中文摘要：

文昌鱼作为研究脊椎动物起源和进化的模式生物，由于缺乏自由循环的血细胞，关于其清除体内病原体的机制，迄今尚无报道。采用体内细菌清除试验、体外杀菌试验、特异性抗体抑制试验、抑制补体途径试验及Westernblot方法，研究了文昌鱼体内细菌清除机制及动力学。试验结果表明，文昌鱼能有效清除入侵的异源微生物，体液对大肠杆菌具有较强的杀灭活性。补体和溶菌酶是参与清除入侵大肠杆菌的主要因子，通过替代途径激活的补体较溶菌酶作用更强，这是关于文昌鱼清除体内细菌机制及其相关因子的首次报道。

英文摘要：

It remains unknown to date about the mechanism that pathogens are eliminated from amphioxus （Branchiostoma belcheri） lacking free circulating blood cells even though amphioxus is widely used as the model organism for evolution and development research. The bacterium clearance dynamics in amphioxus were studied in vivo and in vitro by lysis of Escherichia coli, inhibition of lyric activity with the specific antibodies, and western blot. It was found that the amphioxus was capable of efficiently eliminating the invading bacterium Escherichia coil and that the humoral fluids can readily lyse the bacterium in vitro. Both complement and lysozyme were shown to be involved in the elimination in vivo of the invading bacteria in amphioxus and to act in concert against the invading bacteria, the complement playing a stronger role than the lysozyme doing. Western blot showed that both C3a and lysozyme levels were increased with the challenge with E. coll. This is the first report addressing the factors responsible for the clearance in vivo of invading bacteria in amphioxus.