Endotoxin tolerance of RAW264.7 correlates with p38-dependent up-regulation of scavenger receptor-A.
Pre-exposure to lipopolysaccharide (LPS) leads to hyposensitivity to secondary LPS stimulation, known as endotoxin tolerance. The role of macrophage scavenger receptor-A (SR-A) in endotoxin tolerance is unknown. In this study, LPS was shown to induce SR-A expression in the mouse macrophage cell line, RAW264.7, in dose- and time-dependent manners, which correlated with inflammatory cytokine suppression in RAW264.7 on secondary LPS stimulation. Over-expression of SR-A in RAW264.7 suppressed tumour necrosis factor (TNF)-alpha release and nuclear factor (NF)-kappa B activation, demonstrating the involvement of SR-A in endotoxin tolerance. LPS-pre-treated RAW264.7 cells could bind and internalize more fluorescein isothiocyanate (FITC)-LPS than untreated cells and both the SR-A ligand, fucoidan, and anti-SR-A 2F8 antibodies completely suppressed LPS-induced binding and internalization of FITC-LPS by RAW264.7. LPS-induced SR-A expression on RAW264.7 was completely suppressed by the p38-specific inhibitor, SB203580, but not by inhibition of toll-like receptor 4 (TLR4) signalling with MTS510, demonstrating that p38- but not TLR4-dependent up-regulation of SR-A was involved in endotoxin tolerance through binding and internalization of LPS.
Xiang
Q
Q
Department of Critical Care Medicine, Southwest Hospital, Third Military Medical University, Chongqing, China. xqiang163@163.com
Wen
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L
Liu
M H
MH
Zhang
Y
Y
Qu
J F
JF
Tian
J
J
D000818:Animals; D002460:Cell Line; D016207:Cytokines / Q000096:biosynthesis; D004705:Endocytosis / Q000187:drug effects; D004731:Endotoxins / Q000494:pharmacology*; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D007108:Immune Tolerance / Q000187:drug effects*; D018836:Inflammation Mediators / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D051117:Scavenger Receptors, Class A / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D016207:Cytokines; D004731:Endotoxins; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D016328:NF-kappa B; D051117:Scavenger Receptors, Class A; D051197:Toll-Like Receptor 4; D048051:p38 Mitogen-Activated Protein Kinases; D016650:Fluorescein-5-isothiocyanate