信号素Semaphorin 4D及其受体Plexin B2负向调控树突状细胞应答参与银屑病发病及机制研究

T cells and the cytokines secreted by T cells are central to the pathogenesis of psoriasis. Dendritic cells (DC) play a decisive role in T cells activation and function in the up-stream of T cells. However, the mechanism of DC activaton regulation is not clear yet. Semaphorin4D (Sema4D) is exressed on T cells and promote T cell activation. The receptor of Sema4D, Plexin B2(PxnB2) was recently shown expressing on DC and inhibit DC production of IL-12/23. In our previous study, we found that the level of soluble Sema4D elavated in sera of psoriasis patients, and the psoriatic leision of Sema4D knockout mice was more severe than that of control. We hypothesize that Sema4D negatively regulate the function of DC via PxnB2 in the pathogenesis of psoriasis. In ther present proposal, we plan to analyze the expression of Sema4D and PxnB2 on DC and T cells in psoriatic leision of psoriasis patients, and to explore the role and mechanism of PxnB2 on DC activation, matuation and migration. We furthur plan to produce conditional knockout mice with PxnB2 deficient in DC, and explore the role and mechanism of Sema4D-PxnB2 in the pathogenesis of psoriasis by ultilizing PxnB2 conditional knockout mice. Our ultimate goal is to find a new target for the treatment of psoriasis.

T细胞及其分泌的细胞因子是银屑病发病的核心环节，位于其上游的树突状细胞(DC)是T细胞活化的始动因素，然而DC应答的调控机制尚知之甚少。信号素Semaphorin4D(Sema4D)表达于T细胞并促进其活化，最近发现Sema4D的受体Plexin B2(PxnB2)表达于DC并抑制DC分泌IL-12/23；我们发现银屑病患者血清Sema4D水平升高，Sema4D敲除小鼠咪喹莫特银屑病模型比对照小鼠明显严重。我们提出假说认为Sema4D通过结合PxnB2发挥对DC的负向调控作用而参与银屑病发病。本项目拟全面分析Sema4D和PxnB2在银屑病患者皮损DC、T细胞的表达，深入研究PxnB2对DC活化、成熟和迁徙等的作用及机制，进一步构建条件性PxnB2敲除小鼠，利用在DC特异性敲除PxnB2的小鼠研究Sema4D-PxnB2在银屑病发病中的作用和机制，为寻找银屑病治疗的新靶点进行积极地探索。

本项目针对信号素Semaphorin4D(Sema4D)通过调节角质形成细胞(KC)和树突状细胞(DC)应答在银屑病中的作用和机制进行了深入研究。在银屑病发病的DC/IL-23IL-17轴中，T细胞及其分泌的细胞因子是银屑病发病的核心环节，位于其上游的DC是T细胞活化的始动因素，然而DC应答的调控机制尚知之甚少。我们发现银屑病患者血清Sema4D水平升高，Sema4D敲除小鼠咪喹莫特银屑病模型比对照小鼠明显严重，结合以往研究发现的Sema4D的受体Plexin B2(PxnB2)表达于DC并抑制DC分泌IL-12/23，我们提出假说认为Sema4D通过结合PxnB2发挥对DC的负向调控作用而参与银屑病发病。本项目研究结果显示银屑病患者皮损KC表达Sema4D及其受体PlxnB2的水平均显著高于正常皮肤，Th1型和Th2型细胞因子促进Sema4D和PxnB2的表达；Sema4D促进培养的KC表达CCL20、CXCL1等趋化因子和IL-1β等炎症因子，并活化KC的炎症小体和NF-kB信号途径；小鼠皮肤表面外用PxnB2的siRNA有效抑制小鼠的咪喹莫特诱导的银屑病样炎症模型，提示Sema4D-PxnB2参与了银屑病的皮肤炎症。进一步应用Sema4D转基因小鼠制备咪喹莫特银屑病模型，发现该模型呈现先减轻后加重的动态变化；进行骨髓移植实验发现，来自Sema4D敲除小鼠的造血来源细胞抑制了银屑病模型的炎症。进一步发现DC通过PxnB2介导了Sema4D的免疫抑制作用，Sema4D刺激的DC针对Th17应答特异性地表现为免疫抑制。本项目较为完整地阐明了Sema4D-PxnB2在银屑病炎症应答中的作用和机制，为下一步有针对性地调节银屑病的应答奠定了基础，具有重要的理论意义和实际应用价值。