Allergen-induced Changes in Bone Marrow and Airway Dendritic Cells in Subjects with Asthma

Comparative phenotype of circulating versus tissue immune cells in human lung and blood compartments during health and disease

The lung is a dynamic mucosal surface constantly exposed to a variety of immunological challenges including harmless environmental antigens, pollutants, and potentially invasive microorganisms. Dysregulation of the immune system at this crucial site is associated with a range of chronic inflammatory conditions including asthma and Chronic Pulmonary Obstructive Disease (COPD). However, due to its relative inaccessibility, our fundamental understanding of the human lung immune compartment is limited. To address this, we performed flow cytometric immune phenotyping of human lung tissue and matched blood samples that were isolated from 115 donors undergoing lung tissue resection. We provide detailed characterization of the lung mononuclear phagocyte and T cell compartments, demonstrating clear phenotypic differences between lung tissue cells and those in peripheral circulation. Additionally, we show that CD103 expression demarcates pulmonary T cells that have undergone recent TCR and IL-7R signalling. Unexpectedly, we discovered that the immune landscape from asthmatic or COPD donors was broadly comparable to controls. Our data provide a much-needed expansion of our understanding of the pulmonary immune compartment in both health and disease.

Mild asthma: Lessons learned and remaining questions

Patients living with mild disease represent the largest proportion of asthma patients. There are significant challenges in proposing a definition that would best describe these patients, while also accurately identifying at-risk individuals. Current literature suggests considerable inflammatory and clinical heterogeneity within this group. Research has shown that these patients are at risk of poor control, exacerbations, lung function decline, and death. Despite conflicting data on its prevalence, eosinophilic inflammation appears to be a predictor of poorer outcomes in mild asthma. There is an immediate need to better understand phenotypic clusters in mild asthma. It is also important to understand factors that influence disease progression and remission, as it is evident that both vary in mild asthma. Guided by robust literature that supports inhaled corticosteroid-based strategies over short-acting beta-agonist (SABA) reliant regimens, the management of these patients has evolved considerably. Unfortunately, SABA use remains high in clinical practice despite strong advocacy from the Global Initiative for Asthma. Future mild asthma research should explore the role of biomarkers, develop prediction tools based on composite risk scores, and explore targeted therapies at least for at-risk individuals.

Questions in Mild Asthma: An Official American Thoracic Society Research Statement

Background: Patients with mild asthma are believed to represent the majority of patients with asthma. Disease-associated risks such as exacerbations, lung function decline, and death have been understudied in this patient population. There have been no prior efforts from major societies to describe research needs in mild asthma. Methods: A multidisciplinary, diverse group of 24 international experts reviewed the literature, identified knowledge gaps, and provided research recommendations relating to mild asthma definition, pathophysiology, and management across all age groups. Research needs were also investigated from a patient perspective, generated in conjunction with patients with asthma, caregivers, and stakeholders. Of note, this project is not a systematic review of the evidence and is not a clinical practice guideline. Results: There are multiple unmet needs in research on mild asthma driven by large knowledge gaps in all areas. Specifically, there is an immediate need for a robust mild asthma definition and an improved understanding of its pathophysiology and management strategies across all age groups. Future research must factor in patient perspectives. Conclusions: Despite significant advances in severe asthma, there remain innumerable research areas requiring urgent attention in mild asthma. An important first step is to determine a better definition that will accurately reflect the heterogeneity and risks noted in this group. This research statement highlights the topics of research that are of the highest priority. Furthermore, it firmly advocates the need for engagement with patient groups and for more support for research in this field.

Catching Our Breath: Updates on the Role of Dendritic Cell Subsets in Asthma

Dendritic cells (DCs), as potent antigen presenting cells, are known to play a central role in the pathophysiology of asthma. The understanding of DC biology has evolved over the years to include multiple subsets of DCs with distinct functions in the initiation and maintenance of asthma. Furthermore, asthma is increasingly recognized as a heterogeneous disease with potentially diverse underlying mechanisms. The goal of this review is to summarize the role of DCs and the various subsets therein in the pathophysiology of asthma and highlight some of the crucial animal models shaping the field today. Potential future avenues of investigation to address existing gaps in knowledge are discussed.

