In the middle and late stages of the disease, IL-33 induces ILC2 hyperactivation, differentiation of alternately activated M2 macrophages, and the secretion of TGF-β and IL-13 from mast cells, resulting in the transformation of epithelial cells to mesenchymal cells and leading to pulmonary fibrosis. Here, TGFB1 is linked to pulmonary fibrosis.