The cascade of biological events leading to clot formation in vascular APS. Loss of tolerance against PL-binding proteins leads to aPL production (first hit), which is not enough by itself for triggering a clot. A second hit responsible for the increase in endothelial β2GPI in the presence of complement activation allows the clustering of β2GPI/membrane receptor complexes and cell signaling. A second wave of cells involved in the coagulation amplifies thrombus formation