Murine CD4CD25 Regulatory T Cells Fail to Undergo Chromatin Remodeling Across the Proximal Promoter Region of the IL-2 Gene1

CD4CD25 regulatory T cells (Treg) 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 inves-tigated the mechanism underlying one component of this naturally anergic phenotype, the inability of the Treg cells to produce IL-2 following activation. Analysis of freshly isolated murine CD4CD25 Treg and conventional CD4CD25 T cells following PMA/ ionomycin stimulation demonstrated no differences in inducible AP-1 formation, an important transcriptional complex in regu-lating 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 CD4CD25 Treg 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 CD4CD25 Treg cells, unlike conventional CD4 T cells, did not undergo chromatin remodeling following stimulation, suggesting that the inability of CD4CD25 Treg cells to secrete IL-2 following activation is controlled at the chromatin level. The Journal of Immunology, 2004, 173: 4994–5001. C D4CD25 regulatory T cells (Treg)3 are important me-diators of peripheral immune tolerance. In addition totheir unique suppressive properties, CD4CD25 Treg cells display key features of anergic T cells. When activated in vitro, CD4CD25 Treg cells fail to produce IL-2 or undergo pro-liferation under conditions that normally induce robust IL-2 pro