Effects of a neutralizing antibody to vIL-6 on the proliferation of BCBL-1 and BC-1 cells. Cells (5 × 10³cells/microwell) from the BCBL-1 and BC-1 cell lines were cultured for 3 days with or without the addition of 25% autologous conditioned medium either alone or in the presence of a rabbit neutralizing antibody (5 μg/mL) against vIL-6, control rabbit IgG (5 μg/mL), a MoAb against human IL-10 (19F1; 5 μg/mL), or anti–vIL-6 plus antihuman IL-10 antibodies (each at 5 μg/mL). Selected cultures were supplemented with recombinant purified vIL-6 (MBP-vIL-6; 50 ng/mL) or human IL-10 (25 ng/mL). ³H thymidine was added during the final 20 hours of culture. The results represent the mean (±SD) radioactivity of triplicate cultures.