Decreased Binding of Annexin V to Endothelial Cells

The cause of the exceedingly high risk of atherothrombosis in systemic lupus erythematosus (SLE) is not clear but antiphospholipid antibodies (aPL) and potentially antithrombotic annexin V have been implicated.Twenty-six women (52+/-8.2 years) with SLE and a history of cardiovascular disease (CVD) (SLE cases) were compared with 26 women with SLE but no CVD (SLE controls) and 26 healthy women (population controls). Common carotid intima-media thickness (IMT) was determined by B-mode ultrasound as a surrogate measure of atherosclerosis. Annexin V binding to human umbilical vein endothelial cells (HUVECs) as determined by flow cytometry after 24-hour culture with plasma was decreased when plasma from SLE cases was used (SLE cases versus population controls: P=0.002; SLE cases versus SLE controls P=0.02). Antibodies against cardiolipin were among IgG antibodies causing decreased binding. There was a positive association between annexin V binding and IMT (R=0.73; P<0.001) among SLE cases. Immunohistochemical analysis revealed presence of annexin V in all human atherosclerotic plaques tested, especially at sites prone to rupture.Decreased annexin V binding to endothelium caused by antibodies may represent a novel mechanism of atherothrombosis. We hypothesize that even though annexin V may promote plaque growth at some disease stages, it may also stabilize plaque.