Direct repression of BLIMP1 and XBP-1 by Spi-B. Peripheral blood CD19⁺ B cells transduced with Spi-B/fl∼ER-GFP, Spi-B/ΔEts∼ER, or control GFP vector were cultured in conditions allowing for plasma cell differentiation (as in Figure 1) and sorted for GFP expression. After sorting, the cells were preincubated with cycloheximide (CHX) before addition of 4-hydroxytamoxifen (4HT) for 4 hours. Gene expression levels were analyzed by quantitative RT-PCR. Values are normalized to expression in samples without 4HT treatment. Mean plus or minus SD values of PCR duplicates are shown. One representative experiment of 2 is shown.