Characterization of synovial fluid fibronectin from patients with rheumatic inflammatory diseases and healthy subjects

Synovial fluid fibronectin from normal subjects and from patients who have rheumatic inflammatory diseases has been studied and compared with plasma fibronectin. The average fibronectin concentration in synovial fluids from normal subjects was 172 ± 69 μg/ml; it was 721 ± 315 and 556 ± 349 μg/ml in synovial fluids from patients with rheumatoid arthritis and osteoarthritis, respectively. This is the first report on fibronectin concentrations in normal synovial fluids. Synovial fluid fibronectin from healthy subjects and patients with rheumatoid arthritis or osteoarthritis showed a molecular weight identical to that of plasma fibronectin. All normal and pathologic synovial fluid fibronectins showed a remarkably lower electrophoretic mobility compared with that of plasma fibronectin, when separated according to net molecular charge on agarose gel. Peptides from thermolysin digests of fibronectin from plasma and synovial fluid, when compared on sodium dodecyl sulphate-polyacrylamide gel electrophoresis, showed distinct differences. These data demonstrate that synovial fluid fibronectin represents a molecular form which is structurally different from that of plasma fibronectin. This suggests that synovial fluid fibronectin is locally synthesized, possibly by a cell type which differs from that responsible for the production of the plasmatic fibronectin pool.