Interleukin-6 supports human megakaryocytic proliferation and differentiation in vitro

The effect of interleukin-6 (IL-6) on cells of human megakaryocyte (MK) lineage from cord blood was explored. In semisolid colony assays containing human plasma, a greater number of both MK colonies and cells per colony was seen in the presence of IL-6 and IL-3 than in the presence of IL-3 alone. This stimulatory effect of IL-6, observed on both small and large MK colonies, was completely eliminated by the addition of anti-IL-6 antibody to the culture. IL-6 alone had no effect on MK colony formation. In the primary culture, MKs showed larger cell size and DNA content in the presence of both IL-3 and IL-6 than IL-3 alone. The replating experiments using immature MKs grown in the presence of IL-3 showed that IL-6 significantly augmented both cell size and DNA content. This effect was also neutralized by an anti-IL-6 antibody. IL-3 had no tangible effect on MK differentiation. Synergism between IL-6 and IL-3 on MK differentiation was not confirmed. These results suggest that IL-6 is a synergistic factor in the proliferation of MK progenitors and a direct effector of differentiation of immature MKs on in vitro human megakaryocytopoiesis.