An Intact Phosphocholine Binding Site Is Necessary for Transgenic Rabbit C-Reactive Protein to Protect Mice against Challenge with Platelet-Activating Factor

C-reactive protein (CRP) is not an acute-phase protein in mice, and therefore, mice are widely used to investigate the functions of human CRP. It has been shown that CRP protects mice from pneumococcal infection, and an active complement system is required for full protection. In this study, we assessed the contribution of CRP’s ability of activating the classical pathway of complement in the protection of mice from lethal infection with virulent Streptococcus pneumoniae type 3. We used two CRP mutants, Y175A and K114A. The Y175A CRP does not bind C1q and does not activate complement in human serum. The K114A CRP binds C1q and activates complement more efficiently than wild-type CRP. Passively administered, both CRP mutants and the wild-type CRP protected mice from infection equally. Infected mice injected with wild-type or mutant CRP had reduced bacteremia, resulting in lower mortality and increased longevity compared with mice that did not receive CRP. Thus, the protection of mice was independent of CRP-mediated activation of the classical pathway of complement. To confirm that human CRP does not differentiate between human and mouse complement, we analyzed the binding of human CRP to mouse C1q. Surprisingly, CRP did not react with mouse C1q, although both mutant and wild-type CRP activated mouse C3, indicating species specificity of CRP-C1q interaction. We conclude that the mouse is an unfit animal for exploring CRP-mediated activation of the classical complement pathway, and that the characteristic of CRP to activate the classical complement pathway has no role in protecting mice from infection.

Section: Discussionmentioning

confidence: 89%

Role of the Property of C-Reactive Protein to Activate the Classical Pathway of Complement in Protecting Mice from Pneumococcal Infection

Suresh¹,

Singh²,

Ferguson

et al. 2006

“…The mechanisms responsible for these effects are not well understood, although a direct inhibitory effect of CRP on neutrophil chemotaxis was proposed (8,11,12). CRP has also been shown to interact with PAF, and inhibition of PAF was proposed to account for its protective effect on PAF-induced shock (13). We have shown that CRPmediated protection against endotoxin shock requires Fc␥R and is associated with the induction of IL-10 and suppression of IL-12 synthesis (14).…”

Section: -Reactive Protein (Crp)mentioning

confidence: 86%

C-Reactive Protein-Mediated Suppression of Nephrotoxic Nephritis: Role of Macrophages, Complement, and Fcγ Receptors

Rodriguez¹,

Mold

Kataranovski

et al. 2007

C-reactive protein (CRP) is a member of the pentraxin family of proteins and an acute phase reactant. CRP modulates the response to inflammatory stimuli including LPS and C5a. We recently demonstrated that CRP prevents and reverses proteinuria in accelerated nephrotoxic nephritis (NTN). NTN is a model of active inflammatory immune complex-mediated nephritis induced by injection of antiglomerular basement membrane. CRP treatment prevented the induction of NTN in C57BL/6 (B6) mice, increased survival, and reversed ongoing nephritis. Protection was associated with a decrease in IL-1β and chemokines in the kidney and peritoneal cells as measured by quantitative RT-PCR. However, IL-10−/− mice were not protected by CRP either when given before disease onset or when disease activity was maximal. FcγRI−/− mice developed NTN, but were only transiently protected by CRP treatment. This transient protection was abrogated by cobra venom factor depletion of complement from FcγRI−/− mice. However, complement depletion did not prevent CRP-mediated protection in B6 mice, and CRP was protective in C3−/− mice. The role of macrophages in the protection provided by CRP was tested by treating B6 mice with liposomes containing clodronate. Clodronate-containing liposomes deplete mice of splenic and hepatic macrophages for 5–7 days. Pretreatment of NTN mice with clodronate but not control liposomes completely prevented CRP-mediated protection. These studies suggest that CRP mediates protection from NTN through the induction of IL-10 and that macrophages are required. In addition, FcγRI plays an important role but is not the sole mediator of CRP-mediated protection.

“…CRP has been shown to block the attachment of PCh-expressing bacteria to the receptors for platelet-activating factor on the host cells (42). In addition, the PCh-binding ability of CRP was required for the protection of mice from challenge with plateletactivating factor (43).…”

Section: Discussionmentioning

confidence: 99%

Human C-Reactive Protein Protects Mice fromStreptococcus pneumoniaeInfection without Binding to Pneumococcal C-Polysaccharide

Suresh

Singh

Ferguson

et al. 2007

Human C-reactive protein (CRP) protects mice from lethality after infection with virulent Streptococcus pneumoniae type 3. For CRP-mediated protection, the complement system is required; however, the role of complement activation by CRP in the protection is not defined. Based on the in vitro properties of CRP, it has been assumed that protection of mice begins with the binding of CRP to pneumococcal C-polysaccharide on S. pneumoniae and subsequent activation of the mouse complement system. In this study, we explored the mechanism of CRP-mediated protection by utilizing two CRP mutants, F66A and F66A/E81A. Both mutants, unlike wild-type CRP, do not bind live virulent S. pneumoniae. We found that passively administered mutant CRP protected mice from infection as effectively as the wild-type CRP did. Infected mice injected with wild-type CRP or with mutant CRP lived longer and had lower mortality than mice that did not receive CRP. Extended survival was caused by the persistence of reduced bacteremia in mice treated with any CRP. We conclude that the CRP-mediated decrease in bacteremia and the resulting protection of mice are independent of an interaction between CRP and the pathogen and therefore are independent of the ability of CRP to activate mouse complement. It has been shown previously that the Fcγ receptors also do not contribute to such CRP-mediated protection. Combined data lead to the speculation that CRP acts on the effector cells of the immune system to enhance cell-mediated cytotoxicity and suggest investigation into the possibility of using CRP-loaded APC-based strategy to treat microbial infections.