The roles of factors from lung in murine megakaryocytopoiesis.

The roles of factors from mouse lung in stimulating murine megakaryocytopoiesis were examined. Conditioned medium from normal mice was found to contain interleukin 3 (IL-3) activity in addition to granulocyte-macrophage colony-stimulating factor (GM-CSF) and megakaryocyte potentiator (Mk-potentiator). The Mk-potentiator activity of mouse lung-conditioned medium (MLCM) was found to be immunologically distinct from IL-3. Biochemical separation of MLCM showed Mk-potentiator activity with an activity profile distinct from IL-3 and GM-CSF. When titrated, Mk-potentiator was the major activity enhancing megakaryocyte colony formation in MLCM. By contrast, at high concentrations of MLCM, all factors were present and may play a role in megakaryocyte colony growth and development.