Epithelium‐derived cystatin SN inhibits house dust mite protease activity in allergic asthma

Background Allergen source‐derived proteases are a critical factor in the formation and development of asthma. The cysteine protease activity of house dust mite (HDM) disrupts the epithelial barrier function. The expression of cystatin SN (CST1) is elevated in asthma epithelium. CST1 inhibits the cysteine protease activity. We aimed to elucidate the role of epithelium‐derived CST1 in the development of asthma caused by HDM. Methods CST1 protein levels in sputum supernatants and serum of patients with asthma and healthy volunteers were measured by ELISA. The ability of CST1 protein to suppress HDM‐induced bronchial epithelial barrier function was examined in vitro. The effects of exogenous CST1 protein on abrogating HDM‐induced epithelial barrier function and inflammation were examined in mice in vivo. Results CST1 protein levels were higher in sputum supernatants (142.4 ± 8.95 vs 38.87 ± 6.85 ng/mL, P