Interleukin 3 promotes maturation of murine megakaryocytes in vitro

A fluorescence assay for the quantitation of acetylcholinesterase (AchE) has been adapted for measurement of megakaryocytic maturation in short-term serum-free cultures of murine marrow. When marrow cells were cultured for 3 days in the presence of pokeweed mitogen-stimulated spleen cell conditioned medium (PWM-SCM) under serum-free conditions, AchE production was found to be related to the concentration of PWM-SCM. Interleukin 3 (IL3), a purified glycoprotein promoting the proliferation of several early hematopoietic progenitors including megakaryocytic colony-forming cells, also induced AchE production in a dose-responsive manner. The response to IL3 was linearly related to the number of cells cultured. When marrow was first subjected to plastic adherence and the nonadherent cells then separated on Percoll gradients, a small megakaryocyte-enriched population markedly depleted of colony-forming cells and large megakaryocytes, responded to IL3 in a similar dose-responsive manner. A significant amount of AchE was produced in the absence of any added factors. The data show that AchE production can be measured in 3-day serum-free cultures, and suggest that IL3, a factor promoting megakaryocytic proliferation in vitro, also promotes maturation.