VWF and idiopathic pulmonary arterial hypertension: Immunofluorescent staining found that strong intensity staining of PRDC, colocalized with smooth muscle α-actin (a smooth muscle marker) and von Willebrand factor (an endothelium biomarker), presented in normal pulmonary arteries of control human lungs (Figure 1D4, E4), but slight staining of PRDC in severely remodeled and obliterated pulmonary arteries of lungs from patients with IPAH (Figure 1D8, E8).