Dectin-2 promotes house dust mite-skewed Th2 response through the activation of cDC2s

The role of Dectin-2 (gene symbol, Clec4n) in house dust mite (HDM) induced Th2 immune response and the exact mechanism remains controversial. In this study, we illustrated that, Clec4n^-/- mice had decreased Th2 immune response following HDM challenge, which may ascribe to dramatically reduced type 2 conventional dendritic cells (cDC2s) in lung of Clec4n^-/- mice, as cDC2s from lung of Clec4n^-/- mice after challenging had less ability to induce Th2 response with decreased production of IL-4/IL-13. Further in vitro experiments showed the activation of Clec4n^-/--BMDCs significantly decreased after HDM stimulation accompanied with decreased activation of Syk-NF-κB and Syk-JNK signal pathway. Importantly, Dectin-2 expression in PBMCs from asthmatic patients was significantly higher than that in healthy controls. Taken together, these results demonstrated that Dectin-2 could promote cDC2s activation in lung, which polarizes Th2 immune response outlining a novel mechanism of asthma development.

Sex Plays a Multifaceted Role in Asthma Pathogenesis

Sex is considered an important risk factor for asthma onset and exacerbation. The prevalence of asthma is higher in boys than in girls during childhood, which shows a reverse trend after puberty—it becomes higher in adult females than in adult males. In addition, asthma severity, characterized by the rate of hospitalization and relapse after discharge from the emergency department, is higher in female patients. Basic research indicates that female sex hormones enhance type 2 adaptive immune responses, and male sex hormones negatively regulate type 2 innate immune responses. However, whether hormone replacement therapy in postmenopausal women increases the risk of current asthma and asthma onset remains controversial in clinical settings. Recently, sex has also been shown to influence the pathophysiology of asthma in its relationship with genetic or other environmental factors, which modulate asthmatic immune responses in the airway mucosa. In this narrative review, we highlight the role of sex in the continuity of the asthmatic immune response from sensing allergens to Th2 cell activation based on our own data. In addition, we elucidate the interactive role of sex with genetic or environmental factors in asthma exacerbation in women.

Allergen Provocation Tests in Respiratory Research: Building on 50 Years of Experience

Allergen provocation test is an established model of allergic airway diseases, including asthma and allergic rhinitis, allowing the study of allergen-induced changes in respiratory physiology and inflammatory mechanisms in sensitised individuals as well as their associations. In the upper airways, allergen challenge is focused on the clinical and pathophysiological sequelae of the early allergic response and applied both as a diagnostic tool and in research settings. In contrast, the bronchial allergen challenge has almost exclusively served as a research tool in specialised research settings with a focus on the late asthmatic response and the underlying type 2 inflammation. The allergen-induced late asthmatic response is also characterised by prolonged airway narrowing, increased non-specific airway hyperresponsiveness and features of airway remodelling including the small airways, and hence, allows the study of several key mechanisms and features of asthma. In line with these characteristics, the allergen challenge has served as a valued tool to study the crosstalk of the upper and lower airways and in proof of mechanism studies of drug development. In recent years, several new insights into respiratory phenotypes and endotypes including the involvement of the upper and small airways, innovative biomarker sampling methods and detection techniques, refined lung function testing as well as targeted treatment options, further shaped the applicability of the allergen provocation test in precision medicine. These topics, along with descriptions of subject populations and safety, in line with the updated GINA2021, will be addressed in this paper.

