疟原虫CSP分子逃避或抑制按蚊免疫作用及机制研究

Malaria is a global infectious disease that inflicts a heavy health burden on human beings. Plasmodium parasites have a complex life cycle, involving various developmental stages in the Anopheles mosquito and human hosts. The Plasmodium evasion of mosquito immunity is critical for the development of Plasmodium in mosquito. However, the evasion molecular basis of Plasmodium remains largely unknown. Our previous study found that the development of malaria parasite in mosquitoes was blocked by the melanization at oocyst stage when the pexel domain of CSP was mutated, and whereas the wild type parasite could produce normal sporozoites and could complete the whole development cycle in mosquito. This phenomenon is a fantastic model for the mechanism study of Plasmodium evasion or inhibition of mosquito immunity. In order to reveal molecular mechanism, we may firstly analyse the correlation between the melanization and the upregulation of immune genes in mosquito infected by the mutated Plasmodium; and then we may identify that the role of TEP1 is necessary for the melanization; finally, the possible signal pathway of TEP1 induced by the mutated Plasmodium will be analyzed, such as the JNK and LL3signal pathway. The elucidation of its molecular mechanisms may contribute to the theoretical understanding of mechanism of CSP-mediated Plasmodium evasion of mosquito immunity, lay a theoretical foundation for the blocking the spread of malaria and provide reference for prevention of other insect borne disease.

疟疾是严重危害人类健康的全球性寄生虫传染病，按蚊是疟疾传播媒介，疟原虫逃避按蚊免疫是疟原虫能在按蚊体内发育及传播关键。然而目前对疟原虫如何逃避按蚊免疫了解少，我们前期发现，CSP突变疟原虫感染按蚊后疟原虫卵囊出现黑化免疫现象，且不能产生唾液腺子孢子(成熟子孢子是入侵肝细胞的关键)，而野生株感染按蚊可以产生成熟子孢子，该现象为研究疟原虫逃避按蚊免疫提供良好模型。为了探讨其分子机理，本研究首先进一步分析CSP突变株感染按蚊出现黑化现象与突变株诱导按蚊免疫相关；其次通过筛选免疫基因并从正反方向鉴定该突变株主要通过促进按蚊重要免疫分子TEP1表达，导致黑化产生；最后分析CSP突变株诱导TEP1表达可能信号通路(如血细胞JNK和/或LL3通路)。将有助于从理论上深入认识疟原虫逃避按蚊免疫机制，从而为阻断按蚊传播疟疾奠定理论基础，还为从媒介水平防控其他虫媒传播疾病提供借鉴。

疟原虫在蚊体内由动合子阶段转变成卵囊阶段后，疟原虫不容易受到蚊免疫反应的影响，从而利于疟原虫在蚊体内的发育。然而，卵囊抵抗蚊子防御的潜在机制仍不清楚。通过本项目研究我们发现疟原虫卵囊需要环子孢子蛋白 (circumsporozoite protein，CSP) 来逃避蚊的防御。研究发现在疟原虫的CSP pexel I/II 域中发生突变，蚊感染CSPmut 疟原虫，可诱导蚊NOX5介导的血细胞硝化，并导致激活Toll途径和上调血细胞TEP1表达，成熟卵囊黑化激活，成熟卵囊黑化和释放子孢子的缺陷。此外，当蚊受到CSPwt 疟原虫的再次攻击时，通过诱导血细胞硝化，预感染 CSPmut 疟原虫可大大降低感染虫荷。因此，我们证明了为什么卵囊对蚊子免疫是“不可见的” ，并揭示了 CSP在卵囊免疫逃避中的未知作用，表明 CSP 它可能是阻断疟疾传播的潜在靶点。