Identification of Genes Expressed by Human Airway Eosinophils after an In Vivo Allergen Challenge

Abstract

BackgroundThe mechanism for the contribution of eosinophils (EOS) to asthma pathophysiology is not fully understood. Genome-wide expression analysis of airway EOS by microarrays has been limited by the ability to generate high quality RNA from sufficient numbers of airway EOS.ObjectiveTo identify, by genome-wide expression analyses, a compendium of expressed genes characteristic of airway EOS following an in vivo allergen challenge.MethodsAtopic, mild asthmatic subjects were recruited for these studies. Induced sputum was obtained before and 48h after a whole lung allergen challenge (WLAC). Individuals also received a segmental bronchoprovocation with allergen (SBP-Ag) 1 month before and after administering a single dose of mepolizumab (anti-IL-5 monoclonal antibody) to reduce airway EOS. Bronchoalveolar lavage (BAL) was performed before and 48 h after SBP-Ag. Gene expression of sputum and BAL cells was analyzed by microarrays. The results were validated by qPCR in BAL cells and purified BAL EOS.ResultsA total of 299 transcripts were up-regulated by more than 2-fold in total BAL cells following SBP-Ag. Mepolizumab treatment resulted in a reduction of airway EOS by 54.5% and decreased expression of 99 of the 299 transcripts. 3 of 6 post-WLAC sputum samples showed increased expression of EOS-specific genes, along with the expression of 361 other genes. Finally, the intersection of the 3 groups of transcripts (increased in BAL post SBP-Ag (299), decreased after mepolizumab (99), and increased in sputum after WLAC (365)) was composed of 57 genes characterizing airway EOS gene expression.ConclusionWe identified 57 genes that were highly expressed by BAL EOS compared to unseparated BAL cells after in vivo allergen challenge. 41 of these genes had not been previously described in EOS and are thus potential new candidates to elucidate EOS contribution to airway biology.

Cannabinoid receptor 2 augments eosinophil responsiveness and aggravates allergen‐induced pulmonary inflammation in mice

“…Consistent with these data, we found that purified human eosinophils from healthy subjects express an appreciable amount of CB 2 on mRNA (data not shown) and protein levels. Enhanced gene expression of CB 2 has been shown for lung eosinophils in allergic patients after allergen challenge 44. Accordingly, we could demonstrate that also CB 2 protein expression is significantly increased on the cell surface of peripheral blood eosinophils from symptomatic allergic donors, supporting a role for CB 2 and its ligands in the regulation of allergen‐induced eosinophilic inflammation.…”

Carbonic Anhydrase IV Is Expressed on IL-5–Activated Murine Eosinophils

“…Accordingly, in the context of the induction of asthma and CAR4 expression, the gene ontology analysis of the lung tissue microarray data highlights a variety of potential functions for eosinophil CAR4, including the regulation of the keratinization, differentiation of the epithelium, and bicarbonate and anion transport. A recent microarray study from human asthmatic sputum identified a series of 57 genes characterizing airway eosinophil activation (34). Despite intriguing results and similar genome-wide approaches, this was not an eosinophil-specific approach, which may explain the absence of CAR4 on their screening list.…”

Semaphorin 7A is expressed on airway eosinophils and upregulated by IL-5 family cytokines

“…Genetic ablation of EOS attenuated submucosal matrix deposition and reduced airway smooth muscle hyperplasia [17, 18]. Using genome-wide expression analyses, we recently reported that sema7A mRNA was among the transcripts that were increased in parallel with the increase of EOS in bronchoalveolar lavages (BAL) and sputum of mild allergic asthmatics following an in vivo allergen challenge [19]. While airway remodeling has been linked at least in part to the presence of EOS, their expression of sema7A has not yet been reported.…”