Abstract
The spontaneously occurring pulmonary foam cells were detected in 97 of 989 Fischer 344 rats of both sexes ranging in age from 13 to 150 weeks. The cells were first detected in the lungs of 52 weeks old rats. An increase in number of the lungs with foam cells and degrees of pulmonary accumulation of the cells were associated with age, the highest incidence (28.8%) being observed in rats over 120 weeks of age. The foam cells, being most frequent in the alveoli, were generally round and had an abundant, foamy cytoplasm and a relatively small nucleus. The cells contained various lipids in their cytoplasm. The plasma cholesterol levels increased with advancing age, seemingly correlated with the incidence of the pulmonary foam cells.
