Fibronectin binding with immunoglobulin aggregates and its association with rheumatic disorders.

Fibronectin was shown to bind heat-aggregated, but not monomeric, human IgG, suggesting that fibronectin may bind directly to IgG immune complexes. The presence of material both binding and already containing fibronectin was demonstrated in polyethylene glycol precipitates of sera and synovial fluids from patients with rheumatoid arthritis (RA) and gout, but not normal sera. By contrast, complement-fixing complexes contained fibronectin in RA synovial fluids and sera, but not in sera and synovial fluids from other rheumatic disorders. It is considered that fibronectin binds to immune complexes in RA synovial fluids and sera but that some other, as yet unidentified material, is effective in binding fibronectin in sera and synovial fluids from patients with osteoarthritis and crystal synovitis.