrophages (MDMs), and peripheral blood monocytes consitutively expressed sfTSLP mRNA. Incubation of HLMs, MDMs, and monocytes with lipopolysaccharide (LPS) or IL-4, but not with IL-13, induced TSLP release from HLMs. LPS, but not IL-4 or IL-13, induced CXCL8 release from HLMs. LPS, IL-4 alone or in combination with IL-13, induced the expression of lfTSLP, but not of sfTSLP from HLMs. Preincubation of HLMs with IL-4, alone or in combination with IL-13, but not IL-13 alone, synergistically enhanced TSLP release from LPS-activated macrophages. By contrast, IL-4, alone or in combination with IL-13, inhibited LPS-induced CXCL8 release from HLMs. Immunoreactive TSLP was detected in lysates of HLMs, MDMs, and monocytes. Incubation of HLMs with TSLP induced the release of proinflammatory (TNF-α), angiogenic (VEGF-A, angiopoietin 2), and lymphangiogenic (VEGF-C) factors. TSLP, TSLPR, and IL-7Rα were expressed in intratumoral and peritumoral areas of human lung cancer. sfTSLP and lfTSLP mRNAs were differentially expressed in peritumoral and intratumoral lung cancer tissues. The TSLP system, expressed in HLMs, MDMs, and monocytes, could play a role in chronic inflammatory disorders including lung cancer.

Efficacy of Tezepelumab in Patients with Severe, Uncontrolled Asthma and Perennial Allergy

BACKGROUND

Tezepelumab is an anti-thymic stromal lymphopoietin monoclonal antibody. In the PATHWAY phase IIb study (NCT02054130), tezepelumab significantly reduced annualized asthma exacerbation rates (AAERs) versus placebo in adults with severe, uncontrolled asthma.

OBJECTIVE

This post hoc analysis assessed the efficacy of tezepelumab in PATHWAY participants with perennial allergy.

METHODS

Adults (N=550) with severe, uncontrolled asthma were randomized to receive tezepelumab (70 mg or 210 mg every 4 weeks or 280 mg every 2 weeks) or placebo, for 52 weeks. The AAER over 52 weeks was analyzed in patients grouped by sensitivity to perennial aeroallergens and by eligibility for omalizumab treatment according to the US or EU prescribing information. Change from baseline to week 52 in pre-bronchodilator forced expiratory volume in 1 second (FEV₁) and type 2 (T2) biomarkers were assessed in the perennial allergy subgroups.

RESULTS

Across doses, tezepelumab reduced the AAER versus placebo by 66-78% in patients with perennial allergy (n=254) and 67-71% in patients without perennial allergy (n=261). Tezepelumab improved pre-bronchodilator FEV₁ and reduced blood eosinophil counts and fractional exhaled nitric oxide levels over 52 weeks, irrespective of perennial allergy status. Tezepelumab reduced the AAER versus placebo by 61-82% in omalizumab-eligible patients (US, n=159; EU, n=101) and 63-70% in omalizumab-ineligible patients (US, n=372; EU, n=440), respectively.

CONCLUSIONS

Treatment with tezepelumab reduced exacerbations, improved lung function and reduced T2 biomarkers versus placebo in patients with severe, uncontrolled asthma with or without perennial allergy, further supporting its efficacy in a broad population of patients with severe, uncontrolled asthma.

Lactic Acid Bacteria and Natural Product Complex Ameliorates Ovalbumin-Induced Airway Hyperresponsiveness in Mice

The incidence of respiratory diseases, such as asthma, has substantially increased in recent times owing to environmental changes, such as air pollution. Induction of a chronic inflammatory response begins with production of biologically active mediators from the airway epithelium, which attracts and recruits inflammatory cells into the lung airway. In our previous study, we confirmed that Lactobacillus casei HY2782 and Bifidobacterium animalis spp. lactis HY8002 could improve lung inflammation in the COPD animal model. In this study, we investigated the effect of the HY2782 complex against airway hyperresponsiveness by using an ovalbumin (OVA)-induced animal model. An orally administered HY2782 complex on OVA-induced allergic asthma in a BALB/c mouse model was used. The present results showed that the HY2782 complex suppressed total immunoglobulin E in serum and bronchoalveolar lavage fluid (BALF). The cytokine production profile in BALF and serum revealed that the HY2782 complex showed reduced levels of Th2 cytokines among immune factors released due to the elevated allergic response. Levels of inflammatory mediators in BALF, MCP-1, MIP-2, and CXCL-9 were decreased by oral administration of the HY2782 complex. Lower numbers of eosinophils and neutrophils in BALF suggested that inflammation was ameliorated by the HY2782 complex. Histological observation of lung sections also showed infiltration of fewer cells. From results, we suggested that the HY2782 complex effectively responds to improvement of the immune response and airway hypersensitivity reaction because of the anti-inflammatory effect of the Pueraria lobata root extract and antioxidant effect of HY2782.

