TGFB1 and pulmonary fibrosis: Transforming growth factor β1 (TGFB1/TGFβ1) is the main pro-fibrotic cytokine in the progression of idiopathic pulmonary fibrosis, which induces lung fibroblasts to differentiate into myofibroblasts that produce high levels of collagen, resulting in a loss of lung elasticity and function.