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（CRP）能够与多种细菌病原体结合，包括肺炎链球菌。小鼠实验揭示了CRP的一项功能，即通过结合肺炎链球菌并激活补体系统，以抵御肺炎球菌感染。然而，为了实现保护作用，CRP必须在给予肺炎链球菌数小时内注入小鼠体内，即CRP对早期感染具有保护作用，而对晚期感染则无能为力。假设如果肺炎链球菌有足够的时间在其表面招募补体抑制剂因子H，从而形成对补体攻击的抵抗力，那么CRP将无法提供保护。由于CRP在炎症条件下会发生构象变化，而构象改变的CRP也会与固定的因子H结合，因此我们推测，为了抵御晚期感染，CRP需要改变其结构，而这在老鼠身上并未发生。因此，我们设计了一种CRP分子（E-CRP），它能够与肺炎链球菌上的因子H结合，但不会与血液中任何宿主细胞的因子H结合。我们发现，E-CRP与野生型CRP的协同作用，无论E-CRP在何时注入小鼠体内，都具有保护作用。我们得出结论，CRP通过两种不同的构象来执行其抗肺炎球菌的功能，并提出了CRP作用机制的模型。这些结果表明，预先修饰的CRP，如E-CRP，在治疗肺炎球菌感染时具有降低菌血症的疗效。我们的发现对于抗生素耐药的肺炎球菌菌株感染以及其他利用宿主蛋白逃避补体介导的杀伤作用的细菌物种感染也可能具有影响。