Differential morphologic and metabolic alterations in permissive versus nonpermissive murine macrophages infected with Legionella pneumophila.

Legionella pneumophila infection of macrophages from permissive guinea pigs and from A/J mice compared with infection of cells from nonpermissive BDF1 mice was studied by electron microscopy. The cells from the BDF1 mice were nonpermissive for legionella growth in vitro and showed few if any bacteria in phagosomes by electron microscopic examination. Similar electron micrographic examination of macrophages from A/J mice permissive for legionella growth showed numerous intact intracellular bacteria within 24 to 48 h of culture and the transition of intracellular bacteria from localization in a few large vacuoles early in the course of infection to later localization in areas surrounded and studded by ribosomes. These electron microscopic observations were similar to those seen in the case of guinea pig macrophages infected with legionellae. Biochemical studies of macrophages from permissive versus nonpermissive animals showed little or no differences in respiratory burst and lysosomal enzyme activity for macrophages from all animals tested. However, when zymosan was used as a stimulant, macrophages from the nonpermissive mouse strain produced a larger amount of H2O2 and O2- than did cells from permissive guinea pigs or A/J mice. However, legionella vaccine itself induced no detectable or very little H2O2 and O2- in macrophages tested from any source. These results suggest that permissiveness of A/J mouse macrophages to legionella growth may involve mechanisms similar to those occurring in guinea pig macrophages in terms of morphologic and possibly even biochemical events. The relatively higher production of reactive oxygens by BDF1 mouse macrophages in response to zymosan correlated with nonpermissiveness for legionella growth, although further analysis is necessary to link these observations.