Specificity of Action of Colony‐Stimulating Factors in the Differentiation of Granulocytes and Macrophages

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Abstract
Four colony-stimulating factors (CSFs) (M-CSF, GM-CSF, Multi-CSF and G-CSF) can each stimulate the production of macrophages from progenitor cells in murine bone marrow or fetal liver. However, they differ in their relative selectivity for macrophage progenitor cells and in their dose-response characteristics for stimulating macrophage progenitors relative to other progenitors. It is unresolved whether distinct subsets of progenitor cells exist with a unique responsiveness to one or other CSF or whether the macrophages produced by different CSFs are all functionally equivalent. However, it is shown here that various CSFs can generate from blast progenitor cells an intermediate macrophage progenitor cell whose growth is specifically inhibited by a substance in lectin-stimulated spleen cell-conditioned media. It is also shown that, for at least one myelomonocytic leukaemic cell line, differentiation to macrophages and granulocytes can be induced most effectively by G-CSF but not by M-CSF or Multi-CSF. Finally, the involvement of macrophages and macrophage cell lines in the induced production of these CSFs as well as their display of specific receptors for the different CSFs is examined.