KIT and pulmonary arterial hypertension: Our group has previously described the implication of CD117+ cells, comprising tryptase-positive mast cells and tryptase-negative bone-marrow derived progenitor cells in human PAH [24], and increase of pulmonary mast cells has been described in human PAH [25], as well as in experimental left-heart independent and left-heart-dependent PH-models [26,27].