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Abstract An analysis has been made of cell colonies developing in agar cultures from mouse bone marrow cells following stimulation either by neonatal kidney cell feeder layers or AKR lymphoid leukemia serum. Colonies arose by cell proliferation and were mixtures of granulocytic and mononuclear cells. Colonies stimulated by kidney feeder layers reached a mean size of 2000 cells by day 10 of incubation and remained predominantly granulocytic in nature. When bovine serum was substituted for fetal calf serum, cell colonies grew to a smaller size and lost their granulocytic nature, finally becoming almost pure populations of mononuclear cells. Colonies stimulated by AKR leukemic serum reached a mean size of 350 cells by day 10 of incubation. Although these colonies initially were granulocytic in nature, they finally became almost pure populations of mononuclear cells. The colony mononuclear cells actively phagocytosed carbon, and contained metachromatic granules probably derived from ingestion of agar. The mononuclear cells in these colonies may not have been members of the original colony, but may have been incorporated in the colony as it expanded in size, subsequently proliferating in the favourable environment of the colony.
Metcalf et al. (Wed,) studied this question.