Plasma fibronectin level in patients with connective tissue diseases.

The level of plasma fibronectin (Fn) was studied in 40 patients with connective tissue diseases. Fn concentration was found increased in patients with rheumatoid arthritis (mean +/- SE, 560 +/- 30 micrograms/ml, p less than 0.01) decreased in patients with mixed connective tissue disease (337 +/- 12 micrograms/ml, p less than 0.05) and was not significantly different from controls in systemic lupus erythematosus, scleroderma, polymyositis. The value of plasma Fn level was found increased in active diseases and decreased in the cases, with presence of cryoprecipitates. The factors which might influence the level of plasma Fn and the possibility of using the changes of Fn concentration in the estimation of the evolution of connective tissue diseases are discussed.