Analysis of immunostained lung sections revealed that the endothelial markers CD31, CD34, and VE-cadherin show diffuse staining in the intima and plexiform lesions of PAH samples and sometimes co-localize with ACTA2 expression, as opposed to strong staining of the thin endothelial layer adjacent to ACTA2+ VSMCs in the non-PAH group [18]. This evidence concerns the gene CD34 and pulmonary arterial hypertension.