Strengthening previously reported data that IAV can induce metalloproteases in the lung and other organs (44–48), we further demonstrated that induced MMP activity (including that of MMP-9) by IAV pre-infection was indeed likely an important factor in sensitization of mice to further PAO1-mediated lung damage, since the MMP inhibitor batimastat significantly delayed lethality (Figure 10A) and diminished inflammatory responses (Figures 10D–G) and tissue damage (Figure 10L). Here, MMP9 is linked to infection.