Despite our finding that IFNα prevents and reverses experimental pulmonary hypertension in 2 distinct models, chronic treatment with IFNα for hepatitis C or chronic myelogenous leukemia was associated with the onset of PH in humans and the Food and Drug Administration has labeled IFNα with a warning about the risk of PH with its use. This evidence concerns the gene IFNA2 and pulmonary arterial hypertension.