棕榈酸酯酶对CD8+ 树突状细胞的交叉抗原提呈的机制研究

Cross-presentation is an important antigen presentation pathway to prime CD8+ T cells to eliminate pathogens and tumors. Although there is enormous interest in the molecular mechanism of cross-presentation, it is unclear how the cross-presented antigen is trafficked through endosomal compartments. Palmitoylation is a key factor regulating membrane vesicle trafficking, and the function of palmitoyl protein thioesterase 1 (PPT1) in the immune system is currently unknown. According to our preliminary data, PPT1 is specifically expressed in CD8+ dendritic cells at a high level, and PPT1 knockout mice have a greatly enhanced ability to cross-prime CD8+ T cells. Thus, we hypothesize PPT1 may play an important role in the cross-presentation ability of CD8+ dendritic cells. Using PPT1 transgenic mouse models, this project will examine the function of PPT1 in cross-presentation ability of CD8+ dendritic cells under steady state and inflammatory conditions, evaluate the importance of PPT1 in immune response with infection and tumor transplantation models, and analyze the molecular mechanism of how PPT1 controls cross-presentation by modifying endosomal recycling in CD8+ dendritic cells. The completion of this project will not only further our understanding of the molecular mechanism of cross-presentation, it will also facilitate the design of a novel immunotherapy against infectious diseases and cancer by modulating the activity of PPT1.

交叉提呈是一种通过激活CD8+ T细胞来消灭病菌及癌细胞的重要抗原提呈通路。免疫界对交叉提呈抗原在树突状细胞内如何转运有极大的兴趣和争议。棕榈酸修饰是指导蛋白质在液泡之间转运的一种主要机理，而在溶酶体里的棕榈酸酯酶PPT1在交叉提呈的功能是未知的。根据申请者的初步数据表明PPT1特异性在CD8+ 树突状细胞中高表达，而PPT1敲除基因小鼠的交叉提呈功能得到了明显地提高。因此，申请者推论PPT1可能对CD8+树突状细胞交叉提呈功能有重要作用。本课题通过PPT1转基因小鼠模型，研究PPT1在稳定状态和炎症情况下的交叉提呈功能，利用感染和肿瘤移植模型来证明PPT1对体内免疫反应的重要性，进而阐明PPT1在交叉提呈中控制CD8+树突状细胞内涵体回收的机理。本课题的研究成果不仅可以进一步阐明CD8+ 树突状细胞交叉提呈分子机制，而且可以设计一种通过调控PPT1功能来治疗病菌感染和肿瘤的新免疫疗法。

交叉提呈 (cross-presentation) 是一种指导CD8+ T 细胞识别和消灭细胞外病菌及癌细胞的重要抗原提呈机制， 但是具体机理不明朗。我们发现，PPT1缺陷的DCs更易受水泡性口炎病毒（VSV）感染，作为宿主的小鼠对VSV的免疫反应相应减弱。但是，PPT1缺陷的cDC1s交叉能力显著增强，更好的启动了组织内KLRG1+ 效应性记忆T细胞，并促进肿瘤和李斯特菌（LM）的快速清除。从机制上讲，1）PPT1通过激活V-ATPase维持溶酶体酸化，促进抗原降解，来保护稳态DCs免受病毒的侵害。2）DCs激活后，PPT1的快速下调促进交叉提呈、共刺激分子的表达和炎症细胞因子的产生。因此，PPT1作为一种分子调节开关，动态调节中即要使cDC1s能够有效地交叉提呈，而又不损害病毒的抵抗力。增强cDC1s的交叉提呈可作为一种潜在的治疗方法。