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Cutting edge: endotoxin tolerance in mouse peritoneal macrophages correlates with down-regulation of surface
1Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.
Abstract:
Monocytes/macrophages exposed to LPS show reduced responses to second stimulation with LPS, which is termed LPS tolerance. In this study, we investigated molecular mechanism of LPS tolerance in macrophages. Mouse peritoneal macrophages pre-exposed to LPS exhibited reduced production of inflammatory cytokines in a time- and dose-dependent manner. Activation of neither IL-1 receptor-associated kinase nor NF-kappaB was observed in macrophages that became tolerant by LPS pretreatment, indicating that the proximal event in Toll-like receptor 4 (TLR4)-MyD88-dependent signaling is affected in tolerant macrophages. Although TLR4 mRNA expression significantly decreased within a few hours of LPS pretreatment and returned to the original level at 24 h, the surface TLR4 expression began to decrease within 1 h, with a gradual decrease after that, and remained suppressed over 24 h. A decrease in inflammatory cytokine production in tolerant macrophages well correlates with down-regulation of the surface TLR4 expression, which may explain one of the mechanisms for LPS tolerance.
Insights
Lipopolysaccharide (LPS) tolerance in macrophages involves reduced inflammatory cytokine production. This occurs due to decreased surface Toll-like receptor 4 (TLR4) expression, impacting signaling pathways crucial for immune response.
Area of Science:
- Immunology
- Cellular Biology
- Molecular Medicine
Background:
- Macrophages play a critical role in innate immunity.
- Lipopolysaccharide (LPS) is a potent immune activator.
- LPS tolerance describes a state of reduced responsiveness to subsequent LPS stimulation.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying LPS tolerance in macrophages.
- To investigate the signaling pathways affected during LPS tolerance.
Main Methods:
- Primary mouse peritoneal macrophages were pre-exposed to LPS.
- Assessed inflammatory cytokine production.
- Evaluated the activation of IL-1 receptor-associated kinase (IRAK) and NF-kappaB.
- Measured Toll-like receptor 4 (TLR4) mRNA and surface expression levels over time.
Main Results:
- Pre-exposure to LPS resulted in a time- and dose-dependent reduction in inflammatory cytokine production.
- Tolerant macrophages showed no activation of IRAK or NF-kappaB.
- TLR4 mRNA expression decreased initially but returned to baseline within 24 hours.
- Surface TLR4 expression significantly decreased within 1 hour and remained suppressed for over 24 hours.
Conclusions:
- LPS tolerance in macrophages is associated with impaired proximal signaling in the TLR4-MyD88 pathway.
- Down-regulation of surface TLR4 expression is a key mechanism contributing to LPS tolerance and reduced inflammatory responses.