Tezepelumab: A Potential New Biological Therapy for Severe Refractory Asthma

Thymic stromal lymphopoietin (TSLP) is an innate cytokine, belonging to the group of alarmins, which plays a key pathogenic role in asthma by acting as an upstream activator of cellular and molecular pathways leading to type 2 (T2-high) airway inflammation. Released from airway epithelial cells upon tissue damage induced by several noxious agents including allergens, viruses, bacteria, and airborne pollutants, TSLP activates dendritic cells and group 2 innate lymphoid cells involved in the pathobiology of T2-high asthma. Tezepelumab is a fully human monoclonal antibody that binds to TSLP, thereby preventing its interaction with the TSLP receptor complex. Preliminary results of randomized clinical trials suggest that tezepelumab is characterized by a good safety and efficacy profile in patients with severe, uncontrolled asthma.

Increased Thrombin-Activatable Fibrinolysis Inhibitor in Response to Sublingual Immunotherapy for Allergic Rhinitis

OBJECTIVES/HYPOTHESIS

The objective of this study was to determine the role of thrombin-activatable fibrinolysis inhibitor (TAFI) as a candidate biomarker for therapeutic efficacy of sublingual immunotherapy (SLIT) and to identify the role of TAFI in the pathogenesis of allergic rhinitis (AR).

STUDY DESIGN

Retrospective cohort study and laboratory study.

METHODS

Serum was collected from patients with allergies to Japanese cedar pollen before, during, and after treatment with SLIT. We measured the levels of immunoreactive TAFI, C3a, and C5a in serum by enzyme-linked immunosorbent assay (ELISA) and assessed their relative impact on a combined symptom-medication score. We also examined the impact of TAFI on mast cells and fibroblasts in experiments performed in vitro.

RESULTS

Serum levels of TAFI increased significantly in response to SLIT. By contrast, serum C3a levels decreased significantly over time; we observed a significant negative correlation between serum levels of TAFI versus C3a and symptom-medication score. Mast cell degranulation was inhibited in response to TAFI, as it was the expression of both CCL11 and CCL5 in cultured fibroblasts.

CONCLUSIONS

High serum levels of TAFI may be induced by SLIT. TAFI may play a critical protective role in pathogenesis of AR by inactivating C3a and by inhibiting mast cell degranulation and chemokines expression in fibroblasts.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Severe Adult Asthmas: Integrating Clinical Features, Biology, and Therapeutics to Improve Outcomes

Evaluation and effective management of asthma, and in particular severe asthma, remains at the core of pulmonary practice. Over the last 20-30 years, there has been increasing appreciation that "severe asthma" encompasses multiple different subgroups or phenotypes, each with differing presentations. Using clinical phenotyping, in combination with rapidly advancing molecular tools and targeted monoclonal antibodies (human knockouts), the understanding of these phenotypes, and our ability to treat them, have greatly advanced. Type-2 (T2)-high and -low severe asthmas are now easily identified. Fractional exhaled nitric oxide and blood eosinophil counts can be routinely employed in clinical settings to identify these phenotypes and predict responses to specific therapies, meeting the initial goals of precision medicine. Integration of molecular signals, biomarkers, and clinical responses to targeted therapies has enabled identification of critical molecular pathways and, in certain phenotypes, advanced them to near-endotype status. Despite these advances, little guidance is available to determine which class of biologic is appropriate for a given patient, and current "breakthrough" therapies remain expensive and even inaccessible to many patients. Many of the most severe asthmas, with and without T2-biomarker elevations, remain poorly understood and treated. Nevertheless, conceptual understanding of "the severe asthmas" has evolved dramatically in a mere 25 years, leading to dramatic improvements in the lives of many.

Targetable pathogenic mechanisms in nasal polyposis

Chronic rhinosinusitis with nasal polyps (CRSwNP) represents a challenging disease entity with significant rates of recurrence following appropriate medical and surgical therapy. Recent approval of targeted biologics in CRSwNP compels deeper understanding of underlying disease pathophysiology. Both of the approved biologics for CRSwNP modulate the type 2 inflammatory pathway, and the majority of drugs in the clinical trials pathway are similarly targeted. However, there remain multiple other pathogenic mechanisms relevant to CRSwNP for which targeted therapeutics already exist in other inflammatory diseases that have not been studied directly. In this article we summarize pathogenic mechanisms of interest in CRSwNP and discuss the results of ongoing clinical studies of targeted therapeutics in CRSwNP and other related human inflammatory diseases.

