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Role of lysozyme in the microbicidal activity of rat alveolar macrophages
Abstract:
Lysozyme release from alveolar macrophages is stimulated by exposure to particles, such as latex and zymosan, and to bacteria. Rat alveolar marcophages contain 10-fold-greater intracellualr concentrations of lysozyme and release more lysozyme after stimulation than rat blood neutrophils. During 30 min of incubation in vitro, alveolar macrophages kill more than 99% of Micrococcus lysodeikticus in the incubation mixture, whereas neutrophils kill approximately 50% of the bacteria. The bactericidal capacity of alveolar macrophages for M. lysodeikticus exceeds that of neutrophils at all bacteria-to-cell ratios tested. This bacterial killing by alveolar macrophages is inhibited when specific rabbit antirat lysozyme serum is added to the incubation mixture. Electron microscopy studies indicate that bacterial killing occurs extracellularly. Initial degradation of bacteria occurs within 5 min, and lysis is complete by 25 to 30 min. Phagocytosis of lysed bacteria is maximum after 25 to 30 min. The greater quantities of lysozyme, both intracellularly and released into the extracellular environment by alveolar macrophages, suggest that this factor may be a mechanism by which alveolar macrophages contribute to pulmonary defense.
Insights
Alveolar macrophages release more lysozyme than neutrophils, effectively killing bacteria extracellularly. This suggests lysozyme is key to macrophage-mediated pulmonary defense against microbes.
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Alveolar macrophages are crucial immune cells in the lungs.
- Lysozyme is an enzyme with known antimicrobial properties.
- The role of lysozyme in alveolar macrophage antimicrobial activity requires further elucidation.
Purpose of the Study:
- To investigate the role of lysozyme in the bactericidal activity of rat alveolar macrophages.
- To compare the antimicrobial capacity of alveolar macrophages with that of neutrophils.
Main Methods:
- In vitro incubation of alveolar macrophages and neutrophils with Micrococcus lysodeikticus.
- Measurement of lysozyme release and bacterial killing.
- Inhibition studies using anti-lysozyme serum.
- Electron microscopy to visualize bacterial killing.
Main Results:
- Alveolar macrophages contain higher intracellular lysozyme concentrations and release more lysozyme than neutrophils.
- Alveolar macrophages killed >99% of M. lysodeikticus in 30 min, compared to ~50% by neutrophils.
- Bacterial killing by macrophages was inhibited by anti-lysozyme serum.
- Extracellular bacterial killing and subsequent phagocytosis were observed.
Conclusions:
- Lysozyme is a critical factor in the potent bactericidal activity of alveolar macrophages.
- Alveolar macrophages contribute significantly to pulmonary defense through lysozyme-mediated extracellular killing of bacteria.