Blocking IL6 significantly improved PAH MVEC barrier functions (1629 ± 32.46 vs. 1961 ± 120.10 Ω, p = 0.01) and cell–cell contacts (4.65 ± 0.20 vs. 6.28 ± 0.73, p = 0.02) after 72-h BMP9 treatment while cell–matrix adhesion strength was maintained at levels of unstimulated conditions (5.26 ± 0.04 vs. 5.64 ± 0.19). Here, IL6 is linked to pulmonary arterial hypertension.