Baicalin suppresses type 2 immunity through breaking off the interplay between mast cell and airway epithelial cell

ETHNOPHARMACOLOGICAL RELEVANCE

The traditional Japanese herbal medicine Shin'iseihaito was reported to ameliorate the airway type 2 inflammatory response in clinical and experimental studies. Airway type 2 inflammatory diseases, including bronchial asthma and eosinophilic chronic rhinosinusitis (ECRS), often coexist and interact with each other. However, it is still unclear how Shin'iseihaito exerts its pharmacological effects on cells involved in airway mucosa.

AIM OF THE STUDY

This study aims to examine the direct effect of baicalin, a representative bioactive compound of Shin'iseihaito, on type 2 immune responses in human airway epithelial cells and mast cells.

MATERIAL AND METHODS

We measured the plasma pharmacokinetics of flavonoids derived from Shin'iseihaito and investigated the effects of baicalin on type 2 immune responses in human airway epithelial cells and human mast cells.

RESULTS

Baicalin, wogonin, and wogonoside were detected in the plasma. The maximum plasma concentration of baicalin was highest at 1610 ng/ml (3.6 μM). In the normal human bronchial epithelial cells treated with baicalin, with or without stimulation by IFN-γ, the IL-33 expression was significantly downregulated. However, baicalin treatment did not affect the levels of thymic stromal lymphopoietin and IL-25. We noted that IL-33-dependent expression of tryptase mRNA in mast cells was significantly inhibited by baicalin. Also, the expression of IL-5 in mast cells enhanced by stimulation with TSLP plus IL-1β was significantly downregulated by baicalin treatment. Moreover, the enhancement of IL-13 expression in mast cells by IL-33 simulation was also significantly inhibited by baicalin.

CONCLUSIONS

Our results prove that by breaking off the vicious circle of mast cells and airway epithelial cells, baicalin may be an effective alternative therapeutic option for the treatment of type 2 inflammatory diseases, such as ECRS and comorbid asthma.

Divergent Mast Cell Responses Modulate Antiviral Immunity During Influenza Virus Infection

Influenza A virus (IAV) is a respiratory pathogen that infects millions of people each year. Both seasonal and pandemic strains of IAV are capable of causing severe respiratory disease with a high risk of respiratory failure and opportunistic secondary infection. A strong inflammatory cytokine response is a hallmark of severe IAV infection. The widespread tissue damage and edema in the lung during severe influenza is largely attributed to an overexuberant production of inflammatory cytokines and cell killing by resident and infiltrating leukocytes. Mast cells (MCs) are a sentinel hematopoietic cell type situated at mucosal sites, including the lung. Poised to react immediately upon detecting infection, MCs produce a vast array of immune modulating molecules, including inflammatory cytokines, chemokines, and proteases. As such, MCs have been implicated as a source of the immunopathology observed in severe influenza. However, a growing body of evidence indicates that MCs play an essential role not only in inducing an inflammatory response but in suppressing inflammation as well. MC-derived immune suppressive cytokines are essential to the resolution of a number of viral infections and other immune insults. Absence of MCs prolongs infection, exacerbates tissue damage, and contributes to dissemination of the pathogen to other tissues. Production of cytokines such as IL-10 and IL-6 by MCs is essential for mitigating the inflammation and tissue damage caused by innate and adaptive immune cells alike. The two opposing functions of MCs—one pro-inflammatory and one anti-inflammatory—distinguish MCs as master regulators of immunity at the site of infection. Amongst the first cells to respond to infection or injury, MCs persist for the duration of the infection, modulating the recruitment, activation, and eventual suppression of other immune cells. In this review, we will discuss the immune modulatory roles of MCs over the course of viral infection and propose that the immune suppressive mediators produced by MCs are vital to minimizing immunopathology during influenza infection.

Effect of lipopolysaccharide and polyinosinic:polycytidylic acid in a murine model of nasal polyp

Several factors, including bacterial and viral infections, have been associated with rhinosinusitis and nasal tissue remodelling that may result in nasal polyp formation. However, the potential role of bacterial or viral stimuli triggering polyp development is unclear. Here, we used lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid [poly(I:C)] in a murine model of allergic rhinosinusitis to compare different effects of bacterial- and virus-derived stimuli in the pathogenesis of nasal polyp formation. Briefly, BALB/c mice were sensitised and challenged with ovalbumin and staphylococcal enterotoxin, with or without LPS or poly(I:C), and the consequent histopathological profiles, cytokines, and systemic humoral responses were studied. While no significant differences in polyp formations and epithelial disruptions were observed among the experimental groups, the local cell recruitment patterns slightly differed in animals that received either LPS or poly(I:C). Additionally, the local immune environments generated by LPS or poly(I:C) stimulation varied. LPS stimulation induced a marked Th1/Th17 response and predominantly neutrophilic nasal polyp formations, whereas poly(I:C) induced a Th2-skewed environment in neutrophilic nasal polyp development. Overall, our findings show that both cell recruitment patterns and local immune environments induced by these two stimuli differ, which may have implications in the physiopathology of rhinosinusitis with nasal polyp.

