Dataset Information

Siglec-7 on peripheral blood eosinophils: Surface expression and function.

ABSTRACT: BACKGROUND:Siglec-7 is an inhibitory receptor (IR) expressed on human blood eosinophils. Whereas activation of other IRs, including Siglec-8 and CD300a, has been shown to downregulate eosinophil function, little is known about the role of Siglec-7 on human eosinophils. OBJECTIVE:To examine Siglec-7 expression and function in eosinophils from normal (ND) and eosinophilic (EO) donors. METHODS:Eosinophil expression of Siglec-7 was quantified by flow cytometry and quantitative PCR. Soluble Siglec-7 (sSiglec-7) levels were measured by ELISA in serum. The effect of Siglec-7 on eosinophil viability and degranulation was assessed in vitro by AnnexinV-FITC/7-AAD staining and by measuring GM-CSF-induced mediator release in culture supernatants. Signal transduction was studied by Western blot. RESULTS:Siglec-7 was expressed ex vivo on blood eosinophils from all eosinophilic and normal individuals studied. Siglec-7 surface, but not SIGLEC-7mRNA expression, was correlated with absolute eosinophil count (AEC). Siglec-7 was upregulated on purified eosinophils after in vitro stimulation with GM-CSF or IL-5. Serum sSiglec-7 was detectable in 133/144 subjects tested and correlated with AEC. Siglec-7 cross-linking inhibited GM-CSF-induced release of eosinophil peroxidase, TNF-?, and IL-8 (n = 7-8) but did not promote eosinophil apoptosis (n = 5). Finally, Siglec-7 cross-linking on GM-CSF-activated eosinophils induced phosphorylation of SHP-1 and de-phosphorylation of ERK1/2 and p38. CONCLUSIONS:Siglec-7 is constitutively expressed on human eosinophils and downmodulates eosinophil activation. Targeting of Siglec-7 on eosinophils might enhance treatment efficacy in eosinophil-driven disorders. Conversely, therapeutic interventions that inhibit Siglec-7 could have unanticipated consequences and promote eosinophilic inflammation.

SUBMITTER: Legrand F

PROVIDER: S-EPMC6661208 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Siglec-7 on peripheral blood eosinophils: Surface expression and function.

Legrand Fanny F Landolina Nadine N Zaffran Ilan I Emeh Robert O RO Chen Elizabeth E Klion Amy D AD Levi-Schaffer Francesca F

Allergy 20190226 7

<h4>Background</h4>Siglec-7 is an inhibitory receptor (IR) expressed on human blood eosinophils. Whereas activation of other IRs, including Siglec-8 and CD300a, has been shown to downregulate eosinophil function, little is known about the role of Siglec-7 on human eosinophils.<h4>Objective</h4>To examine Siglec-7 expression and function in eosinophils from normal (ND) and eosinophilic (EO) donors.<h4>Methods</h4>Eosinophil expression of Siglec-7 was quantified by flow cytometry and quantitative ...[more]

PMID: 30690753

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Project description:Eosinophilia is a characteristic feature of allergic airway inflammation and remodeling. Chloride channel-3 (CLC3) in eosinophils has been associated with superoxide generation and respiratory burst. The CLC3 gene may produce multiple transcript variants through alternative splicing. However, the presence of CLC3 variants in human eosinophils is unknown. We examined the expression of CLC3 transcript variants in peripheral blood eosinophils of allergic asthmatics and healthy individuals. Potential of these obligatory dimers to form homo- or hetero-dimers was examined in HEK293 cells co-transfected with CLC3b-GFP and CLC3e-RFP. Eosinophils were isolated from peripheral blood by negative selection. Expression of CLC3 and CLC3 transcript variants was examined by qPCR, Western blot, and immunofluorescence. Confocal micrographs were analyzed with Image J software. Higher levels of novel transcript variants of CLC3 (CLC3b and CLC3e) were found in peripheral blood eosinophils of asthmatics compared to healthy non-atopic subjects. We also found higher CLC3 protein expression in the blood and nasal lavage eosinophils of asthmatics than healthy subjects. Both membranous and intracellular CLC3 expression were observed. Also, we found the presence of both homodimers and heterodimers of CLC3b-GFP and CLC3e-RFP in HEK293 cells. Higher and differential expression of novel CLC3 transcript variants in mild-to-moderate and moderate-to-severe asthmatic eosinophils suggest their critical role in allergic asthma. Membranous and intracellular (granular) expression of CLC3 in nasal lavage and peripheral blood eosinophils suggest their involvement in the activation and migration of eosinophils in allergic asthma. Moreover, homo- and hetero-dimerization of these transcript variants may change the channel properties to exhibit these states. Presence of CLC3 variants may serve as a biomarker in allergic asthma and additional knowledge of interaction between CLC3 transcript variants and their specific role in the activation and migration of eosinophils will allow to explore novel therapeutic approach in allergic asthma.

