TIMP1 and idiopathic pulmonary fibrosis: With the aim of recapitulating the in vivo evidence on the role of epithelial alveolar cells and macrophages in MMP and TIMP production, we performed in vitro experiments using respective human cell types, namely, epithelial alveolar type II cells (A549), human primary monocytes/macrophages, and human lung fibroblasts (MRC5 cell line and primary IPF fibroblasts).