OPC cells (2 × 10⁵/mL) and U266 cells (1 × 10⁵mL) were cultured alone, or cocultured with PBMC-OCs (1 × 10⁴/mL) or primary bone marrow stromal cells (1 × 10⁵/mL) in alpha-MEM containing 1% FBS in 24-well culture plates. Cells were cultured in quadruplicate. Viable MM cell number was counted at day 4 by trypan blue staining. At the same time, culture supernatants were harvested, and IgG or Igλ concentrations were measured by ELISA. Because OPC cells secrete IgG and U266 cells secrete Igλ, respective immunoglobulin concentrations were measured. The data were expressed as means ± SD.

Significantly different from the group with OPC or U266 cells alone, P < .05, and from the group with OPC or U266 cells in the presence of stromal cells, P < .05.