Proliferation response of XG cells in the presence of agonist anti-gp130 MoAbs. XG-1 or XG-2 myeloma cells were extensively washed and cultured for 5 days with various concentrations of a mixture (1:1) of agonist anti-gp130 MoAbs or of control murine IgG1 or of IL-6. At the end of the culture, the proliferation was assayed by tritiated thymidine incorporation. XG-1 cells were cultured with B-S12 + B-P8 antibodies and XG-2 cells with B1 + I2 antibodies. Results are the mean ± SD tritiated thymidine incorporation determined on sextuplate culture wells. For some points, the SD was too small to be visible on the graph.