Complement-mediated anti-pneumococcal functions of C-reactive protein

项目摘要/摘要 在链球菌感染患者的血液中发现了C反应蛋白(CRP) 肺炎，并被发现是先天免疫和炎症反应的组成部分。在小鼠体内 在感染模型中，人类C反应蛋白对肺炎链球菌的致死性感染具有保护作用。它的作用机制 C反应蛋白的抗肺炎球菌作用尚未明确。有趣的是，CRP只在早期起到保护作用 感染阶段，即在注射肺炎球菌后6小时内将CRP注射到小鼠体内。C反应蛋白是 在感染的后期没有保护作用，即在6h后注射到小鼠体内时，CRP没有保护作用 使用肺炎链球菌。在体外，CRP与细胞壁中存在的磷胆碱基团结合。 肺炎球菌的多糖，随后激活补体系统。因此，它是 假设CRP具有保护性，因为配体结合的CRP激活了补体系统 肺炎球菌表面导致菌血症减少。这一假说解释了 C反应蛋白在感染的早期阶段，但这不能解释为什么C反应蛋白在感染的早期阶段失去其保护作用 感染的晚期。我们假设CRP通过两种机制工作：一种是基于 C反应蛋白与磷胆碱结合及补体激活的一种机制 关于C反应蛋白与补体抑制因子H的结合这一假设将在以下三个方面得到验证 明确的目标。在目标1中，假设“补体系统对肺炎球菌的激活 表面，在C反应蛋白与肺炎球菌结合后，参与C反应蛋白介导的保护 测试过。在目标2中，两个假设是“肺炎球菌在其体内招募补体抑制蛋白因子H 在晚期感染期间表面和逃避补体攻击“和”结构改变的CRP能够 与H因子的结合也可以在后期保护小鼠免受感染“，将进行测试。在目标3中， C反应蛋白与磷胆碱基的结合是补体激活和杀伤的关键 肺炎球菌“将接受检测。这些假说将通过使用不能激活CRP的突变体来检验 小鼠补体，能与H因子结合，不能与磷胆碱结合 同时使用野生型和CRP基因敲除小鼠。该项目的成功完成将提供对 C反应蛋白的抗肺炎球菌作用机制可能导致以C反应蛋白为基础的肺炎球菌的发展 治疗晚期肺炎球菌感染的策略。

Project Summary / Abstract C-reactive protein (CRP) was discovered in the blood obtained from patients infected with Streptococcus pneumoniae and was found to be a component of innate immunity and inflammatory response. In murine models of infection, human CRP is protective against lethal infection with S. pneumoniae. The mechanisms of anti-pneumococcal action of CRP are not defined yet. Interestingly, CRP was protective only during the early stages of infection, i.e., when CRP was injected into mice within 6 h of administering pneumococci. CRP was not protective during the late stages of infection, i.e., CRP was not protective when injected into mice after 6 h of administering pneumococci. In vitro, CRP binds to phosphocholine groups present in the cell wall C- polysaccharide of pneumococci and subsequently activates the complement system. Accordingly, it is hypothesized that CRP is protective because ligand-bound CRP activates the complement system on the pneumococcal surface leading to the reduction of bacteremia. This hypothesis explains the protective effects of CRP during the early stages of infection, but this does not explain why CRP loses its protective effect during the late stages of infection. We hypothesize that CRP works through two mechanisms: one mechanism based on the binding of CRP to phosphocholine and subsequent complement activation and one mechanism based on the binding of CRP to complement inhibitor factor H. This hypothesis will be tested in the following three specific aims. In aim 1, the hypothesis that “the activation of the complement system on the pneumococcal surface, subsequent to the binding of CRP to pneumococci, participate in CRP-mediated protection” will be tested. In aim 2, two hypotheses that “pneumococci recruit complement inhibitory protein factor H on their surface and evade complement attack during late stage infection” and that “structurally altered CRP capable of binding to factor H can protect mice against infection during the late stages also” will be tested. In aim 3, the hypothesis that “the binding of CRP to phosphocholine groups is critical for complement activation and killing of pneumococci” will be tested. These hypotheses will be tested by using mutants of CRP incapable of activating murine complement, capable of binding to factor H, and incapable of binding to phosphocholine and by employing both wild-type and CRP knockout mice. Successful completion of this project will provide insight into the mechanisms of anti-pneumococcal functions of CRP which may lead to the development of a CRP-based strategy to treat late stage pneumococcal infection.