IFNA1 and idiopathic pulmonary arterial hypertension: Consistent with our finding of decreased number of proliferating cells in IFNα treated rats, IFNα dose-dependently inhibited the proliferation of human pulmonary artery smooth muscle cells (HPASMC) and human pulmonary artery endothelial cells (HPAEC) (Fig. 6G–H) from both control and IPAH patients.