IL10 and pulmonary arterial hypertension: High baseline levels of IL-10 are seen in the serum of patients with PAH, which could be interpreted as a protective anti-inflammatory measure occurring in response to an ongoing injury process.43 Interestingly, patients with severe PAH being treated with intravenous prostacyclin agonists actually had higher circulating IL-10 levels compared with untreated counterparts.63 Whether these observations suggest that PAH target therapies amplify an immunoprotective response or, conversely, that IL-10 is a marker of disease severity, is unclear.