Representative dot plots derived from analysis of intracellular IL-6 in BMMC by flow cytometry in 2 representative patients with MM.

BMMC were stimulated for 6 hours with 1 μ/mL LPS (A-E, G-M) or culture medium (F,N) in the presence of 2 μM monensin. Cells were fixed, permeabilized (C-F, I-N), and stained with PE-conjugated anti–IL-6 mAb (Y axis) and FITC-conjugated anti-syndecan-1 mAb (X axis). Shown are BMMC gate (A,G); unpermeabilized (B,H) and permeabilized (C,I) LPS-stimulated BMMC (B-C and H-I) stained with PE-conjugated anti–IL-6 mAb and isotype control; LPS-stimulated BMMC incubated with 500 U/mL recombinant IL-6 before staining and stained with PE-conjugated anti–IL-6 mAb and FITC-conjugated anti-syndecan-1 mAb (D,L); and LPS-stimulated (E,M) and unstimulated (F,N) BMMC (E,F and M,N) stained with PE-conjugated anti–IL-6 mAb and FITC-conjugated anti-syndecan-1 mAb. In panel E, I shows syndecan-1⁻/IL-6⁺ cells corresponding to paracrine IL-6 production; and II shows syndecan-1⁺/IL-6⁺ cells corresponding to autocrine IL-6 production.