Lung Pathologies in a Chronic Inflammation Mouse Model Are Independent of Eosinophil Degranulation

Utility of eosinophil peroxidase as a biomarker of eosinophilic inflammation in asthma

BACKGROUND

The relative utility of eosinophil peroxidase (EPX) and blood and sputum eosinophil counts as disease biomarkers in asthma is uncertain.

OBJECTIVE

We sought to determine the utility of EPX as a biomarker of systemic and airway eosinophilic inflammation in asthma.

METHODS

EPX protein was measured by immunoassay in serum and sputum in 110 healthy controls to establish a normal reference range and in repeated samples of serum and sputum collected during 3 years of observation in 480 participants in the Severe Asthma Research Program 3.

RESULTS

Over 3 years, EPX levels in patients with asthma were higher than normal in 27% to 31% of serum samples and 36% to 53% of sputum samples. Eosinophils and EPX correlated better in blood than in sputum (rs values of 0.74 and 0.43, respectively), and high sputum EPX levels occurred in 27% of participants with blood eosinophil counts less than 150 cells/μL and 42% of participants with blood eosinophil counts between 150 and 299 cells/μL. Patients with persistently high sputum EPX values for 3 years were characterized by severe airflow obstruction, frequent exacerbations, and high mucus plug scores. In 59 patients with asthma who started mepolizumab during observation, serum EPX levels normalized in 96% but sputum EPX normalized in only 49%. Lung function remained abnormal even when sputum EPX normalized.

CONCLUSIONS

Serum EPX is a valid protein biomarker of systemic eosinophilic inflammation in asthma, and sputum EPX levels are a more sensitive biomarker of airway eosinophilic inflammation than sputum eosinophil counts. Eosinophil measures in blood frequently miss airway eosinophilic inflammation, and mepolizumab frequently fails to normalize airway eosinophilic inflammation even though it invariably normalizes systemic eosinophilic inflammation.

Eosinophil extracellular traps in respiratory ailment: Pathogenic mechanisms and clinical translation

Background

Eosinophilic extracellular traps (EETs) are reticular complexes comprising deoxyribonucleic-Acid (DNA) fibers and granule proteins.

Aims

EETs play a crucial role in antimicrobial host responses and are pathogenic when overproduced or under degraded. EETs created by eosinophils appear to enable vital immune responses against extra-cellular pathogens, nevertheless, trap overproduction is evident in pathology.

Materials & Methods

As considerably research is performed, new data affirmed that EETs can alter the outcome of respiratory ailment.

Results

We probe into the disclosure and specificity of EETs produced in reaction to various stimuli and propose a role for those frameworks in ailment pathogenesis and the establishment of chronic, unresolved inflammation.

Discussion

Whether EETs can be used as a prospective brand-new target for the diagnosis, treatment and prognosis of respiratory ailments is a scientific theme worth studying.

Conclusion

We probe into the disclosure and specificity of EETs produced in reaction to various stimuli and propose a role for those frameworks in ailment pathogenesis and the establishment of chronic, unresolved inflammation.

TGF-β signaling promotes eosinophil activation in inflammatory responses

Eosinophils, traditionally associated with allergic phenomena, play a pivotal role in inflammatory responses. Despite accumulating evidence suggesting their pro-inflammatory function upon activation, the underlying mechanisms governing eosinophil activation remain incompletely characterized. In this study, we investigate the local activation of pulmonary and colon eosinophils within the inflammatory microenvironment. Leveraging transcriptional sequencing, we identify TGF-β as a putative regulator of eosinophil activation, leading to the secretion of granule proteins, including peroxidase. Genetic deletion of TGF-β receptors on eosinophils resulted in the inhibition of peroxidase synthesis, affirming the significance of TGF-β signaling in eosinophil activation. Using models of HDM-induced asthma and DSS-induced colitis, we demonstrate the indispensability of TGF-β-driven eosinophil activation in both disease contexts. Notably, while TGF-β signaling did not significantly influence asthmatic inflammation, its knockout conferred protection against experimental colitis. This study delineates a distinct pattern of eosinophil activation within inflammatory responses, highlighting the pivotal role of TGF-β signaling in regulating eosinophil behavior. These findings deepen our comprehension of eosinophil-related pathophysiology and may pave the way for targeted therapeutic approaches in allergic and inflammatory diseases.

