Murine CD4+ CD25+ regulatory T cells fail to undergo chromatin remodeling across the proximal promoter region of the IL-2 gene

CD4(+)CD25(+) regulatory T cells (T-reg) acquire unique immunosuppressive properties while maintaining an anergy phenotype when activated in vitro under conditions that induce IL-2 production and proliferation in conventional CD4(+) T cells. We investigated the mechanism underlying one component of this naturally anergic phenotype, the inability of the T-reg cells to produce IL-2 following activation. Analysis of freshly isolated murine CD4(+)CD25(+) T-reg and conventional CD4(+)CD25(-) T cells following PMA/ ionomycin stimulation demonstrated no differences in inducible AP-1 formation, an important transcriptional complex in regulating IL-2 gene expression. Although p38 MAPK and ERK1/2 protein kinases were phosphorylated with similar kinetics, we observed diminished activation of JNK in the CD4(+)CD25(+) T-reg cells. However, lentiviral-mediated reconstitution of the JNK pathway using a constitutively active construct did not overcome the block in IL-2 synthesis. Using a PCR-based chromatin accessibility assay we found that the minimal IL-2 promoter region of CD4(+)CD25(+) T-reg cells, unlike conventional CD4 T cells, did not undergo chromatin remodeling following stimulation, suggesting that the inability of CD4(+)CD25(+) T-reg cells to secrete IL-2 following activation is controlled at the chromatin level.