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Acquisition of complement inhibitor serine protease factor I and its cofactors C4b-binding protein and factor H by

Sven Malm1, Monika Jusko, Sigrun Eick

  • 1Section of Medical Protein Chemistry, Department of Laboratory Medicine, Skåne University Hospital, Lund University, Malmö, Sweden.

Plos One
|April 20, 2012
PubMed

Insights

Prevotella intermedia, a pathogen linked to periodontitis and rheumatoid arthritis, acquires the complement inhibitor Factor I (FI). This binding helps the bacteria evade the host immune system, representing a novel evasion mechanism.

Area of Science:

  • Microbiology
  • Immunology
  • Molecular Biology

Background:

  • Prevotella intermedia is a Gram-negative pathogen associated with periodontitis and rheumatoid arthritis.
  • The serine protease Factor I (FI) is crucial for inhibiting complement system components C3b and C4b, requiring cofactors like C4b-binding protein (C4BP) and Factor H (FH).

Purpose of the Study:

  • To investigate whether Prevotella intermedia acquires complement inhibitor Factor I (FI).
  • To determine if acquired FI retains its enzymatic activity and if associated cofactors are also acquired.
  • To explore a potential novel complement evasion mechanism by P. intermedia.

Main Methods:

  • Incubation of Prevotella intermedia isolates with purified FI and FI from heat-inactivated human serum.
  • Assessing the serine protease activity of bound FI using (125)I-labeled C4b.
  • Investigating the binding and functional activity of cofactors C4BP and FH in the presence of acquired FI.

Main Results:

  • Prevotella intermedia isolates successfully bound purified FI and FI from human serum.
  • Bound FI retained its serine protease activity, degrading C4b.
  • P. intermedia also acquired active C4BP and FH, which supported FI-mediated degradation of C3b and C4b.

Conclusions:

  • Prevotella intermedia acquires the complement inhibitor Factor I (FI), retaining its activity.
  • The bacterium also acquires active cofactors C4BP and FH, enhancing FI's inhibitory function.
  • FI acquisition represents a novel complement evasion strategy for this Gram-negative pathogen linked to chronic diseases.

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