IL-6 concentrations were increased in patients with IPAH vs. controls (4.6 ± 0.5 ng/L vs. 2.8 ± 0.3 ng/L; p < 0.01) and CTD-PAH versus controls (4.5 ± 0.5 ng/L vs. 2.8 ± 0.3 ng/L; p < 0.05; Figure 1C,D). Here, IL6 is linked to pulmonary arterial hypertension.