Expression of CatK in mouse lungs and its effects on airway epithelium. Representive immunohistochemical staining (A) of a small airway from a 3 months old WT mouse and an age matched Ctsk-/- lung tissue sample (original magnification, ×200). (B) Morphometric analysis of CatK expression in airway epithelium from mice of various ages. The density of CatK expression was normalized to the perimeter of the basement membrane. Representative H&E staining (C) of small airways from 2 months old WT and Ctsk-/- mice (original magnification, ×200). Morphometric analysis shows epithelium thickness (D) and integrity (E) in lung sections from mice of various ages. Representative image and band analysis (F) of immunoblots show cytokeratin expression in 2 month old lung homogenates. The results revealed that airway epithelium was increased in thickness and diminished in integrity in Ctsk-/- mice. Morphometry and image analysis were processed using Openlab software and Chemigenius system, respectively. All values are expressed as means ± SE for 5 separate experiments. (●(WT) and ◆(Ctsk-/-) indicate the number of mouse at a certain score.