NATURAL ANTICOAGULANT PROTEINS AND ANTIPHOSPHOLIPID ANTIBODIES IN SYSTEMIC LUPUS-ERYTHEMATOSUS

Objective. Thrombosis is a relatively common complication in patients with systemic lupus erythematosus (SLE) and is strongly associated wit h the presence of antiphospholipid antibodies (aPL). The mechanism inv olved in the pathogenesis of this prothrombotic state remains obscure. We studied 4 natural anticoagulant proteins: protein C, protein S, an tithrombin III, and plasminogen in 50 patients diagnosed with SLE. Met hods. Protein C, antithrombin III, and plasminogen were measured by ch romogenic substrates and total and free protein S by electrophoresis. We also determined the prevalence of different aPL (lupus anticoagulan t and antibodies against cardiolipin, phosphatidylserine, and phosphat idylinositol). Results. Ten patients (20%) had a history of thrombosis . Some type of aPL was present in 26 patients (52%). Nine of the 10 pa tients with history of thrombosis had aPL (p = 0.007). Functional assa ys for protein C, antithrombin III, and plasminogen were in the normal range in all patients. Low free protein S levels were documented in 1 9 patients and were associated with the presence of aPL (13/19 were aP L positive) (p < 0.05). Only 4 patients with acquired free protein S d eficiency had a history of thrombosis. Conclusion. This study shows an association between aPL and reduced free protein S levels in patients with SLE. Further studies are needed to determine the mechanism and r ole of this acquired deficiency in the pathogenesis of thrombotic epis odes in patients with SLE.