Accumulation of c-kit positive cells [48] and SDF-1 and its chemokine receptor CXCR4 [13] has been described in proximity of plexiform lesions while targeting of c-kit positive cells and CXCR-4 has been shown to ameliorate pulmonary hypertension in animal models [49,50]. Here, CXCL12 is linked to pulmonary arterial hypertension.