CCR3 gene knockout inhibits proliferation, differentiation, and migration of eosinophils in allergic rhinitis model mice

Allergic rhinitis (AR) is characterized by various bothersome clinical symptoms of the nasal mucosa that impaired the quality of daily life. Different chemokine receptors play a crucial role in the recruitment of inflammatory cells in AR. However, the effect of CC chemokine receptor (CCR) 3 on the function of eosinophils (EOS) is still unclear. We investigated the effect of CCR3 on EOS in a murine model of OVA-mediated allergic rhinitis using CCR3-deficient (CCR3-/-) mice. In vitro, bone marrow of CCR3-/- and wild-type (WT) mice were used to investigate the induction and development of EOS. In vivo, Allergic rhinitis was initiated in CCR3-/- and wild-type (WT) mice by passive transfer OVA, followed by detecting the eosinophil infiltration of the nasal mucosa and bone marrow. Then CD34+ progenitor cells in bone marrow and blood were evaluated by IHC analysis. Furthermore, the degranulation proteins of EOS in nasal mucosa, marrow, blood and NALF were determined by IHC, real-time PCR analysis and Western blot. We found that CCR3 gene can regulate the growth and development of primary cultured eosinophils. Knockout CCR3 gene can inhibit the proliferation and degranulation of EOS. The infiltration of eosinophils in the nasal mucosa following OVA-challenged, was significantly higher in WT mice compared with those stimulated with phosphate-buffered saline (PBS) for WT, but that was not seen in similarly treated CCR3-/- mice. Besides, the number of CD34+ progenitor cells in bone marrow and blood were also suppressed in CCR3-/- mice. The degranulation proteins of EOS expressed in nasal mucosa, marrow, blood and NALF were decreased in CCR3-/- AR mice compared with WT-AR mice. And the clinical symptoms were significantly alleviated. The expression of granulation proteins in NALF were not detected in both untreated CCR3-/- mice and WT mice. These results demonstrate a contribution of CCR3 to both the growth, migration, and degranulation of EOS during allergic rhinitis.

Eosinophils promote effector functions of lung group 2 innate lymphoid cells in allergic airway inflammation in mice

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are critical mediators of type 2 respiratory inflammation, releasing IL-5 and IL-13 and promoting the pulmonary eosinophilia associated with allergen provocation. Although ILC2s have been shown to promote eosinophil activities, the role of eosinophils in group 2 innate lymphoid cell (ILC2) responses is less well defined.

OBJECTIVE

We sought to investigate the role of eosinophils in activation of ILC2s in models of allergic asthma and in vitro.

METHODS

Inducible eosinophil-deficient mice were exposed to allergic respiratory inflammation models of asthma, such as ovalbumin or house dust mite challenge, or to innate models of type 2 airway inflammation, such as inhalation of IL-33. Eosinophil-specific IL-4/13-deficient mice were used to address the specific roles for eosinophil-derived cytokines. Direct cell interactions between ILC2s and eosinophils were assessed by in vitro culture experiments.

RESULTS

Targeted depletion of eosinophils resulted in significant reductions of total and IL-5+ and IL-13+ lung ILC2s in all models of respiratory inflammation. This correlated with reductions in IL-13 levels and mucus in the airway. Eosinophil-derived IL-4/13 was necessary for both eosinophil and ILC2 accumulation in lung in allergen models. In vitro, eosinophils released soluble mediators that induced ILC2 proliferation and G protein-coupled receptor-dependent chemotaxis of ILC2s. Coculture of ILC2s and IL-33-activated eosinophils resulted in transcriptome changes in both ILC2s and eosinophils, suggesting potential novel reciprocal interactions.

CONCLUSION

These studies demonstrate that eosinophils play a reciprocal role in ILC2 effector functions as part of both adaptive and innate type 2 pulmonary inflammatory events.

Eosinophils Restrict Diesel Exhaust Particles Induced Cell Proliferation of Lung Epithelial A549 Cells, Vial Interleukin-13 Mediated Mechanisms: Implications for Tissue Remodelling And Fibrosis

BACKGROUND

Diesel exhaust particulates (DEPs) affect lung physiology and cause serious damage to the lungs. A number of studies demonstrated that, eosinophils play a very important role in the development of tissue remodelling and fibrosis of lungs. However, the exact mechanism of pathogenesis of tissue remodelling and fibrosis is not known.

