Megakaryocyte potentiating activity of IL‐1, IL‐6 and GM‐CSF as evaluated by their action on in vitro human megakaryocytic colonies

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Abstract
Summary We examined whether recombinant cytokines enhance the in vitro platelet production of interleukin‐3 (IL‐3)‐induced human megakaryocytic colonies (Meg‐colony). We classified Meg‐colonies into four categories based on platelet production during in situ observation on day 14: type 0, absence of cytoplasmic processes in a colony; type 1, one to three processes in at least one megakaryocyte in a colony; type 2, four to eight processes; type 3, more than nine processes or division of cytoplasm. Type 3 colonies were considered to be platelet‐producing. In control cultures, type 1 Meg‐colonies were dominant, followed by type 2, type 3 and type 0. Of the cytokines added at the initiation of culture, interleukin‐1 alpha (IL‐1α), interleukin‐6 (IL‐6), and granulocyte/macrophage colony stimulating factor (GM‐CSF) significantly increased the number of colonies. Furthermore, these three cytokines significantly elevated the proportion of type 3 colonies. Interleukin‐4 (IL‐4), granulocyte‐CSF, macrophage‐CSF and erythropoietin did not affect the colony count or distribution of colony type. IL‐1α. IL‐6 and GM‐CSF also significantly elevated the proportion of type 3 colonies, even when added to the culture on days 8 or 11. These results indicate that IL‐1α, IL‐6 and GM‐CSF promote platelet production of in vitro Meg‐colonies.