Dynamic adaptation mutations and pathogenic characterization of a mouse-adapted seasonal human H3N2 influenza virus.

BACKGROUND

H3N2 influenza A viruses [A(H3N2)] circulate as seasonal influenza in humans worldwide, resulting in a huge disease burden. Adaptation study of A(H3N2) in mice could provide a basis for preclinical evaluation of antivirals and vaccines targeting A(H3N2) and identify the genetic markers responsible for the viral adaptation, replication, and pathogenesis.

METHODS

Lung-to-lung passaging of wild-type (WT) A(H3N2) strain was performed in C57BL/6J mice. Amino acid (AA) mutations occurred during the passaging and temporal dynamics of these mutations were identified using the next-generation sequencing. We determined the polymerase activity of the ribonucleoprotein (RNP) complex containing mutation genes and compared the pathogenicity between the mouse-adapted (MA) and A(H3N2)-WT strains based on body weight change, survival rate, lung index, lung viral load, and lung pathology of the infected mice.

RESULTS

The A(H3N2)-MA strain was obtained after seventeen lung-to-lung passages in mice. 14 AA mutations in the PB2, PB1, PA, HA, NP, and M1 genes were identified in the A(H3N2)-MA strain compared to the A(H3N2)-WT strain. In addition, the polymerase activity of the RNP complex containing mutation genes was increased, and the pathogenicity of the MA virus is significantly higher than that of the WT strain.

CONCLUSIONS

One A(H3N2)-MA strain has been developed that can infect and kill mice. The MA strain showed stronger replication ability and pathogenicity than the A(H3N2)-WT strain. This A(H3N2)-MA model provides a valuable basis for evaluating the effects of drugs and vaccines and for studying pathogenesis.