ABSTRACT
An 8-21 fold multiplication of myeloid cells and macrophages was observed in tissue culture from human fetal bone marrow. Proliferation of the cells was triggered by medium conditioned by acute myelocytic leukemic cells exposed to 12-O-tetradecanoyl phorbol 13-acetate (TPA). The medium was designated as TPA-treated cell conditioned medium (TPACCM). The cycle of events in fetal bone marrow cell culture began with a sharp decrease in the total number of cells. At this juncture a predominance of primitive macrophage-like cells positive for macrophage markers was present in the culture. The process of multiplication began with rapid proliferation of promyelocytes. Simultaneous proliferation of granulocyte-macrophage (GM) colony forming cells (CFC) indicated that at least some of the promyelocytes might act like CFC. The absolute number of committed CFC then increased 5-11 fold, the number that approximated a total multiplication of FBM cells. The proliferation continued with the culture containing some blast cells and showing simultaneous differentiation of the cells into mature granulocytes and macrophages. The cells with macrophage markers persisted throughout the culture period. To determine more precise definition of the role of primitive macrophages and promyelocytes in FBM cell multiplication, experiments with purified fractions of these cells have to be done. TPACCM purification and isolation of active substances is also suggested. These investigations might result in obtaining a pool of BM cells in vitro suitable for BM transplantation.