However, both lung fibroblasts isolated from IPF patients and TGF-β1-activated lung fibroblasts have been shown to be associated with reduced PGE2 production as a result of down-regulation of cyclooxygenase-2 (COX-2), a rate-limiting enzyme responsible for PGE2 production [[3], [4], [5]]. Here, TGFB1 is linked to idiopathic pulmonary fibrosis.