Morphological characterization of ALI human airway cultures. ALI cultures were fixed in 10% formalin 5 weeks after the initial seeding onto the permeable membrane support. Tissue sections were stained with H&E (A), p63 (B), Ki67 (C), and PAS (D). Examples of positively stained cells are indicated by arrows. The arrows in (A), (B), (C), and (D) indicate ciliated cells, basal cells, actively proliferating cells, and goblet cells, respectively.