Complement evasion factor (CEF), a novel immune evasion factor of Streptococcus pyogenes

Area of Science:

• Microbiology
• Immunology
• Molecular Biology

Background:

• Streptococcus pyogenes is a major human pathogen causing diverse infections.
• S. pyogenes employs virulence factors, including immune evasion strategies, to cause disease.
• A protein encoded by spy0136 in S. pyogenes was of unknown function.

Purpose of the Study:

• To identify the function of the S. pyogenes protein encoded by spy0136.
• To investigate the role of spy0136 in S. pyogenes pathogenesis and immune evasion.
• To characterize the interaction of Spy0136 with host immune factors.

Main Methods:

• Recombinant Spy0136 protein was used in pull-down assays and ELISA with human plasma.
• Complement proteins were treated with PNGase F to assess glycan-dependent binding.
• Wieslab complement assays and in vitro whole blood killing assays were performed.
• A Galleria mellonella infection model was used to evaluate bacterial virulence.
• Serum samples from patients with invasive S. pyogenes infections were analyzed for sero-conversion.

Main Results:

• Spy0136 binds to complement proteins C1r, C1s, C3, and C5 in a glycan-dependent manner.
• Recombinant Spy0136 inhibits complement-mediated hemolysis and all three complement pathways.
• Spy0136 inhibits C3b opsonization and membrane attack complex deposition on S. pyogenes.
• A spy0136 deletion mutant exhibited reduced virulence in vivo and in vitro.
• Sero-conversion to Spy0136 was observed in patients with invasive S. pyogenes infections.

Conclusions:

• Spy0136 is a novel immune evasion factor, named complement evasion factor (CEF).
• CEF interferes with complement function through glycan-dependent binding to multiple complement proteins.
• CEF plays a significant role in S. pyogenes virulence and immune evasion during infection.