TGFB1 and pulmonary arterial hypertension: Because Activin A, Gremlin 1 and TGF-β are shown to regulate cell growth and proliferation in an autocrine-dependent manner [33,34,35,36], we next evaluated an impact of therapeutic anti-Activin A, anti-Gremlin 1 and anti-TGF-β antibodies on self-supported growth of human PAH PAVSMC.