METHODS

Both in vitro and in vivo models were used in the study. HL-60 and A549 cells were used in the study. Balb/C mice of 8 to 12 weeks old were used for in vivo study. Cell viability by MTT assay, RNA isolation by tri reagent was accomplished. mRNA expression of inflammatory genes were accomplished by real time PCR or qPCR. Immunohistochemistry was done to asses the localization and expressions of proteins. One way ANOVA followed by post hoc test were done for the statistical analysis. Graph-Pad Prism software was used for statistical analysis.

RESULTS

We for the first time demonstrate that, Interleukin-13 plays a very important role in the development of tissue remodelling and fibrosis. We report that, diesel exhaust particles significantly induce eosinophils cell proliferation and interleukin-13 release in in vitro culture conditions. Supernatant collected from DEP-induced eosinophils cells significantly restrict cell proliferation of epithelial cells in response to exposure of diesel exhast particles. Furthermore, purified interleukin-13 decreases the proliferation of A549 cells, highliting the involvement of IL-13 in tissue remodeling. Notably, Etoricoxib (selective COX-2 inhibitor) did not inhibit DEP-triggered release of interleukin-13, suggesting another cell signalling pathway. The in vivo exposer of DEP to the lungs of mice, resulted in high level of eosinophils degranulation as depicted by the EPX-1 immunostaining and altered level of mRNA expressions of inflammatory genes. We also found that, a-SMA, fibroblast specific protein (FSP-1) has been changed in response to DEP in the mice lungs along with the mediators of inflammation.

CONCLUSION

Altogether, we elucidated, the mechanistic role of eosinophils and IL-13 in the DEP-triggered proliferation of lungs cells thus providing an inside in the pathophysiology of tissue remodelling and fibrosis of lungs.

Detection of Eosinophils in Tissue Sections by Immunohistochemistry

Eosinophils are bone marrow-derived hematopoietic cells which represent a small subset in the peripheral blood, and under homeostatic conditions predominantly reside in certain organs, such as the gastrointestinal tract. However, eosinophil numbers increase both in the peripheral blood and tissues during allergic inflammation, parasitic infestation, drug reactions, vasculitides, as well as certain hematopoietic neoplasms. Their presence in tissues can be detected by hematoxylin and eosin staining; however, this may be challenging particularly at times of activation and/or degranulation, e.g., during allergic lung inflammation. Thus, detection of eosinophils and/or their released granule proteins is significantly enhanced by immunohistochemistry. This chapter describes methods for the detection of mouse or human eosinophils by using granule protein-specific antibodies in formalin-fixed paraffin-embedded tissue.

Pulmonary Eosinophils at the Center of the Allergic Space-Time Continuum

Eosinophils are typically a minority population of circulating granulocytes being released from the bone-marrow as terminally differentiated cells. Besides their function in the defense against parasites and in promoting allergic airway inflammation, regulatory functions have now been attributed to eosinophils in various organs. Although eosinophils are involved in the inflammatory response to allergens, it remains unclear whether they are drivers of the asthma pathology or merely recruited effector cells. Recent findings highlight the homeostatic and pro-resolving capacity of eosinophils and raise the question at what point in time their function is regulated. Similarly, eosinophils from different physical locations display phenotypic and functional diversity. However, it remains unclear whether eosinophil plasticity remains as they develop and travel from the bone marrow to the tissue, in homeostasis or during inflammation. In the tissue, eosinophils of different ages and origin along the inflammatory trajectory may exhibit functional diversity as circumstances change. Herein, we outline the inflammatory time line of allergic airway inflammation from acute, late, adaptive to chronic processes. We summarize the function of the eosinophils in regards to their resident localization and time of recruitment to the lung, in all stages of the inflammatory response. In all, we argue that immunological differences in eosinophils are a function of time and space as the allergic inflammatory response is initiated and resolved.

The Enigma of Eosinophil Degranulation

Eosinophils are specialized white blood cells, which are involved in the pathology of diverse allergic and nonallergic inflammatory diseases. Eosinophils are traditionally known as cytotoxic effector cells but have been suggested to additionally play a role in immunomodulation and maintenance of homeostasis. The exact role of these granule-containing leukocytes in health and diseases is still a matter of debate. Degranulation is one of the key effector functions of eosinophils in response to diverse stimuli. The different degranulation patterns occurring in eosinophils (piecemeal degranulation, exocytosis and cytolysis) have been extensively studied in the last few years. However, the exact mechanism of the diverse degranulation types remains unknown and is still under investigation. In this review, we focus on recent findings and highlight the diversity of stimulation and methods used to evaluate eosinophil degranulation.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Eosinophil Shape Change and Secretion

