TNF and pulmonary arterial hypertension: In addition to these known data, our study showed that, after 4 weeks of MCT administration at PAH hamster model, increases were observed in circulating levels of both ET-1 and proinflammatory cytokines TGF-β1, IL-1β and TNF-α, important mediators of tissue fibrosis, which are responsible not only for the initiation of inflammation at the respiratory level but also for pulmonary arterial remodelling that causes the activation of key molecules involved in the fibrotic process namely AP-1, ERK and FAK.