The roles of granulocyte-macrophage colony-stimulating factor and interleukin 3 in stromal cell-mediated hemopoiesis in vivo.

Adherent cells from murine long-term marrow cultures (LTMC) were examined for presence of mRNA for granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (Il-3). Six hours after medium replacement, GM-CSF mRNA was detected but was no longer detectable 24 h after feeding; Il-3 mRNA was not detected at any time. Neutralizing antibodies against these factors had no effect on hemopoiesis. Exogenous Il-3 increased cell production, notably mature erythroid progenitors, whereas GM-CSF had little long-term effect even at high concentrations. Furthermore, GM-CSF appeared to be specifically removed from the medium, whereas virtually all of the Il-3 could be recovered under identical incubation conditions. These results show that Il-3 is not required for maintaining long-term hemopoiesis in vitro, whereas the precise role of GM-CSF in this system remains unclear

Stimulation of hematopoiesis in vivo by recombinant bacterial murine interleukin 3.

Mouse interleukin 3 (IL-3) cDNA was cloned into a plasmid construction, allowing the synthesis of very high quantities of IL-3 in Escherichia coli. The recombinant (r) IL-3, purified to homogeneity, was active in vitro on the proliferation and differentiation of various hematopoietic progenitor cells at 1 pM. To maintain detectable blood levels of IL-3, osmotic pumps containing rIL-3 or control solutions were placed under the skin of normal and irradiated C3H/HeJ and (BALB X B10) F1 mice. The effect of IL-3 on hematopoietic progenitor cell numbers in spleen and bone marrow was evaluated 3 and 7 days later by using an in vitro clonal assay. The results demonstrated the following: (i) Doses of IL-3 infused at the rate of 2.5-5 ng per g of body weight per hr were sufficient to increase the numbers of hematopoietic progenitors in normal mice by at least 2-fold within 3 days. (ii) In mice with progenitor cell levels depressed by sublethal irradiation, 7-day treatment with IL-3 resulted in a 10-fold increase to near normal levels. (iii) The erythroid and myeloid lineages appeared to be enhanced to the same extent. (iv) Enhancement of hematopoiesis occurred primarily in spleen, but hematopoietic foci were also evident in the liver; in contrast, total cell and progenitor cell numbers were decreased in the bone marrow