Changes in histone modifications in the PU.1 gene locus and IRF4 promoter in response to Th9-inducing conditions. (A) Schematic diagram of the enhancer region of the PU.1 gene located 17 kb upstream of the PU.1 transcription start site. (B-D) Naive cord blood CD4 T cells or adult naive and memory CD4 T cells were stimulated with anti-CD3/28 in the presence of the indicated cytokines. After fixation and DNA shedding, DNA fragments were immunoprecipitated with anti-H3K4me3, anti-H3ac, or anti-H3K27me3 Abs. Eluted DNA was analyzed by quantitative PCR using primers spanning the promoter region of PU.1 (B), the PU.1 upstream enhancer region (C), and the promoter region of IRF4 (D). The mean ± SEM of at least 3 independent experiments with cells from different donors is shown. *P < .05; **P < .01; ***P < .001 by Student t test.