Here, we investigated the mechanisms associated with the decreased expression of Fas in the lung fibroblasts of mice with bleomycin-induced pulmonary fibrosis and of patients with IPF and identified several histone modifications associated with the FAS (TNFRSF6) gene promoter that are responsible for the decreased expression of Fas and resistance to Fas-mediated apoptosis. The gene discussed is FAS; the disease is idiopathic pulmonary fibrosis.