IL-33 receptor expression on myeloid and plasmacytoid dendritic cells after allergen challenge in patients with allergic rhinitis

The diversity of immune responses in allergic diseases is critically mediated by dendritic cells (DCs), including myeloid and plasmacytoid DCs. Allergen inhalation increased the release of IL-33 from patients with allergic rhinitis (AR), which affecting the downstream cells by binding to its receptor (ST2). However, the effects of inhaled allergens on the expression of ST2 by DCs and IL-33 on the function of mDCs are unknown. The levels of ST2⁺mDCs and ST2⁺pDCs in the blood from patients with AR and healthy subjects were examined using flow cytometry. Moreover, the patients were challenged using the allergens and the levels of ST2⁺mDCs and ST2⁺pDCs were investigated at different time points. We found that there were higher levels of ST2⁺ mDCs and ST2⁺ pDCs in patients with AR, and these levels were further increased 0.5 h after allergen inhalation. Additionally, the type 2 immune response was upregulated after challenge. IL-33 treatment increased the expression of ST2 on mDCs. Our study demonstrated that ST2 was upregulated on DCs after allergen inhalation and that mDCs responded directly to IL-33 through ST2, suggesting that the IL-33/ST2 axis might play an important role in the pathogenesis of allergic rhinitis by DCs.

Response of upper and lower airway inflammation to bronchial challenge with house dust mite in Chinese asthmatics: a pilot study

Background

Allergen nasal challenge can induce increase of eosinophils in sputum, but report about eosinophilic inflammation in upper airway after allergen bronchial challenge in Chinese asthmatics was rare. The article aims to evaluate response of upper and lower airways to house dust mite (HDM) allergen bronchial challenge.

Methods

HDM allergen bronchial challenge was carried out in asthmatic patients with allergic rhinitis (AR). Bronchial methacholine challenge and blood test were performed before and at 24 hours after allergen challenge. Nasal lavage and induced sputum for differential cells count and fractional exhaled nitric oxide (FeNO) measurement were performed before, 7 and 24 hours after allergen challenge.

Results

Eighteen asthmatic patients with AR underwent HDM allergen bronchial challenge with no serious adverse events reported. Fifteen patients showed dual asthmatic response (DAR), while 2 patients showed early (EAR) and 1 late asthmatic response (LAR) only. At 24 hours after allergen bronchial challenge testing, average PC₂₀FEV₁ to methacholine significantly decreased (1.58 to 0.81 mg/mL, P=0.03), while both FeNO and the percentage of eosinophils in blood and sputum were significantly increased [52.0 (54.0) to 69.0 (56.0) ppb, P=0.01; 4.82% to 6.91%, P<0.001; 20.70% to 27.86%, P=0.03, respectively], but with no significant differences found in the percentage of eosinophils in nasal lavage (39.36% to 38.58%, P=0.89). However, at 7 hours after allergen challenge, the eosinophils in sputum were significant increased to 40.45% (P<0.001), but there was an increase (39.36% to 48.07%) with no statistical difference (P=0.167) found in nasal lavage.

Conclusions

HDM allergen bronchial challenge induced different response of airway inflammation in upper and lower airways.

Identification of biomarkers and pathogenesis in severe asthma by coexpression network analysis

BACKGROUND

Severe asthma is a heterogeneous inflammatory disease. The increase in precise immunotherapy for severe asthmatics requires a greater understanding of molecular mechanisms and biomarkers. In this study, we aimed to identify the underlying mechanisms and hub genes that determine asthma severity.

METHODS

Differentially expressed genes (DEGs) were identified based on bronchial epithelial brushings from mild and severe asthmatics. Then, weighted gene coexpression network analysis (WGCNA) was used to identify gene networks and the module most significantly associated with asthma severity. Furthermore, hub gene screening and functional enrichment analysis were performed. Replication with another dataset was conducted to validate the hub genes.

RESULTS

DEGs from 14 mild and 11 severe asthmatics were subjected to WGCNA. Six modules associated with asthma severity were identified. Three modules were positively correlated (P < 0.001) with asthma severity and contained genes that were upregulated in severe asthmatics. Functional enrichment analysis showed that genes in the most significant module were mainly enriched in neutrophil activation and degranulation, and cytokine receptor interaction. Hub genes included CXCR1, CXCR2, CCR1, CCR7, TLR2, FPR1, FCGR3B, FCGR2A, ITGAM, and PLEK; CXCR1, CXCR2, and TLR2 were significantly related to asthma severity in the validation dataset. The combination of ten hub genes exhibited a moderate ability to distinguish between severe and mild-moderate asthmatics.

