title: Expression of the peptide C4b-binding protein beta in the arthritic joint.
abstract: BACKGROUND
  C4b-binding protein (C4BP) is a plasma oligomeric glycoprotein that participates in the regulation of complement and haemostasis. Complement-regulatory activity depends on the C4BPalpha-polypeptide, whereas the C4BPbeta-polypeptide inactivates protein S, interfering with the anti-coagulatory protein C-dependent pathway.
  
  
  OBJECTIVE
  To investigate the expression of C4BPbeta in the rheumatoid joint.
  
  
  METHODS
  Expression of C4BP was studied in synovial explants from patients with rheumatoid arthritis, osteoarthritis and healthy controls, using immunohistochemistry and in situ hybridisation. C4BP isoforms and free C4BPbeta were studied in synovial effusions from patients with rheumatoid arthritis, osteoarthritis and microcrystalline arthritis (MCA) by immunoblotting; total and free protein S levels were studied by enzyme immunoassay.
  
  
  RESULTS
  C4BPbeta was overexpressed in the synovial membranes of patients with rheumatoid arthritis, in close association with the severity of synovitis and the extension of interstitial fibrin deposits. As many as 85% fluids from patients with rheumatoid arthritis contained free C4BPbeta, whereas this unusual polypeptide was present in 50% fluids from patients with MCA and 40% fluids from patients with osteoarthritis. Free protein S at the effusions was pathologically reduced in patients with rheumatoid arthritis and MCA, and remained normal in patients with osteoarthritis.
  
  
  CONCLUSIONS
  C4BPbeta is expressed by the inflamed synovial tissue, where it can participate in processes of tissue remodelling associated with invasive growth.
authors: Division of Rheumatology, Fundación Jiménez Díaz, Universidad Autónoma, 28040 Madrid, Spain. OSanchez@fjd.es
authors: O
authors: O
authors: Sánchez-Pernaute
authors: J
authors: J
authors: Esparza-Gordillo
authors: R
authors: R
authors: Largo
authors: E
authors: E
authors: Calvo
authors: M A
authors: MA
authors: Alvarez-Soria
authors: M E
authors: ME
authors: Marcos
authors: G
authors: G
authors: Herrero-Beaumont
authors: S R
authors: SR
authors: de Córdoba