Endotoxin tolerance in human intrahepatic biliary epithelial cells is induced by upregulation of IRAK-M.
OBJECTIVE
Biliary epithelial cells possess an innate immune system consisting of Toll-like receptors (TLRs). Although the human bile contains lipopolysaccharide (LPS) in normal as well as diseased livers, LPS physiologically does not elicit an inflammatory response in the biliary tree. This absence of a response to LPS could be due to the 'endotoxin tolerance' speculated to maintain innate immune homeostasis in organs. Our aim here is to clarify the presence and molecular mechanisms of endotoxin tolerance of biliary epithelium.


RESULTS
In nuclear factor-kappaB (NF-kappaB)-DNA binding assays using three-cultured human intrahepatic biliary epithelial cell (HIBEC) lines, all the cells responded to LPS (TLR4 ligand) by activating NF-kappaB, but pretreatment with LPS for 24 h effectively induced tolerance against any subsequent stimulation with LPS (endotoxin tolerance). This tolerance was also induced by pretreatment with Pam(3)Cys-Ser-(Lys)(4) trihydrochloride (Pam(3)CKS(4), TLR1/2 ligand). Then, real-time polymerase chain treaction and Western blotting revealed that LPS treatment upregulated the expression of IRAK-M (a negative regulator of TLR signaling), but did not affect interleukin-1 receptor-associated kinase-1 (IRAK-1, an essential molecule of TLR signaling), in HIBECs. Moreover, immunohistochemistry revealed that IRAK-M was diffusely expressed in intrahepatic bile ducts.


CONCLUSIONS
This study showed that the mechanism of endotoxin tolerance exists in the intrahepatic biliary tree and is possibly induced by the expression of IRAK-M in the intrahepatic biliary epithelium, suggesting that the endotoxin tolerance is important in maintaining innate immune biliary homeostasis.
Harada
Kenichi
K
Department of Human Pathology, Kanazawa University Graduate School of Medicine, Kanazawa, Japan.
Isse
Kumiko
K
Sato
Yasunori
Y
Ozaki
Satoru
S
Nakanuma
Yasuni
Y
D001653:Bile Ducts, Intrahepatic / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D001659:Biliary Tract / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D004731:Endotoxins / Q000276:immunology*; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000276:immunology / Q000378:metabolism; D055666:Lipopeptides; D008070:Lipopolysaccharides / Q000276:immunology / Q000494:pharmacology; D016328:NF-kappa B / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism; D051193:Toll-Like Receptors / Q000276:immunology / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism
D004731:Endotoxins; D047908:Intracellular Signaling Peptides and Proteins; D055666:Lipopeptides; D008070:Lipopolysaccharides; D016328:NF-kappa B; C508075:Pam(3)CSK(4) peptide; D010455:Peptides; C495345:TLR4 protein, human; C410602:TOLLIP protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; C507768:IRAK1 protein, human; C507771:IRAK3 protein, human; D053592:Interleukin-1 Receptor-Associated Kinases