Distribution of Ventilation in Cynomolgus Monkeys

This study has demonstrated the fine structure of the type 1 and 2 alveolar epithelial cells at different time periods after intrabronchial instillation of dilute (1%) nitric acid. The damaged type 2 cells were partially or largely covered by cytoplasmic extensions of adjacent type 1 cells. This covering is considered to be a mechanism by which the alveolar epithelium maintains an intact surface. Alveolar epithelial cells having the morphologic characteristics suggesting transition from type 1 membranous pneumonocytes to type 2 granular pneumonocytes were seen. These intermediate type alveolar epithelial cells have large nuclei and microvilli but lacked lamellar bodies. This demonstrates a possible source of origin for the physiologically important type 2 cells. Occasional phagocytosis of carbon particles by type 2 cells was observed.