Perivascular cellular recruitment—especially of macrophages—has been described in PAH [50], with the process facilitated through a diverse array of mediators, including leukotriene signaling [51], and granulocyte-macrophage colony-stimulating factor (GM-CSF) production [52], in patients that carry a common mutation in BMPR2. This evidence concerns the gene BMPR2 and pulmonary arterial hypertension.