Background: Idiopathic pulmonary fibrosis (IPF) is characterized by abnormally activated fibroblasts, differentiated into myofibroblasts, modulating the extracellular matrix (ECM). The altered ECM further propagates the disease by affecting additional cells. Our established IPF fibroblast-conditioned matrix (IPF-CM) system, utilizing primary human lung fibroblasts (HLFs) was shown as a relevant platform for testing drug candidates in IPF. Aim and Objectives: To test the involvement of PGE2 in the IPF-CM system.Methods: Primary normal/IPF derived HLFs (N/IPF-HLF) were cultured on Matrigel for 48hr, then removed by NH4OH to create the N/IPF-CM. N-HLF were exposed to the IPF-CM system with/ without PGE2 (1nM), and phosphodiesterase-4 (PDE4) inhibitor roflumilast N-oxide (1µM) for 24hr. N-HLF cultured on N-CM served as control. The effect of IPF-CM on aggregate size, cell number and pro-fibrotic gene expression (e.g., MMP2, ?SMA, COL1A, TGFB1, and IL-8) was tested.Results: N-HLF cultured on IPF-CM arranged in large aggregates due to increased proliferation, migration and differentiation, in addition to increased pro-fibrotic gene expression. Addition of PGE2 induced partial responses in the N-HLF. Roflumilast, with the addition of PGE2 blocked the large aggregate formation induced by the IPF-CM, as well as other cellular responses. The 'HIF-1 signaling pathway' was significantly affected (P<0.0001), as well as TGFB1 and IL-8 expression.Conclusions: The combination of PGE2 and roflumilast inhibited the pro-fibrotic effects of the IPF-CM on N-HLF cells. These findings should be further investigated