Loss of methylation at the IFNG promoter and CNS-1 associates with the development of functional IFN-γ memory in human CD4(+) T lymphocytes

Cytokine memory for IFN-{gamma} production by effector/memory Th1 cells plays a key role in both protective and pathological immune responses. To understand the epigenetic mechanism determining the ontogeny of effector/memory Th1 cells characterized by stable effector functions, we identified a T-cell-specific methylation pattern at the IFNG promoter and CNS-1 in ex vivo effector/memory Th1 cells, and investigated methylation dynamics of these regions during the development of effector/memory Th1 cells. During Th1 differentiation, demethylation occurred at both the promoter and CNS-1 regions of IFNG as early as 16 hours, and this process was independent of cell proliferation and DNA synthesis. Using an IFN-{gamma} capture assay, we found early IFN-{gamma}-producing cells from two-day differentiating cultures acquired "permissive" levels of demethylation and developed into effector/memory Th1 cells undergoing progressive demethylation at the IFNG promoter and CNS-1 when induced by IL-12. Methylation levels of these regions in effector/memory Th1 cells of peripheral blood from rheumatoid arthritis patients correlated inversely with reduced frequencies of IFN-{gamma}-producers, coincident with recruitment of effector/memory Th1 cells to the site of inflammation. Thus, after termination of TCR stimulation, IL-12 signaling potentiates the stable functional IFN-{gamma} memory in effector/memory Th1 cells characterized by hypomethylation at the IFNG promoter and CNS-1.