The analysis of eosinophil shape change and mediator secretion is a useful tool in understanding how eosinophils respond to immunological stimuli and chemotactic factors. Eosinophils undergo dramatic shape changes, along with secretion of the granule-derived enzyme eosinophil peroxidase (EPX) in response to chemotactic stimuli including platelet-activating factor (PAF) and CCL11 (eotaxin-1). Here, we describe the analysis of eosinophil shape change by confocal microscopy analysis and provide an experimental approach for comparing unstimulated cells with those that have been stimulated to undergo chemotaxis. In addition, we illustrate two different degranulation assays for EPX using OPD and an ELISA technique and show how eosinophil degranulation may be assessed from in vitro as well as ex vivo stimulation.

Asthma-related inflammation promotes lung metastasis of breast cancer cells through CCL11-CCR3 pathway

BACKGROUND

Mechanisms that preclude lung metastasis are still barely understood. The possible consequences of allergic airways inflammation on cancer dissemination were studied in a mouse model of breast cancer.

METHODS

Balb/c mice were immunized and daily exposed to ovalbumin (OVA) from day 21. They were subcutaneously injected with 4T1 mammary tumor cells on day 45 and sacrificed on day 67. Lung metastases were measured by biophotonic imaging (IVIS® 200 Imaging System) and histological measurement of tumor area (Cytomine software). Effects of CCL11 were assessed in vivo by intratracheal instillations of recCCL11 and in vitro using Boyden chambers. CCR3 expression on cell surface was assessed by flow cytometry.

RESULTS

The extent of tumor metastases was significantly higher in lungs of OVA-exposed mice and increased levels of CCL11 expression were measured after OVA exposure. Migration of 4T1 cells and neutrophils was stimulated in vitro and in vivo by recCCL11. 4T1 cells and neutrophils express CCR3 as shown by flow cytometry and a selective CCR3 antagonist (SB-297006) inhibited the induction of 4T1 cells migration and proliferation in response to recCCL11.

CONCLUSIONS

Allergic inflammation generated by exposure to allergens triggers the implantation of metastatic cells from primary breast tumor into lung tissues plausibly in a CCL11-CCR3-dependent manner. This indicates that asthma related inflammation in lungs might be a risk factor for lung metastasis in breast cancer patients.

Assessment of Lung Eosinophils In Situ Using Immunohistological Staining

Eosinophils are rare white blood cells that are recruited from circulation to accumulate in the lung in mouse models of allergic respiratory inflammation. In hematoxylin-eosin (HE) stained lungs, eosinophils may be difficult to detect despite their bright eosin staining in the secondary granules. For this reason, antibody-mediated detection of eosinophils is preferable for specific and clearer identification of these cells. Moreover, eosinophils may degranulate, releasing their granule proteins into surrounding tissue, and remnants of cytolysed cells cannot be detected by HE staining. The methods here demonstrate the use of eosinophil-specific anti-mouse antibodies to detect eosinophil granule proteins in formalin-fixed cells both in situ in paraffin-embedded lungs, as well as in cytospin preparations from the lung. These antibody staining techniques enable either colorimetric or fluorescence imaging of eosinophils or their granule proteins with the potential for additional antibodies to be added for detection of multiple molecules.

Repetitive nasal allergen challenge in allergic rhinitis: Priming and Th2-type inflammation but no evidence of remodelling

BACKGROUND

Local tissue eosinophilia and Th2 cytokines are characteristic features of seasonal allergic rhinitis. Airway remodelling is a feature of asthma whereas evidence for remodelling in allergic rhinitis (AR) is conflicting.

OBJECTIVE

By use of a novel human repetitive nasal allergen challenge (RAC) model, we evaluated the relationship between allergic inflammation and features of remodelling in AR.

METHODS

Twelve patients with moderate-severe AR underwent 5 alternate day challenges with diluent which after 4 weeks were followed by 5 alternate day challenges with grass pollen extract. Nasal symptoms, Th1/Th2 cytokines in nasal secretion and serum were evaluated. Nasal biopsies were taken 24 hours after the 1st and 5th challenges with diluent and with allergen. Sixteen healthy controls underwent a single challenge with diluent and with allergen. Using immunohistochemistry, epithelial and submucosal inflammatory cells and remodelling markers were evaluated by computed image analysis.

