Pathologic differences between systemic sclerosis-associated and idiopathic pulmonary arterial hypertension

Advances in pulmonary arterial hypertension therapies have led to improvements in the quality of life and survival for patients with idiopathic pulmonary arterial hypertension, but these trends have not uniformly translated to patients with systemic sclerosis-associated pulmonary arterial hypertension. In order to better understand the heterogeneity in treatment response and survival, we aimed to examine the histological and immunophenotypic differences between the systemic sclerosis-associated pulmonary arterial hypertension and idiopathic pulmonary arterial hypertension pulmonary vasculopathies. We performed a semi-quantitative lung morphometry-based analysis comparing sections obtained from systemic sclerosis-associated pulmonary arterial hypertension (n = 24), idiopathic pulmonary arterial hypertension (n = 9), and control (n = 13) bio-banked lung tissue specimens. H&E (Hematoxylin and Eosin) and VVG (Verhoeff-Van Gieson)-stained lung sections were analyzed for interstitial and vascular pathology. Immunohistochemistry was used to stain for an array of inflammatory and fibrosis mediators. Baseline demographic and hemodynamic data for each patient were collected via chart review at the time of lung explantation. Plexiform lesions were present in 5/9 (55%) of idiopathic pulmonary arterial hypertension samples, but absent in all systemic sclerosis-associated pulmonary arterial hypertension samples (0/24). Systemic sclerosis-associated pulmonary arterial hypertension lungs demonstrated significantly worse interstitial fibrosis (p = 0.0001) and interstitial cellularity (p = 0.0002) compared to idiopathic pulmonary arterial hypertension lungs. The degree of smooth muscle hypertrophy and pulmonary artery intimal proliferation were not different between systemic sclerosis-associated pulmonary arterial hypertension and idiopathic pulmonary arterial hypertension lungs. Immunohistochemistry analysis revealed that systemic sclerosis-associated pulmonary arterial hypertension lungs exhibited increased interstitial infiltration of CD3 T-cells (p = 0.009), CD20 B-cells (p = 0.01), and CD163 macrophages (p = 0.048) when compared to idiopathic pulmonary arterial hypertension and control lungs. Systemic sclerosis-associated pulmonary arterial hypertension lungs display a distinct pulmonary vascular pathology as well as significant interstitial fibrosis when compared to idiopathic pulmonary arterial hypertension lungs.