Intensity of plateled-derived growth factor-receptor (PDGFR)-β-immunostaining in the intima of pulmonary vessels in SScPAH, IPAH, PVOD and controls. A: arterioles. B: small vessels.For the pooled arterioles and small vessels, intensity in SScPAH was stronger than in IPAH (P = 0.02). Each image represents one case. Small vessels: those arterioles and/or venules that cannot be distinguished as such based on their anatomical localisation.