Egr-1 staining in human PAH lesions. A: Egr-1 staining of a normal lung vessel from a control subject free of lung disease (original magnification, ×200). B: Egr-1 staining of vessel with media hypertrophy in PAH patient associated with a congenital cardiac shunt (original magnification, ×200). C: Egr-1 staining of plexiform lesion in PAH patient associated with a congenital cardiac shunt (original magnification, ×200). D: Enlarged view of the same vessel in A, showing no Egr-1 staining. E: Enlarged view of the same vessel in B, showing marked Egr-1 staining in the endothelial layer. F: Enlarged view of the plexiform lesion in C, showing Egr-1 staining mainly in endothelial cells bordering the lumen (arrows). G: Egr-1 staining of a larger plexiform lesion (original magnification, ×100) showing as similar pattern of Egr-1 expression (arrows) compared with F. H: Egr-1 staining of a concentric intima lesion with diffuse staining throughout the vessel wall. Scale bar = 100 μm.