The response of haemopoietic cells to growth factors: developmental implications of synergistic interactions.

Haemopoietic cell growth factors are normally assayed using unfractionated marrow cells (NBM). However, using this population it is difficult to distinguish between direct versus indirect effects, because of the low incidence of colony forming cells (CFC) and the presence of possible accessory cells (which may themselves be acted upon by the growth factors and stimulated to produce other growth stimulatory or inhibitory molecules that influence the development of the CFC). Furthermore, NBM contain the whole spectrum of multipotent and lineage-restricted CFC and it is often difficult to determine precisely which populations are being stimulated to develop. This latter problem can be solved, in part, by using marrow from mice previously treated with 5-fluorouracil (5-FU): an agent that preferentially kills the more mature, actively cycling CFC but spares the proliferatively quiescent multipotent stem cells. Since the 5-FU-treated marrow also contains many possible accessory cells, however, it is again not clear whether or not the responses elicited by growth factors are due to direct or indirect effects upon the CFC. To circumvent this problem we have obtained a highly enriched population of multipotent stem cells (FACS-BM) that is free of accessory cells, and have compared the responses of these cells to NBM and to 5-FU-BM in the presence of a variety of growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)