Microbicidal activity and superoxide production by macrophages in aging rats.

: This study examined the effects of aging on the immunobiological properties of alveolar macrophages in young adult and aged rats. Macrophages, obtained by lung lavage, were enumerated and tested in vitro for yeast phagocytosis and fungicidal activities. Superoxide anion (O2-) generation stimulated by opsonized zymosan was compared between the two groups. Total numbers of alveolar cells and the differential cell distribution were comparable in both the groups. The difference between the groups was not statistically significant, even though the yeast phagocytic capacity in the cells from senescent animals was consistently higher than in the controls. This may be due to the wide degree of variability observed in the aged animals. However, cell fungicidal activity was statistically lower in the aged animals at 90 minutes of incubation which correlated with a significant decline in the O2- production. Aging may adversely affect some of the immunobiologic functions of lung macrophages and thus compromise host defense mechanisms in the respiratory tract.