CONCLUSION

Our results identified biomarkers and characterized potential pathogenesis of severe asthma, providing insight into treatment targets and prognostic markers.

Allergen inhalation generates pro-inflammatory oxidised phosphatidylcholine associated with airway dysfunction

Oxidised phosphatidylcholines (OxPCs) are produced under conditions of elevated oxidative stress and can contribute to human disease pathobiology. However, their role in allergic asthma is unexplored. The aim of this study was to characterise the OxPC profile in the airways after allergen challenge of people with airway hyperresponsiveness (AHR) or mild asthma. The capacity of OxPCs to contribute to pathobiology associated with asthma was also to be determined.Using bronchoalveolar lavage fluid from two human cohorts, OxPC species were quantified using ultra-high performance liquid chromatography-tandem mass spectrometry. Murine thin-cut lung slices were used to measure airway narrowing caused by OxPCs. Human airway smooth muscle (HASM) cells were exposed to OxPCs to assess concentration-associated changes in inflammatory phenotype and activation of signalling networks.OxPC profiles in the airways were different between people with and without AHR and correlated with methacholine responsiveness. Exposing patients with mild asthma to allergens produced unique OxPC signatures that associated with the severity of the late asthma response. OxPCs dose-dependently induced 15% airway narrowing in murine thin-cut lung slices. In HASM cells, OxPCs dose-dependently increased the biosynthesis of cyclooxygenase-2, interleukin (IL)-6, IL-8, granulocyte-macrophage colony-stimulating factor and the production of oxylipins via protein kinase C-dependent pathways.Data from human cohorts and primary HASM cell culture show that OxPCs are present in the airways, increase after allergen challenge and correlate with metrics of airway dysfunction. Furthermore, OxPCs may contribute to asthma pathobiology by promoting airway narrowing and inducing a pro-inflammatory phenotype and contraction of airway smooth muscle. OxPCs represent a potential novel target for treating oxidative stress-associated pathobiology in asthma.

Anti-alarmin approaches entering clinical trials

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Dendritic Cells: Critical Regulators of Allergic Asthma

Allergic asthma is a chronic inflammatory disease of the airways characterized by airway hyperresponsiveness (AHR), chronic airway inflammation, and excessive T helper (Th) type 2 immune responses against harmless airborne allergens. Dendritic cells (DCs) represent the most potent antigen-presenting cells of the immune system that act as a bridge between innate and adaptive immunity. Pertinent to allergic asthma, distinct DC subsets are known to play a central role in initiating and maintaining allergen driven Th2 immune responses in the airways. Nevertheless, seminal studies have demonstrated that DCs can also restrain excessive asthmatic responses and thus contribute to the resolution of allergic airway inflammation and the maintenance of pulmonary tolerance. Notably, the transfer of tolerogenic DCs in vivo suppresses Th2 allergic responses and protects or even reverses established allergic airway inflammation. Thus, the identification of novel DC subsets that possess immunoregulatory properties and can efficiently control aberrant asthmatic responses is critical for the re-establishment of tolerance and the amelioration of the asthmatic disease phenotype.

Plasmacytoid dendritic cells and asthma: a review of current knowledge

INTRODUCTION

While medications are available to treat asthma symptoms and control inflammation, no treatments can cure asthma, and efforts to develop primary prevention strategies or improved exacerbation management are limited by incomplete knowledge of the mechanisms responsible for asthma development and progression. Plasmacytoid dendritic cells (pDC) are involved in anti-viral host defense and immune regulation, and increasing evidence suggests a role for pDC in asthma pathogenesis.

