Number of cases with HLA-DR expression in the arterial wall
| No | Arterial endothelium | Regions of intimal proliferation | Capillary endothelium | |
| Normal | 6 | 0 | 0 | 1 |
| IPAH untreated | 8 | 4 | 6 | 8 |
| IPAH, epoprostenol and bosentan | 6 | 1 | 2 | 1 |
| APAH | 9 | 0 | 1 | 1 |
APAH, pulmonary arterial hypertension associated with congenital heart disease; HLA, human leucocyte antigen; IPAH, idiopathic pulmonary arterial hypertension.