A Novel Host Defense System of Airways Is Defective in Cystic Fibrosis

Abstract

Rationale:The respiratory tract is constantly exposed to airborne microorganisms. Nevertheless, normal airways remain sterile without recruiting phagocytes. This innate immune activity has been attributed to mucociliary clearance and antimicrobial polypeptides of airway surface liquid. Defective airway immunity characterizes cystic fibrosis (CF), a disease caused by mutations in the CF transmembrane conductance regulator, a chloride channel. The pathophysiology of defective immunity in CF remains to be elucidated. Objective: We investigated the ability of non-CF and CF airway epithelia to kill bacteria through the generation of reactive oxygen species (ROS). Methods: ROS production and ROS-mediated bactericidal activity were determined on the apical surfaces of human and rat airway epithelia and on cow tracheal explants. Measurements and Main Results: Dual oxidase enzyme of airway epithelial cells generated sufficient H 2 O 2 to support production of bactericidal hypothiocyanite (OSCN ؊ ) in the presence of airway surface liquid components lactoperoxidase and thiocyanate (SCN ؊ ). This OSCN ؊ formation eliminated Staphylococcus aureus and Pseudomonas aeruginosa on airway mucosal surfaces, whereas it was nontoxic to the host. In contrast to normal epithelia, CF epithelia failed to secrete SCN ؊ , thereby rendering the oxidative antimicrobial system inactive. Conclusions: These data indicate a novel innate defense mechanism of airways that kills bacteria via ROS and suggest a new cellular and molecular basis for defective airway immunity in CF.

IFNβ/TNFα synergism induces a non-canonical STAT2/IRF9-dependent pathway triggering a novel DUOX2 NADPH Oxidase-mediated airway antiviral response

“…In our setting, the H 2 O 2 /LPO system is unlikely to have a role based on the following observations. First, LPO is not secreted from in vitro cultured AECs [44] and all the studies that previously demonstrated an LPO-dependent antimicrobial function required the addition of LPO in the experiments [38,39,43]. However, here we observe an antiviral effect of DUOX2 without the ectopic addition of LPO.…”

“…At airway surfaces, H 2 O 2 in combination with the secreted lactoperoxidase (LPO) enzyme and thiocyanite forms the microbicidal compound hypothiocyanate. To date, studies based on the use of antioxidant enzymes support the necessity of H 2 O 2 in the LPOdependent antibacterial defense [38]. Further studies suggest that DUOX2 is a source of H 2 O 2 production in the airways [39,40].…”

Biological Roles for the NOX Family NADPH Oxidases

“…(40), providing oxidants to support the lactoperoxidase-H 2 O 2 -thiocyanate antimicrobial system (41,42). Defective thiocyanate transport in cystic fibrosis subverts optimal activity of this system and contributes in part to the frequent respiratory infections seen in patients with this disorder.…”

NADPH oxidases in lung biology and pathology: Host defense enzymes, and more

“…(30,100). Direct experimental evidence for the role of DUOX in fueling this LPO-SCN − -mediated antimicrobial host defense system was recently obtained in in vitro studies of rat and bovine tracheal epithelial cells (86). Although LPO is a secreted enzyme, interactions with hyaluronan at the apical epithelial surface protect it from mucocilliary clearance (101), and presumably facilitate efficient DUOX-LPO interaction at the airway surface.…”