Phosphorylated plateled-derived growth factor receptor (pPDGFR)-β immunoreactivity in pulmonary vessels in SScPAH, IPAH and PVOD. (Original magnification 200×) A) pPDGFR-β immunoreactivity in endothelial cell nuclei in a small vessel with intimal fibrosis in a patient with SScPAH. B) pPDGFR-β immunoreactivity in cell nuclei in the intima of an arteriole with concentric laminar intimal fibrosis in a patient with SScPAH (see also 6B). C) pPDGFR-β immunoreactivity in cell nuclei of a small vessel and capillaries in a PVOD patient. D) pPDGFR-β immunoreactivity in the basal side of the endothelium, the thickened intima and in smooth muscle cells of the hyperplastic media of an arteriole of an IPAH patient (see also Figures 1G and 6D). E) pPDGFR-β immunoreactivity in stroma and endothelium of a plexiform lesion in an IPAH patient. Lower right quadrant parent artery. In the center a glomeruloid lesion surrounded by vein-like branches (dilatation lesions).