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In vitro response of murine alveolar and peritoneal macrophages to Mycobacterium intracellulare
Abstract:
Normal resident and BCG-activated alveolar and peritoneal macrophages from female Swiss Webster mice were compared for their ability to ingest and subsequently control the multiplication of Mycobacterium intracellulare in vitro. Resident peritoneal macrophages failed from the moment of ingestion to control the multiplication of engulfed bacilli resulting in host cell lysis, whereas activated peritoneal macrophages and both resident and activated alveolar macrophages constrained bacterial division for at least 7 days before comparable bacterial multiplication led to phagocyte death. The number of bacilli needed to lyse a macrophage was impossible to determine precisely because viable macrophages commonly contained several hundred mycobacteria. Minimal intracellular bacterial generation times were 20 h for each macrophage type. Differences in the rates of bacterial phagocytosis between both macrophage types, either resident or activated, are intrinsic properties of the macrophages and were not induced by the mycobacteria, because the same patterns of particle ingestion were observed after exposure to latex microspheres.
Insights
Resident peritoneal macrophages poorly control Mycobacterium intracellulare, leading to lysis. Activated peritoneal and all alveolar macrophages (resident and activated) better control bacterial growth, delaying host cell death in vitro.
Area of Science:
- Immunology
- Microbiology
Background:
- Macrophages are critical immune cells involved in phagocytosis and pathogen clearance.
- Mycobacterium intracellulare is an opportunistic pathogen that can cause disease in susceptible individuals.
Purpose of the Study:
- To compare the in vitro phagocytic and intracellular control capabilities of different macrophage populations against Mycobacterium intracellulare.
Main Methods:
- Resident and BCG-activated alveolar and peritoneal macrophages from mice were isolated.
- These macrophages were exposed to Mycobacterium intracellulare in vitro.
- Bacterial growth and macrophage viability were monitored over time.
Main Results:
- Resident peritoneal macrophages failed to control Mycobacterium intracellulare multiplication, leading to rapid host cell lysis.
- Activated peritoneal macrophages and both resident and activated alveolar macrophages demonstrated control of bacterial growth for at least 7 days.
- Intracellular bacterial generation time was approximately 20 hours across all macrophage types.
- Differences in phagocytosis rates were intrinsic macrophage properties, not induced by the bacteria.
Conclusions:
- Alveolar macrophages and activated peritoneal macrophages possess superior intrinsic mechanisms for controlling Mycobacterium intracellulare replication compared to resident peritoneal macrophages.
- These findings highlight the differential functional capacities of macrophage subsets in host defense against mycobacterial infections.