While pulmonary arteries from control subjects revealed rare CD117+ vWF (von Willebrand Factor)+, CD117+ CD31+ or CD117+ podocalyxin (PODXL)+ cells with faint CD117 staining, multiple CD117+ vWF+, CD117+ CD31+ or CD117+ PODXL+ cells were detected in the occlusive pulmonary arterial lesions of PAH patients, particularly in plexiform lesions (Fig. 1 and Supplemental Fig. S1). Here, PECAM1 is linked to pulmonary arterial hypertension.