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Defective fibrinolysis due to decreased tissue-type plasminogen activator (t-PA) activity is a well-established finding in patients with systemic lupus erythematosus (SLE). The possibility that this decrease in t-PA activity may be related to the presence of autoantibodies directed against t-PA, and the possible role of these autoantibodies in the pathophysiology of fibrinolysis in SLE, were investigated. Serum samples from 115 SLE patients and 63 normal volunteers were analyzed for the presence of such antibodies. The search for antibodies to t-PA was performed by means of several systems, allowing for the identification of epitopes presented in different conformational physical states of t-PA: free or associated to its inhibitor (PAI-1) in plasma, specifically bound to fibrin surface, or passively adsorbed to solid supports. Antibodies in variable amounts were detected by all systems used; however, t-PA activity was not inhibited by the IgG fraction of the positive sera in a fibrin-agar fibrinolysis system. Moreover, the demonstration of serum anti-t-PA antibodies was not associated with clinical or laboratory abnormalities related to vasoocclusive episodes. These results indicate that, as in the case of other autoantibodies, their detection in serum does not imply their direct participation in the pathophysiology of thrombosis in SLE.

We studied 28 patients with SLE, five of whom had had thrombotic episodes. Platelet function and coagulation and fibrinolytic studies were performed to determine whether any of these factors may predispose to thrombosis in SLE. An inhibitor of blood coagulation was detected in 12 patients, and von Willebrand's syndrome was observed in two others. The most striking findings which could be correlated with thromboembolic phenomena were the increase in VII R:WF and the absence of plasminogen activator release after venous occlusion. Both proteins are synthesized by the endothelial cell, and the abnormalities observed are possibly related to damage of the vascular endothelium by immune complexes observed in SLE.