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

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 (M phi) cultured with serum plus GM-CSF (GM-M phi) were different from control M phi (SER-M phi) in terms of lipopolysaccharide (LPS)-stimulated cytokine release: GM-M phi showed an increased tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) production, especially at lower LPS concentrations, but the secretion of IL-10 was diminished. In addition, GM-M phi secreted TNF-alpha but not IL-6 and IL-10, spontaneously. The spontaneous TNF-alpha 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-M phi and those M phi released twice as much soluble CD14 into the supernatant as compared with SER-M phi. The higher CD14 expression also resulted in an enhanced LPS-binding capacity of GM-M phi. Furthermore, the LPS-response of GM-M phi could only be blocked by about fourfold higher concentration of anti-CD14 antibody compared with SER-M phi. In summary, GM-CSF promotes the generation of a proinflammatory type of M phi in two different ways: first, the down-regulation of autocrine IL-10 production increases the release of cytokines such as IL-6 and TNF-alpha and second, the up-regulation of membrane and soluble CD14 expression leads to a higher sensitivity towards LPS-stimulation.