Rapid demethylation of the IFN-gamma gene occurs in memory but not naive CD8 T cells.
DNA methylation is an epigenetic mechanism of gene regulation. We have determined that specific modifications in DNA methylation at the IFN-gamma locus occur during memory CD8 T cell differentiation in vivo. Expression of the antiviral cytokine IFN-gamma in CD8 T cells is highly developmental stage specific. Most naive cells must divide before they express IFN-gamma, while memory cells vigorously express IFN-gamma before cell division. Ag-specific CD8 T cells were obtained during viral infection of mice and examined directly ex vivo. Naive cells had an IFN-gamma locus with extensive methylation at three specific CpG sites. An inhibitor of methylation increased the amount of IFN-gamma in naive cells, indicating that methylation contributes to the slow and meager production of IFN-gamma. Effectors were unmethylated and produced large amounts of IFN-gamma. Interestingly, while memory cells were also able to produce large amounts of IFN-gamma, the gene was partially methylated at the three CpG sites. Within 5 h of antigenic stimulation, however, the gene was rapidly demethylated in memory cells. This was independent of DNA synthesis and cell division, suggesting a yet unidentified demethylase. Rapid demethylation of the IFN-gamma promoter by an enzymatic factor only in memory cells would be a novel mechanism of differential gene regulation. This differentiation stage-specific mechanism reflects a basic immunologic principle: naive cells need to expand before becoming an effective defense factor, whereas memory cells with already increased precursor frequency can rapidly mount effector functions to eliminate reinfecting pathogens in a strictly Ag-dependent fashion.
Kersh
Ellen N
EN
Emory Vaccine Center and Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Fitzpatrick
David R
DR
Murali-Krishna
Kaja
K
Shires
John
J
Speck
Samuel H
SH
Boss
Jeremy M
JM
Ahmed
Rafi
R
D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D018414:CD8-Positive T-Lymphocytes / Q000737:chemistry / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D002478:Cells, Cultured; D018899:CpG Islands; D004247:DNA / Q000737:chemistry / Q000235:genetics; D019175:DNA Methylation; D005786:Gene Expression Regulation / Q000187:drug effects; D007113:Immunity, Innate / Q000187:drug effects / Q000276:immunology*; D007156:Immunologic Memory / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D007371:Interferon-gamma / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D007376:Interleukin-2 / Q000235:genetics; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics
D007376:Interleukin-2; D012333:RNA, Messenger; D007371:Interferon-gamma; D004247:DNA; D001374:Azacitidine