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Phagocytosis of Staphylococcus aureus induces a selective stress response in human monocytes-macrophages (M phi):
1Allergy Unit, University Hospital, Geneva, Switzerland.
Abstract:
Phagocytosis of microorganisms represents a stress not only for the phagocytosed agent but also for the host cell. We have investigated the stress response induced in human monocytes-macrophages (M phi) phagocytosing inactivated Staphylococcus aureus. Exposure of human M phi to S. aureus induced in these cells (i) a threefold increase in superoxide dismutase activity, (ii) a selective and differentiation-dependent induction of host heat shock protein synthesis (HSP70 but not HSP65), and (iii) de novo synthesis of heme oxygenase, but only when exogenous iron was added to the cultures. The coordinate upregulation of two scavenging enzymes and of HSP70 suggests that all three are part of cellular protective mechanisms against phagocytosis-related oxidative injury to host cells.
Insights
Phagocytosis of Staphylococcus aureus triggers a protective stress response in human macrophages. This involves increased antioxidant enzymes and heat shock proteins (HSP70) to combat oxidative damage.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Phagocytosis is a critical immune process but also induces cellular stress.
- Host cells require protective mechanisms to mitigate damage during microbial engulfment.
Purpose of the Study:
- To investigate the specific stress response pathways activated in human macrophages (M phi) during phagocytosis of inactivated Staphylococcus aureus.
- To identify key proteins and enzymes involved in the host cell's defense against phagocytosis-induced oxidative injury.
Main Methods:
- Human monocytes-macrophages (M phi) were exposed to inactivated Staphylococcus aureus.
- Enzyme activity assays were performed for superoxide dismutase.
- Protein synthesis was analyzed using techniques to detect heat shock proteins (HSP70, HSP65) and heme oxygenase.
- Experiments included manipulation of exogenous iron levels.
Main Results:
- Phagocytosis of S. aureus led to a threefold increase in superoxide dismutase activity in M phi.
- A selective, differentiation-dependent induction of heat shock protein 70 (HSP70) synthesis was observed, but not HSP65.
- De novo synthesis of heme oxygenase was detected only when exogenous iron was supplied.
Conclusions:
- The coordinated upregulation of superoxide dismutase, HSP70, and heme oxygenase suggests a multi-component cellular defense system.
- These protective mechanisms are crucial for mitigating oxidative stress and cellular damage incurred by host cells during phagocytosis.
- The findings highlight the host cell's adaptive strategies against bacterial challenge.