Histone H3K9 acetylation prior to rapid and robust gene expression. (A) High levels of H3K9 acetylation precede activation-induced gene expression changes in memory CD8⁺ T cells. The relative gene expression levels of 5 activated memory cell highly expressed genes in resting (left) and activated (middle) memory cells versus naive cells, and the levels of H3K9 acetylation of resting memory cells versus naive cells (right). Gene expression levels are presented as the mean ± SEM in log₁₀ scale (n = 5 for RT-PCR), and the dashed line represents a 2-fold difference. The H3K9 acetylation levels are presented as the mean fraction of input ± SEM of naive and memory cells (n = 8-12, P < .01). (B) Increased levels of H3K9 acetylation and mRNA after TSA treatment in naive CD8⁺ T cells. The relative changes of H3K9 acetylation levels were determined by ChIP and real-time PCR between TSA-treated and untreated naive CD8⁺ T cells (left) and the relative levels of mRNA of the same 4 genes (right) between TSA-treated and untreated naive CD8⁺ T cells after anti-CD3/CD28 stimulation for 24 hours. H3K9 acetylation levels are presented as the mean fraction of input of TSA-treated and untreated naive CD8⁺ T cells (mean ± SEM, n = 4-6, P < .01). mRNA levels are presented as the ratio (mean ± SEM, n = 4-6) of TSA-treated and untreated naive CD8⁺ T cells in log₁₀ scale.