Roles of CFU-S and CFU-C in Maintaining Cell Growth in Diffusion Chamber Cultures of Murine Marrow

Abstract

Our previous studies have demonstrated that when murine bone marrow cells are cultured in diffusion chambers (DCs) in irradiated host mice, there is rapid growth and differentiation of granulocytic cells followed by a prolonged steady-state of granulocyte renewal. In studies to assess the roles of CFU-S and CFU-C in the initiation and maintenance of granulocyte growth in this model of normal granulopoiesis, we have found rapid fluctuations in the numbers of these progenitor cells during the first few days of culture followed by prolonged plateaus similar to those observed for the numbers of total nucleated cells. Studies with the cycle-specific drug, cytosine arabinoside (Ara-C), have shown that both CFU-S and CFU-C are in active cycle during the initial phases of cell growth; during the plateau phase CFU-C remain in active cycle, whereas the cycle activity of CFU-S returns toward the basal low levels characteristic of the normal marrow. Experiments were then performed to determine the effect of killing most of the CFU-C while preserving most of the CFU-S in plateau phase cultures by incubating the cultured cells with Ara-C followed by re-culture in new DCs and new host mice. In contrast to the reestablishment of the original plateau level observed on retransplantation of control cultures not exposed to Ara-C, cultures plated with CFU-C-depleted cells demonstrated a decreased final level of granulocyte growth. The kinetics of CFU-S and CFU-C proliferation in these cultures appear consistent with the hypothesis that the CFU-C are immediately responsible for the growth of differentiated white cells but that under conditions of increased demand, the CFU-C compartment is fed by, and is ultimately dependent upon, the CFU-S present in these cultures.