In vitro and in vivo differentiated effector CD8 T cells display divergent histone acetylation patterns within the Ifng locus.

Epigenetic remodeling of genes encoding effector cytokines that permit accessibility to the transcriptional machinery is a central event in the differentiation of naive T cells into effectors that can attack pathogens and tumors. Covalent modifications of histones that cause a loosening of nucleosomal structures occur not only in promoter regions, but also at upstream and downstream enhancer elements that integrate various cellular stimuli to modulate the rate of transcriptional initiation. This knowledge derives mostly from the analysis of in vitro differentiated effector T cells. Here, we compared acetylation of histone H3 (AcH3) at several sites within the Ifng locus in CD8 T cells that underwent effector differentiation in vitro vs. in vivo. While AcH3 was similar at the proximal promoter, it displayed a reciprocal pattern at two well-characterized upstream and downstream sites. These data suggest that certain epigenetic remodeling events may be artifactual consequences of in vitro culturing conditions, and indicate the importance of using in vivo models to study effector cytokine gene remodeling.