IL13 and pulmonary arterial hypertension: Inflammatory cytokines relevant to PAH pathogenesis, such as IL-1β, IL-6, IL-8, IP-10, IL-12p40, IL-13 and IL-18, are elevated in the blood [5,75,77-81], lungs [82,83] and RV [40,74] of PAH patients, and levels of these cytokines correlate directly with disease severity and mortality [77,78,81].