Short term morphologic effects of high ambient levels of ozone on lungs of rhesus monkeys.

Groups of laboratory-reared, young adult rhesus monkeys were exposed to 0.8 p.p.m. or 0.5 p.p.m. of ozone for 8 hours a day on 7 consecutive days. Lesions were studied using correlated techniques which permitted examination of specified levels of airways and adjacent lung parenchyma by light microscopy, scanning electron microscopy, and transmission electron microscopy. Lesions were observed in the trachea and lungs of all exposed animals. The extent and severity of damage, but not its nature, varied with exposure concentration. Damage was most severe in respiratory bronchioles and more distal parenchymal regions were unaffected. Major features of the response within respiratory bronchioles were hyperplasia and hypertrophy of nonciliated bronchiolar epithelial cells and intraluminal accumulations of macrophages. Replacement of type 1 epithelium in alveoli by type 2 cells and forms intermediate between types 1 and 2 were also observed. In large conducting airways, damage to ciliated cells was observed but mlcus-producing cells were morphologically unaltered. Two gradients in severity of ozone-induced lesions were appreciable in the trachea and lungs. The most obvious gradient was in respiratory bronchioles where the degree of damage was most severe in proximal locations. A second gradient in severity was noted in conducting airways in which more severe and extensive lesions occurred in the trachea and major bronchi than in small bronchi and terminal bronchioles.