Electron microscopic observations on pulmonary fibrosis and emphysema in smoking dogs

Abstract

Electron microscopic observations in areas of fibrosis and emphysema of the lungs of dogs subjected to experimental cigarette smoking show that alterations occur both in the pleura and the lung parenchyma. In the pleura the major alteration is the increased thickness of the stroma due to large amounts of collagen present. In the lung parenchyma two major alterations appear in the interstitium of the alveolar septa where there is a complete loss or a great reduction in the number of capillaries and a marked thickening of the septa due to the increased amounts of collagen. Changes in the alveolar epithelium are slight; changes in capillary endothelium, such as rarefication of cytoplasm and blebbing of the plasmalemma, are found. More frequently noted are the changes involving the basement membrane of the alveolar epithelium which in some places appear to be greatly thickened and in others to be exceptionally thin or missing entirely. Another of the most striking alterations noted in both the pleura and parenchyma is the presence of large numbers of macrophages occurring singly, in clumps, and in granulomas. Although macrophages are found in the lungs of nonsmoking dogs they are not found in such numbers nor with the unique content observed in the lungs of smoking dogs. Crystalline-like structures are found in membrane-bound inclusions and ferritin-like particles occur both in large membrane-bound aggre-gates and lying free in the cytoplasm. Conclusive identification of these structures and their relationship to inhalation of cigarette smoke requires further study.