Taken together, it is demonstrated that type-I interferon induced by the viral infection should be associated with the induction of FasL protein which should play a negative effect on host protection against lethal influenza virus infection, and it is therefore suggested to explore the detail mechanism of regulation by the FasL/Fas system for the host immunological response; doing so should be beneficial to the controlling of the severity of influenza. This evidence concerns the gene FASLG and viral infectious disease.