Mechanisms of thrombosis in systemic lupus erythematosus and antiphospholipid syndrome

The presence of antiphospholipid antibodies is one of the most common acquired risk factors for thrombosis. Antiphospholipid antibodies is a collective term for a set of autoantibodies with closely related but different specificity. Experiments in which isolated patient antibodies were injected into mice have shown that a specific subset of autoantibodies, those directed against the first domain of plasma protein β₂-glycoprotein I, can explain the increased risk of thrombosis. Experiments performed with these mice have shown that autoantibodies against β₂-glycoprotein I bind to and activate cells such as endothelial cells, monocytes, and platelets. Activation of these cells, all involved in the regulation of hemostasis, results in a shift towards a prothrombotic state. How this process is regulated, whether this is the only mechanism involved, and whether this is the only subpopulation responsible for the increased thrombotic risk is unknown. In this review, we will critically discuss what is known and what is debatable on the pathophysiology of antiphospholipid syndrome.