RESULTS

There was an increase in early and late-phase symptoms after every allergen challenge compared to diluent (both P < .05) with evidence of both clinical and immunological priming. Nasal tissue eosinophils and IL-5 in nasal secretion increased significantly after RAC compared to corresponding diluent challenges (P < .01, P = .01, respectively). There was a correlation between submucosal mast cells and the early-phase clinical response (r = 0.79, P = .007) and an association between epithelial eosinophils and IL-5 concentrations in nasal secretion (r = 0.69, P = .06) in allergic rhinitis. No differences were observed after RAC with regard to epithelial integrity, reticular basement membrane thickness, glandular area, expression of markers of activation of airway remodelling including α-SMA, HSP-47, extracellular matrix (MMP7, 9 and TIMP-1), angiogenesis and lymphangiogenesis for AR compared with healthy controls.

CONCLUSION

Novel repetitive nasal allergen challenge in participants with severe persistent seasonal allergic rhinitis resulted in tissue eosinophilia and increases in IL-5 but no structural changes. Our data support no link between robust Th2-inflammation and development of airway remodelling in AR.

Increased chemokines levels in patients with chronic obstructive pulmonary disease: correlation with quantitative computed tomography metrics

OBJECTIVE

We sought to explore the relationships between multiple chemokines with spirometry, inflammatory mediators and CT findings of emphysema, small airways disease and bronchial wall thickness.

METHODS

All patients with COPD (n = 65) and healthy control subjects (n = 23) underwent high-resolution CT, with image analysis determining the low attenuation area (LAA), ratio of mean lung attenuation on expiratory and inspiratory scans (E/I MLD) and bronchial wall thickness of inner perimeter of a 10-mm diameter airway (Pi10). At enrollment, subjects underwent pulmonary function studies, chemokines and inflammatory mediators measurements.

RESULTS

Multiple chemokines (CCL2, CCL3, CCL5, CX3CL1, CXCL8, CXCL9, CXCL10, CXCL11 and CXCL12) and inflammatory mediators (MMP-9, MMP-12, IL-18 and neutrophil count) were markedly increased in the serum of COPD patients compared with healthy controls. There were associations between small airway disease (E/I MLD) and CCL11, CXCL8, CXCL10, CXCL11, CXCL12 and CX3CL1. Especially CXCL8 and CX3CL1 are strongly associated with E/I MLD (r = 0.74, p < 0.001; r = 0.76, p < 0.001, respectively). CXCL8, CXCL12 and CX3CL1 were moderately positively correlated with emphysema (%LAA) (r = 0.49, p < 0.05; r = 0.51, p < 0.05; r = 0.54, p < 0.01, respectively). Bronchial wall thickness (Pi10）showed no significant differences between the COPD and healthy controls,，but there was an association between Pi10 and FEV₁% in COPD patients (r=-0.420, p = 0.048). Our statistical results showed that there were not any associations between airway wall thickness (Pi10) and chemokines.

CONCLUSION

Pulmonary chemokines levels are closely associated with the extent of gas trapping, small airways disease and emphysema identified on high-resolution chest CT scan.

ADVANCES IN KNOWLEDGE

This study combines quantitative CT analysis with multiplex chemokines and inflammatory mediators to identify a new role of pathological changes in COPD.

An endothelial microRNA-1-regulated network controls eosinophil trafficking in asthma and chronic rhinosinusitis

BACKGROUND

Airway eosinophilia is a prominent feature of asthma and chronic rhinosinusitis (CRS), and the endothelium plays a key role in eosinophil trafficking. To date, microRNA-1 (miR-1) is the only microRNA known to be regulated in the lung endothelium in asthma models.

OBJECTIVE

We sought to determine the role of endothelial miR-1 in allergic airway inflammation.

METHODS

We measured microRNA and mRNA expression using quantitative RT-PCR. We used ovalbumin and house dust mite models of asthma. Endothelium-specific overexpression of miR-1 was achieved through lentiviral vector delivery or induction of a transgene. Tissue eosinophilia was quantified by using Congo red and anti-eosinophil peroxidase staining. We measured eosinophil binding with a Sykes-Moore adhesion chamber. Target recruitment to RNA-induced silencing complex was assessed by using anti-Argonaute2 RNA immunoprecipitation. Surface P-selectin levels were measured by using flow cytometry.

