Harada Kenichi, Isse Kumiko, Sato Yasunori, Ozaki Satoru, Nakanuma Yasuni
Department of Human Pathology, Kanazawa University Graduate School of Medicine, Kanazawa, Japan.
Liver Int. 2006 Oct;26(8):935-42. doi: 10.1111/j.1478-3231.2006.01325.x.
BACKGROUND/AIM: 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.
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.
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.
背景/目的：胆管上皮细胞拥有由Toll样受体（TLR）组成的固有免疫系统。尽管在正常肝脏和患病肝脏中，人胆汁中都含有脂多糖（LPS），但在生理状态下，LPS不会在胆管树中引发炎症反应。对LPS无反应可能是由于推测存在“内毒素耐受”以维持器官中的固有免疫稳态。我们在此的目的是阐明胆管上皮细胞内毒素耐受的存在及其分子机制。
在使用三种培养的人肝内胆管上皮细胞（HIBEC）系进行的核因子-κB（NF-κB）-DNA结合试验中，所有细胞通过激活NF-κB对LPS（TLR4配体）产生反应，但用LPS预处理24小时可有效诱导对任何后续LPS刺激的耐受（内毒素耐受）。用Pam(3)Cys-Ser-(Lys)(4)三盐酸盐（Pam(3)CKS(4)，TLR1/2配体）预处理也可诱导这种耐受。然后，实时聚合酶链反应和蛋白质印迹分析显示，LPS处理上调了IRAK-M（TLR信号的负调节因子）的表达，但不影响HIBECs中白细胞介素-1受体相关激酶-1（IRAK-1，TLR信号的必需分子）。此外，免疫组织化学显示IRAK-M在肝内胆管中呈弥漫性表达。
本研究表明肝内胆管树中存在内毒素耐受机制，且可能由肝内胆管上皮细胞中IRAK-M的表达诱导，提示内毒素耐受在维持胆管固有免疫稳态中很重要。
