Different synovial fluid fibronectin levels in rheumatoid variants.

A circulating high-molecular-weight glycoprotein called fibronectin plays a part in cell adhesion and migration before phagocytosis and in morphology, differentiation, and metabolism in inflammatory synovial effusions of patients with rheumatic diseases. A technique of nephelometric immunoassay, based on the measurement of an antigen-antibody reaction, was applied to the analysis of fibronectin concentrations in synovial fluids from 20 patients with rheumatoid arthritis (RA) and other diseases (non-RA). RA synovial fluids have a significantly higher concentration than the specimens obtained from Yersinia arthritis patients (n = 12). The mean concentration of other synovial fluids, from 12 patients with osteoarthritis of the knees, did not significantly differ from the synovial fluids of control values obtained from patients who underwent meniscectomy. There was a considerably negative correlation between fibronectin levels and overall indices of inflammatory activity, such as Ritchie articular indices or a whole number of painful rheumatoid arthritis joints. However, a particularly distinct correlation was obtained when raised fibronectin levels were compared with the inflammatory activity of the knee joint, from which the specimen was aspirated. Thus, these findings suggest that the measurements of fibronectin in synovial fluid may be of some differential-diagnostic value in rheumatoid variants, but may only serve as an indicator of inflammatory activity if the joint, from which the specimen is obtained, is taken into account.