Glycosylation of HA and NA can affect the host specificity, virulence and infectivity of an influenza strain either directly, by changing the biological properties of HA and NA [8], or indirectly, by attenuating receptor binding [9], [10], [11], [12], [13], masking antigenic regions of the protein [8], [14], [15], [16], [17], impeding the activation of the protein precursor HA0 via its cleavage into the disulfide-linked subunits HA1 and HA2 [18], [19], [20], regulating catalytic activity or preventing proteolytic cleavage of the stalk of NA [2], [21], [22]. This evidence concerns the gene XK and influenza.