Fibronectin in rheumatoid and non-rheumatoid arthritic synovial fluids and in synovial fluid cryoproteins

Concentrations of fibronectin, immunoglobulins G, M, and A, and C3 and C4 components of complement, and other plasma proteins were determined in synovial fluids from patients with rheumatoid arthritis (RA) and other diseases (non-RA). Fibronectin concentrations were two to three times greater in all synovial fluids than in plasma, and RA synovial fluids had a significantly higher mean concentration than non-RA fluids (883 microgram per ml vs. 588 microgram per ml, respectively, p less than 0.01). The mean concentrations of other synovial fluid constituents were less than their mean plasma concentrations. These results suggest that unlike other plasma constituents, either plasma fibronectin is concentrated in synovial fluids or that a substantial portion of synovial fluid fibronectin may be derived from synovial tissue cells. Both the C3 and C4 complement components were present in lower concentrations in RA than in non-RA synovial fluids. The C3 contents showed a statistically significant negative correlation with the fibronectin contents. Fibronectin was also found in all synovial fluid cryoprotein fractions tested, although its content varied greatly as a percent of the total cryoprotein protein (0.01 to 43 percent). The data show that fibronectin is a consistent constituent of synovial fluid cryoproteins in agreement with our previously reported finding that fibronectin is found in all serum cryoglobulin fraction tested.