AREAS COVERED

We undertook a literature search using PubMed for articles including the phrase 'plasmacytoid dendritic cells and asthma' published from 2015 to 2020. We reviewed the remarkable progress made over the past 5 years in understanding the role of pDC in asthma pathogenesis and how pDC regulate anti-viral immune function. This review highlights key recent findings in asthma pathogenesis and virus-triggered asthma exacerbations; pDC biology and functionality; how pDC regulate the immune response; and pDC function in asthma.

EXPERT OPTION

A deeper understanding of pDC function provides an important foundation for future pDC-targeted therapies that might prevent and treat asthma.

A profile of TNFR2+ regulatory T cells and CD103+ dendritic cells in the peripheral blood of patients with asthma

The interaction of tolerogenic CD103⁺ dendritic cells (DCs) with regulatory T (Tregs) cells modulates immune responses by inducing immune tolerance. Hence, we determined the proportion of these cells in the peripheral blood mononuclear cells (PBMC) of asthmatic patients. We observed lower trends of CD11b^-CD103⁺ DCs and CD86 within CD11b^-CD103⁺ DCs, while increased levels of Foxp3 expressing CD25^+/-TNFR2⁺ cells in asthmatics. There was a positive correlation in the expression of Foxp3 within CD3⁺CD4⁺CD25⁺TNFR2⁺ Tregs and CD11b^-CD103⁺ as well as the expression of CD86 within HLA-DR⁺CD11c⁺CD11b^-CD103⁺ DCs. In conclusion, we suggest that the increased levels of Tregs in blood could continuously suppress the T helper 2 (Th2) cells activation in the circulation which is also supported by the increase of anti-inflammatory cytokines IL-10 and TNF. Overall, functional immunoregulation of the regulatory cells, particularly Tregs, exhibit immune suppression and induce immune tolerance linked with the immune activation by the antigen presenting cells (APC).

Increased nasal mucosal interferon and CCL13 response to a TLR7/8 agonist in asthma and allergic rhinitis

BACKGROUND

Acute respiratory viral infections are a major cause of respiratory morbidity and mortality, especially in patients with preexisting lung diseases such as asthma. Toll-like receptors are critical in the early detection of viruses and in activating innate immunity in the respiratory mucosa, but there is no reliable and convenient method by which respiratory mucosal innate immune responses can be measured.

OBJECTIVE

We sought to assess in vivo immune responses to an innate stimulus and compare responsiveness between healthy volunteers and volunteers with allergy.

METHODS

We administered the Toll-like receptor 7/8 agonist resiquimod (R848; a synthetic analogue of single-stranded RNA) or saline by nasal spray to healthy participants without allergy (n = 12), those with allergic rhinitis (n = 12), or those with allergic rhinitis with asthma (n = 11). Immune mediators in blood and nasal fluid and mucosal gene expression were monitored over time.

RESULTS

R848 was well tolerated and significantly induced IFN-α2a, IFN-γ, proinflammatory cytokines (TNF-α, IL-2, IL-12p70), and chemokines (CXCL10, C-C motif chemokine ligand [CCL]2, CCL3, CCL4, and CCL13) in nasal mucosal fluid, without causing systemic immune activation. Participants with allergic rhinitis or allergic rhinitis with asthma had increased IFN-α2a, CCL3, and CCL13 responses relative to healthy participants; those with asthma had increased induction of IFN-stimulated genes DExD/H-box helicase 58, MX dynamin-like GTPase 1, and IFN-induced protein with tetratricopeptide repeats 3.

CONCLUSIONS

Responses to nasal delivery of R848 enables simple assessment of mucosal innate responsiveness, revealing that patients with allergic disorders have an increased nasal mucosal IFN and chemokine response to the viral RNA analogue R848. This highlights that dysregulated innate immune responses of the nasal mucosa in allergic individuals may be important in determining the outcome of viral exposure.

