GRANULOCYTIC-MACROPHAGIC AND MACROPHAGIC COLONY-STIMULATING FACTORS ELICIT COLONIES OF MAST-CELLS IN MOUSE BONE-MARROW AGAR CULTURE - AN ELECTRON-MICROSCOPE STUDY

Granulocytic-macrophagic colony stimulating factor (GM-CSF) and macrop hagic colony stimulating factor (M-CSF or CSF-1) stimulate bone marrow cells of mouse to produce in semisolid agar colonies in which mononuc lear cells were reported to be macrophages. We verified in such coloni es the ultrastructure of the mononuclear cells which had cytoplasmic g ranules of the mast cells and lacked lysosomes, therefore we considere d them as mast cells. However, the granules content did not reach the degree of condensation typically found in granules of mouse peritoneal mature mast cells. The mast cells of colonies obtained in agar can be mast cells arrested at some point in the maturative process, mast cel ls of a yet unrecognized type or cells with mast cells ultrastructural features which behave as precursors for cells of myeloid lineage.