Cutting edge: stable epigenetic inheritance of regional IFN-gamma promoter demethylation in CD44highCD8+ T lymphocytes.

Genomic DNA methylation patterns influence the development and maintenance of function during cellular differentiation. Methylation of regulatory sequences can have long-lasting effects on gene expression if inherited in an epigenetic manner. Recent work suggests that DNA methylation has a regulatory role in differential cytokine gene expression in primary T lymphocytes. Here we show, by clonal lineage analysis, that methylation patterns in the IFN-gamma promoter exhibit long term faithful inheritance in CD44highCD8+ T cells and their progeny, through 16 cell divisions and a clonal expansion of 5 orders of magnitude. Moreover, the demethylated IFN-gamma promoter is faithfully inherited following the withdrawal of T cell stimulation and the loss of detectable IFN-gamma mRNA, consistent with passive rather than active maintenance mechanisms. This represents a form of stable cellular memory, of defined epigenetic characteristics, that may contribute to the maintenance of T cell cytokine expression patterns and T cell memory.