Thymic Stromal Lymphopoietin Promotes MRGPRX2-Triggered Degranulation of Skin Mast Cells in a STAT5-Dependent Manner with Further Support from JNK

Thymic stromal lymphopoietin (TSLP) is released by epithelial cells following disturbed homeostasis to act as “alarmin” and driver of Th2-immunity. Aberrant TSLP expression is a hallmark of atopic diseases, including atopic dermatitis (AD). Mast cells (MCs) are overabundant in AD lesions and show signs of degranulation, but it remains unknown whether TSLP contributes to granule discharge. Degranulation of skin MCs proceeds via two major routes, i.e., FcεRI-dependent (allergic) and MRGPRX2-mediated (pseudo-allergic/neurogenic). Evidence is accumulating that MRGPRX2 may be crucial in the context of skin diseases, including eczema. The current study reveals TSLP as a novel priming factor of human skin MCs. Interestingly, TSLP selectively cooperates with MRGPRX2 to support granule discharge, while it does not impact spontaneous or FcεRI-driven exocytosis. TSLP-assisted histamine liberation triggered by compound 48/80 or Substance P, two canonical MRGPRX2 agonists, was accompanied by an increase in CD107a+ cells (a MC activation marker). The latter process was less potent, however, and detectable only at the later of two time points, suggesting TSLP may prolong opening of the granules. Mechanistically, TSLP elicited phosphorylation of STAT5 and JNK in skin MCs and the reinforced degranulation critically depended on STAT5 activity, while JNK had a contributory role. Results from pharmacological inhibition were confirmed by RNA-interference, whereby silencing of STAT5 completely abolished the priming effect of TSLP on MRGPRX2-mediated degranulation. Collectively, TSLP is the first factor to favor MRGPRX2- over FcεRI-triggered MC activation. The relevance of TSLP, MCs and MRGPRX2 to pruritis and atopic skin pathology indicates broad repercussions of the identified connection.

Differences in the mechanism of type 1 and type 2 diabetes-induced skin dryness by using model mice

Diabetes induces dry skin that may cause infective diseases. In this study, we aimed to clarify the mechanism of diabetes-induced skin dryness in animal models. We also examined the difference in the mechanism of skin dryness in type 1 and type 2 diabetes. We examined skin dryness in type 1 diabetes model mice (streptozotocin [STZ] induction), non-obesity type 2 diabetes model mice (newborn STZ injection), and obesity type 2 diabetes model mice (KK-Ay/TaJcl). An increase in transepidermal water loss was observed in the type 1 diabetes model mice, and reduced skin hydration was observed in the type 2 diabetes model mice. In the type 1 diabetes model mice, an increase in advanced glycation end products and matrix metalloproteinase-9 led to a decline in collagen IV level, inducing skin dryness. In the obesity type 2 diabetes model mice, an increase in the release of histamine and hyaluronidase by mast cells resulted in a decline in the level of hyaluronic acid, inducing skin dryness. However, in the non-obesity type 2 diabetes model mice, the main factors of skin dryness could not be clearly identified. Nevertheless, inflammatory cytokine levels increased. We hypothesize that inflammatory cytokines disrupt the collagen of the skin. Diabetes caused skin dryness in each mouse model, and the mechanism of skin dryness differed by diabetes type.

The Airway Epithelium-A Central Player in Asthma Pathogenesis

Asthma is a chronic inflammatory airway disease characterized by variable airflow obstruction in response to a wide range of exogenous stimuli. The airway epithelium is the first line of defense and plays an important role in initiating host defense and controlling immune responses. Indeed, increasing evidence indicates a range of abnormalities in various aspects of epithelial barrier function in asthma. A central part of this impairment is a disruption of the airway epithelial layer, allowing inhaled substances to pass more easily into the submucosa where they may interact with immune cells. Furthermore, many of the identified susceptibility genes for asthma are expressed in the airway epithelium. This review focuses on the biology of the airway epithelium in health and its pathobiology in asthma. We will specifically discuss external triggers such as allergens, viruses and alarmins and the effect of type 2 inflammatory responses on airway epithelial function in asthma. We will also discuss epigenetic mechanisms responding to external stimuli on the level of transcriptional and posttranscriptional regulation of gene expression, as well the airway epithelium as a potential treatment target in asthma.

