Role of host cellular proteases in the pathogenesis of influenza and influenza-induced multiple organ failure

► Cellular proteases play key roles in virus entry and vascular hyperpermeability. ► Influenza A virus (IAV)-cytokine-protease cycle. ► IAV infection results in marked upregulation of cellular trypsins and MMP-9. ► Processing of IAV hemagglutinin (HA) is a pre-requisite for viral entry into cells. ► Identification of HA processing proteases for highly pathogenic avian IAV.