Figure 2. Lung injury and fibrosis in rodent model of inhalation injury.

Male C57BL/6 mice were exposed to air or Br₂ gas (400 ppm, 30 minutes) and returned to room air. Plasma heme and acute and chronic lung injury parameters were measured in mice on days 1, 7, 14, or 21 after Br₂ exposure. Plasma levels of total heme were elevated in mice until 14 days after Br₂ inhalation (n = 6–11) (A). Bronchoalveolar lavage fluid (BALF) showed a significant increase in protein levels (n = 9–14) (B) and total cell count (n = 9–17) (C) on days 14 and 21 after Br₂ inhalation. Peripheral lung tissue staining for α-smooth muscle actin (α-SMA) (n = 5) (D) and with Masson’s trichrome stain (n = 5) (E) demonstrated an increased accumulation of α-SMA and thickening of the smooth muscle layer and collagen deposition (blue stain) primarily around airways on days 14 and 21 after Br₂. Characteristic images were obtained from the indicated number of lungs for each condition. Similarly, the quantification of collagen by measuring lung hydroxyproline levels showed significant increases at 14 and 21 days after Br₂ inhalation (F). Values are means ± SEM. *P < 0.05 versus air-exposed C57BL/6 mice by 1-way ANOVA followed by Tukey’s post hoc test. Scale bars are 100 µm.