Mueller Tobias, Terada Tomohiro, Rosenberg Ian M, Shibolet Oren, Podolsky Daniel K
Gastrointestinal Unit, Department of Medicine, Center for the Study of Inflammatory Bowel Disease, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA.
J Immunol. 2006 May 15;176(10):5805-14. doi: 10.4049/jimmunol.176.10.5805.
TLRs serve important immune and nonimmune functions in human intestinal epithelial cells (IECs). Proinflammatory Th1 cytokines have been shown to promote TLR expression and function in IECs, but the effect of key Th2 cytokines (IL-4, IL-5, IL-13) on TLR signaling in IECs has not been elucidated so far. We stimulated human model IECs with Th2 cytokines and examined TLR mRNA and protein expression by Northern blotting, RT-PCR, real-time RT-PCR, Western blotting, and flow cytometry. TLR function was determined by I-kappaBalpha phosphorylation assays, ELISA for IL-8 secretion after stimulation with TLR ligands and flow cytometry for LPS uptake. IL-4 and IL-13 significantly decreased TLR3 and TLR4 mRNA and protein expression including the requisite TLR4 coreceptor MD-2. TLR4/MD-2-mediated LPS uptake and TLR ligand-induced I-kappaBalpha phosphorylation and IL-8 secretion were significantly diminished in Th2 cytokine-primed IECs. The down-regulatory effect of Th2 cytokines on TLR expression and function in IECs also counteracted enhanced TLR signaling induced by stimulation with the hallmark Th1 cytokine IFN-gamma. In summary, Th2 cytokines appear to dampen TLR expression and function in resting and Th1 cytokine-primed human IECs. Diminished TLR function in IECs under the influence of Th2 cytokines may protect the host from excessive TLR signaling, but likely also impairs the host intestinal innate immune defense and increases IEC susceptibility to chronic inflammation in response to the intestinal microenvironment. Taken together, our data underscore the important role of Th2 cytokines in balancing TLR signaling in human IECs.
Toll样受体（TLRs）在人肠道上皮细胞（IECs）中发挥着重要的免疫和非免疫功能。促炎性Th1细胞因子已被证明可促进IECs中TLR的表达和功能，但关键的Th2细胞因子（IL-4、IL-5、IL-13）对IECs中TLR信号传导的影响迄今尚未阐明。我们用Th2细胞因子刺激人模型IECs，并通过Northern印迹法、逆转录聚合酶链反应（RT-PCR）、实时RT-PCR、蛋白质印迹法和流式细胞术检测TLR mRNA和蛋白表达。通过I-κBα磷酸化分析、用TLR配体刺激后检测IL-8分泌的酶联免疫吸附测定（ELISA）以及检测脂多糖（LPS）摄取的流式细胞术来确定TLR功能。IL-4和IL-13显著降低TLR3和TLR4 mRNA及蛋白表达，包括必需的TLR4共受体MD-2。在经Th2细胞因子预处理的IECs中，TLR4/MD-2介导的LPS摄取以及TLR配体诱导的I-κBα磷酸化和IL-8分泌均显著减少。Th2细胞因子对IECs中TLR表达和功能的下调作用也抵消了由标志性Th1细胞因子干扰素-γ刺激诱导的增强的TLR信号传导。总之，Th2细胞因子似乎会减弱静息状态以及经Th1细胞因子预处理的人IECs中的TLR表达和功能。在Th2细胞因子影响下，IECs中TLR功能的减弱可能会保护宿主免受过度的TLR信号传导，但也可能损害宿主肠道先天免疫防御，并增加IECs对肠道微环境中慢性炎症的易感性。综上所述，我们的数据强调了Th2细胞因子在平衡人IECs中TLR信号传导方面的重要作用。
