FIG 1.

Secondary pneumococcal infection significantly increases pulmonary edema and tissue damage in a serotype-specific manner. (A) BALB/c mice were infected with a sublethal dose of the PR8 virus, followed by S. pneumoniae infection. Representative H&E images of influenza-infected lung tissue show bronchiolar epithelial damage and alveolar infiltration at 7 dpi. Influenza infection caused cell infiltration into alveolar spaces (black arrows) and bronchiolar epithelial damage (red arrow), compared to the clean alveolar spaces and intact bronchiolar epithelium (blue arrow) in control lung sections from healthy mouse lungs. Scale bar = 50 μm. (B) Representative images of infected lungs showing pulmonary edema and tissue damage. BALB/c mice were infected with a sublethal dose of the PR8 virus, followed by either serotype 3 of S. pneumoniae (Flu+S3), serotype 19F of S. pneumoniae (Flu+19F), or sterile PBS (Flu) at 7 dpi. Mice infected directly with S3 or 19F of S. pneumoniae or sterile PBS (control) were included for comparison. n = 3 independent experiments with 5 mice per time point for each experimental group. Infection-induced edema was evident as early as 9 dpi. Scale bar = 5 mm. (C) Graph showing the mean volume (cm³) of lung samples from infected and control mice in panel B.