We produced four different types of influenza pseudoparticles: pseudoparticles containing HA only (H3X-31), X-31 HA and NA matching pseudoparticles (H3X-31/N2X-31), and to model N2 NA gene reassortment, human:human mismatching pseudoparticles (H3X-31/N2Japan) and human:avian mismatching pseudoparticles (H3X-31/N2MS96). This evidence concerns the gene XK and influenza.