While it is cardioprotective in conditions like atherosclerosis, its upregulation in respiratory diseases, including chronic obstructive pulmonary disease and asthma, is linked to disease severity.21,22 In PAH, recent evidence suggests that prolonged IL-33 administration increases right ventricular pressure in mice, further supporting that IL-33 contributes to the progression of PAH pathogenesis.23 However, the exact source and regulation of IL-33 in PAH remain poorly understood. This evidence concerns the gene IL33 and chronic obstructive pulmonary disease.