宿主补体蛋白C3a介导弓形虫入侵中枢神经系统的分子机制

弓形虫（T. gondii）慢性感染导致动物行为异常的关键原因是破坏血脑屏障而侵入中枢神经系统（CNS）。已证实T.gondii入脑方式有两种：通过血管上皮细胞直接进入和利用被其感染的宿主免疫细胞的迁移入侵。T. gondii入侵宿主CNS是否存在其他途径及优势入侵途经？和宿主免疫系统是否存在辅助其入侵的分子？我们发现：T. gondii慢性感染可激活宿主补体C3，并下调屏障紧密连接蛋白。进一步实验表明：宿主C3的效应分子C3a的上调可导致其入侵CNS显著提高。据此提出假设：T. gondii入侵CNS是通过C3a介导的宿主血脑屏障功能发生障碍。本项目以补体C3-/-敲除鼠及T. gondii感染小鼠为模型，拟采用透射电镜、流式细胞分选等方法，研究T. gondii是否存在C3a介导的“细胞旁路”入侵途径，及其入侵CNS的优势路径。解析C3a促进T.gondii入侵CNS的分子机制。

T. gondii destructs the blood-brain barrier (BBB) to invade the hosts’ central nervous system (CNS), which causes abnormal behaviors. Some studies have shown two main mechanisms of T. gondii’s CNS invasion, which are the transcellular crossing mechanism and the immune cells carrying mechanism. But, is there a more efficient way for T. gondii to break through the BBB? Are there hosts’ molecules that can assist the invasion of T. gondii? Our previous paper reported that hosts chronically infected with T. gondii could up-regulate the complement component C3, and the expressions of tight junction proteins were down-regulated. In further experiments, we found that T. gondii increased the expression of C3a during the infection, and the C3a protein promoted CNS invasion of T. gondii. Thus, we hypothesized that T. gondii invades CNS through mediating the impairment of hosts’ BBB by C3a. To figure out whether the “paracellular entry” or a more efficient way exist, the C3 knockout (C3-/-) mice and T. gondii infected mice will be used as experimental animals in this study, and transmission electron microscopy, flow cytometry and other methods will be established. To investigate whether T. gondii has a C3a-mediated "paracellular entry" invasion pathway and its dominant pathway of invasion. The results may show molecular mechanisms why C3a promote CNS invasion of T. gondii.