Formation of eosinophilic‐like granulocytic colonies by mouse bone marrow cells in vitro

Abstract Formation of granulocytic and macrophage colonies in agar cultures of mouse marrow or spleen cells was stimulated by the addition of medium from pokeweed mitogen‐stimulated cultures of mouse spleen cells (PKW‐CM). Approximately 5% of the colonies developing were large, dispersed granulocytic colonies (DG‐colonies) composed of cells with eosinophilic cytoplasmic granules. The capacity to stimulate DG‐colonies was shown by media conditioned by PKW‐treated lymphoid and peritoneal cells but not by other cells or organ fragments. Velocity sedimentation studies indicated that cells generating DG‐colonies were separable from cells generating regular granulocytic or macrophage colonies. DG‐colonies did not survive if transfered to cultures containing other forms of CSF. The active colony stimulating factor in pokeweed mitogen‐conditioned medium which stimulates DG‐colony formation was antigenically distinct from the factor stimulating granulocytic and macrophage colony formation, was separable electrophoretically from the latter factor and on gel filtration had an apparent molecular weight of 50,000. Although the cells in DG‐colonies have not been established to be eosinophils, DG‐colonies represent an interesting new system for analysing further aspects of the control of growth and differentiation in hemopoietic populations.