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 p rogenitor cells that can proliferate and develop into macrophages in r esponse to macrophage CSF or into neutrophils in response to stem cell factor or granulocyte CSF. These cytokines promoted growth and develo pment in highly enriched GM-CFC. In [H-3]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 c lonogenic potential of enriched GM-CFC over a 2-day period. However, a fter 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 neutrophil ic stimuli, the response of these cells was altered because macrophage s 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, li ke macrophage CSF, translocates PKC-ar to the nucleus in GM-CFC, this redistribution of protein kinase C alpha (PKC-alpha) being inhibited b y calphostin C (a PKC inhibitor). Calphostin C also blocked IL-4-media ted development of macrophages in stem cell factor- and granulocyte-CS F-treated cells. This is further evidence that PKC-alpha translocation is involved in the commitment of GM-CFC to macrophage development. Th is data also suggests that agonist-stimulated lineage commitment can b e uncoupled from development in normal hematopoietic cells.