CIITA-related abrogation of STAT6, NF-AT and CBP/p300 binding to IL-4 promoter. (a) The expression patterns of IL-4, IL-2, CBP and p300 in pcDNA3·1- or CIITA-transfected Jurkat cells were examined by real-time PCR. In contrast to depressed expression of IL-4, the relative expression levels of the measured genes between pcDNA3·1- and CIITA-transfected Jurkat cells were basically unaffected (around 1·0). Fold changes were calculated by comparing CIITA-transfected cells with those transfected by pcDNA3·1 (designated as 1·0), followed by normalization to GAPDH levels. (b) The association of CBP/p300 with IL-4 promoter, however, was abrogated in the CIITA-transfected Jurkat cells stimulated with PMA plus ionomycin, as determined by ChIP assay. TSA treatment shows the recovery effect. In the experiment, the chromatin harvested from formaldehyde-fixed cells was immunoprecipitated with anti-CBP/p300 antibody and amplified by PCR with specific primers to IL-4 promoter. The binding of NFAT and STAT6 to IL-4 promoter was also blocked in CIITA-transfected cells.