Comparing epithelial alarmin responses to different aeroallergens in bronchial epithelial cells from allergic asthma patients

Background: Exposure of the airway epithelium to allergens is a major trigger of allergic asthma inflammation potentially involving release of epithelial alarmins; TSLP, IL33 and IL25 and metabolite danger associated molecular patterns, ATP and uric acid (UA). In turn these alarmins orchestrate type2 inflammatory responses in asthma. Aim: To compare the alarmin response to four different aeroallergens in human bronchial epithelial cells (HBECs) from patients with allergic asthma. Methods: Primary HBECs from allergic asthmatic donors (n=8) were cultured in vitro and exposed to House dust mite (HDM; 20µg/mL), Alternaria alternata (200µg/mL), Betula pendula (200µg/mL) and Artemisia Vulgaris (1000µg/mL) for 3 and 24h. Gene expression of TSLP and IL33 was analysed by RT-qPCR, whereas TSLP, IL33 and IL25 protein levels were measured by ELISA. Extracellular release of UA was measured by biochemical assay. Results: All four allergens induced TSLP and IL33 gene expression at 3h compared to unstimulated cells. However, only HDM induced a significant release of IL33 and TSLP an early time-point at 3h with TSLP being sustained at 24h. Further, only HDM induced UA release in HBECs compared to unstimulated cells. There was a trend to IL25 release in response to A. alternata. Conclusion: The four different aeroallergens differed as regards effects on alarmin expression and release in HBECs obtained from individuals with allergic asthma. All allergens induced early gene expression of TSLP and IL33, but HDM stood out by also causing release of TSLP (3h and 24h), IL33 (3h), and UA (24h). These data support the view that HDM is a major pathogenic allergen in allergic asthma.