FIG 6.

Progression of infection in the lungs of mice infected with A/mallard/MN/AI08_5469/2008 (H7N3). (A) Hyperplastic bronchiole at 2 dpi with many epithelial nuclei staining positive for influenza virus. (B) Epithelial cell nuclei in a bronchiole and nuclei of interstitial cells (the arrows point to two examples) both stained positive for influenza virus at 4 dpi. (C) Many epithelial cell nuclei in a bronchiole and multiple nuclei of interstitial cells (the arrows point to three examples) stained positive for influenza virus at 6 dpi. DAB chromogen was used to stain influenza virus-positive cells (brown), with hematoxylin as a counterstain (blue). B, bronchiole. Scale bars = 100 μm. (D) The amounts of influenza virus antigen detected in mice inoculated with viruses classified as PI-4, PI-3, and PI-2 were similar; however, less antigen was detected in mice inoculated with the PI-2 virus at 4 and 5 dpi than in mice inoculated with the PI-3 or PI-4 virus. The amount of influenza virus antigen detected by immunohistochemistry was scored subjectively 0 to 4: 0, none; 1, minimal; 2, mild; 3, moderate; and 4, severe.