An eosinophil-Sos1-RAS axis licenses corticosteroid resistance in patients with allergic rhinitis

Background Corticosteroid resistance (CR) is a serious disadvantage in treating many chronic inflammatory conditions. Eosinophils are the main inflammation cells in allergic reactions. Environmental pollution, such as PM2.5, is associated with the pathogenesis of allergic disorders. The objective of this study is to elucidate the mechanism by which the exposure to PM2.5 confers eosinophil CR status. Methods Patients with allergic rhinitis were recruited and assigned to corticosteroid sensitive (CS) and CR groups. Eosinophils were purified from nasal lavage fluids collected from patients with allergic rhinitis. A murine AR mouse model was developed with dust mite allergens and PM2.5 as the sensitization reagents. Results CR status was detected in about 60% eosinophil collected in patients with AR. Upon exposure to eosinophil activators, CS eosinophils released a large quantity of mediators, which was suppressed by the presence of steroids in the culture. CR eosinophils demonstrated resistance to steroidal therapy. RAS activation levels in eosinophils were higher in CR eosinophils than in CS eosinophils. Higher expression of the Son of sevenless-1 (Sos1) was detected in CR eosinophils, which formed a complex with RAS and glucocorticoidreceptor-α in CR eosinophils to prevent the binding between steroids and glucocorticoidreceptor-α. The presence of an Sos1 inhibitor dissociated glucocorticoid receptor-α from RAS/Sos1 complex, that restored the sensitivity to steroids in eosinophils. Administering the Sos1 inhibitor effectively attenuated the experimental allergic rhinitis. Conclusions CR status was detected in approximately 1/3 eosinophils sampled from patients with allergic rhinitis. Sos1 was instrumental in the development and perseverance of CR in eosinophils. Sos1 inhibition restored sensitivity to steroids in CR eosinophils, which effectively reduced experimental allergic rhinitis.