title: Human C-reactive protein protects mice from Streptococcus pneumoniae infection without binding to pneumococcal C-polysaccharide.
abstract: 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 Fcgamma 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.
authors.affiliation: Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614.
authors.forename: Madathilparambil V
authors.initials: MV
authors.lastname: Suresh
authors.affiliation: Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614.
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Singh
authors.affiliation: Department of Microbiology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Ferguson
authors.affiliation: Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614.
authors.forename: Alok
authors.initials: A
authors.lastname: Agrawal
mesh_terms: D000818:Animals; D001419:Bacteria; D002097:C-Reactive Protein / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D004731:Endotoxins / Q000494:pharmacology; D005260:Female; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics; D010649:Phenylalanine / Q000235:genetics / Q000378:metabolism; D011008:Pneumococcal Infections / Q000378:metabolism* / Q000382:microbiology / Q000517:prevention & control*; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D011485:Protein Binding; D013296:Streptococcus pneumoniae / Q000472:pathogenicity; D015996:Survival Rate
chemical_list: D004731:Endotoxins; D011135:Polysaccharides, Bacterial; C027158:polysaccharide C-substance (Streptococcus); D018698:Glutamic Acid; D010649:Phenylalanine; D002097:C-Reactive Protein