Biochemical Methods for the Characterization of Influenza Viruses with Reduced Sensitivity to 4-Guanidino-Neu5Ac2en

Viruses that are less sensitive to the influenza neuraminidase (NA)-specific inhibitor 4-guanidino-Neu5Ac2en (zanamavir) (1 ) can be isolated after several passages in MDCK cells in the presence of the inhibitor. Although there are three reports of a mutation in the NA gene at the same conserved site, glu119 (2 –4 ), most of the variants have mutations in the hemagglutinin (HA) gene (5 ). Many of these mutations appear to lower the affinity of the HA for the cellular receptor, so there is less requirement for significant NA activity for the newly synthesized progeny virus to elute. In this chapter we describe noncell culture-based methods for characterization of both HA and NA variants.