Changes in histone H4 acetylation level at IRF1 promoter, their relation with the level of IRF1 transcripts, and HDAC2 recruitments after IFN-γ stimulation. (A) Ex vivo PBMCs from HIV-S (n = 10, ▵) and HIV-R (n = 11, □) individuals were stimulated with exogenous IFN-γ (10 ng/mL). At the indicated time points, chromatin was isolated and immunoprecipitated with antibodies specific for acetylated histone H4. Chromatin-immunoprecipitated DNA products were analyzed for the presence of IRF1 promoter using quantitative PCR. Quantitative PCR signals were normalized to input DNA. There was no difference in the level of acetylated histone H4 between the unstimulated samples cultured in media alone for 0, 60, or 180 minutes. Unstimulated sample from time = 0 is used as reference for calculating relative fold increases. (B) The correlation between the IRF1 primary transcripts level (from Figure 2A) and the level of histone H4 acetylation at IRF1 promoter (from Figure 4A) in each study group was analyzed using Pearson correlation test. The results of linear regression were graphed with 95% confidence interval for each group. The results of Pearson correlation analyses were tabulated.