Granulocyte colony-stimulating factor induces neutrophils to secrete macrophage colony-stimulating factor.

In this work we provide evidence showing that granulocytes produce macrophage colony-stimulating factor (M-CSF) from the band cell stage and secrete this factor when induced to differentiate into polymorphonuclear cells by recombinant human granulocyte colony-stimulating factor (rhG-CSF). Using an enriched population of myeloid band cells from murine bone marrow, we identified the presence of M-CSF with a chromophore-labelled monoclonal anti-M-CSF antibody. Using ELISA we detected the secretion of M-CSF in the supernatants of cultures of enriched band cells when induced with rhG-CSF to differentiate into mature neutrophils. We also found that M-CSF is the only factor responsible for the colony forming activity in the supernatants and lysates of band cells treated with rhG-CSF.

Evidence that G-CSF is a fibroblast growth factor that induces granulocytes to increase phagocytosis and to present a mature morphology, and that macrophages secrete 45-kd molecules with these activities as well as with G-CSF-like activity.

Evidence is provided that conditioned medium from a macrophage-like cell line contains molecules of approximately 45 kd molecular weight with granulocyte colony-stimulating factor (G-CSF)-like activity as well as with the property of inducing granulocytes to phagocytose latex particles and to mature morphologically. This type of differentiation was found to be induced on either bone marrow or induced granulocytes, but not on resident or induced macrophages. On the other hand, resident but not induced macrophages are shown to induce these types of activities when challenged by bacterial lipopolysaccharides. Evidence that macrophages produce a factor that is mitogenic for fibroblasts is also provided. This activity was measured by the induction of increased proliferation by either low-density or saturated cultures of fibroblasts. Human recombinant G-CSF was employed and found also to possess these dual capabilities of inducing both the proliferation and differentiation of granulocytes as well as the proliferation of fibroblasts. Finally, a mechanism for the regulation of myeloid cell production and differentiation is described in which G-CSF produced by macrophages not only induces granulocytes to differentiate but induces fibroblasts to proliferate and secrete macrophage colony-stimulating factor (M-CSF), which in turn makes myeloid monocyte precursors proliferate and secrete more G-CSF.

Evidence that the macrophage-granulocyte inducer (MGI) is produced during cell proliferation, stored in G0, released in G1, cell specific, and induces the secretion of other colony-stimulating activities (CSA).

The secretion of the macrophage and granulocyte inducer (MGI), also known as colony-stimulating factor (CSF), by epithelial cells from lungs and kidneys, and by fibroblasts from lungs, was determined as a function of time in culture; it was found to be secreted during the initial exponential proliferation period, and not when the cells approached saturation density. When the cells were again induced to proliferate, large amounts of CSF were released after 3 h, thus hinting at the existence of a reserve pool. A CSF activity of 70,000 daltons was found in cultures of fibroblasts from lungs, kidneys, and the peritoneal cavity, a 45,000-dalton CSF was obtained from mouse peritoneal macrophages, and from bone marrow cells when activated for macrophage proliferation, and a 22,000-dalton CSF was found from epithelial cells, thus suggesting that the different CSFs are cell specific. When fibroblast CSF was used to induce bone marrow cells, three new molecules with colony-stimulating activity were produced, of 45,000, 30,000, and 17,000 daltons. The fraction with the 17,000-dalton activity also contained interleukin 1 activity, hinting at an indirect induction of colony formation by this factor. Finally the possible existence of a cascade reaction in which one CSF induces the appearance of other CSFs during the normal regulation of myeloid cell differentiation is discussed.

Evidences that fibroblasts and epithelial cells produce a specific type of macrophage and granulocyte inducer, also known as colony-stimulating factor, and that monocyte-macrophages can produce another factor with proliferative inducing activity on myeloid cells and differentiative activity on macrophages.

Molecules with the property to induce proliferation of bone marrow cells in liquid cultures, and with colony-stimulating activity, were found on media conditioned (MC) by lung fibroblasts and kidney epithelial cells. These factors presented an apparent mol wt of 70,000 and 22,000 d respectively. Also when MC by epithelial cells from lungs was tested for the induction of proliferation of bone marrow cells a molecule with 22,000 d was detected. These molecules are thought to be CSF because they induce colony formation, and they are also similar in mol wt to two of the already known CSF. In fact the GM-CSF obtained from endotoxic lungs with a large epithelial cell content has a mot wt of 22,000 d, and the CSF-1 produced by a fibroblast cell line had 70,000. When the MC by fibroblast was used to induce bone marrow cells to proliferate, three new molecules with colony-stimulating activity were secreted. These molecules with apparent mol wts of 45,000, 30,000 and 17,000 d were also found in the MC by bone marrow cells when induced to proliferate with MC by epithelial cells. When the 45,000-d molecules was used in induced bone marrow cells to proliferate, once again the 30,000- and the 17,000-d molecules were secreted. Evidence is also provided that the 45,000-d molecule is produced by the monocyte-macrophage cells, and that it can induce Fc receptors or resident and elicited peritoneal macrophages. The possibility that the production of CSF is cell specific is discussed together with two models to explain the way in which these molecules can participate as proliferative (MGI-1) and differentiative (MGI-2) function in normal myeloid cell differentiation. Finally, a new terminology is proposed to classify this family of molecules.