Differences in the buoyant density characteristics of murine granulocyte-macrophage progenitor cells cloned in the presence of serum and/or hemolysate.

Bone marrow-derived progenitor cells of granulocytes and macrophages undergo proliferation and maturation in vitro in the presence of colony-stimulating factors and suitable sera. It has recently been found that rat hemolysate can replace serum as a source of growth-supporting activities for cloning these progenitor cells. It is unclear, however, whether serum or hemolysate allows the growth of separate or identical precursor cell subpopulations. Granulocyte-macrophage progenitor cell populations cloned in either serum or hemolysate were identical in their buoyant density characteristics. However, an additional population of granulocyte-macrophage progenitors was preferentially detected when both substances were added to the cell cultures. Different responding cells may, therefore, differ in their nutritional requirements for in vitro cloning. Variability in the respective amounts of these growth factors in the stimulator source would influence the number of CFU-C cloned. The actual amount of stimulator in unpurified sources may, therefore, be grossly overestimated.