Fig 5.

Histopathologic changes in lungs of mice with secondary bacterial pneumonia. The images shown are H&E-stained sections of lungs collected at 7 dpi from BALB/c mice infected with 0.5 MLD₅₀ of PR8 (A), WT H2N2 (B), ΔNA mutant H2N2 (C), WT H9N2 (D), or ΔNA mutant H9N2 (E) virus. All viruses carry the PR8 isogenic background. Original magnification, ×40. (F to M) Mice were infected with the indicated viruses and then challenged at 7 dpi with 10⁴ CFU of pneumococci. Lungs were collected at 2 dppc. Representative H&E-stained sections are shown at ×200 magnification. (F) Mock-infected mice challenged with pneumococci. (G) Mice infected with PR8 and then mock challenged with PBS. The virus-S. pneumoniae groups correspond to WT H2N2 (H), ΔNA mutant H2N2 (I), WT H9N2 (J), ΔNA mutant H9N2 (K), and PR8 (L).