Interleukin 4 alters human bone marrow stroma and modulates its interaction with hematopoietic progenitors

To investigate the functional activity of interleukin 4 (IL-4) on human marrow stroma formation, normal bone marrow (BM) samples were cultured in "Dexter-type" long-term cultures in the presence and absence of IL-4. IL-4 (0.001 to 1.0 micrograms/ml) added at the initiation of culture and once weekly when the cultures were fed effaced the culture architecture. In four-week old confluent cultures smooth muscle-like and endothelial-like cells were rare, the fibronectin network and cobblestone areas were absent, and a preponderance of monocyte-macrophages characterized the adherent layer. Exposure to IL-4 reduced the numbers of CD34+ cells, colony-forming unit granulocyte-macrophage (GFU-GM) cells and burst-forming unit-erythroid (BFU-E) cells in the adherent layer, and increased their numbers in the nonadherent layer. In five of eight IL-4-containing cultures the concentrations of macrophage colony-stimulating factor (M-CSF) were increased and in two of eight IL-4-treated cultures the concentrations of tumor necrosis factor-alpha (TNF-alpha) were significantly elevated as compared to those in control cultures, whereas there were no consistent differences in the levels of either IL-6 or transforming growth factor-beta (TGF-beta). IL-1 beta and granulocyte-macrophage CSF (GM-CSF) were not detected in any culture. These data suggest that IL-4 suppresses stroma formation and alters its structure and cellular composition.