Histopathological findings in the lungs
Haematoxylin and eosin staining of lung tissues from mice at 3, 7, and 10 days post-infection is shown in Fig. 5 . Inflammatory cell infiltration was prominently observed in A(H1N1)pdm09-infected mice, whereas this was rarely observed in mice infected with seasonal H1N1 at 3 days post-infection (Fig. 5A ). The lung inflammation was clearly observed in A(H1N1)pdm09- and seasonal H1N1-infected mice at 7 days post-infection, but was more severe in A(H1N1)pdm09-infected mice (Fig. 5B ). In contrast, the magnitude of inflammation was attenuated by 10 days post-infection (Fig. 5C ).