Inhibition of uric acid or IL-1β ameliorates respiratory syncytial virus immunopathology and development of asthma

BACKGROUND

Respiratory syncytial virus (RSV) affects most infants early in life and is associated with increased asthma risk. The specific mechanism remains unknown.

OBJECTIVE

To investigate the role of uric acid (UA) and IL-1β in RSV immunopathology and asthma predisposition.

METHODS

Tracheal aspirates from human infants with and without RSV were collected and analyzed for pro-IL-1β mRNA and protein to establish a correlation in human disease. Neonatal mouse models of RSV were employed, wherein mice infected at 6-7 days of life were analyzed at 8 days postinfection, 5 weeks postinfection, or after a chronic cockroach allergen asthma model. A xanthine oxidase inhibitor or IL-1 receptor antagonist was administered during RSV infection.

RESULTS

Human tracheal aspirates from RSV-infected infants showed elevated pro-IL-1β mRNA and protein. Inhibition of UA or IL-1β during neonatal murine RSV infection decreased mucus production, reduced cellular infiltrates to the lung (especially ILC2s), and decreased type 2 immune responses. Inhibition of either UA or IL-1β during RSV infection led to chronic reductions in pulmonary immune cell composition and reduced type 2 immune responses and reduced similar responses after challenge with cockroach antigen.

CONCLUSIONS

Inhibiting UA and IL-1β during RSV infection ameliorates RSV immunopathology, reduces the consequences of allergen-induced asthma, and presents new therapeutic targets to reduce early-life viral-induced asthma development.

Contribution of mast cells in irritant-induced airway epithelial barrier impairment in vitro

The airway epithelium is continuously exposed to environmental irritants, which can cause adverse effects such as irritant-induced asthma (IIA). Mast cells are located near airway epithelia and are able to respond to a variety of stimuli. We aimed to investigate whether mast cells influence the response of the epithelium upon irritant exposure. Two cell lines and three different seeding conditions, that is, bronchial epithelial cells (16HBE) only, 16HBE with mast cells (HMC-1's) basolaterally, and 16HBE with HMC-1's apically, were established. Upon exposure to the environmental irritants, graphene (G), graphene oxide (GO), diesel exhaust particles (DEPs) or hypochlorite (ClO^-), transepithelial electrical resistance (TEER) and paracellular flux of fluorescent-labeled dextrans were determined, along with the release of mediators. Identical experiments were conducted with the Ca²⁺ ionophore ionomycin. Exposure to G and GO induced a significant and permanent decrease of approximately 70% in TEER after 3 h of exposure, whereas DEP and ClO^- exposure resulted in a transient decrease of approximately 20% in TEER. This response pattern was similar in all the different seeding conditions. After 24 h of exposure, fluorescein isothiocyanate-dextran transport was 10-fold greater for G and 5-fold greater for GO in each of the tested seeding conditions, while DEP and ClO^- induced no change compared to the control. Upon exposure to the irritants, 16HBE did not release thymic stromal lymphopoietin, interleukin 33 (IL-33), or IL-1α, and HMC-1 cells did not release histamine, IL-6, or IL-8. Epithelial barrier integrity upon treatment with ionomycin was not affected by the presence of HMC-1 cells. A limited amount of IL-6 and IL-8 was released by ionomycin-exposed HMC-1 cells. To conclude, we found that the studied environmental irritants do not directly or indirectly activate HMC-1 cells. These mast cells did not influence the epithelial barrier function upon environmental exposure, and thus currently do not provide additional information for the underlying mechanism of IIA.

Thymic stromal lymphopoietin: its role and potential as a therapeutic target in asthma

INTRODUCTION

Thymic stromal lymphopoietin (TSLP), an epithelial cytokine (alarmin), is a central regulator of the immune response to inhaled environmental insults such as allergens, viruses and pollutants, initiating a cascade of downstream inflammation. There is compelling evidence that TSLP plays a major role in the pathology of asthma, and therapies that aim to block its activity are in development.

AREAS COVERED

We review studies conducted in humans and human cells, largely published in PubMed January 2010-October 2019, that investigated the innate and adaptive immune mechanisms of TSLP in asthma relevant to type 2-driven (eosinophilic/allergic) inflammation and non-type 2-driven (non-eosinophilic/non-allergic) inflammation, and the role of TSLP as a mediator between immune cells and structural cells in the airway. Clinical data from studies evaluating TSLP blockade are also discussed.

EXPERT OPINION

The position of TSLP at the top of the inflammatory cascade makes it a promising therapeutic target in asthma. Systemic anti-TSLP monoclonal antibody therapy with tezepelumab has yielded positive results in clinical trials to date, reducing exacerbations and biomarkers of inflammation in patients across the spectrum of inflammatory endotypes. Inhaled anti-TSLP is an alternative route currently under evaluation. The long-term safety and efficacy of TSLP blockade need to be evaluated.

