G蛋白偶联受体EBI2在CD8+ T 细胞抗乙肝病毒免疫应答中的作用及机制研究

The hepatitis B virus (HBV) belongs to the family Hepadnaviridae, which exclusively infects hepatocytes, and approximately 350 million people are chronically infected worldwide. CD8+ T cells are crucial for HBV clearance during acute infection. However, it is currently unclear how the proliferation and differentiation occur for HBV-specific CD8+ T cells, and how the differentiated effector CD8+ T cells migrate to liver tissues and locate the virus-infected hepatocytes. The G-protein coupled receptor EBI2 (GPR183), responding to the oxysterol ligand, 7α,25-hydroxycholesterol (OHC), plays a key role in regulating B cell migration and DC positioning to enhance adaptive immune responses. EBI2 is expressed by CD8+ T cells and upregulated after activation, and EBI2 ligand activity is detectable in lymphoid and nonlymphoid tissues, but it’s function in CD8+ T cells are unknown. I hypothesize that EBI2 might regulate CD8+ T cell migration and positioning and thus promote CD8+ T cell proliferation and differentiation in spleen and liver-draining lymph nodes after HBV infection and that EBI2 could guide effector CD8+ T cell migration to locate virus-infected cells in liver tissue. In specific aim 1, we will clarify the role of of EBI2 expression on CD8+ T cells in the CD8+ T cell-mediated anti-HBV immune response. In specific aim 2, we will define the function of EBI2 in the CD8+ T cell proliferation, differentiation and positioning, and their relationships. In specific aim 3, we will study whether EBI2 enables effector CD8+ T cell migration for the destruction of HBV-infected cells in liver tissue. In specific aim 4, we will investigate how EBI2 ligand 7α,25-OHC gradients are established to recruit antiviral CD8+ T cells after HBV infection. The proposed studies will expand our understanding of the mechanism of CD8+ T cell migration and differentiation and might lead to the novel therapeutic approaches to completely eradicate persistent HBV infections.

CD8+ T细胞介导的抗病毒免疫应答在机体清除乙肝病毒（Hepatitis B virus，HBV）过程中发挥关键作用，但是其增殖分化机制以及分化后如何定位病毒感染的肝细胞尚未阐明。G蛋白偶联受体EBI2在B细胞和DC的迁移与定位起重要作用。申请人在前期预实验的基础上，提出HBV感染后EBI2可能通过影响CD8+ T细胞在脾脏和淋巴结中的定位促进其增殖分化并帮助分化的CD8+ T细胞定位HBV感染的肝细胞从而控制病毒感染的假设。为此，将首先确定EBI2的表达在CD8+ T细胞抗HBV感染中的作用，然后研究EBI2对CD8+ T细胞增殖分化和定位的影响，并探讨他们的相互关系，随后研究EBI2在介导分化的效应性CD8+ T细胞定位HBV感染的肝细胞中的作用，最后研究EBI2配体7α, 25-双羟氧固醇在肝脏中浓度梯度的形成机理。本项目的开展将为开发新一代具有HBV清除潜能的药物打下良好基础。

乙型肝炎病毒（Hepatitis B virus, HBV）感染引起的乙型肝炎仍然是严重危害人类健康的传染性疾病，CD8+ T细胞介导的抗病毒免疫应答在机体清除HBV过程中发挥关键作用，但是其增殖分化机制以及分化后如何定位病毒感染的肝细胞尚未阐明。本研究首先构建了EBI2 KO，CH25H KO，CH25Hfl/fl等小鼠模型；利用这些小鼠模型发现羟固醇-EBI2轴在调控CD8+ T细胞的功能方面起重要作用；一方面羟固醇-EBI2轴对CD8+ T细胞的扩增有影响，进一步我们发现对CD4+T细胞也有类似的作用；对扩增的影响可能主要是由于对T细胞的存活有影响；最后，我们发现羟固醇-EBI2轴调控T细胞与B细胞的相互作用的位置，这可能在促进T和B细胞分化中起重要作用。总之本项目系统研究了羟固醇-EBI2轴对T细胞功能的调控，为开发新一代具有HBV清除能力药物打下了坚实的基础。

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