高等脊椎动物CD209在介导病原体的识别与内化、免疫逃逸、参与细胞间的信息传递等方面发挥重要作用。本项目前期发现罗非鱼CD209（OnCD209）在非特异性细胞毒性细胞（Non-specific Cytotoxic Cell，NCC）中特异性表达，病原刺激后，表达量显著升高，表明OnCD209参与了鱼体的免疫应答，且能影响NCC活性。但其如何介导罗非鱼NCC的活性调控尚无报道。基于此，本项目首先利用过表达和RNA干扰实验检测OnCD209对NCC活性的影响；随后应用酵母双杂交、Pull-down和CO-IP方法筛选与验证OnCD209胞内、胞外互作蛋白及其互作机制；进一步采用qRT-PCR及流式细胞技术分析NCC效应分子的表达、NCC的增殖以及对靶细胞的杀伤活性，从而解析OnCD209介导NCC杀伤活性的分子机制。研究结果为阐明CD209在低等脊椎动物免疫应答中的调节机制奠定理论基础。

Higher vertebrate CD209 plays an important role in the recognition and internalization of pathogens, immune escape, and information transmission between cells. In the early stage of this project, it was found that Tilapia CD209 (OnCD209) was only expressed in non-specific cytotoxic cells (NCC), and its expression was significantly increased after pathogen stimulation, which indicating that OnCD209 is involved in the immune response of fish and could affect NCC activity, but how it mediates the activity of Tilapia NCC has not been reported. Based on these result, the project firstly detected the effect of OnCD209 on NCC activity by overexpression and RNA interference experiments; Then yeast two-hybrid, Pull-down, and CO-IP methods were used to screen and verify OnCD209 intracellular and extracellular interaction proteins and their interaction mechanism; Subsequently, qRT-PCR and flow cytometry were used to analyze the expression of NCC effector molecules, the proliferation of NCC and its killing activity on target cells mediated by OnCD209 and its interaction proteins, thereby analyzing the mechanism of OnCD209's regulation of NCC killing activity. The results lay a theoretical foundation for elucidating the regulatory mechanism of CD209 in the immune response of lower vertebrates.