• TLR7 contributes to the rapid progression but not to the overall fatal outcome of secondary pneumococcal disease following influenza A virus infection.

      Stegemann-Koniszewski, Sabine; Gereke, Marcus; Orrskog, Sofia; Lienenklaus, Stefan; Pasche, Bastian; Bader, Sophie R; Gruber, Achim D; Akira, Shizuo; Weiss, Siegfried; Henriques-Normark, Birgitta; Bruder, Dunja; Gunzer, Matthias; Immune Regulation Group, Helmholtz Centre for Infection Research, Braunschweig, Germany. (2013)
      Increased risk for bacterial superinfections substantially contributes to the mortality caused by influenza A virus (IAV) epidemics. While the mechanistic basis for this lethal synergism is still insufficiently understood, immune modulation through the viral infection has been shown to be involved. Since the pattern-recognition receptor (PRR) toll-like receptor 7 (TLR7) is a major sensor for the viral genome, we studied how IAV recognition by TLR7 influences the development of secondary pneumococcal infection. In a mouse model of IAV, TLR7-deficient hosts induced a potent antiviral response and showed unchanged survival. In secondary pneumococcal infection during acute influenza, TLR7ko mice showed a fatal outcome similar to wild-type (WT) hosts, despite significantly delayed disease progression. Also, when bacterial superinfection occurred after virus clearance, WT and TLR7-deficient hosts showed similar mortality, even though we found the phagocytic activity of alveolar macrophages isolated from IAV-pre-infected hosts to be enhanced in TLR7ko over WT mice. Thus, we show that a virus-sensing PRR modulates the progression of secondary pneumococcal infection following IAV. However, the fatal overall outcome in WT as well as TLR7ko hosts suggests that processes distinct from TLR7-triggering override the contribution of this single PRR.