The exact link between epithelial injury and CCL2 secretion are not fully determined, but stimulation with TGF-β1 or tunicamycin (mimicking ER-stress), 2 components implicated in AEC2 dysfunction in IPF, directly upregulate CCL2 secretion by isolated AEC2 (197). This evidence concerns the gene TGFB1 and idiopathic pulmonary fibrosis.