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The Pneumococcal Surface Proteins PspA and PspC Sequester Host C4-Binding Protein To Inactivate Complement C4b on the
Kashif S Haleem1,2, Youssif M Ali1,3, Hasan Yesilkaya1
1Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, United Kingdom.
Infection and Immunity
|October 17, 2018
Summary
Streptococcus pneumoniae uses PspA and PspC proteins to bind complement regulator C4BP, preventing complement attack. This mechanism inactivates C4b, a key component in bacterial defense evasion.
Area of Science:
- Immunology
- Microbiology
- Bacterial Pathogenesis
Background:
- Complement system is crucial for antimicrobial immunity.
- Pathogens evade complement by sequestering host complement regulators.
- Streptococcus pneumoniae utilizes virulence factors to evade immune attack.
Purpose of the Study:
- Investigate the mechanism of complement evasion by Streptococcus pneumoniae.
- Determine the role of PspA and PspC in complement regulation.
- Elucidate how pneumococcal virulence factors contribute to immune evasion.
Main Methods:
- Opsonization of S. pneumoniae D39 with human serum.
- Analysis of complement activation products (C4b, iC4b, C4dg) and C4BP deposition.
- Generation of PspA and PspC deletion mutants.
- Infection experiments in mice.
- Binding assays with recombinant PspA and PspC.
Main Results:
- S. pneumoniae D39 rapidly converts surface-bound C4b/iC4b to C4dg, preventing C3 convertase formation.
- PspA and PspC sequester C4b-binding protein (C4BP) from host plasma.
- Deletion of PspA/PspC reduced C4BP and C4dg deposition, increasing C4b/iC4b.
- Loss of PspA/PspC resulted in reduced bacterial pathogenicity in mice.
Conclusions:
- PspA and PspC facilitate S. pneumoniae complement evasion by binding C4BP.
- This binding inactivates C4b, preventing complement-mediated bacterial killing.
- PspA and PspC are key virulence factors contributing to pneumococcal pathogenicity.
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