The influence of fibronectin on cryoprecipitate formation in rheumatoid arthritis and systemic lupus erythematosus.

Fibronectin, a human fibroblast surface and plasma protein, is present in cryoprecipitates of synovial fluids and/or sera from patients with rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, and mixed essential cryoglobulinemia. Fibronectin was shown to be capable of influencing cryoprecipitate formation. No antibodies to fibronectin could be detected, thus ruling out the possibility that it was directly involved in the formation of cold-insoluble antigen--antibody complexes. Fibrinogen or fibrinogen degradation products were frequently present in synovial fluid cryoprecipitates but rarely in serum cryoprecipitates. Since complexes of fibronectin--fibrin--fibrinogen are known to be cold-insoluble, such interactions could occur in synovial fluids and contribute to the formation of cryoprecipitates. In serum, however, this is not likely to occur, and the mechanism by which fibronectin influences cryoprecipitate formation remains to be elucidated.