IL-4 promotes macrophage development by rapidly stimulating lineage restriction of bipotent granulocyte-macrophage colony-forming cells.

Granulocyte macrophage colony-forming cells (GM-CFC) are bipotential progenitor cells that can proliferate and develop into macrophages in response to macrophage CSF or into neutrophils in response to stem cell factor or granulocyte CSF. These cytokines promoted growth and development in highly enriched GM-CFC. In [3H]thymidine suicide assays, IL-4 was shown to stimulate proliferation of GM-CFC to the same degree as IL-3 and other potent mitogens for GM-CFC. IL-4 also maintained the clonogenic potential of enriched GM-CFC over a 2-day period. However, after several days in the presence of IL-4, the GM-CFC began to die and retained blast cell morphology characteristic of the isolated GM-CFC. When a high concentration of IL-4 was added to GM-CFC with neutrophilic stimuli, the response of these cells was altered because macrophages were formed. This effect was achieved by a 4-h preincubation with IL-4, suggesting that an early signal produced by IL-4 promotes lineage restriction, although IL-4 itself cannot promote development. IL-4, like macrophage CSF, translocates PKC-alpha to the nucleus in GM-CFC, this redistribution of protein kinase C alpha (PKC-alpha) being inhibited by calphostin C (a PKC inhibitor). Calphostin C also blocked IL-4-mediated development of macrophages in stem cell factor- and granulocyte-CSF-treated cells. This is further evidence that PKC-alpha translocation is involved in the commitment of GM-CFC to macrophage development. This data also suggests that agonist-stimulated lineage commitment can be uncoupled from development in normal hematopoietic cells.