NA-specific immunity reduces the severity of clinical illness and
virus shedding in influenza virus-infected persons With respect to the
pandemic preparedness for H9N2, NA antibodies is of special importance as the majority of human population is naïve to H9, but
cross-reactive immunity against the NA may be preset due to prior
exposure to H2N2 and/or H3N2 viruses. The crystal structure of
H9N2 NA-antibody complex has not been solved yet, and therefore
there is no detailed information about the antigenic sites/epitopes
in the NA of H9N2 virus. Antigenic mapping through characterization
of antibody escape mutants represents preliminary effort to
elucidate the antigenic H9N2 virus NA will facilitate the development
of NA-based therapeutic antibody reagents and novel
influenza vaccines that utilizes NA immunity.