Oxidative epithelial host defense is regulated by infectious and inflammatory stimuli

Epithelia express oxidative antimicrobial protection that uses lactoperoxidase (LPO), hydrogen peroxide (H2O2), and thiocyanate to generate the reactive hypothiocyanite. Duox1 and Duox2, found in epithelia, are hypothesized to provide H2O2 for use by LPO. To investigate the regulation of oxidative LPO-mediated host defense by bacterial and inflammatory stimuli, LPO and Duox mRNA were followed in differentiated primary human airway epithelial cells challenged with Pseudomonas aeruginosa flagellin or IFN-γ. Flagellin upregulated Duox2 mRNA 20-fold, but upregulated LPO mRNA only 2.5-fold. IFN-γ increased Duox2 mRNA 127-fold and upregulated LPO mRNA 10-fold. DuoxA2, needed for Duox2 activity, was also upregulated by flagellin and IFN-γ. Both stimuli increased H2O2 synthesis and LPO-dependent killing of P. aeruginosa. Reduction of Duox1 by siRNA showed little effect on basal H2O2 production, whereas Duox2 siRNA markedly reduced basal H2O2 production and resulted in an 8-fold increase in Nox4 mRNA. In conclusion, large increases in Duox2-mediated H2O2 production seem to be coordinated with increases in LPO mRNA and, without increased LPO, H2O2 levels in airway secretion are expected to increase substantially. The data suggest that Duox2 is the major contributor to basal H2O2 synthesis despite the presence of greater amounts of Duox1.