Modulation of toll-like receptor 4 expression on human monocytes by tumor necrosis factor and interleukin-6: tumor necrosis factor evokes lipopolysaccharide hyporesponsiveness, whereas interleukin-6 enhances lipopolysaccharide activity.
Toll-like receptors (TLR) play a pivotal role in the innate immune response, and the expression levels of these receptors may reflect the sensitivity of immune cells to infections. The binding of lipopolysaccharide (LPS) to TLR-4 triggers human monocytes to produce cytokines, which play a dominant role in the inflammatory response, as can be observed during sepsis and after polytrauma. Here, we evaluated TLR-4 expression of isolated monocytes in the presence of tumor necrosis factor (TNF)-alpha, interleukin (IL) 6, IL-8, and IL-10, and we investigated cellular activation of this treatment. TNF-alpha significantly down-regulated TLR-4 mRNA expression after 6 h (100% vs. 38.5% +/- 4%; P < 0.05). This down-regulation was followed by a dose- and time-dependent diminished expression of TLR-4 surface protein (100% vs. 8.0% +/- 5%; P < 0.01). Forty-eight hours after TNF-alpha treatment, a reduced nuclear factor (NF)-kappaB translocation and a diminished IL-6 secretion after LPS stimulation were found (100% vs. 42.0% +/- 23%; P < 0.05). In contrast, IL-6 incubation upregulated TLR-4 cell surface protein (100% vs. 165.8% +/- 24%; P < 0.05) and increased the ability to activate NF-kappaB and AP-1 after LPS stimulation. Stimulation with IL-8 or IL-10 had no significant effects. We conclude that not only LPS but also TNF-alpha and IL-6 have the potency to regulate the immune response via TLR-4. Down-regulation of TLR-4 by TNF-alpha is associated with LPS hyporeactivity for NF-kappaB formation, whereas upregulation of TLR-4 via IL-6 can increase the responsiveness of mononuclear phagocytes.
Tamandl
Dietmar
D
Department of Surgical Research, University of Vienna, 1090 Vienna, Austria.
Bahrami
Minu
M
Wessner
Barbara
B
Weigel
Günter
G
Ploder
Martin
M
Fürst
Walter
W
Roth
Erich
E
Boltz-Nitulescu
Georg
G
Spittler
Andreas
A
D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005434:Flow Cytometry; D006801:Humans; D007249:Inflammation; D016753:Interleukin-10 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D009000:Monocytes / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010586:Phagocytes / Q000378:metabolism; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018805:Sepsis; D013997:Time Factors; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D016207:Cytokines; D018076:DNA, Complementary; D015850:Interleukin-6; D016209:Interleukin-8; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D012313:RNA; D004247:DNA