Cell-cell contact between MM cells and OCs enhanced MM cell growth. OPC cells (2 × 105/mL) were cultured in the presence or absence of PBMC-OCs (1 × 104/mL) in 24-well culture plates in quadruplicate for 7 days. Cell-cell contact was prevented by membrane filters in the indicated wells. (A) Culture supernatants were harvested at day 2, and IL-6 concentrations were measured by ELISA. (B) Either anti–IL-6 neutralizing antibody or control mouse IgG was added at 20 μg/mL to the indicated wells. (C) OPC cells (2 × 105/mL) were cocultured with a mouse preosteoclastic cell line, C7 (1 × 104/mL) for 7 days. Viable cell number was counted by trypan blue staining. Horizontal dashed lines indicate baseline. The data are expressed as means ± SD of the percentage of change from the baseline. *Significantly different by one-way ANOVA with Scheffe post hoc tests, P < .05.
