Antibodies to Phospholipid-Binding Plasma Proteins and Occurrence of Thrombosis in Patients with Systemic Lupus Erythematosus

Abstract

There is accumulating evidence that anti-phospholipid (aPL) antibodies in the sera of patients with autoimmune diseases bind to a complex of anionic phospholipids and plasma phospholipid-binding proteins, namely β2-glycoprotein I (β2-GPI) and prothrombin. It has been suggested that a conformational change in β2-GPI, induced by binding either to anionic phospholipids or to the oxygen molecules on the irradiated microtiter plate, reveals cryptic antigenic epitope(s) in the native protein. We used an enzyme-linked immunoassay for measuring antibodies against two phospholipid-binding proteins, i.e., β2-GPI and prothrombin, absorbed to an irradiated plate in an unselected series of 139 patients with systemic lupus erythematosus (SLE). Elevated levels of antibodies against β2-GPI were found in 49% of patients and antibodies against prothrombin in 34% of patients. Both antibodies were significantly associated with deep venous thrombosis in patients with SLE (P= 0.009 for both antibodies). Accordingly, testing of these antibodies seems to be clinically useful in evaluating the risk of thrombosis.