RESULTS

Serum miR-1 levels had inverse correlations with sputum eosinophilia, airway obstruction, and number of hospitalizations in asthmatic patients and sinonasal tissue eosinophilia in patients with CRS. IL-13 stimulation decreased miR-1 levels in human lung endothelium. Endothelium-specific overexpression of miR-1 reduced airway eosinophilia and asthma phenotypes in murine models and inhibited IL-13-induced eosinophil binding to endothelial cells. miR-1 recruited P-selectin, thymic stromal lymphopoietin, eotaxin-3, and thrombopoietin receptor to the RNA-induced silencing complex; downregulated these genes in the lung endothelium; and reduced surface P-selectin levels in IL-13-stimulated endothelial cells. In our asthma and CRS cohorts, miR-1 levels correlated inversely with its target genes.

CONCLUSION

Endothelial miR-1 regulates eosinophil trafficking in the setting of allergic airway inflammation. miR-1 has therapeutic potential in asthmatic patients and patients with CRS.

Profiling cellular heterogeneity in asthma with single cell multiparameter CyTOF

Asthma is a chronic inflammatory disease of the airways that afflicts over 30 million individuals in the United States and over 300 million individuals worldwide. The inflammatory response in the airways is often characterized by the analysis of sputum, which contains multiple types of cells including neutrophils, macrophages, lymphocytes, and rare bronchial epithelial cells. Subtyping patients using microscopy of the sputum has identified both neutrophilic and eosinophilic infiltrates in airway inflammation. However, with the extensive heterogeneity among these cell types, a higher resolution understanding of the inflammatory cell types present in the sputum is needed to dissect the heterogeneity of disease. Improved recognition of the distinct phenotypes and sources of inflammation in asthmatic granulocytes may identify relevant pathways for clinical management or investigation of novel therapeutic mediators. Here, we employed mass cytometry or cytometry by time-of-flight to quantify frequency and define functional status of sputum derived airway cells in asthmatic patients and healthy controls. This in-depth single cell analysis method identified multiple distinct subtypes of airway immune cells, especially in neutrophils. Significance was discovered by statistical analysis as well as a data-driven unbiased clustering approach. Our multidimensional assessment method identifies differences in cellular function and supports identification of cellular status that may contribute to diverse clinical responses. This technical advance is relevant for studies of pathogenesis and may provide meaningful insights to advance our knowledge of asthmatic inflammation.

Elevated Levels of Activated and Pathogenic Eosinophils Characterize Moderate-Severe House Dust Mite Allergic Rhinitis

Eosinophils play a critical role in the pathogenesis of allergic airway inflammation. However, the relative importance of eosinophil activation and pathogenicity in driving the progression of disease severity of allergic rhinitis (AR) remains to be defined. We aimed to assess the relation of activated and pathogenic eosinophils with disease severity of patients with AR. Peripheral blood and nasal samples were collected from patients with mild (n = 10) and moderate-severe (n = 21) house dust mite AR and healthy control subjects (n = 10) recruited prospectively. Expressions of activation and pathogenic markers on eosinophils in the blood and nose were analyzed by flow cytometry. The eosinophilic cation protein- (ECP-) releasing potential and the pro-Th2 function of blood eosinophils were compared between the mild and moderate-severe patients and healthy controls. Our results showed that the numbers of activated (CD44⁺ and CD69⁺) and pathogenic (CD101⁺CD274⁺) eosinophils in the blood and nose as well as blood eosinophil progenitors were increased in moderate-severe AR compared with the mild patients and healthy controls. In addition, the levels of activated and pathogenic eosinophils in the blood were positively correlated with the total nasal symptom score and serum ECP and eosinophil peroxidase (EPX) levels in patients with AR. Furthermore, the blood eosinophils obtained from the moderate-severe patients exhibited a higher potential of releasing ECP and EPX induced by CCL11 and of promoting Th2 responses than those from the mild patients and healthy controls. In conclusion, patients with moderate-severe AR are characterized by elevated levels of activated and pathogenic eosinophils, which are associated with higher production of ECP, EPX, and IL-4 in the peripheral blood.

Deciphering the role of eosinophils in solid organ transplantation

Eosinophils are rare granulocytes that belong to the innate arm of the immune system. This cell population is traditionally defined as a destructive and cytotoxic mediator in asthma and helminth infection. Limited data in transplantation have suggested that eosinophils play a similar role in potentiating deleterious organ inflammation and immunologic rejection. Contrary to this long-held notion, recent data have uncovered the possibility that eosinophils play an alternative role in immune homeostasis, defense against a wide range of pathogens, as well as downregulation of deleterious inflammation. Specifically, translational data from small animal models of lung transplantation have demonstrated a critical role for eosinophils in the downregulation of alloimmunity. These findings shed new light on the unique immunologic features of the lung allograft and demonstrate that environmental polarization may alter the phenotype and function of leukocyte populations previously thought to be static in nature. In this review, we provide an update on eosinophils in the homeostasis of the lung as well as other solid organs.

