We utilized our original model of initially infecting B10.S mice with “X-31” influenza, a recombinant influenza virus containing the hemagglutinin (HA) and neuraminidase (NA) proteins of A/Aichi/2/68 (H3N2), with all other proteins derived from A/Puerto Rico/8/34 (H1N1). The gene discussed is XK; the disease is influenza.