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Differential morphologic and metabolic alterations in permissive versus nonpermissive murine macrophages infected
Y Yamamoto1, T W Klein, K Brown
1Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, Tampa 33612.
Abstract:
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.
Insights
Legionella pneumophila growth in macrophages differs between mouse strains. Nonpermissive BDF1 mouse cells produced more reactive oxygen species, suggesting a role in controlling Legionella infection.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Legionella pneumophila is an intracellular bacterium that infects macrophages.
- Differential permissiveness of host macrophages to L. pneumophila infection is observed across animal models.
- Understanding macrophage-pathogen interactions is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the differences in Legionella pneumophila infection between permissive and nonpermissive macrophages using electron microscopy.
- To compare the biochemical responses, including respiratory burst and reactive oxygen species production, of macrophages from different animal models upon stimulation.
- To elucidate the mechanisms underlying macrophage permissiveness or nonpermissiveness to L. pneumophila.
Main Methods:
- Electron microscopy was used to examine L. pneumophila within macrophages from guinea pigs, A/J mice (permissive), and BDF1 mice (nonpermissive).
- Biochemical assays were performed to measure respiratory burst and lysosomal enzyme activity.
- Reactive oxygen species (H2O2 and O2-) production was quantified in response to zymosan and L. pneumophila vaccine stimulation.
Main Results:
- BDF1 mouse macrophages were nonpermissive to L. pneumophila, showing few intracellular bacteria, unlike A/J mouse and guinea pig macrophages.
- Morphological changes in L. pneumophila-infected A/J mouse macrophages resembled those in guinea pig macrophages.
- While overall biochemical activity was similar, BDF1 macrophages produced significantly more reactive oxygen species upon zymosan stimulation, correlating with nonpermissiveness.
Conclusions:
- Macrophage permissiveness to L. pneumophila in A/J mice shares similarities with guinea pig macrophages in terms of morphology.
- Elevated reactive oxygen species production in BDF1 mouse macrophages upon stimulation may contribute to their nonpermissiveness to L. pneumophila growth.
- Further research is needed to fully establish the link between reactive oxygen species and L. pneumophila non-permissiveness in macrophages.