Innate Immune Evasion Strategies of Influenza A Virus

Vertebrates possess a highly sophisticated sensing machinery to detea RNA viruses, including influenza A viruses, resulting in induction of interferon and antiviral responses. However, influenza A viruses, similar to other viruses, have acquired inhibitory activities of the sensing and interferon mediated antiviral activities of their hosts, facilitating viral replication. In the last years, a complex picture of these activities has emerged, that includes multiple mechanisms by which influenza A viruses evade the antiviral host innate response. While the NS1 protein of the virus is dedicated to antagonize the interferon response at multiple levels, other viral proteins, such as PB1-F2 and the polymerase complex, also appear to contribute to immune evasion. After briefly describing how the interferon response is induced by influenza A, we discuss the multiple interferon evasion strategies encoded by the virus and their possible implications in virulence and host tropism.