Respiratory Viral Infections in Exacerbation of Chronic Airway Inflammatory Diseases: Novel Mechanisms and Insights From the Upper Airway Epithelium

Respiratory virus infection is one of the major sources of exacerbation of chronic airway inflammatory diseases. These exacerbations are associated with high morbidity and even mortality worldwide. The current understanding on viral-induced exacerbations is that viral infection increases airway inflammation which aggravates disease symptoms. Recent advances in in vitro air-liquid interface 3D cultures, organoid cultures and the use of novel human and animal challenge models have evoked new understandings as to the mechanisms of viral exacerbations. In this review, we will focus on recent novel findings that elucidate how respiratory viral infections alter the epithelial barrier in the airways, the upper airway microbial environment, epigenetic modifications including miRNA modulation, and other changes in immune responses throughout the upper and lower airways. First, we reviewed the prevalence of different respiratory viral infections in causing exacerbations in chronic airway inflammatory diseases. Subsequently we also summarized how recent models have expanded our appreciation of the mechanisms of viral-induced exacerbations. Further we highlighted the importance of the virome within the airway microbiome environment and its impact on subsequent bacterial infection. This review consolidates the understanding of viral induced exacerbation in chronic airway inflammatory diseases and indicates pathways that may be targeted for more effective management of chronic inflammatory diseases.

Comparison of asthma phenotypes in OVA-induced mice challenged via inhaled and intranasal routes

Background

The respiratory system is exposed to various allergens via inhaled and intranasal routes. Murine models of allergic lung disease have been developed to clarify the mechanisms underlying inflammatory responses and evaluate the efficacy of novel therapeutics. However, there have been no comparative studies on differences in allergic phenotypes following inhaled vs. intranasal allergen challenge. In this study, we compared the asthmatic features of mice challenged via different routes following allergen sensitization and investigated the underlying mechanisms.

Methods

To establish ovalbumin (OVA)-induced allergic asthma models, BALB/c mice were sensitized to 20 μg OVA with 1 mg aluminum hydroxide by the intraperitoneal route and then challenged by inhalation or intranasal administration with 5% OVA for 3 consecutive days. Cellular changes and immunoglobulin (Ig) E levels in bronchoalveolar lavage fluid (BALF) and serum, respectively, were assessed. Histological changes in the lungs were examined by hematoxylin and eosin (H&E) and periodic acid Schiff (PAS) staining. Levels of T helper (Th)2 cytokines including interleukin (IL)-4, -5, and -13 in BALF and epithelial cytokines including IL-25 and -33 in BALF and lung tissues were measured by enzyme-linked immunosorbent assay and western blotting. Airway hyperresponsiveness (AHR) was evaluated by assessing airway resistance (Rrs) and elastance (E) via an invasive method.

Results

OVA-sensitized and challenged mice showed typical asthma features such as airway inflammation, elevated IgE level, and AHR regardless of the challenge route. However, H&E staining showed that inflammation of pulmonary vessels, alveolar ducts, and alveoli were enhanced by inhaled as compared to intranasal OVA challenge. PAS staining showed that intranasal OVA challenge induced severe mucus production accompanied by inflammation in bronchial regions. In addition, Th2 cytokine levels in BALF and AHR in lung were increased to a greater extent by inhalation than by intranasal administration of OVA. Epithelial cytokine expression, especially IL-25, was increased in the lungs of mice in the inhaled OVA challenge group.

Conclusion

OVA-sensitized mice exhibit different pathophysiological patterns of asthma including expression of epithelial cell-derived cytokines depending on the OVA challenge route. Thus, some heterogeneous phenotypes of human asthma can be replicated by varying the mode of delivery after OVA sensitization.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Airway epithelium-shifted mast cell infiltration regulates asthmatic inflammation via IL-33 signaling

Asthma is a heterogeneous syndrome that has been subdivided into physiologic phenotypes and molecular endotypes. The most specific phenotypic manifestation of asthma is indirect airway hyperresponsiveness (AHR), and a prominent molecular endotype is the presence of type 2 inflammation. The underlying basis for type 2 inflammation and its relationship to AHR are incompletely understood. We assessed the expression of type 2 cytokines in the airways of subjects with and without asthma who were extensively characterized for AHR. Using quantitative morphometry of the airway wall, we identified a shift in mast cells from the submucosa to the airway epithelium specifically associated with both type 2 inflammation and indirect AHR. Using ex vivo modeling of primary airway epithelial cells in organotypic coculture with mast cells, we show that epithelial-derived IL-33 uniquely induced type 2 cytokines in mast cells, which regulated the expression of epithelial IL33 in a feed-forward loop. This feed-forward loop was accentuated in epithelial cells derived from subjects with asthma. These results demonstrate that type 2 inflammation and indirect AHR in asthma are related to a shift in mast cell infiltration to the airway epithelium, and that mast cells cooperate with epithelial cells through IL-33 signaling to regulate type 2 inflammation.

