elution proving most effective. ELISA results with the isolated NA from the H1N1 strain and recombinant full-length N1 showed that a commercial vaccine contains functional N1 and H1 at a ratio of ∼1:10. Structure determination by cryo-electron microscopy confirmed the native tetrameric conformation of the isolated N1 and provided insight into the stalk conformation of a virus-derived NA. Finally, comparative analyses of NAs isolated from recent egg-propagated vaccine strains (H1N1, H3N2 and type B) revealed a unique proteolytic susceptibility of type B NA and strain-specific differences in sialic acid affinities and catalytic rates. These results demonstrate that INAAC supports multiple applications from NA structural analysis to producing NA vaccine antigens and reference standards, addressing longstanding challenges for incorporating NA into influenza vaccine development and quality control.
Kang et al. (Fri,) studied this question.