Lipopolysaccharide pretreatment produces macrophage endotoxin tolerance via a serum-independent pathway.
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.


CONCLUSIONS
Induction of the alterations in subsequent LPSa-stimulated cytokine secretion characteristic of endotoxin tolerance by LPSp occurs via a serum-independent signal transduction pathway.
Department of Surgery, Hennepin County Medical Center, University of Minnesota, Minneapolis 55415, USA.
J
J
Kraatz
L
L
Clair
J
J
Bellingham
K
K
Wahlstrom
J L
JL
Rodriguez
M A
MA
West
D000209:Acute-Phase Proteins; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002352:Carrier Proteins; D016895:Culture Media, Serum-Free; D004731:Endotoxins; D007375:Interleukin-1 / Q000378:metabolism*; D018950:Lipopolysaccharide Receptors / Q000187:drug effects / Q000378:metabolism; D008070:Lipopolysaccharides / Q000008:administration & dosage / Q000494:pharmacology*; D008262:Macrophage Activation; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins; D051379:Mice; D008807:Mice, Inbred BALB C; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002352:Carrier Proteins; D016895:Culture Media, Serum-Free; D004731:Endotoxins; D007375:Interleukin-1; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D000099231:Lipopolysaccharide-Binding Protein