Impact of influenza A infection on airway remodeling in adulthood. (a) Separate groups of 8-day-old mice were infected with influenza virus or given PBS alone. Seven days later, PBS- and Flu-infected groups are exposed either to 3 weeks of HDM or Sal, then, after the last HDM exposure, mice were rested for 3 weeks and killed at 8 weeks of age. Images are representative light photomicrographs of paraffin-embedded cross-sections of lung tissue. Lung histopathology as evaluated by (b) periodic-acid-Schiff (PAS) staining indicating mucus production of epithelial goblet cells (magenta; insets show color-inverted image used for morphometric analysis) and Picro Sirus Red (PSR) staining visualized under polarized light indicating subepithelial collagen deposition. (c) Morphometric analysis of PAS and PSR tissues. (d) Comparison of PSR tissues after 3 weeks of HDM exposure or after additional 3 weeks cessation (resolution). All images were taken at × 200 total magnification. For all data, n=8–10 mice per group. Data represent mean±s.e.m. P<0.05 compared with *Sal, ‡Flu, and §HDM, respectively. HDM, house dust mite; PBS, phosphate-buffered saline.