Synovial fibronectin fragmentation and domain expressions in relation to rheumatoid arthritis progression.

OBJECTIVE To determine whether the expression of some fibronectin (FN) domains and a degree of FN degradation are associated with the progression of rheumatoid arthritis (RA). METHODS Based on the radiographs of the hands of RA patients, three groups of synovial fluid and plasma samples were distinguished: (i) those with early radiological changes, (ii) established and (iii) late progressive radiological changes. The expressions of FN domains were determined by ELISA using appropriate domain-specific monoclonal antibodies. FN fragmentation was analysed by immunoblotting. RESULTS In the early RA group, synovial FN was found to be totally degraded to a mixture of FN fragments. In the established group, it consisted of a portion of intact FN molecules and a smaller part of FN fragments, whereas in the late group the synovial FN immunoblotting pattern was similar to that of intact FN. The FN fragmentation was accompanied by decreases in FN immune reactivity with monoclonal antibodies specific to the collagen, fibrin and C-terminal FN domains. In the blood plasma of all studied groups of RA patients, the FN immunopattern was analogous to that in normal plasma. However, the expressions of the plasma FN domains were higher than those of healthy individuals. CONCLUSIONS Profound degradation of FN and low collagen, fibrin and C-terminal domain expressions in FN were only associated with early destructive changes observed in radiographs of the RA patients' hands.