MMP12 and idiopathic pulmonary fibrosis: In consistent with the idea, as was indicated in PPAR-γ deficient macrophages from influenza infected mice 30 days after viral infection (20 days after viral clearance), there were differences in pro-inflammatory (Ccl2), growth factor (Pdgfa), and fibrosis-associated gene expression (Mmp7, Mmp12, and Timp1) in macrophages from human IPF patients versus healthy control (Fig 3B).