Tissue-resident innate immunity in the lung

The lung is a unique organ that must protect against inhaled pathogens and toxins, without mounting a disproportionate response against harmless particulate matter and without compromising its vital function. Tissue-resident immune cells within the lung provide local immunity and protection from infection but are also responsible for causing disease when dysregulated. There is a growing appreciation of the importance of tissue-resident memory T cells to lung immunity, but non-recirculating, tissue-resident, innate immune cells also exist. These cells provide the first line of defence against pulmonary infection and are essential for co-ordinating the subsequent adaptive response. In this review, we discuss the main lung-resident innate immune subsets and their functions in common pulmonary diseases, such as influenza, bacterial pneumonia, asthma and inflammatory disorders.

Serum levels of epithelial-derived mediators and interleukin-4/interleukin-13 signaling after bronchial challenge with Dermatophagoides pteronyssinus in patients with allergic asthma

Allergens are the main trigger that enhances airway type 2 inflammation, and the epithelium is the first line of defense that reacts to its exposure. Therefore, epithelial-derived mediators, such as interleukin (IL)-25, IL-33, thymic stromal lymphopoietin (TSLP) and ezrin, may play a role as alarmins in IL-4/IL-13 signaling in allergic asthma (AA). We investigated the serum levels of IL-25, IL-33, TSLP, ezrin, IL-4 and IL-13, after bronchial challenge with Dermatophagoides pteronyssinus in patients with AA. We examined 18 subjects: nine steroid-free stable patients with AA sensitized to D. pteronyssinus and nine non-atopic healthy subjects (HS). Bronchial allergen challenge was performed using inhaled D. pteronyssinus allergen. IL-4, IL-13, IL-25, IL-33, TSLP and ezrin levels in serum were measured by ELISA at two time points - before and 24 hours after bronchial allergen challenge. The serum levels of IL-25, TSLP and ezrin did not differ between AA and HS groups at baseline. However, after allergen exposure, significant increases in serum levels of IL-25, TSLP and ezrin were observed only in patients with AA. The serum level of IL-33 at baseline was significantly higher in the AA group compared with HS, but the allergen challenge did not provoke an increase of this cytokine in any group. IL-4 and IL-13 levels were significantly higher at baseline in the AA group compared with HS and, after allergen exposure, were significantly increased in the AA group, with no effect on HS. Thus, the epithelial-derived mediators IL-25, TSLP and ezrin, via IL4/IL13 signaling, enhance type 2 inflammation after bronchial challenge with D. pteronyssinus in AA.

Novel Blood-based Transcriptional Biomarker Panels Predict the Late-Phase Asthmatic Response

RATIONALE

The allergen inhalation challenge is used in clinical trials to test the efficacy of new treatments in attenuating the late-phase asthmatic response (LAR) and associated airway inflammation in subjects with allergic asthma. However, not all subjects with allergic asthma develop the LAR after allergen inhalation. Blood-based transcriptional biomarkers that can identify such individuals may help in subject recruitment for clinical trials as well as provide novel molecular insights.

OBJECTIVES

To identify blood-based transcriptional biomarker panels that can predict an individual's response to allergen inhalation challenge.

METHODS

We applied RNA sequencing to total RNA from whole blood (n = 36) collected before and after allergen challenge and generated both genome-guided and de novo datasets: genes, gene-isoforms (University of California, Santa Cruz, UCSC Genome Browser), Ensembl, and Trinity. Candidate biomarker panels were validated using the NanoString platform in an independent cohort of 33 subjects.

MEASUREMENTS AND MAIN RESULTS

The Trinity biomarker panel consisting of known and novel biomarker transcripts had an area under the receiver operating characteristic curve of greater than 0.70 in both the discovery and validation cohorts. The Trinity biomarker panel was useful in predicting the response of subjects that elicited different responses (accuracy between 0.65 and 0.71) and subjects that elicit a dual response (accuracy between 0.70 and 0.75) upon repeated allergen inhalation challenges.

CONCLUSIONS

Interestingly, the biomarker panel containing novel transcripts successfully validated compared with panels with known, well-characterized genes. These biomarker-blood tests may be used to identify subjects with asthma who develop the LAR, and may also represent members of novel molecular mechanisms that can be targeted for therapy.

