Impact of influenza A infection on parenchymal remodeling in adulthood. 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. Pictures show immunofluorescence images of α-SMA+ alveolar cells (arrow heads) in the lungs from (a) saline and (b) influenza and HDM-treated mice. (c) Higher magnification reveals the interstitial distribution of the alveolar α-SMA cells in influenza and HDM-treated mice. (d) Combined staining for α-SMA and the pro-collagen peptide PINP revealed ongoing collagen synthesis among α-SMA-positive cells in patchy regions of aggravated and cell-rich alveolar inflammation. (e) Quantification of α-SMA-positive alveolar cells parenchymal tissue of 8 week-old mice. Scale bars in panels a and b=100 μm; panel c=35 μm; panel d=15 μm. n=8–10 mice per group. Data represent mean±s.e.m. **P<0.01; ***P<0.001. α-SMA, α-smooth muscle actin; HDM, house dust mite; PBS, phosphate-buffered saline; PV, pulmonary vessel.