A study on associations between antiprothrombin antibodies, antiplasminogen antibodies and thrombosis.

Anti-prothrombin antibodies are a frequent cause of lupus anticoagulant (LAC), a thrombotic risk factor. Prothrombin shares structural homology with plasminogen, a kringle protein with an important role in fibrinolysis. Cross-reactivity between antiprothrombin antibodies and plasminogen has been described. To study associations between LAC, IgG and IgM class antiprothrombin and antiplasminogen antibodies, plasminogen activity levels and thrombosis in selected patients with systemic autoimmune diseases. Patients included forty-six consecutive LAC-positive patients (29 with systemic lupus erythematosus (SLE); 33 with a thrombotic history), 38 patients without LAC (36 with SLE; seven with a history of thrombosis) and 40 healthy controls. In the total group of 84 patient samples, the prevalence of antiprothrombin and antiplasminogen antibodies was 30 and 38%, respectively. There was no significant relationship between the presence of these antibodies. In contrast to presence of antiplasminogen antibodies, presence of antiprothrombin antibodies was statistically significant related to thrombosis. Thirteen samples had antiprothrombin and antiplasminogen antibodies of similar isotype (IgG, n= 4; IgM, n= 9). Of these, all but one had LAC and 11/13 came from patients with a history of thrombosis. Simultaneous presence of IgM-class antiprothrombin and antiplasminogen antibodies had a significant association with thrombosis. Levels of plasminogen activity were similar in samples from healthy controls and patients (with or without antiplasminogen antibodies or thrombosis). Anti-prothrombin antibodies and antiplasminogen antibodies occur frequently in patients with systemic autoimmune disease. Anti-prothrombin antibodies, but not antiplasminogen antibodies are a risk factor for thrombosis. Anti-plasminogen are in most cases unrelated to antiprothrombin antibodies.