Inhibition of lipopolysaccharide-induced signal transduction in endotoxin-tolerized mouse macrophages: Dysregulation of cytokine, chemokine, and Toll-like receptor 2 and 4 gene expression
Ae. Medvedev et al., Inhibition of lipopolysaccharide-induced signal transduction in endotoxin-tolerized mouse macrophages: Dysregulation of cytokine, chemokine, and Toll-like receptor 2 and 4 gene expression, J IMMUNOL, 164(11), 2000, pp. 5564-5574
In this study, the effect of in vitro endotoxin tolerance on LPS-induced mi
togen-activated protein kinase activation, transcription factor induction,
and cytokine, chemokine, and Toll-like receptor (TLR) 2 and 4 gene expressi
on, as well as the involvement of TNF and IL-1 signaling pathways in tolera
nce, were examined, Pretreatment of mouse macrophages with LPS inhibited ph
osphorylation of the extracellular signal-regulated kinases, c-jun NH2-term
inal kinases, and p38 kinase; degradation of I-kappa B alpha (inhibitory pr
otein that dissociates from NF-kappa B) and I-kappa B beta; and activation
of the transcription factors NF-kappa B and AP-1 in response to subsequent
LPS stimulation, These changes were accompanied by suppression of LPS-induc
ed expression of mRNA for GM-CSF, IFN-gamma-inducible protein-10, KC, JE/mo
nocyte chemoattractant protein-1, macrophage-inflammatory protein-1 beta, a
nd macrophage-inflammatory protein-2, with concurrent inhibition of chemoki
ne secretion, In contrast to control cells, endotoxin-tolerant macrophages
exhibited an increased basal level of TLR2 mRNA, and failed to increase lev
els of TLR2 mRNA or to down-regulate TLR4 gene expression upon restimulatio
n with LPS, As judged by transcription factor activation, LPS and IL-1 were
found to induce a state of cross-tolerance against each other, while no su
ch reciprocal effect was seen for LPS and TNF-alpha. In addition. macrophag
es from TNFR I/II double knockout mice were LPS tolerizable, and blocking o
f endogenous TNF-alpha with TNFR-Fc fusion protein did not affect the capac
ity of LPS to tolerize macrophages, These data extend our understanding of
LPS-signaling mechanisms that are inhibited in endotoxin-tolerized macropha
ges and suggest that endotoxin tolerance might result from impaired express
ion and/or functions of common signaling intermediates involved in LPS and
IL-I signaling.