The parallel changes of PPAR-γ and a group of fibrosis related genes observed between murine PPAR-γ deficient macrophages (from influenza virus infection) and macrophages from pulmonary fibrosis patients might reflect important roles of PPAR-γ in macrophages in regulating the development and/or maintenance of progressive fibrosis leading to respiratory failure in IPF patients. The gene discussed is PPARG; the disease is idiopathic pulmonary fibrosis.