Immunofluorescence study showing the expression of caveolin-1 (green) and smooth muscle α-actin (red) in pulmonary arteries from the controls (A and F), and from the patients with idiopathic pulmonary arterial hypertension (B-E) and with heritable pulmonary arterial hypertension (G-J). In controls, endothelial caveolin-1 is well preserved and there is no enhanced expression of caveolin-1 in smooth muscle layer. Two arteries each from patients, IPAH (B and C), HPAH (G and F) show loss of endothelial caveolin-1 in B and G, and the appearance of increased expression of caveolin-1 in SMC in C and H. The next panels D, E, I and J from 4 different patients show loss of endothelial caveolin-1 and enhanced expression of caveolin-1 in SMC. PAH: Pulmonary arterial hypertension; IPAH: Idiopathic PAH; HPAH: Heritable PAH; SMC: Smooth muscle cells.