This research will characterize the role of complement proteins in the immune-mediated opsonophagocytosis and killing of pathogenic Staphylococcus aureus. S. aureus is a leading cause of death from infection in hospitals and is increasingly resistant to current antibiotics. For many bacteria adequate opsonization by complement proteins is critical for effectively preventing and fighting infections. Studying complement-mediated opsonization of S. aureus may provide clues to unlock new therapies against S. aureus. Encapsulated (CP+) strains, serotypes 5 and 8, cause 70% of severe S. aureus infections, however their opsonization by complement remains largely unstudied. Our preliminary in vivo and in vitro studies and in vitro studies have investigated three CP+ strains, two heavily- encapsulated strains, and one capsule-negative mutant in terms of lethality in complemented mice, C3 binding kinetics, pathways of complement activation, the nature of C3 fragments deposited and shed, the relationship between growth and C3 binding, and the effect of capsule on C3 binding. The data from these studies suggest that complement is important for surviving bacteremia with clinically relevant S. aureus serotypes. CP+ strains appear to inhibit opsonization by decreasing C3 binding, inhibiting bound C3-fragment recognition by complement receptors, and sh4edding bound C3-fragments. The global hypothesis guiding this research is that the severity of S. aur5eus infection depends on serotype dependent staphylococcal-capsule modulation of complement-mediated opsonization. In light of the preliminary data the following focused hypotheses will be tested: 1) Opsonization by complement is critical in host defense against S. aureus. 2) Capsular polysaccharide and impairs opsonphagocytosis of S. aureus by interfering with normal complement function. 3) S. aureus protects itself by degrading and shedding the major complement opsonins C3b and iC3b. 4) Anti-capsular antibodies improve the complement-mediated opsonophagocytosis and killing of S. aureus. These experiments will be performed using radiolabeled complement components, and antibodies raised against specific complement peptides. Human neutrophils will be incubated with opsonized bacteria and stained with acridine orange to measure phagocytosis and intracellular killing. In vivo experiments will be performed using complement deficient mice. Collaborating laboratories have provided special S. aureus stains and anti-S. aureus antibodies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Clinical Investigator Award (CIA) (K08)
Project #
1K08AI001835-01A1
Application #
6435230
Study Section
Microbiology and Infectious Diseases B Subcommittee (MID)
Project Start
2002-04-01
Project End
2002-06-30
Budget Start
2002-04-01
Budget End
2002-06-30
Support Year
1
Fiscal Year
2002
Total Cost
$20,214
Indirect Cost
Name
Duke University
Department
Pediatrics
Type
Schools of Medicine
DUNS #
071723621
City
Durham
State
NC
Country
United States
Zip Code
27705
Hair, Pamela S; Ward, Michael D; Semmes, O John et al. (2008) Staphylococcus aureus clumping factor A binds to complement regulator factor I and increases factor I cleavage of C3b. J Infect Dis 198:125-33
Cunnion, Kenji M; Buescher, E Stephen; Hair, Pamela S (2005) Serum complement factor I decreases Staphylococcus aureus phagocytosis. J Lab Clin Med 146:279-86
Cunnion, K M; Hair, P S; Buescher, E S (2004) Cleavage of complement C3b to iC3b on the surface of Staphylococcus aureus is mediated by serum complement factor I. Infect Immun 72:2858-63
Cunnion, K M; Frank, M M (2003) Complement activation influences Staphylococcus aureus adherence to endothelial cells. Infect Immun 71:1321-7
Cunnion, K M; Zhang, H-M; Frank, M M (2003) Availability of complement bound to Staphylococcus aureus to interact with membrane complement receptors influences efficiency of phagocytosis. Infect Immun 71:656-62