Inhibitory effect of anti–IL-6 mAb on the proliferative rate of IL-6–producing MCCs.

MCCs were incubated in culture medium or the presence of 100 ng/mL anti–IL-6 mAb. Myeloma cell proliferation was evaluated by using BrdU-PI cell incorporation. The inhibitory effect of anti–IL-6 mAb was calculated as follows: (percentage of BrdU⁺ cells plus anti–IL-6 mAb divided by percentage of BrdU⁺ cells) times 100. Addition of the anti–IL-6 mAb inhibited proliferation of IL-6⁺ MCC-2, MCC-3, MCC-5, and the IM-9 cell line, whereas IL-6⁻ MCCs and the U-266-1970 cell line were only slightly affected.