Histopathology and immunohistochemistry of the lungs of infected dogs. The left cranial lobes of the lungs from dogs (Korean mongrel, n = 2) infected with A/Korea/S1/Canine/2012 (H3N2) and from PBS mock-infected dogs were collected 5 days after infection. The lung tissues from PBS mock-infected (A) or infected (B) dogs were stained with H&E stain. In addition, the lung tissues from PBS mock-infected (C) or infected (D) dogs were stained with mouse anti-influenza A nucleoprotein antibody, biotin-labeled goat anti-mouse immunoglobulin, and red alkaline phosphatase substrate. The stained sections were imaged with an Olympus DP70 microscope.