Interaction between M-like protein and macrophage thioredoxin facilitates antiphagocytosis for Streptococcus equi...

Area of Science:

• Microbiology
• Immunology
• Veterinary Science

Background:

• Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is a significant veterinary pathogen.
• M-like protein (SzP) is a key virulence factor in S. zooepidemicus infections.
• Bacterial evasion of host immunity is crucial for pathogenesis.

Purpose of the Study:

• To investigate the interaction between S. zooepidemicus SzP and porcine thioredoxin (TRX).
• To elucidate the role of this interaction in bacterial virulence and immune evasion.
• To understand how SzP-TRX interaction affects the complement system.

Main Methods:

• Yeast two-hybrid assay to identify protein interactions.
• Co-immunoprecipitation to confirm SzP-TRX interaction.
• Functional assays to assess TRX activity and complement pathway regulation.

Main Results:

• SzP directly interacts with both reduced and oxidized forms of TRX.
• Membrane-bound SzP recruits TRX to the bacterial surface.
• TRX inhibits alternative complement pathway activity by targeting C3 convertase and associating with Factor H (FH).
• SzP-recruited TRX reduces C3 deposition on bacteria, hindering phagocytosis.

Conclusions:

• S. zooepidemicus employs SzP to recruit TRX, a host protein.
• This recruitment modulates the alternative complement pathway, facilitating immune evasion.
• The SzP-TRX interaction is a novel mechanism for S. zooepidemicus to evade host phagocytosis.