To further verify the presence of altered macrophage polarization in PAH patients, it was investigated that an M1/M2 imbalance was observed between macrophage low (MacLow) bone marrow-derived macrophages in men and monocyte-derived macrophages in PAH patients under doxycycline and interleukin-4 (IL-4) stimulation. Here, IL4 is linked to pulmonary arterial hypertension.