PTGS2 and idiopathic pulmonary fibrosis: Our current study showed that the increase in DNA methylation was correlated with increased H3K9me3 and H3K27me3 and decreased H3 and H4 acetylation at the COX-2 promoter in F-IPFs, suggesting that DNA methylation and histone modifications act cooperatively in COX-2 repression in IPF.