CSF-1 regulation of I6 gene expression by murine macrophages: a pivotal role for GM-CSF

Abstract

We test the hypothesis that the monocyte-macrophage colony-stimulating factor (CSF-1 or M-CSF) plays a major role in the inflammatory responses of M by acting as a priming agent that heightens their responsiveness to secondary stimulation by other mediators. We previously reported that CSF-1 induced peritoneal M (PM ) to transcribe several genes including interleukin-6 (Il6) and granulocyte-macrophage colony-stimulating factor (Csfgm). It was reported that the Il6 and Csfgm genes were individually regulated by different pathways but it was not clear to what extent the two genes interacted during M -mediated inflammatory responses. We now show that CSF-1 induces the release of bioactive GM-CSF from mouse resident PM . GM-CSF induces Il6 gene expression and synergizes with CSF-1 to induce the release of large amounts of IL-6. PM from C57BL/6J-Csfgm null mice were shown to release minimal IL-6 in response to CSF-1 and to express a much reduced response to the highly stimulatory combination of CSF-1 and lipopolysaccharide (LPS). Exogenous recombinant GM-CSF restored the IL-6 response of GM-CSF null PM to a great extent but not completely. As controls, three other recombinant proteins were tested but of these only tumor necrosis factor ␣ (TNF-␣) was shown to synergize with both CSF-1 and GM-CSF. Using PM from mice deficient in the expression of the Il6 gene, it was shown that they released two-to threefold more GM-CSF in response to CSF-1 than their control counterparts. However, an exogenous supply of recombinant IL-6 had no effect on GM-CSF release. The data indicate that the pathways regulating Il6 gene expression are under the control of a complex network of cytokine interactions involving at least CSF-1, GM-CSF, and TNF-␣, with the added possibility that IL-6 may exert modulatory activity within this network. J. Leukoc. Biol. 64: 810-816; 1998.

CSF-1 (M-CSF) Enhances the Inflammatory Response of Fibronectin-Primed Macrophages: Pathways Involved in Activation of the Cytokine Network

“…Recent data have indicated that CSF-1 drives multiple pathways during the expression of the Il6 gene and is influenced by Csfgm and Tnfa gene expression [4]. To determine if the elevation of IL-6 release by resident PMÊ upon stimulation by the combination of CSF-1 and FN is paralleled in GM-CSF and TNF-· release, resident PMÊ were incubated in 24-well plates coated with FN (10 Ìg/ml) and a fixed concentration of CSF-1 (10 4 U/ml) and culture supernatants were assayed at intervals over 24 h for IL-6, GM-CSF and TNF-·.…”

“…Cytokine Enzyme-Linked Immunosorbent Assays IL-6, GM-CSF and TNF-· were assayed by enzyme-linked immunosorbent assays (ELISAs) developed in our laboratory [1][2][3][4]10]. The lower and upper values for the detection of IL-6 were 0.039 and 2.5 ng/ ml.…”

“…In addition, spleen cells and PBL were added to wells (10 6 / well) to show that cell populations rich in lymphoid cells but poor in MNP did not respond under these conditions [1][2][3][4]14]. IL-6 was assayed after 24 h (table 1).…”

“…This priming effect results in the production of large amounts of defined cytokines and growth factors, the resident PMÊ secreting many more mediators than the elicited PMÊ. It has also been shown that the ability of CSF-1 to induce cytokine expression in resident PMÊ can be amplified by other cytokines, such as GM-CSF and TNF-·, both of which not only enhance Il6 gene expression alone, but synergize with each other and CSF-1 to further augment Il6 gene expression [1][2][3][4].…”

“…They achieve this by a complex network of autocrine and paracrine interactions with other cell types, as well as with noncellular elements including numerous growth factors, cytokines and extracellular matrix (ECM) proteins [1][2][3][4][5][6][7][8][9][10][11]. A key growth factor in the differentiation and regulation of macrophage inflammatory responses is the monocyte-macrophage colony-stimulating factor (M-CSF or CSF-1), which we have reported to react with defined populations of macrophages to induce different effects in the context of inflammatory cytokine responses [1][2][3][4]10]. For example, CSF-1 induces resident mouse peritoneal macrophages (PMÊ) to secrete IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) but has no comparable effects on elicited PMÊ or blood monocytes [3].…”