occur in patients with idiopathic PPH. 6, 7 Whether these cells are derived from the endothelial progenitor cells obtained from the mobilization of bone marrow by growth factors such as VEGF, or they are sloughed off (or actively shed) from injured pulmonary vessels, is not known. Study of endothelial cell ultrastructure, and use of vascular bed-specific markers such as lung endothelial cell adhesion molecules and DANCE (developing arteries and neural crest derivatives with multiple epidermal growth factor-like domains) may help clarify the origin of these cells and further improve our understanding of the angiogenesis/vasculogenesis process in the hypertensive lungs.