Project description:Background and objectiveSome children with asthma have low lung growth, putting them at increased risk for COPD later in life. However, it is currently not clear who will experience this adverse growth pattern. We therefore investigated the predictive role of blood eosinophils as a type 2 inflammation marker in lung growth, focusing on the presence and severity of asthma.MethodsWe investigated blood eosinophils and lung function growth (percentage of predicted values) using linear mixed models in children and adolescents from two longitudinal cohorts. One cohort was hospital-based and consisted of asthmatic children at their first outpatient clinic visit after referral by the general practitioner (n = 133, mean age 9.8), while the second was a general population-based birth cohort (PIAMA, asthma n = 52 and non-asthma n = 433, mean age 8.1). The hospital-based cohort had not been treated with inhaled corticosteroids (ICS) before referral.ResultsSubjects in the hospital-based asthma cohort had more severe asthma compared with the asthmatic subjects in the population-based cohort, defined by lower lung function levels and a higher prevalence of bronchial hyper-responsiveness. In the asthma cohort, higher blood eosinophil numbers were associated with less growth in FEV1 (estimated change in lung function per 1 unit increase in ln blood eosinophils (B): -0.66%/year (95% confidence interval (CI): -1.11 to -0.20, p < .01)) and FVC (B: -0.40%/year (95% CI: -0.75 to -0.05), p = .025)) during follow-up in adolescence (min 7, max 17 years). These associations were not observed in the general population-based birth cohort, regardless of asthma status during follow-up (age 8-16).Conclusions and clinical relevanceBlood eosinophil counts in children with asthma not treated with ICS at referral were predictive of lower growth in FEV1 and FVC during follow-up in adolescence. Our findings indicate that this association is dependent on the degree of asthma severity. Future studies should address whether anti-eosinophilic treatments preserve lung function growth in children with asthma.

Project description:BACKGROUND:Siglec-8 is a CD33 subfamily cell-surface receptor selectively expressed on human eosinophils. After cytokine priming, Siglec-8 mAb or glycan ligand binding causes eosinophil apoptosis associated with reactive oxygen species (ROS) production. Most CD33-related Siglecs function as inhibitory receptors, but the ability of Siglec-8 to stimulate eosinophil ROS production and apoptosis suggests that Siglec-8 might instead function as an activating receptor. OBJECTIVE:We sought to determine the role of IL-5 priming and identify the signaling molecules involved in Siglec-8 function for human eosinophils. METHODS:We used an mAb and/or a multimeric synthetic sulfated sialoglycan ligand recognizing Siglec-8 in combination with integrin blocking antibodies, pharmacologic inhibitors, phosphoproteomics, and Western blot analysis to define the necessity of various proteins involved in Siglec-8 function for human eosinophils. RESULTS:Cytokine priming was required to elicit the unanticipated finding that Siglec-8 engagement promotes rapid ?2-integrin-dependent eosinophil adhesion. Also novel was the finding that this adhesion was necessary for subsequent ROS production and apoptosis. Siglec-8-mediated ROS was generated through reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation because pretreatment of eosinophils with catalase (an extracellular superoxide scavenger) or NSC 23766 (a Rac GTPase inhibitor) completely inhibited Siglec-8-mediated eosinophil apoptosis. Finally, engagement of Siglec-8 on IL-5-primed eosinophils resulted in increased phosphorylation of Akt, p38, and c-Jun N-terminal kinase 1 that was also ?2-integrin dependent; pharmacologic inhibition of these kinases completely prevented Siglec-8-mediated eosinophil apoptosis. CONCLUSIONS:These data demonstrate that Siglec-8 functions uniquely as an activating receptor on IL-5-primed eosinophils through a novel pathway involving regulation of ?2-integrin-dependent adhesion, NADPH oxidase, and a subset of protein kinases.

Project description:OBJECTIVE:We aimed to investigate peripheral blood eosinophil chemotaxis, generation of spontaneous reactive oxygen species (ROS), and apoptosis in patients with allergic asthma after bronchial allergen challenge. MATERIAL AND METHODS:A total of 18 patients with allergic asthma (AA), 14 with allergic rhinitis (AR), and 10 healthy subjects (HS) underwent bronchial challenge with a specific allergen extract. Eosinophils from peripheral blood were isolated 24 h before as well as 7 and 24 h after bronchial allergen challenge. Chemotaxis, spontaneous ROS production in eosinophils, and apoptosis were analyzed by flow cytometry. Serum and induced sputum IL-5 levels were measured by ELISA; the cell count in sputum was analyzed by the May-Grünwald-Giemsa method. RESULTS:Before bronchial allergen challenge, peripheral blood eosinophil chemotaxis, spontaneous ROS production was enhanced and eosinophil apoptosis was reduced in the patients with AA as compared with AR patients and HS (P?<?0.05). Meanwhile, eosinophil chemotaxis and ROS generation markedly increased in the patients with AA 7 h and 24 h after challenge compared with other groups and baseline values (P?<?0.05). The percentage of apoptotic eosinophils in the patients with AA decreased at 7 h as well as 24 h after challenge when compared with other groups and the baseline values (P?<?0.05). There was a significant correlation between the migrated peripheral blood eosinophil count and the sputum eosinophil count (Rs?=?0.89, P?<?0.0001) and the sputum IL-5 level (Rs?=?0.68, P?=?0.002) at 24 h after bronchial challenge only in the patients with AA. Furthermore, the percentage of peripheral blood apoptotic eosinophils significantly correlated with eosinophil count in sputum (Rs?=?-0.53, P?=?0.02), and ROS production correlated with the serum IL-5 levels (Rs?=?0.71, P?=?0.01). CONCLUSION:During allergen-induced late-phase airway inflammation, peripheral blood eosinophils demonstrated further alterations of their functional activity manifested by enhanced spontaneous ROS production, increased chemotaxis, and diminished apoptosis in patients with AA.

Dataset Information

Siglec-7 on peripheral blood eosinophils: Surface expression and function.

Publications

Siglec-7 on peripheral blood eosinophils: Surface expression and function.

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