Granulocyte-macrophage colony-stimulating factor modulates lipopolysaccharide (LPS)-binding and LPS-response of human macrophages: Inverse regulation of tumour necrosis factor-α and interleukin-10

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a well- known stimulus for the activation, differentiation and survival of monocytes (MO). Up to now most investigations focused on the short-term effects of GM- CSF. In this study we investigated the effects of GM-CSF on the long-term differentiation of human MO in the presence of serum. We found that MO- derived macrophages (Mφ) cultured with serum plus GM-CSF (GM-Mφ) were different from control Mφ (SER-Mφ) in terms of lipopolysaccharide (LPS)- stimulated cytokine release: GM-Mφ showed an increased tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production, especially at lower LPS concentrations, but the secretion of IL-10 was diminished. In addition, GM-Mφ secreted TNF-α but not IL-6 and IL-10, spontaneously. The spontaneous TNF-α production was not due to LPS contamination as it could not be blocked by anti-CD14 antibody. Flow cytometry revealed, however, that the receptor for LPS, CD14, was up-regulated on GM-Mφ and those Mφ released twice as much soluble CD14 into the supernatant as compared with SER-Mφ. The higher CD14 expression also resulted in an enhanced LPS-binding capacity of GM-Mφ. Furthermore, the LPS-response of GM-Mφ could only be blocked by about fourfold higher concentration of anti-CD14 antibody compared with SER-Mφ. In summary, GM-CSF promotes the generation of a proinflammatory type of Mφ in two different ways: first, the down-regulation of autocrine IL-10 production increases the release of cytokines such as IL-6 and TNF-α and second, the up-regulation of membrane and soluble CD14 expression leads to a higher sensitivity towards LPS-stimulation.