Regulation of BIP and PERK expression by anti-IgM. CLL samples (n = 15) were stimulated with soluble (sol) or bead-bound (bead) anti-IgM or thapsigargin as a control (TG; 15 μM) for up to 24 hours, and expression of PERK, BIP, and phosphorylated ERK1/2 was analyzed by immunoblotting. (A) Representative results from 2 CLL samples. Phosphorylated and nonphosphorylated forms of PERK are indicated by white and black triangles, respectively. (B) Quantitation of results. Expression values were normalized so that the average value in control cells at each time point was set to 1.0, and graphs show mean values (±standard deviation). The statistical significance of differences is shown. Vertical values show the P values for difference between that condition and control cells, whereas horizontal values show P values for the differences between soluble and bead-bound anti-IgM–treated samples at each time point (paired Student t test). (C) Correlation between fold induction of PERK and BIP in soluble/bead-bound anti-IgM–treated CLL samples (3-, 6-, and 24-hour data combined; linear regression and Spearman correlation shown).