Increased production of HGF and SDF-1α by primary human pulmonary arterial endothelial cells (PAECs) from PAH. (A) HGF and SDF-1α is secreted by PAH PAEC in culture at higher levels than by control cells under both normoxia and hypoxia conditions (*all P < .05). HGF secretion by PAH PAEC was significantly increased on exposure to hypoxia (ANOVA P = .0001). SDF-1α levels also significantly increased with hypoxia in both PAH (ANOVA P = .0001) and control PAEC (ANOVA P = .0007). (B) HGF and SDF-1α in lung tissues from controls and PAH patients. Endothelial cells in plexiform lesions of PAH lungs had strong positive immunoreactivity for HGF (arrowheads identify endothelial cells lining vascular lumens). Endothelial cells of control lung expressed HGF, but immunopositivity was much less prominent (arrowheads). SDF-1α expression was present in endothelial cells of plexiform lesions in PAH lung (arrowheads). Only mild immunopositivity for SDF-1α was found in vessel endothelium of control lung (arrowheads). Scale bars: 40 μm.