Scanning electron microscopy. Ciliated and non-ciliated (Clara) cells (arrows) in the bronchiolar epithelium of normal control mice (Untreated). Hyperplastic Clara cells in the lungs of EC-UFP-exposed non sensitized (NS/UFP) and sensitized mice (S/UFP). NAC treatment preserved Clara cell morphology (S/NAC/UFP). OVA sensitized and challenged mice showing goblet cell metaplasia (arrows, S/OVA). Highly hyperplastic Clara cells (arrows) between mucous cells in the bronchiolar epithelium of sensitized mice exposed to EC-UFP 24 h prior to OVA challenge (S/UFP/OVA). NAC treatment preserved Clara cell morphology (S/NAC/UFP/OVA). NAC treatment was performed prior to and close to mid EC-UFP exposure. Scale bar, 5 μm.