MDM4 and idiopathic pulmonary fibrosis: To evaluate the levels of MDM4 expression in normal versus fibrotic lungs, we performed immunohistochemical (IHC) analysis on formalin-fixed, paraffin-embedded lung tissues harvested from patients with IPF, failed human donors, and aged (15-mo-old) mice subjected to intratracheal bleomycin or saline treatment.