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Complement inhibitor C4b-binding protein interacts directly with small glycoproteins of the extracellular matrix.

In English

Författare

  • Kaisa Happonen
  • Andreas Holmér
  • Matthias Mörgelin
  • Dick Heinegård
  • Anna Blom

Summary, in English

Components derived from cartilage have been suggested to maintain the inflammation in joints in arthritis. Small leucine-rich repeat proteins (SLRPs) are structural components of cartilage important in organizing the meshwork of extracellular matrix components. It has recently been shown that the SLRP fibromodulin interacts with complement initiator C1q, leading to complement activation. The complement response is limited since fibromodulin also interacts with the complement inhibitor factor H. We have now found that osteoadherin, chondroadherin, fibromodulin, and proline arginine-rich end leucine-rich repeat protein bind to the complement inhibitor C4b-binding protein (C4BP). Using direct binding assays with C4BP fragments and C4BP mutants lacking individual domains in combination with electron microscopy, we have demonstrated that mainly the central core of C4BP mediated binding to SLRPs. Binding of SLRPs to C4BP did not affect its ability to inhibit complement. Osteoadherin, fibromodulin, and chondroadherin, which bind C1q and activate complement, were found to cause significantly higher C9 deposition in C4BP-depleted serum compared with Igs, indicating that the level of complement activation initiated by SLRPs is regulated by simultaneous binding to C4BP. A similar dual binding of C1q and complement inhibitors was observed previously for other endogenous ligands (amyloid, prions, C-reactive protein, and apoptotic cells) but not for exogenous activators (bacteria-bound Igs). These interactions can be significant during inflammatory joint diseases, such as rheumatoid arthritis, where cartilage is degraded, and cartilage components are released into synovial fluid, where they can interact with factors of the complement system.

Publiceringsår

2009

Språk

Engelska

Sidor

1518-1525

Publikation/Tidskrift/Serie

Journal of immunology

Volym

182

Issue

3

Dokumenttyp

Artikel i tidskrift

Förlag

American Association of Immunologists

Ämne

  • Immunology in the medical area

Status

Published

Forskningsgrupp

  • Clinical Chemistry, Malmö
  • Protein Chemistry, Malmö

ISBN/ISSN/Övrigt

  • ISSN: 1550-6606