Electron microscopic studies in desquamative interstitial pneumonia associated with asbestos.

A case of desquamative interstitial pneumonia (DIP) has been studied by electron microscopy in order to determine the nature of the alveolar cells. Those lining the alveolar walls proved to be granular pneumocytes (type II alveolar epithelial cells) while cells free in the lumen were alveolar macrophages. The brief literature describing the electron microscopic findings in DIP is reviewed. All workers agree that the lining cells are granular pneumocytes and most report a mixed free cell population with the emphasis shifting from desquamated epithelial cells to macrophages. In the present case asbestos bodies were also found in the lung, suggesting that DIP is not a specific disease entity. Desquamative interstitial pneumonia (DIP) was first described by Liebow, Steer, and Billingsley in 1965. It was distinguished histologically from other forms of interstitial pneumonia by an abundance of cells filling and lining the alveolar spaces and by relatively little thickening of the alveolar walls, while clinically the disease was notable for a good response to steroids. Scadding and Hinson (1967) challenged the view that DIP represented a specific entity and regarded its features as forming merely one end of a spectrum of changes seen in diffuse fibrosing alveolitis; such cases they term the desquamative type of fibrosing alveolitis. Until the causation and pathogenesis of interstitial pneumonia are better understood this question will remain arguable. Greater agreement has been reached on the beneficial effects of steroids, and whatever terminology is favoured, it is therefore important to recognize the pathological changes so that proper therapy may be instituted. For this reason, the status of DIP is now widely accepted in clinical practice. Another debatable question concerns the nature of the alveolar cells, and to those workers interested in the cytological composition of the lung and the dynamics of its respective cell populations this matter is of considerable importance. The term 'desquamative' is used to imply derivation of the free cells from the alveolar lining cells, but it is recognized that light microscopy is incapable of accurate cytological characterization (Liebow et al., 1965; Scadding and Hinson, 1967). Preliminary ultrastructural studies led the original workers to believe that the free cells were epithelial in origin, but it was admitted that the electron microscopic evidence was fragmentary and the fine structural appearances were neither described nor illustrated. Support for the free cells being desquamated type II alveolar epithelial cells (granular pneumocytes) came from a case studied by …