Prasse et al. found that profibrotic macrophages induced fibrosis through chemokine ligand 18 (CCL-18) and that the CCL-18 concentration in BAL was significantly higher in AE-IPF patients than in those with stable IPF [39,45], which suggests that profibrotic macrophages contribute to AE-IPF pathogenesis. Here, CCL18 is linked to idiopathic pulmonary fibrosis.