Ermann 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

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... lls 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.