Additional work has shown that IL-33 and ST2 expression in pulmonary vascular endothelium is increased under certain pathological conditions, such as bronchiectasis and pulmonary hypertension in humans (68), allergen airway challenge in asthmatic patients (51), and after in vivo exposure to hypoxia or cigarette smoke in mice (68, 69). Here, IL33 is linked to pulmonary hypertension.