Critical roles of antiviral mediators against mucosal influenza virus infection

Abstract

Part I: The role of CISH in adaptive immune responses against influenza infectionCISH is known as the cytokine-inducible negative regulator, which mediates feedback inhibition of cytokine signaling. Although the roles of CISH in anti-tumor immunity and development of allergic airway inflammation have been studied, it remains unclear whether CISH regulates immune responses against infectious pathogens such as influenza virus. In this study, we revealed the role of CISH during influenza infection. Loss of CISH promoted rapid recovery from body weight loss following influenza infection, although anti-influenza T cell responses and viral clearance were comparable. Using conditional Cish knockout mice specific for CD11c$^+$ cells or T cells, we reveled that CISH deficiency in CD11c$^+$ cells enhanced host resistance against influenza virus. While CD11c$^+$ cell-specific CISH deficiency did not affect the T cell responses and viral clearance, flu-specific IgA levels in BAL fluid were elevated in a Th2 response-independent manner. Further, Cish-deficient DCs showed increased IL-6 production following influenza infection. As IL-6 has been shown to facilitate isotype switching to IgA, we suggest that CISH deficiency in DC is responsible for the enhanced IgA production in lung as well as superior anti-influenza resistance in mice. Together, these results demonstrate that CISH is potential negative regulator for the induction of anti-influenza humoral responses and CISH polymorphism may be associated with susceptibility to influenza in hosts.Part II: A novel cell-penetrating MxA, PTD-MxA$_{L617D}$, enhances resistance to influenza A virus infectionThe influenza A virus (IAV), or ‘flu’, causes acute respiratory disease that results in moderate to severe symptoms in patients. While several antiviral drugs have been developed to treat influenza infection, antigenic shift and drift have generated novel subtypes of IAV that are resistant to pre-existing antiviral drugs. Therefore, there is an unmet clinical need for novel antiviral reagents with reduced drug resistance potential. Here, we developed a novel cell-penetrating mutant MxA, PTD-MxA$_{L617D}$, to treat influenza infection. To generate PTD-MxA$_{L617D}$, human MxA was modified to improve solubility and conjugated with protein transduction domain TAT residues to facilitate intracellular delivery. With these modifications, PTD-MxA$_{L617D}$ was efficiently internalized into cells without cytotoxicity. Furthermore, both pre- and post-exposure treatment with PTD-MxA$_{L617D}$ inhibited viral propagation and viral RNA expression levels in infected cells. PTD-MxA$_{L617D}$ treatment also restricted viral propagation of two different IAV subtypes, H1N1 and H3N2, but did not affect the RSV and HSV-2 infection. Finally, intranasal administration of PTD-MxA$_{L617D}$ increased survival of mice during lethal PR8 IAV infection, and this protective effect was independent of the adaptive immune response. Together, these data strongly suggest that the cell-penetrating PTD-MxA$_{L617D}$ could be a novel therapeutic agent against mucosal IAV infection.