Inflammatory mechanisms linking maternal and childhood asthma

Asthma is a chronic inflammatory airway disease characterized by airway hyperresponsiveness, inflammation, and remodeling. Asthma often develops during childhood and causes lifelong decrements in lung function and quality of life. Risk factors for childhood asthma are numerous and include genetic, epigenetic, developmental, and environmental factors. Uncontrolled maternal asthma during pregnancy exposes the developing fetus to inflammatory insults, which further increase the risk of childhood asthma independent of genetic predisposition. This review focuses on the role of maternal asthma in the development of asthma in offspring. We will present maternal asthma as a targetable and modifiable risk factor for childhood asthma and discuss the mechanisms by which maternal inflammation increases childhood asthma risk. Topics include how exposure to maternal asthma in utero shapes structural lung development with a special emphasis on airway nerves, how maternal type-2 cytokines such as IL-5 activate the fetal immune system, and how changes in lung and immune cell development inform responses to aero-allergens later in life. Finally, we highlight emerging evidence that maternal asthma establishes a unique "asthma signature" in the airways of children, leading to novel mechanisms of airway hyperreactivity and inflammatory cell responses.

Protein crystallization promotes type 2 immunity and is reversible by antibody treatment

Although spontaneous protein crystallization is a rare event in vivo, Charcot-Leyden crystals (CLCs) consisting of galectin-10 (Gal10) protein are frequently observed in eosinophilic diseases, such as asthma. We found that CLCs derived from patients showed crystal packing and Gal10 structure identical to those of Gal10 crystals grown in vitro. When administered to the airways, crystalline Gal10 stimulated innate and adaptive immunity and acted as a type 2 adjuvant. By contrast, a soluble Gal10 mutein was inert. Antibodies directed against key epitopes of the CLC crystallization interface dissolved preexisting CLCs in patient-derived mucus within hours and reversed crystal-driven inflammation, goblet-cell metaplasia, immunoglobulin E (IgE) synthesis, and bronchial hyperreactivity (BHR) in a humanized mouse model of asthma. Thus, protein crystals may promote hallmark features of asthma and are targetable by crystal-dissolving antibodies.

Eosinophils downregulate lung alloimmunity by decreasing TCR signal transduction

Despite the accepted notion that granulocytes play a universally destructive role in organ and tissue grafts, it has been recently described that eosinophils can facilitate immunosuppression-mediated acceptance of murine lung allografts. The mechanism of eosinophil-mediated tolerance, or their role in regulating alloimmune responses in the absence of immunosuppression, remains unknown. Using lung transplants in a fully MHC-mismatched BALB/c (H2d) to C57BL/6 (H2b) strain combination, we demonstrate that eosinophils downregulate T cell-mediated immune responses and play a tolerogenic role even in the absence of immunosuppression. We further show that such downregulation depends on PD-L1/PD-1-mediated synapse formation between eosinophils and T cells. We also demonstrate that eosinophils suppress T lymphocyte responses through the inhibition of T cell receptor/CD3 (TCR/CD3) subunit association and signal transduction in an inducible NOS-dependent manner. Increasing local eosinophil concentration, through administration of intratracheal eotaxin and IL-5, can ameliorate alloimmune responses in the lung allograft. Thus, our data indicate that eosinophil mobilization may be utilized as a novel means of lung allograft-specific immunosuppression.

Eosinophil-derived IL-13 promotes emphysema

The inflammatory responses in chronic airway diseases leading to emphysema are not fully defined. We hypothesised that lung eosinophilia contributes to airspace enlargement in a mouse model and to emphysema in patients with chronic obstructive pulmonary disease (COPD).A transgenic mouse model of chronic type 2 pulmonary inflammation (I5/hE2) was used to examine eosinophil-dependent mechanisms leading to airspace enlargement. Human sputum samples were collected for translational studies examining eosinophilia and matrix metalloprotease (MMP)-12 levels in patients with chronic airways disease.Airspace enlargement was identified in I5/hE2 mice and was dependent on eosinophils. Examination of I5/hE2 bronchoalveolar lavage identified elevated MMP-12, a mediator of emphysema. We showed, in vitro, that eosinophil-derived interleukin (IL)-13 promoted alveolar macrophage MMP-12 production. Airspace enlargement in I5/hE2 mice was dependent on MMP-12 and eosinophil-derived IL-4/13. Consistent with this, MMP-12 was elevated in patients with sputum eosinophilia and computed tomography evidence of emphysema, and also negatively correlated with forced expiratory volume in 1 s.A mouse model of chronic type 2 pulmonary inflammation exhibited airspace enlargement dependent on MMP-12 and eosinophil-derived IL-4/13. In chronic airways disease patients, lung eosinophilia was associated with elevated MMP-12 levels, which was a predictor of emphysema. These findings suggest an underappreciated mechanism by which eosinophils contribute to the pathologies associated with asthma and COPD.

