Reduced fibrinolytic activity has been described in primary
antiphospholipid syndrome (PAPS) and may be responsible for thrombotic events. Some evidence supports a relationship between anti-
plasminogen (PLG)
antibodies, anti-beta(2)-glycoprotein 1 (beta(2)GP1)
antibodies, and fibrinolysis, but their relationship is still unclear. The aim of study is to evaluate the association between
IgG anti-beta(2)GP1 and
IgG anti-PLG
antibodies and
thrombosis. Two groups of consecutive patients with PAPS and
systemic lupus erythematosus (SLE): 32 patients with
lupus anticoagulant (LAC), 32 patients without LAC, and 40 healthy controls were included.
IgG against beta(2)GP1 and PLG
antibodies were measured by
enzyme-linked
immunosorbent assay, and a value above the 99th percentile of the normal healthy control was considered as positive, and their interrelationship with
thrombosis was evaluated by Pearson Chi-squared test. Cross-reactive
antibodies binding to PLG and beta(2)GP1 were determined in a competitive and cross-inhibition assay. Levels of fibrinolytic activity in the presence of
IgG fractions from patients and healthy controls were examined using a
plasmin fluorogenic substrate assay. A high frequency of
IgG anti-PLG
antibodies (35.9%) was found in 64 patients, and its presence was associated with
thrombosis (p = 0.001), which may be due to its ability to inhibit exogenous fibrinolysis. Coexistence of
IgG anti-PLG and
IgG anti-beta(2)GP1
antibodies was found in 11 of 64 patients and was related with
thrombosis (p = 0.001). Cross-reactive antibody binding to PLG and beta(2)GP1 was found in
IgG fractions from three patients and a monoclonal anti-beta(2)GP1 antibody BD4, and one of these three patients had thrombotic history. However, no significant association was found between
IgG anti-PLG and
IgG anti-beta(2)GP1
antibodies in patients. In conclusion, the prevalence of
IgG anti-PLG was high in patients with PAPS and SLE and might relate with
thrombosis. Cross-reactivity of
IgG anti-beta(2)GP1
antibodies with PLG may occur in the sera of patients.