A decay of Axl protein in cultured hPAECs was corresponding to its drop in pulmonary endothelium in lung specimens of patients with IPAH, as revealed by immunofluorescence staining with von Willebrand factor (vWF) and α-smooth muscle actin (α-SMA) antibodies (Fig. 9f and Supplementary Fig. 8h). Here, ACTA1 is linked to idiopathic pulmonary arterial hypertension.