EDN1 and pulmonary arterial hypertension: The reason why M2 macrophage-related markers are higher in IPF than in PAH patients is probably involved in many diverse mediators, including prostaglandin (PG) E2, endothelin 1 (ET-1), transforming growth factor- (TGF-) β, or IL-6, in the development of PH [46], which need further study in the future.