The role of CCL17 and CCL17-expressing dendritic cells in intestinal Inflammation

我们可以证明趋化因子CCL17在肠道炎症中起着关键作用。在小鼠结肠炎模型中，缺乏CCL17的小鼠不受严重炎症的影响。CCL17在诱导期可增强树突状细胞（dc）的促炎细胞因子产生，并在结肠炎效应期阻止调节性T细胞的扩增和维持，导致辅助性T细胞（Th）1/Th17效应T细胞和调节性T细胞失衡。在这项研究中，我们揭示了CCL17的一个新功能，即它在响应toll样受体（TLR）刺激时对dc细胞因子产生的自分泌/旁分泌增强作用。目前，该后续项目的总体目标是阐明CCL17如何在肠道中发挥其促炎作用，并为CCL17作为炎症性肠病（IBD）的治疗靶点奠定基础。第一个目的是研究CCL17对肠道DC亚群组成的影响。我们有初步证据表明，缺乏CCL17会导致CD103+ dc的积累和CD103- CD11b+ dc的频率降低，这与调节性T细胞的扩增和结肠炎的保护有关。因此，我们将更详细地表征ccl17缺陷和ccl17正常小鼠在稳态和炎症期间肠道DC和巨噬细胞亚群的频率、表型和迁移功能。此外，将使用CCL17-eGFP报告小鼠，通过一组DC子集定义标记，以及通过选择性地去除表达ccl17的DC，对肠道中表达ccl17的DC进行表型表征。此外，它们在稳态和炎症期间的发育起源将通过确定的前体细胞的体内转移来研究。第二个目的是阐明CCL17对表达ccr4的dc的自分泌/旁分泌作用，从而增强炎症细胞因子的产生。TLR和趋化因子受体信号通路可能在几个点汇聚。因此，将研究通过同时触发TLRs和CCR4（通过CCL17）激活这些信号通路的情况，并通过在dc中敲低siRNA进一步研究特定分子的作用。第三个目的是探索CCL17作为临床前结肠炎模型和人类炎症性肠病治疗靶点的作用。我们计划在小鼠实验性结肠炎中使用阻断抗体来中和CCL17。此外，我们将在IBD患者和正常对照的炎症和非炎症结肠组织活检中确定表达CCL17的dc的频率和表型，以验证CCL17表达是人类IBD炎症性dc的标志物的假设。因此，我们希望产生支持进一步研究CCL17作为IBD治疗靶点的数据。

We could show that the chemokine CCL17 plays a critical role in intestinal inflammation. Mice lacking CCL17 were protected from severe inflammation in murine colitis models. CCL17 amplifies proinflammatory cytokine production by dendritic cells (DCs) in the induction phase and prevents regulatory T cell expansion and maintenance in the effector phase of colitis leading to a dysbalance of T helper (Th)1/Th17 effector T cells and regulatory T cells. In this study, we have unraveled a novel function of CCL17, namely its autocrine/paracrine enhancing effect on cytokine production by DCs in response to Toll-like receptor (TLR) stimulation. The overall aim of the follow up project is now to clarify how CCL17 exerts its proinflammatory effect in the intestine and to establish a basis for CCL17 as a therapeutic target in inflammatory bowel disease (IBD). The first aim is to investigate the influence of CCL17 on DC subset composition in the intestine. We have preliminary evidence that lack of CCL17 leads to accumulation of CD103+ DCs and a reduced frequency of CD103- CD11b+ DCs correlating with expansion of regulatory T cells and protection from colitis. We will therefore characterize in more detail the frequency, phenotype and migratory function of intestinal DC and macrophage subpopulations in CCL17-deficient and CCL17-competent mice in the steady state and during inflammation. Furthermore CCL17-expressing DCs in the intestine will be characterized phenotypically with a panel of DC subset defining markers using the CCL17-eGFP reporter mice and functionally by selective depletion of CCL17-expressing DCs. In addition, their developmental origin in steady state and during inflammation will be investigated by in vivo transfer of defined precursor cells. The second aim is to elucidate the autocrine/paracrine effect of CCL17 on CCR4-expressing DCs leading to enhanced inflammatory cytokine production. The TLR and chemokine receptor signaling pathways may converge at several points. Therefore activation of these signaling pathways by simultaneous triggering of TLRs and CCR4 (by CCL17) will be investigated and the role of specific molecules will be further studied by siRNA knockdown in DCs.The third aim is to explore the role of CCL17 as therapeutic target in a preclinical colitis model and in human inflammatory bowel disease. We plan to neutralize CCL17 using a blocking antibody in murine experimental colitis. Furthermore we will determine the frequency and phenotype of human CCL17-expressing DCs in biopsies of inflamed and non-inflamed colon tissue from IBD patients and normal controls to test the hypothesis that CCL17 expression is a marker for inflammatory DCs in human IBD. Thus, we hope to generate data supporting further study of CCL17 as therapeutic target in IBD.