HGF and pulmonary fibrosis: It has been demonstrated that HGF functions as a protective protein in pulmonary fibrosis through binding its receptor, c-met, which is expressed by many types of cells (e.g., epithelial cells, fibroblasts) (Dohi et al., 2000; Watanabe et al., 2005; Gazdhar et al., 2007; Gazdhar et al., 2013; Gazdhar et al., 2018).