A beneficial role for IL-10 has been well described in acute inflammatory conditions such as asthma and acute respiratory distress syndrome, but its role in diseases marked by pathological fibrosis is less clear.43–48 These include both restrictive diseases of the pulmonary interstitium, perhaps best exemplified by idiopathic pulmonary fibrosis (IPF), and pulmonary vascular pathologies, as seen in the fibrotic vascular remodeling that characterizes pulmonary hypertension. Here, IL10 is linked to pulmonary arterial hypertension.