Effect of virulent and less virulent strains of Nocardia asteroides on acid-phosphatase activity in alveolar and peritoneal macrophages maintained in vitro.

Since virulent strains of Nocardia asteroides grow within macrophages, experiments were designed to determine whether this intracellular pathogen affects lysosomal enzyme levels. Peritoneal and alveolar macrophages from mice were infected in vitro with live or killed N asteroides of the virulent strain GUH-2 or with live nocardiae of the less virulent strain 10905, which is killed by macrophages. The activity of acid phosphatase in individual macrophages was quantitated by means of a computer-assisted cytospectrophotometry system. Slide preparations were Gram stained for quantitation of ingested nocardiae in the same macrophages. The level of acid phosphatase activity in alveolar and peritoneal macrophages was decreased by infection with live cells of the virulent strain; the level of activity was inversely proportional to the number of nocardiae ingested. This effect was not seen with killed bacteria of this strain or with live bacteria of the less virulent strain. These results demonstrate a relation between the virulence of N asteroides strains and the extent of reductions in lysosomal acid-phosphatase activity of macrophages.