Ultrastructure of terminal respiratory epithelium and prognosis in chronic interstitial pneumonia

Following acute damage, proliferation of granular pneumocytes with subsequent transformation into membranous cells is the basic pattern of repair of the alveolar epithelium. Regarding chronic interstitial pneumonias little is known about the ultrastructural changes of terminal respiratory epithelium and their clinical significance. We studied open lung biopsies from 10 patients showing clinical and light microscopic changes consistent with chronic idiopathic interstitial pneumonia (UIP). We studied the ultrastructure and correlated it with the clinical course of the patients. Only alveolar type epithelium was seen in two cases with a short duration of disease and good response to therapy. Bronchiolar-type epithelium was present in the terminal respiratory units of all other patients with longer duration of disease and less favourable prognosis. Four patients died: all of them showed signs of mucus secretion and keratinization in the terminal respiratory epithelium. Thus in chronic interstitial pneumonia the presence of the alveolar type of epithelium seems to indicate reversibility and that of the bronchiolar type irreversibility of the lesions, while mucous and keratinizing metaplasias apparently occur at a late stage of the disease.