CXCR4 and pulmonary arterial hypertension: Although Young et al. reported that inhibition of CXCR4 activity by AMD3100 decreased hypoxia-induced pulmonary hypertension and vascular remodeling in neonatal mice, which was accompanied with decreased expression of some stem cell markers in the mouse lungs, they did not show any direct evidence to demonstrate the relationship between bone marrow cell migration and the development of pulmonary hypertension.