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

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

Expression and pathological significance of CC chemokine receptor 7 and its ligands in the airway of asthmatic rats exposed to cigarette smoke

Background

Cigarette smoking aggravates the symptoms of asthma, leading to the rapid decline of lung function. Dendritic cells (DCs) and lymphocytes are considered initiating and promoting factors for the airway inflammation reactions of asthma. In addition, activation of CC chemokine receptor 7 (CCR7) by chemokine (C-C motif) ligand (CCL) 19 and 21 promotes DCs and T cells migration to lymphoid tissues during inflammation. We aimed to examine how cigarette smoke affects the expression of CCR7 in the lungs of asthmatic rats and explore the signaling mechanism linking CCR7 expression to exacerbation of symptoms.

Methods

Forty Wistar rats were randomized to four groups: control, asthma, smoke exposure, and asthma with smoke exposure groups. A rat asthma model was established by intraperitoneal ovalbumin injection. CCR7 expression was examined with immunohistochemistry and western blotting. The number of airway DCs was determined by OX62 immunohistochemistry. Interferon (INF)-γ, interleukin (IL)-4, CCL19, and CCL21 expression levels in blood and bronchioalveolar lavage fluid (BALF) were determined by enzyme-linked immunosorbent assays (ELISAs).

Results

Tissue CCR7 expression, peripheral blood and BALF CCL19 and CCL21 concentrations, and the number of airway DCs were significantly higher in the asthma with smoke exposure group than the asthma group (P<0.01). In addition, INF-γ expression was decreased and IL-4 increased in the asthma and asthma with smoke exposure groups compared with the control group (P<0.01), and in the asthma with smoke exposure group compared with the asthma group (P<0.01). Expression of CCR7 correlated negatively with INF-γ expression in peripheral blood and BALF (P<0.01), and positively with the airway DCs and IL-4 expression in the peripheral blood and BALF (P<0.01).

Conclusions

Cigarette smoking may aggravate asthma symptoms by attenuating immunity, possibly through CCR7-mediated DCs aggregation in lung tissue.

Worms: Pernicious parasites or allies against allergies?

Type 2 immune responses are most commonly associated with allergy and helminth parasite infections. Since the discovery of Th1 and Th2 immune responses more than 30 years ago, models of both allergic disease and helminth infections have been useful in characterizing the development, effector mechanisms and pathological consequences of type 2 immune responses. The observation that some helminth infections negatively correlate with allergic and inflammatory disease led to a large field of research into parasite immunomodulation. However, it is worth noting that helminth parasites are not always benign infections, and that helminth immunomodulation can have stimulatory as well as suppressive effects on allergic responses. In this review, we will discuss how parasitic infections change host responses, the consequences for bystander immunity and how this interaction influences clinical symptoms of allergy.

Antialarmins for treatment of asthma: future perspectives

PURPOSE OF REVIEW

Recent studies have highlighted the role of alarmins in asthma pathophysiology and tested the roles of these cytokines in asthmatic patients. This review will discuss the recent advances in the role of alarmins in asthma and the potential of future targeted therapies in asthma.

RECENT FINDINGS

Epithelial-derived cytokines can be released upon exposure to external stimuli, causing damage to the epithelial barrier and resulting in tissue inflammation. Of these cytokines, IL-25, IL-33 and thymic stromal lymphopoeitin (TSLP), have been associated with asthma. These alarmins are all not only overexpressed in asthmatic airways, particularly in airway epithelial cells, but also in other structural and immune cells. Furthermore, all three alarmins drive type-2 pro-inflammatory responses in several immune cells that have been identified as key players in the pathogenesis of asthma, including innate lymphoid type-2 cells. Clinical trials testing therapeutics that block pathways of the alarmins are in progress.

SUMMARY

To-date, only TSLP blockade has been reported in human clinical trials, and this approach has shown efficacy in asthmatic patients. Current body of evidence suggests that alarmins are useful upstream targets for treatment of asthma.

