Bortezomib inhibits XBP1 splicing in pDCs. Purified pDCs, the pDC tumor cell line CAL-1, the myeloma cell line RPMI 8226, or resting T cells were cultured without or with 100nM bortezomib for 1 hour, and 5 μg/mL tunicamycin (Tm) was added 4 hours before harvest. The expression levels of XBP1u and XBP1s mRNA were measured by real-time RT-PCR and normalized to those of GUS. The XBP1s/XBP1u ratios were calculated. The data are normalized to the value obtained with tunicamycin in the absence of bortezomib. *P < .05; **P < .01. The data are shown as means ± SE of 3 (pDC) or 4 (CAL-1, RPMI8226, T) independent experiments.