半胱氨酸蛋白酶类抑制因子Cystatin在无脊椎动物和脊椎动物中均具有免疫防御的功能，但免疫应答方式却存在差异性。文昌鱼处于无脊椎动物向脊椎动物进化的节点位置，探究其Cystatin的免疫机制将对了解该因子免疫功能的进化历程意义重大。因此，我们拟选用文昌鱼为研究对象，聚焦其Cystatin的免疫功能及作用机制，旨在：①通过检测Cystatin响应不同病原体刺激后的表达模式、免疫识别能力以及功能敲降和过表达后的胚胎免疫力确定其是否参与机体的免疫防御；②探索Cystatin作为直接免疫效应分子的功能及对TGF-β、NF-κB等免疫相关信号通路的调控机制；③系统比较分析文昌鱼与无脊椎动物和脊椎动物Cystatin免疫应答方式的异同。本研究工作将确定文昌鱼Cystatin在系统发生中的进化地位，阐明其在文昌鱼免疫防御中的功能及作用机制，并揭示Cystatin免疫功能的演化规律。

Cystatin, originally known as a kind of cysteine protease inhibitor, plays a vital role in the immune defense of invertebrates and vertebrates, but the immune response mechanism is quite different. The cephalochordate amphioxus, which represents the node of evolution from invertebrates to vertebrates, is of particular importance in understanding the evolutionary process of Cystatin immune function. Therefore, we intend to focus on the immune function and mechanism of Cystatin in amphioxus, aiming at: ① Determine the immune defense function by analyzing the expression pattern after pathogens challenging, specific immune recognition and embryonic immunity after functional knockdown and overexpression. ② Explore the mechanism of immune regulation through studying its function as a direct immune effector molecule and immune-related signaling pathways such as TGF-β and NF-κB. ③ Compare and analyze the immune response mechanism of amphioxus Cystatin with invertebrates and vertebrates. These systematical investigations will contribute to determine evolutionary status of amphioxus Cystatin in phylogenesis and elucidate its regulation mechanism in the immune defense. More importantly, this study will further reveal the evolution of Cystatin immune function.