Pathogenic effects of aPL were first described by the demonstration that in vitro incubation of endothelial cells or monocytes with aPL induce an endothelial dysfunction characterized by pro-coagulant (overexpression of tissue factor and modulation of protein C and S), pro-inflammatory (increased level of IL-6(interleukin 6) , IL-1β and TNFα) and pro-adhesive (increased levels of ICAM-1(intercellular adhesion molecule ), VCAM-1 (vascular endothelial cell adhesion molecule) and E-selectin) phenotypes. In parallel the investigators and others reported that endothelial function, assessed by flow mediated dilatation, is altered in patients with primary and secondary forms of APS. Although a role for TLR (toll-like receptor )-mediated NFkB translocation has been advanced, the pathogenic mechanisms that lead to in vivo endothelial injury in APS are incompletely understood.