Regulation of CHOP and XBP1 RNA expression by anti-IgM. (A) Normal B cells and (B) CLL samples were stimulated with soluble (sol) or bead-bound (bead) anti-IgM for 1 or 6 hours, and expression of CHOP and XBP1 RNAs was analyzed by qPCR. Expression values were normalized so that the average value in control normal and CLL cells was set to 1.0. Graphs show mean values ± standard deviation for data obtained with 6 or 4 preparations of normal B cells (for CHOP and XBP1 analysis, respectively). For experiments with CLL, 15 samples were used to compare responses between soluble anti-IgM at 1 and 6 hours, and 10 further samples were used to compare responses to soluble and bead-bound anti-IgM. The statistical significance of differences between treated and control cells are shown for each condition (Student t test). (C) Correlation between fold induction of XBP1 and CHOP RNAs in soluble/bead-bound anti-IgM–treated CLL samples (1- and 6-hour data combined; linear regression and Spearman correlation shown).