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Abstract
Viral and bacterial respiratory infections are among the most common illnesses in human and animal populations globally. Influenza virus and Streptococcus pneumoniae infections affect millions of people worldwide, causing serious mortality and morbidity that result in a major economic burden. The first line of defense against respiratory pathogens is the respiratory epithelium. One of the innate defense mechanisms respiratory epithelial cells use to prevent infections with pathogens such as influenza virus and Streptococcus pneumoniae is the extracellular oxidative antimicrobial ion hypothiocyanite (OSCN-). OSCN- is produced at the airway surface by lactoperoxidase (LPO), thiocyanate anion (SCN-), and hydrogen peroxide (H2O2). Our focus was to determine if OSCN- has an antimicrobial effect against influenza virus and Streptococcus pneumoniae.
Our results demonstrated that in vitro OSCN- is capable of reducing viral titers of influenza A (H1N1, H1N2, H3N2), and B (Yamagata and Victoria lineages) by 2-6 logs. To elucidate the mechanism, we performed neuraminidase (NA) activity assays that showed no reduction in viral NA activity when exposed to hypothiocyanite. Additionally, pre/co-incubation of OSCN- with influenza prevents infection of MDCK cells and primary human tracheobronchial epithelial cells by influenza virus. The ability of influenza to attach to host receptors is decreased by up to 65% when exposed to OSCN-. By utilizing a Duox1-deficient mouse, we determined that Duox1 deficiency plays a negative role, leading to increased mortality and morbidity in a murine influenza infection model. Additionally, we showed that both encapsulated and nonencapsulated Spn strains are susceptible to OSCN- in vitro. Taken together the DUOX1/LPO system represents a novel innate immune mechanism capable of inactivating influenza virus and killing Spn using OSCN-.
Our results demonstrated that in vitro OSCN- is capable of reducing viral titers of influenza A (H1N1, H1N2, H3N2), and B (Yamagata and Victoria lineages) by 2-6 logs. To elucidate the mechanism, we performed neuraminidase (NA) activity assays that showed no reduction in viral NA activity when exposed to hypothiocyanite. Additionally, pre/co-incubation of OSCN- with influenza prevents infection of MDCK cells and primary human tracheobronchial epithelial cells by influenza virus. The ability of influenza to attach to host receptors is decreased by up to 65% when exposed to OSCN-. By utilizing a Duox1-deficient mouse, we determined that Duox1 deficiency plays a negative role, leading to increased mortality and morbidity in a murine influenza infection model. Additionally, we showed that both encapsulated and nonencapsulated Spn strains are susceptible to OSCN- in vitro. Taken together the DUOX1/LPO system represents a novel innate immune mechanism capable of inactivating influenza virus and killing Spn using OSCN-.