The cellular sources for the upregulation of the three isoforms of TGF-β (of which TGF-β1 is the most prevalent isoform found in pulmonary fibrosis) are the bronchial epithelium, myofibroblasts, alveolar macrophages, eosinophils, and hyperplastic type II alveolar epithelial cells (AECs) [14]. Here, TGFB1 is linked to pulmonary fibrosis.