Fig. 6.

Characterization of the extent of SO₂ injury and timing of proliferation. (A–C) Transverse tracheal sections. (A) Uninjured control. (B) Six hours after SO₂ inhalation. Epithelial cells are sloughing off. (C) Twenty-four hours after SO₂ inhalation. The luminal epithelium consists of a monolayer of low cuboidal cells. (D) Percentage of epithelial cells (in the most proximal one-third of the trachea) that incorporated BrdU in a 1-h pulse at different times after the injury. Bars are the standard error of the mean. Epithelial cell proliferation peaks 24 h after the injury. (Scale bars: 200 μm.)