The biology of the colony stimulating factors

Previous in vitro studies with recombinant human Interleukin 3 (IL-3) in serum-replete culture conditions suggested that IL-3 induced the complete differentiation of multipotent and both, erythroid and myeloid progenitor cells. In contrast, serum-free cultures have shown that alone, IL-3, and to a lesser extent granulocyte-macrophage colony-stimulating factor (GM-CSF), are inadequate differentiation stimuli. However, in combination with the lineage-specific growth factors, erythropoietin, granulocyte colony stimulating factor (G-CSF), and macrophage CSF (M-CSF), complete recovery of erythroid, granulocyte, and macrophage colonies, respectively, was obtained. GM-CSF is produced by a variety of mesenchymal cells as well as monocytes and T lymphocytes; in contrast, IL-3 production appears to be restricted to lectin stimulated T lymphocytes. These studies indicate that the CSFs may be more effective in vivo when used as combinations rather than as single factors. The restricted production of IL-3 by activated T cells suggests that IL-3 may be released during infections and may play an important role during stress.