Monocyte and Haemostasis

Human monocytes may play a central role in haemostasis since they are the only circulating blood cells capable to express tissue factor (TF) and therefore trigger the extrinsic pathway of coagulation. The aim of this review is to illustrate that monocytes also participate in haemostasis independently of TF expression. Indeed, the exposure of anionic phospholipids provides a procoagulant surface. Activation of factor X involves specific membrane receptor EPR-1 (Effector cell Protease Receptor-1). Mac-1 and membrane factor Va also bind factor X/Xa. In addition, monocytic proteases have been reported to modulate the coagulation cascade. Monocyte adhesion and cell-cell interactions represent important mechanisms implicated in TF expression. Furthermore, Tissue factor pathway inhibitor (TFPI), the natural inhibitor of TF activity, is expressed by monocytes. This suggests that monocytes could participate to the local regulation of coagulation initiation. The importance of monocytes in the development of vascular diseases remains to be clarified. In thrombotic disorders, it may be worthwhile not to limit the investigations to the expression of TF.