Pdz-Bm Of Influenza Virus Ns1 Protein Increases Host Susceptibility To Super-Infection Via Inhibition Of Ifn Beta Production

Abstract Type I interferon (IFN) signaling is a known contributor to increased host susceptibility to deadly bacterial super-infections (BSIs) following influenza A virus (IAV) pandemics. However, many IAV infections never develop secondary bacterial complications, suggesting that viral-derived factors can influence host susceptibility to BSIs. Utilizing reverse genetics we found that a natural variation in IAV nonstructural protein (NS1) could directly affect the duration of IFNβ signaling, which in turn affected susceptibility of mice to BSIs. Specifically, the presence of PDZ-binding motif (PDZ-bm) on the C terminus of PR8 IAV NS1 was responsible for suppression of IFNβ after day 3 post-PR8, which resulted in transition from reduced (day 3) to increased (day 7) BSI susceptibility determined by increased morbidity, mortality and lung bacterial burden. Introduction of stop codon in the position 220 of PR8 NS gene resulted in PDZ-bm deletion mutant (PR8-Trunc) that sustained production of IFNβ up to day 7 and protected WT mice from S. pnuemoniae BSI. We determined that IFNβ was required for this protective effect as unlike WT mice, IFNβ−/− mice were susceptible to BSI at day 7 post PR8-Trunc infection. Furthermore, treatment of WT mice at day 6 after WT PR8 infection with exogenous IFNβ reduced their susceptibility to BSI on day 7. Through utilization of both blocking antibodies and cell-specific type I IFN receptor −/− mice we found that reduced susceptibility to BSI required IFNβ signaling in both CD11c and Ly6G cells. Conversely, the increased susceptibility to BSIs at day 7 of PR8 infection resulted from IFNα signaling in Ly6G cells in the absence of IFNβ. Thus IAV-regulated duration of IFNβ signaling directly affects host susceptibility to BSIs.