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Lipopolysaccharide pretreatment produces macrophage endotoxin tolerance via a serum-independent pathway
J Kraatz1, L Clair, J Bellingham
1Department of Surgery, Hennepin County Medical Center, University of Minnesota, Minneapolis 55415, USA.
Background:
Lipopolysaccharide activation (LPSa) of macrophages is thought to occur via a CD14-dependent mechanism with a requirement for the serum factor, lipopolysaccharide binding protein. LPS-stimulated, CD14-dependent signal transduction is associated with phosphorylation of mitogen-activated protein kinase (MAPK), nuclear factor-kappaB (NF-kappaB) translocation, and secretion of tumor necrosis factor (TNF) and interleukin-1 (IL-1). Macrophage endotoxin tolerance after low-dose LPS pretreatment (LPSp) is characterized by inhibition of LPSa-stimulated TNF and augmentation of IL-1 secretion. We sought to determine the role of CD14-dependent pathways in the induction of endotoxin tolerance by comparing the effects of LPSp in the presence or absence of serum.
Methods:
Murine peritoneal macrophages were exposed to a range of LPSp concentrations in the presence or absence of serum. MAPK activation and NF-kappaB were assayed 30 minutes after LPSp stimulation. TNF production and IL-1 were measured 6 hours after stimulation with 100 ng/mL LPSa, with or without 24-hour 10 ng/mL LPSp.
Results:
In the presence of serum, 100 ng/mL LPSp activated MAPK and NF-kappaB, whereas no activation of MAPK or NF-kappaB was seen at this LPSp concentration in the absence of serum. The absence of serum during 10 ng/mL LPSp did not prevent LPSp-mediated inhibition of TNF secretion, and it significantly augmented IL-1 secretion after stimulation with 100 ng/mL LPSa in the presence of serum.
Conclusion:
Induction of the alterations in subsequent LPSa-stimulated cytokine secretion characteristic of endotoxin tolerance by LPSp occurs via a serum-independent signal transduction pathway.
Insights
Lipopolysaccharide pretreatment induces endotoxin tolerance in macrophages via a serum-independent pathway. This process alters cytokine secretion, specifically inhibiting tumor necrosis factor and augmenting interleukin-1 production.
Area of Science:
- Immunology
- Cellular Biology
Background:
- Lipopolysaccharide activation (LPSa) of macrophages typically involves CD14 and serum factors.
- LPS stimulation triggers signal transduction pathways like MAPK and NF-kappaB, leading to cytokine release (TNF, IL-1).
- Macrophage endotoxin tolerance is characterized by suppressed TNF and enhanced IL-1 secretion following LPS pretreatment (LPSp).
Purpose of the Study:
- To investigate the role of CD14-dependent pathways in endotoxin tolerance induction.
- To compare the effects of LPSp on macrophage responses in the presence and absence of serum.
Main Methods:
- Murine peritoneal macrophages were pretreated with varying LPSp concentrations, with or without serum.
- Mitogen-activated protein kinase (MAPK) activation and nuclear factor-kappaB (NF-kappaB) translocation were measured post-LPSp.
- Tumor necrosis factor (TNF) and interleukin-1 (IL-1) secretion were quantified after subsequent LPSa stimulation.
Main Results:
- LPSp activated MAPK and NF-kappaB in the presence of serum, but not in its absence.
- Serum-independent LPSp inhibited TNF secretion following LPSa.
- LPSp significantly augmented IL-1 secretion after LPSa stimulation, irrespective of serum presence during pretreatment.
Conclusions:
- Endotoxin tolerance induction, marked by altered cytokine secretion, is mediated by a serum-independent signal transduction pathway.
- The findings highlight a crucial serum-independent mechanism in the development of macrophage endotoxin tolerance.