show Abstracthide AbstractBacterial pulmonary infections are a major cause of morbidity and mortality in neonates, with less severity in older children (juveniles). Previous studies demonstrated that CD4+ T cells in the mouse lung, whose primary responsibility is coordinating the immune response foreign pathogens, are differentially methylated in neonates compared with juveniles. Nevertheless, the effect of this differential methylation on CD4+ T cell gene expression and response to infection remains unclear. We treated E. coli-infected neonatal (4-day-old) and juvenile (13-day-old) mice with decitabine (DAC), a DNA methyltransferase inhibitor with broad-spectrum DNA demethylating activity, and performed simultaneous genome-wide DNA methylation and transcriptional profiling on lung CD4+ T cells. Juvenile and neonatal mice experienced differential demethylation in response to DAC treatment, with larger methylation differences observed in neonates. By cross-filtering differentially expressed genes between juveniles and neonates with those sites that were demethylated in neonates, we found that interferon-responsive genes such as Ifit1 are the most down-regulated methylation-sensitive genes in neonatal mice. DAC treatment shifted neonatal lung CD4+ T cells toward a gene expression program similar to that of juveniles. Following lung infection with E. coli, lung CD4+ T cells in neonatal mice exhibit epigenetic repression of important host defense pathways, which are activated by inhibition of DNA methyltransferase activity to resemble a more mature profile. Overall design: 4 mRRBS replicates were generated from CD4 T cells isolated from mouse lungs for each of the following experimental cohorts: neonatal (P4) DMSO-treatment (control), neonatal DAC-treatment, juvenile (P13) DMSO-treatment (control), and juvenile DAC-treatment. All mice were infected with E. coli prior to DAC/DMSO treatment.