Airway Surface Liquid Has Innate Antiviral Activity That Is Reduced in Cystic Fibrosis

Abstract

While chronic bacterial infections and inflammation are associated with progressive lung disease in cystic fibrosis (CF) patients, much less is known regarding the contributions of respiratory viral infections to this process. Clinical studies suggest that antiviral host defenses may be compromised in individuals with CF, and CF airway epithelia exhibit impaired antiviral responses in vitro. Here, we used the CF pig model to test the hypothesis that the antiviral activity of respiratory secretions is reduced in CF. We developed an in vitro assay to measure the innate antiviral activity present in airway surface liquid (ASL) from CF and non-CF pigs. We found that tracheal and nasal ASL from newborn non-CF pigs exhibited dose-dependent inhibitory activity against several enveloped and encapsidated viruses including Sendai virus (SeV), respiratory syncytial virus (RSV), influenza A, and adenovirus. Importantly, we found that the anti-SeV activity of nasal ASL from newborn CF pigs was significantly diminished relative to non-CF littermate controls. This diminution of extracellular antiviral defenses appears to be driven, at least in part, by the differences in pH between CF and non-CF ASL. These data highlight the novel antiviral properties of native airway secretions, and suggest the possibility that defects in extracellular antiviral defenses contribute to CF pathogenesis.

Non-Coding RNAs and SARS-Related Coronaviruses

“…miRNAs play an important role in the secretion of the airway surface liquid (ASL) by regulating the ion channels and transporters responsible for the para-and transcellular movement of water and electrolytes [44]. The ASL covers the surface of epithelial cells in the respiratory tract, where one of the main functions is the protection of the host from inhaled pathogens, such as SARS-related coronaviruses [44][45][46]. Apart from airway surface liquid homeostasis, miRNAs have various other impacts on the immune defense of the respiratory tract [44].…”

“…The M (membrane) glycoprotein, apart from increasing IFNβ synthesis [68], is also essential for virus budding and assembly [70] and is highly abundant in infected cells [45]. In a study by Wang et al from 2010 [69], two highly conserved regions in the RNA sequence encoding for the M protein were targeted by artificial siRNAs, which led to decreased expression of the M gene.…”

Airway Surface Liquid and Impaired Antiviral Defense in Cystic Fibrosis

“…Compared with ASL antibacterial activity (7), ASL antiviral activity is not as dependent on pH. There is no significant change in anti-SeV activity over the pH range of 6.8–8.0 in non-CF or CF pig ASL (9), whereas antibacterial activity in ASL is significantly increased at pH 8.0 (7). Specific innate immune proteins—LL-37, a human cathelicidin; protegrin-1, a porcine cathelicidin; and human β-defensin 3—have minimal pH-related changes in anti-SEV activity, whereas, in contrast, lysozyme, lactoferrin, human β-defensin-3, and LL-37 have marked pH-dependent changes in antibacterial killing (7, 8).…”

“…On the basis of these studies, Berkebile and colleagues (9) tested whether newborn CF pig nasal ASL has deficient antiviral activity. The rationale for using newborn pigs is to avoid any secondary effects on the innate immune system due to early infections or inflammation, which would degrade critical antimicrobial proteins (10).…”

“…In this issue of the Journal (pp. 104–111), Berkebile and colleagues report that healthy adult human nasal ASL and healthy newborn pig nasal and tracheal ASL inhibit viral replication for Sendai virus (SeV), respiratory syncytial virus, influenza A, and replication-deficient adenovirus (9). Importantly, CF pig nasal ASL has impaired in vitro killing for SeV compared with non-CF pig nasal ASL.…”