Ultrastructural study on human lung in alveolitis versus pulmonary fibrosis.

Lung specimens of 21 patients with diffuse interstitial lung disease were examined. The present ultrastructural study outlines the topography and distribution of inflammatory changes in the interstitium, endothelium, and in pneumocytes and phagocytes. Alveolitis is characterized by marked regenerative activity of type II pneumocytes (cuboid metaplasia), intraluminal macrophage accumulation, endothelial swelling, multilamination of the endothelial basement membrane, pericapillary edema, and primarily by cellular infiltrates in the interstitial space. The most prominent feature of the interstitium in pulmonary fibrosis is the lack of immunoinflammatory cells. In some areas there is a marked absence of alveolar lumen while only a small number of macrophages are present in the remaining alveolar lumen. Most of the capillaries in the fibrous septum have been destroyed. Ultrastructural studies of lung biopsies in patients with diffuse interstitial lung disease allow the differentiation between alveolitis and pulmonary fibrosis and thus contribute to a therapeutic decision.