Revisiting the NIH Taskforce on the Research needs of Eosinophil-Associated Diseases (RE-TREAD)

Eosinophil-associated diseases (EADs) are rare, heterogeneous disorders characterized by the presence of eosinophils in tissues and/or peripheral blood resulting in immunopathology. The heterogeneity of tissue involvement, lack of sufficient animal models, technical challenges in working with eosinophils, and lack of standardized histopathologic approaches have hampered progress in basic research. Additionally, clinical trials and drug development for rare EADs are limited by the lack of primary and surrogate endpoints, biomarkers, and validated patient-reported outcomes. Researchers with expertise in eosinophil biology and eosinophil-related diseases reviewed the state of current eosinophil research, resources, progress, and unmet needs in the field since the 2012 meeting of the NIH Taskforce on the Research of Eosinophil-Associated Diseases (TREAD). RE-TREAD focused on gaps in basic science, translational, and clinical research on eosinophils and eosinophil-related pathogenesis. Improved recapitulation of human eosinophil biology and pathogenesis in murine models was felt to be of importance. Characterization of eosinophil phenotypes, the role of eosinophil subsets in tissues, identification of biomarkers of eosinophil activation and tissue load, and a better understanding of the role of eosinophils in human disease were prioritized. Finally, an unmet need for tools for use in clinical trials was emphasized. Histopathologic scoring, patient- and clinician-reported outcomes, and appropriate coding were deemed of paramount importance for research collaborations, drug development, and approval by regulatory agencies. Further exploration of the eosinophil genome, epigenome, and proteome was also encouraged. Although progress has been made since 2012, unmet needs in eosinophil research remain a priority.

Vesicle-associated membrane protein 7-mediated eosinophil degranulation promotes allergic airway inflammation in mice

Eosinophil degranulation is a determining factor in allergy-mediated airway pathology. Receptor-mediated degranulation in eosinophils requires vesicle-associated membrane protein 7 (VAMP-7), a principal component of the SNARE fusion machinery. The specific contribution of eosinophil degranulation to allergen-induced airway responses remains poorly understood. We generated mice with VAMP-7 gene deficiency exclusively in eosinophils (eoCRE/V7) from a cross using eosinophil-specific Cre recombinase-expressing mice crossed with VAMP-7^f/f mice. Eosinophils from eoCRE/V7 mice showed deficient degranulation responses in vitro, and responses continued to be decreased following ex vivo intratracheal adoptive transfer of eoCRE/V7 eosinophils into IL-5/hE2/EPX^−/− mice. Consistent with diminished degranulation responses, reduced airway hyperresponsiveness was observed in ovalbumin-sensitized and challenged eoCRE/V7 mice following methacholine inhalation. Therefore, VAMP-7 mediates eosinophil degranulation both in vitro and ex vivo, and this event augments airway hyperresponsiveness.

Lian Willetts et al. demonstrate that vesicle-associated membrane protein 7 (VAMP 7), a principal component of the membrane fusion machinery, promotes eosinophil degranulation in allergic airway inflammation. This study suggests VAMP7 as a therapeutic target for ameliorating asthma.

Eosinophils and eosinophil-associated diseases: An update

The goal of this series is to offer a survey of the latest literature for clinicians and scientists alike, providing a list of important recent advances relevant to the broad field of allergy and immunology. This particular assignment was to cover the topic of eosinophils. In an attempt to highlight major ideas, themes, trends, and advances relevant to basic and clinical aspects of eosinophil biology, a search of articles published since 2015 in the Journal of Allergy and Clinical Immunology and other high-impact journals was performed. Articles were then reviewed and organized, and then key findings were summarized. Given space limitations, many outstanding articles could not be included, but the hope is that what follows provides a succinct overview of recently published work that has significantly added to our knowledge of eosinophils and eosinophil-associated diseases.