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Mechanisms of Host-Pathogen Protein Complex Formation and Bacterial Immune Evasion of Streptococcus suis Protein Fhb

Xueqin Li1, Peng Liu2, Shuzhen Gan2

  • 1From the State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071 and the Central Laboratory of Yijishan Hospital, Wannan Medical College, Wuhu 241001, China.

The Journal of Biological Chemistry
|June 26, 2016
PubMed

Insights

Streptococcus suis serotype 2 uses a factor H-binding protein (Fhb) to evade immune clearance. This protein binds complement components, forming immune complexes that help the bacteria survive in the bloodstream.

Area of Science:

  • Microbiology
  • Immunology
  • Molecular Biology

Background:

  • Streptococcus suis serotype 2 (S. suis 2) causes sepsis and meningitis, often with bacteremia.
  • Evasion of phagocytic clearance by polymorphonuclear leukocytes is crucial for S. suis 2 bacteremia.
  • Factor H-binding protein (Fhb) on S. suis 2 binds factor H (FH), inhibiting complement activation and phagocytosis.

Purpose of the Study:

  • To investigate the interaction of S. suis 2 Fhb with host complement components.
  • To elucidate the mechanism by which Fhb contributes to bacterial immune evasion.
  • To understand the multifunctional role of Fhb in S. suis 2 pathogenesis.

Main Methods:

  • Biochemical assays to detect binding of complement components (C3b/C3d) and FH to Fhb.
  • Analysis of Fhb interactions with complement components using domain mapping.
  • Investigation of Fhb localization (cell envelope and supernatant) and its effect on complement activation.

Main Results:

  • Fhb binds both FH and C3b/C3d, forming large immune complexes.
  • Domain II of Fhb mediates these interactions through electrostatic and hydrophobic forces.
  • Secreted Fhb inhibits complement activation, enhancing bacterial survival against phagocytic clearance.

Conclusions:

  • S. suis 2 Fhb is a multifunctional protein with a novel mechanism for immune evasion.
  • Fhb binding to complement components and its secreted form represent a new bacterial strategy against host innate immunity.
  • This interaction facilitates S. suis 2 survival in the bloodstream by interfering with complement-mediated clearance.
Keywords:
Factor H;complement 3FhbStreptococcusStreptococcus suiscomplementhost defenseimmune evasioninfectionsecretionstreptococcusstreptococcus suis

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