CLL cells express significantly increased levels of molecules involved in alleviating the ER stress. (A) CD5⁻/B220⁺ B cells purified from 6-week-old wild-type and Eμ-TCL1 mice were stimulated with LPS for a course of 3 days, and lysed for analysis by immunoblots for indicated proteins. Results shown in each immunoblot are representative of 3 independent experiments. For each experiment, CD5⁻/B220⁺ wild-type and Eμ-TCL1 B cells were purified and pooled from at least 2 mouse spleens. (B) CD5⁻/B220⁺ B cells purified from 8-month-old wild-type mice and CD5⁺/B220⁺ CLL cells from 8-month-old Eμ-TCL1 mice were stimulated by LPS for 3 days and lysed for analysis by immunoblots for indicated proteins. Results shown in each immunoblot are representative of 3 independent experiments. For each experiment, CD5⁻/B220⁺ wild-type B cells and CD5⁺/B220⁺ CLL cells were purified and pooled from at least 2 mouse spleens. (C) Association of TCL1 with XBP-1. CD5⁻/B220⁺ B cells purified from 8-month-old wild-type mice and CD5⁺/B220⁺ CLL cells from 8-month-old Eμ-TCL1 mice were stimulated by LPS for 3 days and lysed for analysis by immunoblots for TCL1, XBP-1, p97, and actin. The anti-XBP-1 Ab was used to perform immunoprecipitations from the same lysates, and the immunoprecipitates were analyzed for the presence of TCL1 (top panel). Results shown in each immunoblot are representative of 3 independent experiments. For each experiment, CD5⁻/B220⁺ wild-type B cells and CD5⁺/B220⁺ CLL cells were purified and pooled from at least 2 mouse spleens. (D) Human CLL cell lines (MEC1, MEC2, and WaC3) and freshly purified primary human CLL cells from 2 clinical patients (patient 1 and patient 2) were analyzed by immunoblots for the expression of indicated proteins. Unspliced and spliced forms of human XBP-1 mRNA (XBP-1u and XBP-1s, respectively), and human GAPDH mRNA were detected by reverse transcription followed by PCR using specific primers. Results are representative of 3 independent experiments.