Airway epithelium interactions with aeroallergens: Role of secreted cytokines and chemokines in innate immunity

Airway epithelial cells are the first line of defense against the constituents of the inhaled air, which include allergens, pathogens, pollutants and toxic compounds. The epithelium not only prevents the penetration of these foreign substances into the interstitium, but also senses their presence and informs the organism’s immune system of the impending assault. Epithelium accomplishes the latter through the release of inflammatory cytokines and chemokines that recruit and activate innate immune cells at the site of assault. These epithelial responses aim to eliminate the inhaled foreign substances and minimize their detrimental effects to the organism. Quite frequently, however, these innate immune responses of the epithelium to inhaled substances may become self-damaging because of chronic and high level release of pro-inflammatory mediators. The interactions of airway epithelial cells with allergens will be discussed with particular focus in the interactions-mediated epithelial release of cytokines-chemokines and their role in the immune response. As pollutants are other major constituents of inhaled air, we will also discuss how pollutants may alter the responses of airway epithelial cells to allergens

Increased Protease-Activated Receptor-2 (PAR-2) Expression on CD14++CD16+ Peripheral Blood Monocytes of Patients with Severe Asthma.

Protease-Activated Receptor-2 (PAR-2), a G protein coupled receptor activated by serine proteases, is widely expressed in humans and is involved in inflammation. PAR-2 activation in the airways plays an important role in the development of allergic airway inflammation. PAR-2 expression is known to be upregulated in the epithelium of asthmatic subjects, but its expression on immune and inflammatory cells in patients with asthma has not been studied.We recruited 12 severe and 24 mild/moderate asthmatics from the University of Alberta Hospital Asthma Clinics and collected baseline demographic information, medication use and parameters of asthma severity. PAR-2 expression on blood inflammatory cells was analyzed by flow cytometry.Subjects with severe asthma had higher PAR-2 expression on CD14++CD16+ monocytes (intermediate monocytes) and also higher percentage of CD14++CD16+PAR-2+ monocytes (intermediate monocytes expressing PAR-2) in blood compared to subjects with mild/moderate asthma. Receiver operating characteristics (ROC) curve analysis showed that the percent of CD14++CD16+PAR-2+ in peripheral blood was able to discriminate between patients with severe and those with mild/moderate asthma with high sensitivity and specificity. In addition, among the whole populations, subjects with a history of asthma exacerbations over the last year had higher percent of CD14++CD16+ PAR-2+ cells in peripheral blood compared to subjects without exacerbations.PAR-2 expression is increased on CD14++CD16+ monocytes in the peripheral blood of subjects with severe asthma and may be a biomarker of asthma severity. Our data suggest that PAR-2 -mediated activation of CD14++CD16+ monocytes may play a role in the pathogenesis of severe asthma

ROC curve of “% of CD14⁺⁺CD16⁺PAR-2⁺ monocytes” in peripheral blood used to identify patients with severe asthma.

<p>Sensitivity and specificity were calculated according to the optimal cutoffs using R software and AUC with a 95% confidence interval is shown.</p

PAR-2 mRNA expression in whole blood of patients with asthma.

<p>(A) PAR-2 mRNA expression in mild/moderate (n = 16) and severe (n = 6) asthmatics. (B) correlation of PAR-2 mRNA expression with percentage of monocytes in peripheral blood. (C) total ICS dose and (D) percentage of FEV₁ predicted in the whole population (n = 22).</p

Asthma exacerbations and CD14⁺⁺CD16⁺PAR-2⁺ expression.

<p>(A) Proportion of CD14⁺⁺CD16⁺PAR-2⁺ cells in peripheral blood was correlated with the total daily dose of ICS in the whole population. (B) Percentage of CD14⁺⁺CD16⁺PAR-2⁺ monocytes in peripheral blood in asthmatics that did not have recent exacerbations (NAE) (n = 26) compared to asthmatics with recent exacerbations (AE) (n = 10). Correlation of the “% of CD14⁺⁺CD16⁺PAR-2⁺ monocytes in peripheral blood” (C) percentage predicted FEV₁ and (D) “% of CRTh2⁺CD4⁺” in peripheral blood in subjects with asthma exacerbations (n = 10).</p

PAR-2 expression on monocytes and severe asthma

<p><b>A.</b> Gating strategy to study PAR-2 expression on peripheral blood monocytes. B-C. Percentage of CD14⁺⁺CD16⁺ (B) and CD14⁺⁺CD16^- (C) monocytes in the peripheral blood of severe asthmatics compared to mild/moderate asthmatics. D-E. PAR-2 expression on CD14⁺⁺CD16⁺ (D) and CD14⁺⁺CD16^- (E) monocytes in patients with mild/moderate and severe asthma. F-G. Percentage of CD14⁺⁺CD16⁺PAR-2⁺ (F) and CD14⁺⁺CD16^-PAR-2⁺ (G) monocytes in peripheral blood of patients with mild/moderate and severe asthma. H-I. PAR-2 MFI on CD14⁺⁺CD16⁺ (H) and CD14⁺⁺CD16^- (I) monocytes from patients with mild/moderate and severe asthma. Data is presented as boxplots (n = 24 for mild/moderate and n = 12 for severe asthma). Statistical significance was assessed by Mann-Whitney rank sum test, with <i>P</i><0.05 considered significant.</p