Transforming growth factor β1 (TGF-β1) is a polypeptide member of the transforming growth factor β superfamily with a variety of cytological functions, including regulation of cell growth, proliferation, differentiation, and apoptosis. TGF-β and TGFA synergistically induce transformation. It also acts as a negative autocrine growth factor. Dysregulation of TGF-β activation and signaling may lead to apoptosis. Many cells can synthesize TGF-β, and almost all have specific receptors. TGF-β1, TGF-β2, and TGF-β3 all function through the same receptor signaling pathway. TGF-β1 plays an important role in the regulation of the immune system and has different activities on different types of cells or cells at different stages of development. Most immune cells (or white blood cells) secrete TGF-β1. TGF-β1 is associated with cancer, autoimmune disease, liver disease, kidney disease, diabetes, cardiovascular disease, asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF).