Haemopoietic growth factors stimulating murine megakaryocytopoiesis: Interleukin-3 is immunologically distinct from megakaryocyte-potentiator

The biological and immunological properties of stimulators of in vitro murine megakaryocytopoiesis were studied using a heterologous anti-interleukin 3 (IL-3) serum. All megakaryocyte colony development was inhibited with the antiserum using three sources of IL-3, including WEHI-3 cell conditioned medium (WEHI-3CM), pokeweed mitogen-spleen conditioned medium (PWM-SCM) and recombinant IL-3. The data indicate that IL-3 is an absolute requirement for murine megakaryocyte colony development in this system. By comparison the antiserum abolished all myeloid colony growth stimulated by WEHI-3CM, but not PWM-SCM. The in vitro development of single megakaryocytes stimulated by a second putative growth factor, megakaryocyte-potentiator, was not inhibited by the antibody. The antiserum precipitated a 26 kd molecular weight protein from a radioiodinated sample of IL-3. No crossreactivity by the antiserum with other colony-stimulating factors (CSF) including CSF-1 and granulocytemacrophage CSF was observed. The data indicates that IL-3 and megakaryocyte-potentiator are immunologically unrelated and provides further support that the two factors are separate molecules.