Differential Patterns of Methylation of the IFN-γ Promoter at CpG and Non-CpG Sites Underlie Differences in IFN-γ Gene Expression Between Human Neonatal and Adult CD45RO− T Cells

Abstract

IFN-γ is a potent pleiotropic Th1 cytokine, the production of which is tightly regulated during fetal development. Negative control of fetal/neonatal IFN-γ production is generally attributed to the Th1-antagonistic effect of mediators produced by the placenta, but evidence exists of additional and more direct transcriptional regulation. We report that neonatal (cord blood) CD3⁺/CD45RO⁻ T cells, in particular the CD4⁺/CD45RO⁻ subset, are hypermethylated at CpG and non-CpG (CpA and CpT) sites within and adjacent to the IFN-γ promoter. In contrast, CpG methylation patterns in cord blood IFN-γ-producing CD8⁺/CD45RO⁻ T cells and CD56⁺/CD16⁺/CD3⁻ NK cells did not differ significantly from those in their adult counterparts. Consistent with this finding, IFN-γ production by stimulated naive cord blood CD4⁺ T cells is reduced 5- to 10-fold relative to adult CD4⁺ T cells, whereas production levels in neonatal and adult CD8⁺ T cells are of a similar order. Evidence of significant CpA and CpT methylation was not discovered in promoter sequence from other cytokines (IL-4, TNF-α, or IFN-γR α-chain). We additionally demonstrate that overexpression of DNA methyltransferase 3a in embryonic kidney carcinoma cells is accompanied by CpA methylation of the IFN-γ promoter.