Inhibition of Plasminogen Activation by Monoclonal Antibodies to the Kringle 5-B Chain Segment of Human Plasminogen

Abstract

Three murine monoclonal antibodies (designated alpha Pg-28, alpha Pg-96, and alpha Pg-247) against human plasminogen were prepared. All three antibodies bound plasminogen and the elastase-digestion product of plasminogen consisting of residues Val442-Asn790 (miniplasminogen). The epitopes recognized by each antibody were distinct. Antibodies alpha Pg-96 and alpha Pg-247 blocked tissue plasminogen activator-dependent lysis in a fibrin plate assay while antibody alpha Pg-28 had no effect. Antibody alpha Pg-96 blocked urokinase- and tissue plasminogen activator-catalyzed, and streptokinase-mediated, plasminogen activation. Antibodies alpha Pg-28 and alpha Pg-247 partially inhibited tissue plasminogen activator-catalyzed plasminogen activation. Antibodies alpha Pg-28 and alpha Pg-247 also inhibited streptokinase-mediated plasminogen activation, but not urokinase-catalyzed activation. Antibody alpha Pg-247 inhibited plasmin catalysis of substrate S-2251 by decreasing the VMAX and increasing the KM of plasmin for the synthetic substrate S-2251 four-fold. The other antibodies had no significant effect on plasmin activity. This differential inhibition of plasminogen activation suggests that activation by urokinase, tissue plasminogen activator, and streptokinase possibly involve distinct regions of miniplasminogen structure.

Identification of an Inhibitor of Tissue-type Plasminogen Activator-mediated Fibrinolysis in Human Neutrophils

“…Thi s si milarity betw een defensin and the pla sminogen kringle may explain th e ability of the in hibitor to compete with plasminogen for th e active site of t PA, as well as t he absence of such competition between t he inhibitor a nd 8-2288 . Resul ts from oth er studies suggest that kringle 5, presen t in the miniplasminogen , is in volved in the activation of plasminogen by t PA, even tho ugh it is located at a dista nce from the cleavage site (36). Therefore, the structural si milarity between defen sin and kringle 5 of pla sminogen may explain the ability of defensin to interfer e with the bin ding of plasminogen to the active site of tPA.…”

Antibodies to prothrombin crossreact with plasminogen in patients developing myocardial infarction

“…The interference of the anti‐kringle antibodies with the fibrinolytic cascade could account for the hypercoagulable state and explain the increased risk of thrombotic events in patients with high levels of antiprothrombin antibodies. Supporting our hypothesis, Church & Messier (1991) tested three murine monoclonal anti‐human plasminogen antibodies in respect to their ability to inhibit the function of plasminogen and found that these antibodies, recognizing the miniplasminogen, containing kringle 5 and the serine protease domain, were able to inhibit fibrinolysis and activation of plasminogen. Also Kanalas (1993) reported an inhibitory effect of antiplasminogen antibodies on the activation of plasminogen by urokinase in an experimental rat glomerulonephritis.…”