Identification of mammalian-adapting mutations involved into antigenic change of H1N1 influenza virus

Abstract Though the 2009 pandemic H1N1 virus has become a seasonal influenza A virus, continued host adaptation and antigenic drift may limit the effectiveness of current vaccines. Here, we assess viral antigenic change of a 2009 pandemic H1N1 virus (A/Changchun/01/2009) in the absence and presence of immune-mediated selective pressures and further identify the key amino acid substitutions involved into the antigenic change of the 2009 pandemic H1N1 virus. We found that serial passage of the 2009 pandemic H1N1 virus in both naïve and previously immunized mice generated antigenically distinct variants and that serial passage in previously immunized mice generated viruses with lower overall antigenic relatedness to the parental virus when compared to variants generated by serial passage in naïve mice, suggesting that antibody pressure may accelerate the antigenic variation rate of the 2009 pandemic H1N1 virus. Furthermore, we found that three amino acid substitutions in the viral HA protein (N159D, S186P, and D225G), both alone and in combination, affected viral antigenicity. It is noted that all three mutations (N159D, S186P, and D225G) in the viral HA protein have been found in the natural 2009 pandemic H1N1 virus isolates and can also enhance the pathogenicity of the 2009 pandemic H1N1 virus to mammals, suggesting that these mutations in the viral HA protein may pose a potential threat to public health and should be paid more attention. Taken together, our work defines some novel molecular determinants of the pandemic H1N1 virus antigenicity and has important implications for ongoing human influenza virus surveillance efforts.