TGFB1 and chronic thromboembolic pulmonary hypertension: Accordingly, with previous in vitro studies showing that TGF-β induces ET-1 production in pulmonary arterial smooth muscle cells (PASMCs) [31] and endothelial cells [32], we have found a significant correlation between preoperative plasma ET-1 and TGF-β levels in the analyzed population of patients with CTEPH awaiting surgical treatment.