Endotoxin tolerance in human intrahepatic biliary epithelial cells is induced by upregulation of IRAK-M
Endotoxin tolerance in human intrahepatic biliary epithelial cells is induced by upregulation of IRAK-M
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DOI：
10.1111/j.1478-3231.2006.01325.x
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发表时间：
2006-10-01
影响因子：
6.7
通讯作者：
Nakanuma, Yasuni
中科院分区：
文献类型：
--
作者：
Harada, Kenichi;Isse, Kumiko;Nakanuma, Yasuni
背景/目的：胆道上皮细胞具有由Toll样受体（TLR）组成的先天性免疫系统。虽然人胆汁中含有脂多糖（LPS）在正常以及患病的肝脏，LPS生理上不会引起炎症反应的胆道树。这种对LPS反应的缺乏可能是由于推测维持器官中先天免疫稳态的“内毒素耐受性”。我们的目的是阐明胆管上皮内毒素耐受的存在和分子机制。方法与结果：在核因子-κ B（NF-κ B）-DNA结合试验中，使用三种培养的人肝内胆管上皮细胞（HIBEC）系，所有细胞通过激活NF-κ B对LPS（TLR 4配体）作出反应，但用LPS预处理24 h有效地诱导对任何随后的LPS刺激的耐受（内毒素耐受）。Pam（3）Cys-Ser-（Lys）（4）trihydrochloride（Pam（3）CKS（4），TLR 1/2 ligand）预处理也能诱导这种耐受。实时荧光定量PCR和Western blotting结果显示，LPS处理可上调HIBECs中IRAK-M（TLR信号负调控因子）的表达，但对IL-1受体相关激酶-1（IRAK-1，TLR信号必需分子）的表达无明显影响。此外，免疫组织化学显示IRAK-M在肝内胆管中弥漫表达。结论：内毒素耐受机制存在于肝内胆管系统，并可能是由胆管上皮细胞表达IRAK-M所诱导，提示内毒素耐受在维持天然免疫胆道稳态中起重要作用。
Background/Aims: 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. Methods and results: In nuclear factor-kappa B (NF-kappa B)-DNA binding assays using three-cultured human intrahepatic biliary epithelial cell (HIBEC) lines, all the cells responded to LPS (TLR4 ligand) by activating NF-kappa B, 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.