Immunochemical discrimination of leukocyte elastase from plasmic degradation products of fibrinogen.

A rabbit antiserum was elicited to the D-like fragment (De) generated by cleavage of human fibrinogen with isolated leukocyte elastase. After absorption with intact fibrinogen and plasmic degradation products, the antiserum retained its capacity to recognize the De fragment in radioimmunoassays. Plasmic digests of fibrinogen, produced at various enzyme-to-substrate ratios, and purified plasmic degradation products of fibrinogen reacted poorly with the absorbed antiserum. In contrast, elastase digests of fibrinogen and purified elastase degradation products reacted well, although earlier derivatives expressed the recognized epitopes less well than the De fragment. These observations indicated the recognition of an elastase-elicited neoantigen that was not expressed by plasmic degradation products of fibrinogen. When elastase degradation products were added to normal plasma, the elastase-elicited neoantigen could be quantitatively detected in radioimmunoassay. Normal plasma was negative (less than or equal to 5 nM) for the elastase-elicited neoantigen. Of 30 pathological plasmas containing high concentrations of leukocyte elastase, four contained low levels of the elastase-elicited neoantigen (greater than 15 nM). These results suggest that under most circumstances the fibrinolytic activity of leukocyte elastase is well regulated but that under certain pathophysiological conditions, the leukocyte protease may participate in the fibrinolytic process.