In addition to infiltration of pulmonary immune cells, elevated levels of serum inflammatory cytokines and chemokines have been reported in patients with PAH [32], and some elevated levels of inflammatory cytokines, such as IL-1β and IL-6, have been shown to predict survival in idiopathic and familial pulmonary arterial hypertension [33]. Here, IL6 is linked to heritable pulmonary arterial hypertension.