TLR4 and pulmonary arterial hypertension: Although TLR4 activation plays a role in the development of murine PH, the classical bacterial-derived TLR4 agonist LPS alone did not induce murine PH (Figures 6E–I), suggesting that the combination of S. mansoni eggs, their antigens, and a disrupted host microbiota plays a key role in the full establishment of Sch-PAH (Figure 7).