Data_Sheet_2_Treatment of Pneumococcal Infection by Using Engineered Human C-Reactive Protein in a Mouse Model.PDF

C-reactive protein (CRP) binds to several species of bacterial pathogens including Streptococcus pneumoniae. Experiments in mice have revealed that one of the functions of CRP is to protect against pneumococcal infection by binding to pneumococci and activating the complement system. For protection, however, CRP must be injected into mice within a few hours of administering pneumococci, that is, CRP is protective against early-stage infection but not against late-stage infection. It is assumed that CRP cannot protect if pneumococci got time to recruit complement inhibitor factor H on their surface to become complement attack-resistant. Since the conformation of CRP is altered under inflammatory conditions and altered CRP binds to immobilized factor H also, we hypothesized that in order to protect against late-stage infection, CRP needed to change its structure and that was not happening in mice. Accordingly, we engineered CRP molecules (E-CRP) which bind to factor H on pneumococci but do not bind to factor H on any host cell in the blood. We found that E-CRP, in cooperation with wild-type CRP, was protective regardless of the timing of administering E-CRP into mice. We conclude that CRP acts via two different conformations to execute its anti-pneumococcal function and a model for the mechanism of action of CRP is proposed. These results suggest that pre-modified CRP, such as E-CRP, is therapeutically beneficial to decrease bacteremia in pneumococcal infection. Our findings may also have implications for infections with antibiotic-resistant pneumococcal strains and for infections with other bacterial species that use host proteins to evade complement-mediated killing.C反应蛋白（C-reactive protein, CRP）可结合多种病原菌，包括肺炎链球菌（Streptococcus pneumoniae）。小鼠实验结果显示，CRP的功能之一是通过结合肺炎链球菌并激活补体系统，抵御肺炎链球菌感染。但要发挥保护作用，CRP需在接种肺炎链球菌后数小时内注入小鼠体内，即CRP仅对早期感染具有保护效果，无法抵御晚期感染。研究推测，若肺炎链球菌获得足够时间在其表面招募补体抑制因子H（factor H）以获得补体攻击抗性，则CRP无法发挥保护作用。由于CRP的构象在炎症条件下会发生改变，且改变后的CRP同样可结合固定化的因子H，我们提出假说：若要抵御晚期感染，CRP需要改变自身构象，但这一过程在小鼠体内并未发生。据此，我们工程化改造了CRP分子（E-CRP），该分子可结合肺炎链球菌表面的因子H，但不会结合血液中宿主细胞表面的因子H。实验发现，E-CRP与野生型CRP协同作用时，无论向小鼠体内注入E-CRP的时机如何，均可发挥保护效果。我们得出结论：CRP通过两种不同的构象来实现其抗肺炎链球菌功能，并提出了CRP作用机制的模型。上述结果表明，经预改造的CRP（如E-CRP）可用于降低肺炎链球菌感染引发的菌血症，具有临床治疗价值。此外，本研究发现对于耐药肺炎链球菌菌株感染，以及利用宿主蛋白逃避补体介导杀伤的其他细菌感染，也具有潜在的指导意义。