Tezepelumab: a novel biological therapy for the treatment of severe uncontrolled asthma

Introduction: Thymic stromal lymphopoietin (TSLP) is overexpressed in the airways of severe asthmatics and is an upstream cytokine that orchestrates inflammatory responses in asthma. TSLP exerts its effects by binding to a high affinity heteromeric receptor complex composed of TSLPR and IL-7Rα. An association of polymorphisms in TSLP with airway hyperresponsiveness, IgE, eosinophilia and asthma has been documented. TSLP has been implicated in asthma pathophysiology. Tezepelumab is a first-in-class human monoclonal antibody that binds to TSLP, thus inhibiting its interaction with TSLP receptor complex. Tezepelumab given as an add-on-therapy to patients with severe uncontrolled asthma has shown safety, tolerability and efficacy. Several trials are evaluating the long-term safety and the efficacy of tezepelumab in adults and adolescents with severe uncontrolled asthma.Areas covered: We provide an overview of the monoclonal antibody therapeutics market for severe uncontrolled asthma, examine the underlying pathophysiology that drives TSLP and discuss the use of tezepelumab for the treatment of severe uncontrolled asthma,Expert opinion: TSLP is a promising target for T2-high and perhaps some patients with T2-low asthma. The results of preliminary clinical trials are encouraging. Several unanswered questions concerning basic pathophysiological aspects of TSLP variants, the long-term safety and efficacy of tezepelumab with different phenotypes/endotypes of asthma should be addressed.

Thymic Stromal Lymphopoietin Interferes with the Apoptosis of Human Skin Mast Cells by a Dual Strategy Involving STAT5/Mcl-1 and JNK/Bcl-xL

Mast cells (MCs) play critical roles in allergic and inflammatory reactions and contribute to multiple pathologies in the skin, in which they show increased numbers, which frequently correlates with severity. It remains ill-defined how MC accumulation is established by the cutaneous microenvironment, in part because research on human MCs rarely employs MCs matured in the tissue, and extrapolations from other MC subsets have limitations, considering the high level of MC heterogeneity. Thymic stromal lymphopoietin (TSLP)—released by epithelial cells, like keratinocytes, following disturbed homeostasis and inflammation—has attracted much attention, but its impact on skin MCs remains undefined, despite the vast expression of the TSLP receptor by these cells. Using several methods, each detecting a distinct component of the apoptotic process (membrane alterations, DNA degradation, and caspase-3 activity), our study pinpoints TSLP as a novel survival factor of dermal MCs. TSLP confers apoptosis resistance via concomitant activation of the TSLP/ signal transducer and activator of transcription (STAT)-5 / myeloid cell leukemia (Mcl)-1 route and a newly uncovered TSLP/ c-Jun-N-terminal kinase (JNK)/ B-cell lymphoma (Bcl)-x_L axis, as evidenced by RNA interference and pharmacological inhibition. Our findings highlight the potential contribution of TSLP to the MC supportive niche of the skin and, vice versa, highlight MCs as crucial responders to TSLP in the context of TSLP-driven disorders.

Thymic stromal lymphopoietin production induced by skin irritation results from concomitant activation of protease-activated receptor 2 and interleukin 1 pathways

BACKGROUND

Thymic stromal lymphopoietin (TSLP) mediates proallergic T helper 2-type responses by acting on leucocytes. Endogenous pathways regulating TSLP production are poorly defined.

OBJECTIVES

To uncover the mechanisms by which skin barrier disruption elicits TSLP production and to delineate the level at which individual mechanistic components may converge.

METHODS

A combination of primary keratinocytes, skin explants and in vivo strategies was employed. Murine skin was tape stripped in the presence of neutralizing antibodies or antagonists. Cells and explants were stimulated with interleukin (IL)-1 and protease-activated receptor 2 agonist (PAR-2-Ag). TSLP levels were quantified by enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction. Chromatin immunoprecipitation and promoter reporter assays were used to examine recruitment and functional activity of nuclear factor kappa B (NF-κB) at the TSLP promoter.

RESULTS

TSLP induction in mouse skin occurred in a PAR-2- and IL-1-dependent manner. This scenario was duplicated by exogenous IL-1 plus PAR-2-Ag vs. each stimulus alone. Joint activity of PAR-2 and IL-1 was also observed in human keratinocytes. The TSLP promoter was identified as the target of PAR-2/IL-1, whereby PAR-2 activation augmented the recruitment of NF-κB and transcriptional activation over IL-1 alone. Combined treatment showed activity at concentrations of IL-1 unable to elicit NF-κB activity on their own.

