TGFB1 and heritable pulmonary arterial hypertension: We used eight PAECs lines—four from patients (two IPAH and two HPAH) and four from controls—and subjected them to stimulation with three different growth factors/signalling molecules that are relevant for endothelial cells: vascular endothelial growth factor (VEGF; 10 ng/ml), transforming growth factor beta (TGFβ; 10 ng/ml), and serotonin (10uM), each for 24 h.