荚膜多糖的支链结构与肺炎链球菌毒力关系的研究

肺炎链球菌的荚膜多糖是关键的抗原，根据其结构将肺炎链球菌分为98个血清型。该菌在人鼻咽部大量定植，但仅有少数血清型可引起肺炎和脑膜炎等疾病，针对这些血清型的多糖疫苗在抗感染方面发挥了巨大作用。但随着疫苗的广泛应用又出现血清型取代，即通过荚膜多糖结构的改变来逃避免疫攻击并成为新毒株。荚膜多糖有支链和O-乙酰化修饰，但支链结构与该菌毒力的关系并不清楚。因此，研究荚膜多糖支链结构与肺炎链球菌毒力的关系迫在眉睫。申请人前期研究发现，支链可影响荚膜厚度、粘附及与补体激活因子的结合，本项目拟以毒力强的血清型1、7F、9V、14、18C、23F为研究对象，用NMR等化学方法解析突变株多糖结构并揭示其合成机制；研究不同血清型与宿主细胞的粘附，分析其在小鼠不同部位的侵染和致死率，阐明支链结构对毒力的影响；进一步分析其补体激活途径以揭示作用机制。本研究对强毒株和潜在的流行株的预测以及新疫苗的设计具有指导意义。

Capsular polysaccharide (CPS) is a critical virulent factor of Streptococcus pneumoniae, but also is an antigen for host antibodies. S. pneumoniae are divided into 98 serotypes based on the CPS structures. Many pneumococci colonize on naso-oropharynx of human, but only a few of serotypes cause invasive diseases such as bacteremia pneumonia and meningitis, therefore, their CPSs are made into polysaccharide-vaccines which have greatly reduced the infection from pneumococci. However, with the broad introduction of polysaccharide-conjugated vaccine, serotype replacement had happened, and some serotypes could evade killing from immune system by changing capsular structure and became new prevalent strains. Many CPSs have the branched sugars and O-acetyl groups, but their effects to pneumococcal virulence have not been disclosed. Therefore, it is necessary to investigate the relationship between the CPS branched structures with the virulence of S. pneumoniae. Our previous studies found that the branches affected capsular thickness, and adherence to host cells as well as binding to complement initiator. In this proposal, we plan to study the vaccine serotypes (i.e., 1、7F、9V、14、18C、23F), which have the strong invasive capacity. The genes predicted for the branches are deleted, and the CPS structures of the mutants are identified by NMR and GC-MS. The molecular basis and antigenic characterization of the branch sugar and O-acetylation are elucidated. In addition, by comparing the adherence to host cells and the invasion to the different positions of mice and the fatality rate, the effects of the CPS branched structures to virulence of S. pneumoniae are elucidated. Furthermore, the mechanism is revealed by investigating the activation of the complement pathways and the complement-dependent opsonophagocytosis of the different strains. The project is expected to provide a guide for predicting the strong virulent strains and potential prevalent serotypes and for designing the next generation vaccine.