病原诱导鱼类适应性免疫活化的共刺激信号途径与调节机制

Adaptive immunity, different from innate immunity, is a more sophisticated and effective system to protect the body against invasion and infection of the pathogens. Activation of adaptive immunity requires two signals delivered by antigen presenting cells: the antigen recognition signal and the precise costimulatory signals. Of the two signals, the formation and interaction of costimulatory molecules is the key link in the dual signal pathway for initial activation of adaptive immunity. To this end, this project focuses on the identification of the representative costimulatory and coinhibitory molecules such as B7.1/B7.2, CD28, CTLA4 and BTLA, and evaluation of their functions in the immune responses mediated by T cells in commercial fish large yellow croaker (Pseudosciaena crocea) and model fish zebrafish (Danio rerio). The initiation of costimulatory molecule B7.1/B7.2 induced by TLR9/NF-КB and RAGE-MAPK-AP-1 signaling pathways and the involvement of epigenetic regulation, including TET2-mediated oxidative demethylation and JMJD3/MLL1-mediated H3 “poised” modification will be clarified in detail, the later of which is a previously unknown mechanism underlying the regulation of the costimulatory molecules. Meanwhile, to understand the regulatory mechanism underlying the costimulatory signaling network, the feedback regulation of B7/CD28 on CTLA4, an important immune checkpoint molecule, and crosstalk regulation among different costimulatory family members represented by BTLA/HVEM/LIGHT are also to be studied. Additionally, a supposed PD-1 independent inhibitory signaling pathway, BTLA/PD-L1, is to be explored to clarify the evolutionary history of this important immune checkpoint molecule from teleost to higher vertebrate, as there is no PD-1 molecule but its ligand PD-L1 in fish. After figuring out all above, we may finally reveal a new mechanism of immune escape of the representative pathogenic bacterium Edwardsiella tarda, which is largely based on the inhibition of costimulatory signals through blocking the innate immune signaling pathways coupled with epigenetic regulation. In this case, this research project is anticipated to enrich the content of fish immunology and expound the mechanisms of costimulatory and coinhibitory molecules in the initiation and regulation of adaptive immunity systematically. Most importantly, the project will provide new perspective for understanding the immune escape mechanisms of pathogen infection and innovative approach for the development and usage of an immune adjuvant, which is of great application values.

本项目拟在大黄鱼中系统开展共刺激信号分子鉴定，阐明鱼类共刺激信号系统的基本组成及其代表性成员在CD4+ T和CD8+ CTL亚群分化和免疫应答中的功能特征。以起始共刺激分子B7.1/B7.2为代表，研究共刺激信号形成的表观遗传调控机制，阐明先天免疫信号通路与表观遗传调控的偶联途径与作用方式，揭示先天免疫通过表观遗传调控适应性免疫的新机制。以B7/CD28超家族作为突破口，研究共刺激信号对免疫检验点共抑制分子CTLA4表达的反馈调节功能。通过研究BTLA/HVEM/LIGHT信号途径，揭示一种以HVEM为界面分子及以LIGHT为开关分子的不同共刺激家族成员间的网络调节机制。探索并揭示一种鱼类特有的PD-1非依赖的BTLA/PD-L1共抑制信号途径，探讨关键免疫检验点调节因子的系统演化。研究迟缓爱德华氏菌通过阻断先天免疫信号偶联的表观遗传途径抑制共刺激信号产生并实现免疫逃逸和入侵感染的新机制。

项目针对适应性免疫起始活化分子机制这一关键科学问题，在鱼类中探索研究了病原诱导适应性免疫活化的共刺激信号途径与调节机制。系统地鉴定了鱼类共刺激信号系统的分子组成和功能特征，揭示了鱼类已开始具备共刺激分子家族的基本成员，表明共刺激分子伴随适应性免疫在鱼类中起源而诞生，并在进化中保持了一定的功能与机制的保守性。阐明了CD80/86、CD28、CD40和CD154等代表性共刺激分子以及PD-L1、BTLA、HVEM和CTLA-4等代表性共抑制分子广泛参与CD4+ T和CD8+ T细胞活性的调节，是鱼类适应性体液和细胞免疫的关键调节因子。以适应性免疫系统最为核心的树突状细胞及其CD80/86/CD40共刺激分子为代表，深入研究了转录因子Zbtb46通过表观遗传调控CD80/86/CD40基因表达及树突状细胞成熟分化的分子机制，揭示了TLR受体通过激活泛素化系统调控Zbtb46活性的信号途径，阐明了先天免疫通过Zbtb46偶联表观遗传进而调控适应性免疫的途径与方式。通过建立鱼类自身免疫性疾病模型，揭示了BTLA/HVEM/LIGHT在免疫自稳维持及炎症发生中的重要调节功能，并阐明了BTLA/HVEM/LIGHT信号途径中三者的内在联系及网络调节机制。揭示了鱼类特色BTLA/PD-L1免疫检查点共抑制信号途径与功能，为揭示脊椎动物免疫检验点的演化规律提供了重要线索和依据。以嗜水气单胞菌为对象，揭示了细菌毒力蛋白通过MyD88/TRAF3/TBK1信号轴抑制CD80/86表达进而逃避宿主适应性免疫防御并实现感染的新机制。研究成果不仅丰富了鱼类免疫学知识，而且补充和完善了适应性免疫活化的双信号学说，充实了适应性免疫调控的基础免疫学理论内涵。同时可为渔业生产病害免疫防控中鱼类疫苗及佐剂的开发与精准应用提供理论基础和科学依据。