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 eels to produce IL-2 following activation. Analysis of freshly isolated murine CD4⁺CD25⁺ T _reg and conventional CB4⁺CD25⁺ T cells following PMA/ ionomycin stimulation demonstrated no differences in indacible 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 constitetively 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.