IRF9 and pulmonary arterial hypertension: Hence, our results demonstrated that the expression level of IRF9 was elevated in the thickened medial wall of pulmonary arterioles in multiple stimulations-induced in vivo and in vitro PAH models, which indicated that IRF9 may be involved in the process of pulmonary arteriole medial wall hyperplasia and PASMC proliferation during PAH formation.