FN1 and idiopathic pulmonary fibrosis: Hence in summary, coculture studies show that fibroblast-mast cell interactions increase the release of enzymes (e.g., tryptase) by mast cells as well as growth factors (e.g., HGF), and ECM proteins (e.g., α-SMA, fibronectin and collagen I) from fibroblasts which may directly contribute to fibrosis of lung tissue in IPF.