Figure 8. Lung viral loads on day 4 post-challenge infection with the homologous virus A/PR8 or the heterosubtypic virus A/Philippines.

Mice immunized IN with designed doses of VLPs were challenged with a lethal dose (40 LD₅₀) of A/PR8 or A/Philippines. Six mice were included in each viral challenge group. Four days after infection, mouse lungs were collected and extracted with medium RPMI 1640. The extract was adjusted to 1 ml per lung. Virus titers in lung extracts were titrated using MDCK-based plaque assay as described in Materials and Methods. The lung virus titer is presented as pfu per lung.