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Streptococcal pyrogenic exotoxin B cleaves properdin and inhibits complement-mediated opsonophagocytosis

Nina Tsao1, Wan-Hua Tsai, Yee-Shin Lin

  • 1Department of Biological Science and Technology, I-Shou University, Kaohsiung County, Taiwan.

Biochemical and Biophysical Research Communications
|December 7, 2005
PubMed

Insights

Group A Streptococcus uses pyrogenic exotoxin B (SPE B) to degrade serum properdin, a novel mechanism that helps bacteria evade immune cells and resist phagocytosis during infection.

Area of Science:

  • Microbiology
  • Immunology
  • Biochemistry

Background:

  • Streptococcal pyrogenic exotoxin B (SPE B) is a key virulence factor in Group A Streptococcus (GAS) infections.
  • SPE B's ability to reduce phagocytic activity suggests a role in bacterial evasion of host immune defenses.

Purpose of the Study:

  • To elucidate the mechanism by which SPE B facilitates bacterial resistance to opsonophagocytosis.
  • To investigate the interaction of SPE B with serum components involved in complement-mediated immunity.

Main Methods:

  • Western blotting was employed to detect interactions between SPE B and serum proteins.
  • Affinity chromatography using immobilized SPE B identified properdin as a binding partner.
  • Functional assays assessed the impact of SPE B on the alternative complement pathway and neutrophil killing.

Main Results:

  • Both active SPE B and its protease-inactive mutant (C192S) bound to serum properdin.
  • Active SPE B, but not C192S, degraded properdin, leading to the blockage of the alternative complement pathway.
  • Properdin reconstitution restored alternative pathway function in SPE B-treated serum.
  • GAS opsonized with SPE B-treated serum exhibited increased resistance to neutrophil-mediated killing.

Conclusions:

  • Group A Streptococcus employs a novel mechanism involving the degradation of serum properdin by SPE B to evade opsonophagocytosis.
  • This degradation of properdin by SPE B impairs the alternative complement pathway, contributing to bacterial survival.

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