Abstract
Fibronectin is a glycoprotein secreted by connective tissue cells into their environment and into the blood. Plasma fibronectin has been isolated and used to prepare an antiserum. This has been shown to be specific for fibronectin and unreactive with fibrin(ogen) and collagen, to which fibronectin binds in vitro. The antiserum has been used to examine the distribution of this protein in the synovium in health, in rheumatoid arthritis, and in osteoarthrosis, and to estimate levels in plasma and synovial fluid. The results suggest that fibronectin is synthesised by synovial cells, and the synovial fluid level of fibronectin was found to be about twice the plasma level in rheumatoid arthritis. In long-standing arthritis fibronectin was also found to be codistributed with (presumably by adsorption upon) fibrin and immature collagen in intra-articular structures but was no longer demonstrable in areas where mature collagen had been formed in areas undergoing fibrosis. The possible significance of local fibronectin production within joints in relation to its possible effect on the resolution or continuance of arthritis is discussed.