Complex effects of interleukin 6 on clonogenic blast cell growth in acute myeloblastic leukemia

The present in vitro study shows how interleukin (IL)-6 modulates clonogenic blast cell growth in complex ways in acute myeloblastic leukemia when used either as a single factor or in different hematopoietic growth factor combinations. In the presence of IL-6, the colony numbers in culture assay decreased to 50 +/- 29% from the basal values (p < 0.001) in 10 cases and increased to 384 +/- 278% of the basal values (p < 0.01) in 5. The inhibitory effect of IL-6 on blast cell colony formation was retained when IL-6 was combined with granulocyte colony stimulating factor, but was lost if IL-6 was used in combination with mast cell growth factor, IL-3, granulocyte-macrophage colony stimulating factor, or IL-4. The stimulatory effect of IL-6 was diminished in the presence of granulocyte colony stimulating factor, but preserved in the presence of other growth factor combinations. IL-6 had a neutral effect on colony growth in 7 cases with acute myeloblastic leukemia. In these cases, however, IL-6 stimulated significantly clonogenic cell growth if combined with mast cell growth factor or granulocyte-macrophage colony stimulating factor.