The nonstructural protein NS1 is employed by influenza virus to evade host immune responses. Several studies have implicated the NS1 protein in conferring increased pathogenicity and virulence on emergent influenza strains. The NS1 virulence factor is believed to participate in multiple host-cell interactions regulating processes as diverse as viral replication, host innate and adaptive immunity, and cellular signaling. The NS1 protein consists of a N-terminal RNA-binding domain and a C-terminal protein-binding "effector" domain. The protein is being studied both for its potential in vaccine development and for its potential in antiviral drug design.