IL-4 and prostaglandin E2 inhibit hypomethylation of the 5′ regulatory region of IFN-γ gene during differentiation of naive CD4+ T cells

We have previously shown that prostaglandin E2 (PGE2) and IL-4 inhibit the priming of IFN-γ-production during the differentiation of naive CD4+ T cells from human cord blood by different signal-transducing mechanisms. To compare and analyse the molecular mechanisms by which PGE2 and IL-4 inhibit the priming of IFN-γ production, we investigated the effects of PGE2 and IL-4 on the methylation of the IFN-γ gene during the in vitro differentiation of naive CD4+ T cells. In human naive CD4+ T cells, which produce primarily IL-2 and a little amount of IFN-γ, the IFN-γ gene was methylated. After stimulation via TCR, CD4+ T cells produced IFN-γ and the CpG dinucleotide contained within the TATA proximal regulatory element of the IFN-γ gene was partially hypomethylated. Both IL-4 and PGE2 inhibited the hypomethylation of this site and the acquisition of IFN-γ-producing ability. In contrast to the SnaBI site in the TATA proximal regulatory element, the HpaII site in the first intron of the IFN-γ gene of the CD4+ T cells from cord blood was completely methylated even after stimulation via TCR. 5-azacytidine restored the IFN-γ-producing ability of these cells treated with IL-4 and PGE2. These findings suggest that, although the signal transduction that inhibits the priming of IFN-γ-production is different for each reagent, the protection from hypomethylation of the regulatory region of the IFN-γ gene is involved in the molecular mechanisms by which these reagents inhibit the priming of IFN-γ-production during the differentiation of human naive CD4+ T cells.