α-SMA expression was elevated in the microvessels of patients with IPAH due to muscularization of the precapillary arteries, consistent with prior reports.20 Moreover, IL-33 expression was significantly higher in the ECs of pulmonary vessels in patients with IPAH compared with healthy controls (Figure 6C). This evidence concerns the gene ACTA1 and idiopathic pulmonary arterial hypertension.