Ability of IL-6–independent cell lines to support the growth of IL-6–dependent cell lines.

The IL-6–dependent cell lines B9 and T1165 were independently cultured (1 × 10⁴ cells/200 μL) with medium alone or medium containing 2 × 10⁴ irradiated (8.0 Gy) IL-6–independent plasmacytoma/hybridoma cells (MPC11, MOPC31C, MOPC315, or SP2/0) as feeders. Twenty-four (T1165 cells) or 72 hours (B9 cells) later, the cells were pulsed with ³H-thymidine for an additional 4 hours, and the radioactivity incorporated into DNA was determined. MPC11 cells, which are known to produce small amounts of IL-6, were included as a positive control.