The ultrastructure of age-associated intimal fibrosis in pulmonary blood vessels.

The pulmonary blood vessels were examined from five human lungs surgically resected for bronchial carcinoma. Age-associated intimal fibrosis in these vessels was acellular in veins but more cellular in muscular pulmonary arteries. In both classes of vessel the cell involved in the production of this fibrosis was the myofibroblast, a cell which shares the properties of fibroblast and smooth muscle. The endothelial cells of pulmonary arteries contained numerous, uniform filaments with a random orientation but such filaments were rare in veins.