Figure 2.

The airway integrin subunit β8 is expressed in the proliferative and nonproliferative basal cell compartment in the bronchial fragment model. a–c: H&E staining. a: Normal human bronchus. b: Bronchial fragment cultured for 1 day. The fragment is only partially covered by an epithelium. Outgrowing epithelial cells (arrows) migrate from the intact epithelium at a transition zone (arrowhead) to cover the exposed subepithelial stroma. c: Bronchial fragment cultured for 7 days. The exposed stroma (area between arrowheads) has been completely covered with outgrowing epithelium (arrow). d–f: Immunostaining using polyclonal anti-β8 Ab. d: The integrin subunit β8 is mostly restricted to basally located cells in normal bronchial epithelium (arrows). e: After 1 day of culture, the integrin subunit β8 is expressed by outgrowing epithelial cells (arrow), in all cells in the tapering transition zone (arrowhead), and in the basal cells of the original epithelium. f: After 7 days of culture, membrane staining for β8 in all layers of the outgrowing epithelium is seen (arrows). g–i: Immunostaining using the anti-HMW keratin Ab 34βE12. g: In normal bronchial epithelium, 34βE12 stains basal cells (arrows). h: After 1 day of culture, 34βE12 staining is seen in the outgrowing epithelium (arrow) and in the basal compartment of the intact ciliated epithelium (arrowhead). i: After 1 week of culture, only basally located cells in the outgrowing epithelium stain with 34βE12. j–l: Immunolabeling using an anti-Ki-67 Ab that labels proliferating cells. j: Ki-67-positive cells are rare in normal adult airway. A single immunopositive stromal cell (arrow) is shown. k: After 2 days of culture a few proliferating cells (arrow) could be found in the transition zone (arrowhead). l: After 1 week of culture, numerous immunopositive cells are seen in the transition zone (arrowhead) and in the outgrowing epithelium (arrow). Shown are representative fields (a–l). Scale bar, 50 μm.