Beta-2-glycoprotein I expression on monocytes is increased in anti-phospholipid antibody syndrome and correlates with tissue factor expression

It is well known that monocytes may play an active role in thrombogenesis, since they may express on their surface tissue factor, the major initiator of the clotting cascade. The results of this investigation demonstrate beta-2-glycoprotein I (beta(2)-GPI) mRNA expression by human peripheral blood monocytes, indicating that these cells synthesize beta(2)-GPI. In addition, we show beta(2)-GPI expression on cell surface of these cells by flow cytometric analysis, and the presence of this protein in cell lysate by Western blot. Interestingly, beta(2)-GPI expression on monocytes is significantly increased in patients with antiphospholipid syndrome (APS) or systemic lupus erythematosus (SLE) as against healthy blood donors and correlates with tissue factor expression on monocytes. These findings support the view that monocytes are able to synthesize beta(2)-GPI and suggest that patients with APS may have increased beta(2)-GPI exposure on cell surface, which leads to persistently high monocyte tissue factor expression and consequently to a prothrombotic diathesis.