IL‐6 and SCF exert different effects on megakaryocyte maturation

Megakaryocytic maturation has two aspects, nuclear maturation and cytoplasmic maturation, both of which are affected by several thrombopoietic cytokines. We cultured murine bone marrow cells separated by BSA velocity sedimentation which contained more immature megakaryocytes with lower ploidy in order to study the effects of rhIL-6 and rmSCF on the two aspects of megakaryocyte maturation. During culture with rhIL-6 or rmSCF for 4 d, the megakaryocytes underwent endomitosis, resulting in DNA polyploidization. These two cytokines had different effects on cytoplasmic maturation. Flow cytometry showed that the megakaryocytes cultured with rhIL-6 became larger and had a more complex intracellular structure than those cultured with rmSCF. Morphological studies showed that the megakaryocytes cultured with rhIL-6 were larger and more granular, whereas those cultured with rmSCF were smaller and more basophilic. rhIL-6 promoted cytoplasmic process formation by the megakaryocytes, but rmSCF did not. Analysis of transcripts of PF-4 and GPIIb by RT-PCR suggested that rmSCF kept more megakaryocytes at the protein synthesis stage than did rhIL-6. Based on our findings, these cytokines exert different effects on megakaryocytic cytoplasmic maturational events.