Becker Christoph, Wirtz Stefan, Blessing Manfred, Pirhonen Jaana, Strand Dennis, Bechthold Oliver, Frick Julia, Galle Peter R, Autenrieth Ingo, Neurath Markus F
Laboratory of Immunology I, Medical Clinic, University of Mainz, Mainz, Germany.
J Clin Invest. 2003 Sep;112(5):693-706. doi: 10.1172/JCI17464.
IL-12 p40-related cytokines such as IL-12 p35/p40 heterodimer and IL-23 (p19/p40) are potent regulators of adaptive immune responses. Little is known, however, about the transcriptional regulation of the p40 gene in vivo. In an attempt toward this goal, we have generated transgenic mice expressing firefly luciferase under the control of the IL-12 p40 promoter. High constitutive transgene expression was found in the small intestine only, whereas little reporter gene activity was observed in other tissues. Within the small bowel, constitutive promoter activity was restricted to the terminal ileum and associated with high expression of p40 mRNA as well as p40 and IL-23 p19/p40 proteins. The cells constitutively producing IL-12 p40 were identified as CD8alpha and CD11b double-negative CD11c+ lamina propria dendritic cells (LPDCs) that represent a major cell population in the lamina propria of the small intestine, but not in the colon. FISH directly demonstrated the uptake of bacteria by a subset of LPDCs in the terminal ileum that was associated with p40 expression. Furthermore, little or no p40 protein expression in LPDCs was found in the terminal ileum of germfree mice, indicating a key role of the intestinal flora for constitutive p40 expression. In addition, analysis of transgenic mice with a mutated NF-kappaB target site in the p40 promoter showed a critical role of NF-kappaB for constitutive transgene expression. Our data reveal important functional differences between the mucosal immune systems of the small and large bowel in healthy mice and suggest that the high bacterial load in the terminal ileum activates p40 gene transcription in LPDCs through NF-kappaB. These data suggest a predisposition of the terminal ileum to develop chronic inflammatory responses through IL-23 and thus may provide a molecular explanation for the preferential clinical manifestation of Crohn disease in this part of the gut.
白细胞介素12 p40相关的细胞因子，如白细胞介素12 p35/p40异二聚体和白细胞介素23（p19/p40），是适应性免疫反应的有效调节因子。然而，关于体内p40基因的转录调控知之甚少。为了实现这一目标，我们构建了在白细胞介素12 p40启动子控制下表达萤火虫荧光素酶的转基因小鼠。结果发现，仅在小肠中存在高水平的组成型转基因表达，而在其他组织中几乎未观察到报告基因活性。在小肠内，组成型启动子活性局限于回肠末端，并与p40 mRNA以及p40和白细胞介素23 p19/p40蛋白的高表达相关。组成型产生白细胞介素12 p40的细胞被鉴定为CD8α和CD11b双阴性CD11c +固有层树突状细胞（LPDCs），它们是小肠固有层中的主要细胞群体，但在结肠中不存在。荧光原位杂交（FISH）直接证明了回肠末端的一部分LPDCs摄取细菌，这与p40表达相关。此外，在无菌小鼠的回肠末端，LPDCs中几乎没有或没有p40蛋白表达，表明肠道菌群对组成型p40表达起关键作用。此外，对p40启动子中具有突变的核因子κB（NF-κB）靶位点的转基因小鼠的分析表明，NF-κB对组成型转基因表达起关键作用。我们的数据揭示了健康小鼠中小肠和大肠黏膜免疫系统之间的重要功能差异，并表明回肠末端的高细菌负荷通过NF-κB激活LPDCs中的p40基因转录。这些数据表明回肠末端易通过白细胞介素23发生慢性炎症反应，因此可能为克罗恩病在肠道这一部分的优先临床表现提供分子解释。
