To determine whether the type I IFN-mediated effects on NK cell functional activity during flu infection is due to direct or indirect action, we used adoptive transfer of IFNAR−/− or WT splenocytes (both carrying the CD45.2 allele) into B6 WT (CD45.1+) host mice, followed by i.v injection of flu. This evidence concerns the gene IFNAR1 and influenza.