SERPINE2 (Protease nexin-1, PN1) is a specific and extremely efficient inhibitor of thrombin. Unlike other thrombin inhibitors belonging to the serpin family, SERPINE2 does not circulate in the blood (Bouton et al. 2012). Rather, it is bound to glycosaminoglycans on the surface of cell types including macrophages, smooth muscle cells and platelets, where it inhibits the signaling functions of thrombin. SERPINE2 sets the threshold for thrombin-induced platelet activation (Gronke et al. 1987, Boulaftali et al. 2010) and has been implicated in atherosclerosis (Bouton et al. 2012). Recent studies have demonstrated an important antithrombotic effect of platelet SERPINE2 in vitro and in vivo (Boulaftali et al. 2010).