Critical Role of IRAK-M in Regulating Antigen-Induced Airway Inflammation

Asthma is an airway epithelium disorder involving allergic lung inflammation. IL-1 receptor-associated kinase M (IRAK-M) is a negative regulator of Toll-like receptor (TLR) signaling on airway epithelial cells and macrophages, and it is known to limit the overproduction of cytokines during the inflammatory process. However, the direct role of IRAK-M in asthma pathogenesis is unclear. In the present study, we found a significant elevation of IRAK-M expression in mouse lungs after ovalbumin (OVA) exposure. Compared with wild-type mice, IRAK-M knockout (KO) mice responded to OVA challenge with significantly worse infiltration of airway inflammatory cells, greater airway responsiveness, higher proinflammatory cytokine levels in lung homogenates, and more prominent T-helper cell type 2 (Th2) and Th17 deviation. OVA exposure also induced higher activities of dendritic cells (DCs) and macrophages from IRAK-M KO mouse lungs. Furthermore, adoptive transfer of either IRAK-M KO bone-marrow-derived DCs or macrophages into wild-type mice aggravated OVA-induced airway inflammation. In vitro experiments showed that IRAK-M KO naive CD4⁺ T cells were more prone to differentiate into Th17 cells, but not regulatory T cells. Consistently, activation of IκBζ was significantly increased in the absence of IRAK-M, facilitating Th17 polarization. These findings suggest that IRAK-M plays a crucial role in the regulation of allergic airway inflammation by modifying the function of airway epithelia, DCs, and macrophages, and the differentiation of naive CD4⁺ T cells. Modulation of IRAK-M may provide a novel target for the control of asthma.

Dendritic Cell Subsets in Asthma: Impaired Tolerance or Exaggerated Inflammation?

Asthma is a prevalent chronic heterogeneous inflammatory disease of the airways, leading to reversible airway obstruction, in which various inflammatory responses can be observed. Mild to moderate asthma patients often present with a Th2-mediated eosinophilic inflammation whereas in severe asthma patients, a Th17-associated neutrophilic or combined Th2 and Th17-mediated eosinophilic/neutrophilic inflammation is observed. The differentiation of these effector Th2 and Th17-cells is induced by allergen-exposed dendritic cells (DCs) that migrate toward the lung draining lymph node. The DC lineage comprises conventional DCs (cDCs) and plasmacytoid DCs (pDCs), of which the cDC lineage consists of type 1 cDCs (cDC1s) and cDC2s. During inflammation, also monocytes can differentiate into so-called monocyte-derived DCs (moDCs). These DC subsets differ both in ontogeny, localization, and in their functional properties. New identification tools and the availability of transgenic mice targeting specific DC subsets enable the investigation of how these different DC subsets contribute to or suppress asthma pathogenesis. In this review, we will discuss mechanisms used by different DC subsets to elicit or hamper the pathogenesis of both Th2-mediated eosinophilic asthma and more severe Th17-mediated neutrophilic inflammation.

Dendritic Cells in Human Lung Disease: Recent Advances

Dendritic cells (DCs) are potent antigen-presenting cells. Because of their particular ability to initiate and regulate cell mediated and humoral immune responses, there is considerable interest in the role that DCs play in the pathogenesis of various lung diseases, especially those in which there is an excessive immune response to specific antigens (as in asthma) or a deficient immune response (as in lung cancer). A number of DC subpopulations have been defined in the lungs, including myeloid or conventional DCs that initiate T-cell immunity and antibody production and plasmacytoid DCs that have an important role in antiviral immunity and immune tolerance. Although an extensive body of literature has documented the role that DCs play in experimental models of lung disease, this review will highlight recent advances in our understanding of DC function in human disease, including asthma, COPD, antimicrobial immunity, and lung cancer. The future is likely to see new approaches whereby antigens and small molecules are targeted to receptors on particular DC subpopulations in order to modify pulmonary immune responses.