CONCLUSIONS

Skin barrier disruption activates the IL-1 and the PAR-2 pathways, which act in concert to activate the TSLP promoter and possibly other inflammatory genes. Awareness of this combined activity may permit a more flexible clinical management by selective targeting of either pathway individually or collectively. What's already known about this topic? Thymic stromal lymphopoietin (TSLP) is rapidly induced upon skin perturbation and mediates proallergic T helper 2-type responses by acting on leucocytes. Endogenous control of TSLP expression is poorly understood, but interleukin (IL)-1 is one regulator in the cutaneous environment In addition to IL-1, protease-activated receptor 2 (PAR-2) organizes central inflammatory pathways in the skin. What does this study add? IL-1 and PAR-2 pathways cooperate in driving TSLP production in mice and humans. Pathway integration occurs at the level of the TSLP promoter through enhanced recruitment and transcriptional activation of nuclear factor kappa B. When PAR-2 is co-stimulated, very low IL-1 levels (inactive by themselves) can induce biologically meaningful responses in the skin environment. What is the translational message? Physical skin irritation results in robust TSLP production by simultaneous activation of PAR-2 and IL-1 pathways.

[Immunology of chronic rhinosinusitis with nasal polyps as a basis for treatment with biologicals]

BACKGROUND

Chronic rhinosinusitis (CRS) is a heterogeneous and multifactorial inflammation of the nasal and paranasal mucosa. Until now, no internationally standardized classification could be developed. In most cases, CRS is phenotypically classified according to chronic rhinosinusitis with (CRScNP) and without nasal polyps (CRSsNP). However, recent studies could show that there are numerous endotypes within these phenotypes based on different inflammatory mechanisms. This review describes the important immunological mechanisms of CRScNP and highlights modern treatment options with biologicals directly addressing particular immunological processes.

METHODS

Current knowledge on immunological and molecular processes of CRS, particularly CRScNP, was extracted from Medline, PubMed, national and international study- and guideline-registers, and the Cochrane library by a systematic review of the literature.

RESULTS

Based on current literature, various immunological mechanisms for CRS and CRScNP could be identified. Relevant studies for the treatment of eosinophilic conditions such as asthma or CRScNP are presented and, if available, results of these studies are discussed.

CONCLUSION

The growing insight into the underlying immunological mechanisms of CRScNP could pave the way for new personalized treatment options such as biologicals in the future.

Thymic Stromal Lymphopoietin Isoforms, Inflammatory Disorders, and Cancer

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine originally isolated from a murine thymic stromal cell line. TSLP exerts its biological effects by binding to a high-affinity heteromeric complex composed of thymic stromal lymphopoietin receptor chain and IL-7Rα. TSLP is primarily expressed by activated lung and intestinal epithelial cells, keratinocytes, and fibroblasts. However, dendritic cells (DCs), mast cells, and presumably other immune cells can also produce TSLP. Different groups of investigators have demonstrated the existence of two variants for TSLP in human tissues: the main isoform expressed in steady state is the short form (sf TSLP), which plays a homeostatic role, whereas the long form (lfTSLP) is upregulated in inflammatory conditions. In addition, there is evidence that in pathological conditions, TSLP can be cleaved by several endogenous proteases. Several cellular targets for TSLP have been identified, including immune (DCs, ILC2, T and B cells, NKT and Treg cells, eosinophils, neutrophils, basophils, monocytes, mast cells, and macrophages) and non-immune cells (platelets and sensory neurons). TSLP has been originally implicated in a variety of allergic diseases (e.g., atopic dermatitis, bronchial asthma, eosinophilic esophagitis). Emerging evidence indicates that TSLP is also involved in chronic inflammatory (i.e., chronic obstructive pulmonary disease and celiac disease) and autoimmune (e.g., psoriasis, rheumatoid arthritis) disorders and several cancers. These emerging observations greatly widen the role of TSLP in different human diseases. Most of these studies have not used tools to analyze the expression of the two TSLP isoforms. The broad pathophysiologic profile of TSLP has motivated therapeutic targeting of this cytokine. Tezepelumab is a first-in-class human monoclonal antibody (1) that binds to TSLP inhibiting its interaction with TSLP receptor complex. Tezepelumab given as an add-on-therapy to patients with severe uncontrolled asthma has shown safety and efficacy. Several clinical trials are evaluating the safety and the efficacy of tezepelumab in different inflammatory disorders. Monoclonal antibodies used to neutralize TSLP should not interact or hamper the homeostatic effects of sf TSLP.