Validation of gene array expression levels. Gene expression levels (left panels) were validated (right panels) using flow cytometry (A-C) or RQ-PCR (D-E). (A) CD38 expression is higher in N PCs than in MGUS PCs (P < .001) or MM PCs (P < .001). (B) CD27 expression is higher in N PCs than in MM PCs (P = .007). (C) CCR2 expression is higher in N PCs than in MGUS or MM PCs (P = .03). (D) Frizzled related protein is higher in MM PCs than in N PCs and MGUS PCs. (E) Selenoprotein P is lower in MM PCs than MGUS PCs and N PCs. (F) Gene expression levels demonstrate that XBP1 is lower in MGUS and MM PCs than in N PCS, though the level of expression is still relatively high. (G) RT-PCR for XBP1 and XBP1s demonstrates both forms are present (2 distinct bands, 442p and 416bp) in plasma cells selected from N, MGUS, and MM patients and in MM cell lines. There is a decreased expression of XBP1s in MM PCs and MM cell lines compared with N PCs and MGUS PCs.