PGF and pulmonary hypertension: Cytokines and adhesion molecules play an important role in the pathophysiology of vaso-occlusion in SCD.6 Placenta growth factor (PlGF) is released by immature erythrocytes and is elevated in SCD and may play a role in the pathophysiology of sickle cell disease-associated pulmonary hypertension by inducing the release of vasoconstrictor substance called endothelin-1.7