TLR4 and pulmonary arterial hypertension: PDGF drives pulmonary vascular wall hypertrophy as it is significantly increased in lung tissue from PAH patient in comparison to control lungs, similar to many other mitogenic and inflammatory factors (TGF-β1, TLR-4, IL-1β, IL-18, etc.)(Raines and Ferri, 2005; Schermuly et al., 2005; Batton et al., 2018).