Effects of IL-3 on the growth of myeloma cells. The IL-6–dependent myeloma-derived KAS6/1 cells were treated with 1 ng/mL IL-3 in the absence (A) and presence (B) of IL-6 (1 ng/mL). IL-3 significantly increased the growth of KAS 6/1 cells in the absence of IL-6 compared with nontreated control culture. IL-6 (1 ng/mL) did not further increase the growth of KAS6/1 cells by induced IL-3, and addition of an anti–IL-6 neutralizing antibody (100 ng/mL) to the cultures did not block the growth of KAS6/1 cells induced by IL-3 (B). IL-3 also increased the growth of the IL-6–independent MM.1S cells (C), and the enhanced growth was not blocked by an anti–IL-6 neutralizing antibody (D). Results represent the mean ± SEM for triplicate determinations for a typical experiment. Similar results were seen in 2 independent experiments (^*P < .05).