Influence of plasma protease activation on electroimmunoassay and nephelometry of plasma fibronectin in sepsis.

In vitro experiments have shown that proteases such as trypsin, kallikrein and plasmin may split plasma fibronectin, yielding changes in apparent mass concentration, i.e.: a decrease when using immunonephelometry (IN), and an increase when using electroimmunoassay (EIA). In the present in vivo study, plasma from 49 patients with severe infections was assayed for fibronectin by IN and EIA, and for prekallikrein, plasminogen and antithrombin. In patients with normal prekallikrein (n = 26) and plasminogen (n = 23), the agreement between the two fibronectin assay methods was good (ratio EIA/IN = 0.99 +/- 0.06); a similar good agreement was found in 45 healthy blood donors (ratio 0.97 +/- 0.02). In contrast, the 20 patients with low prekallikrein showed fibronectin values that were significantly higher by EIA than by nephelometry (ratio 1.27 +/- 0.10, p less than 0.01). Similarly, the 26 patients with low plasminogen had a significantly increased ratio (1.21 +/- 0.09, p less than 0.05). No such difference was seen, however, between patients with low or normal antithrombin. Thus, kallikrein and plasmin activation in vivo appear to increase the fibronectin concentration measured by EIA, possibly due to the formation of small fragments with increased electrophoretic motility.