Abstract
Backgroundβ-1→3-D-glucans represent a pathogen-associated molecular pattern and are able to modify biological responses. Employing a comprehensive methodological approach, the aim of our in vitro study was to elucidate novel molecular and cellular mechanisms of human peripheral blood immune cells mediated by a fungal β-1→3-D-glucan, i.e. glucan phosphate, in the presence of lipopolysaccharide (LPS) or toxic shock syndrome toxin 1 (TSST-1).ResultsDespite an activation of nuclear factor (NF)κB, NFinterleukin(IL)-6 and NFAT similar to LPS or TSST-1, we observed no significant production of IL-1β, IL-6, tumor necrosis factor α or interferon γ induced by glucan phosphate. Glucan phosphate-treated leukocytes induced a substantial amount of IL-8 (peak at 18 h: 5000 pg/ml), likely due to binding of NFκB to a consensus site in the IL-8 promoter. An increase in IL-1receptor antagonist(RA) production (peak at 24 h: 12000 pg/ml) by glucan phosphate-treated cells positively correlated with IL-8 levels. Glucan phosphate induced significant binding to a known NFIL-6 site and a new NFAT site within the IL-1RA promoter, which was confirmed by inhibition experiments. When applied in combination with either LPS or TSST-1 at the same time points, we detected that glucan phosphate elevated the LPS- and the TSST-1-induced DNA binding of NFκB, NFIL-6 and NFAT, leading to a synergistic increase of IL-1RA. Further, glucan phosphate modulated the TSST-1-induced inflammatory response via reduction of IL-1β and IL-6. As a consequence, glucan phosphate shifted the TSST-1-induced IL-1β/IL-1RA ratio towards an anti-inflammatory phenotype. Subsequently, glucan phosphate decreased the TSST-1-induced, IL-1-dependent production of IL-2.ConclusionThus, β-1→3-D-glucans may induce beneficial effects in the presence of pro-inflammatory responses, downstream of receptor binding and signaling by switching a pro- to an anti-inflammatory IL-1RA-mediated reaction. Our results also offer new insights into the complex regulation of the IL-1RA gene, which can be modulated by a β-1→3-D-glucan.
Highlights
Background β-1→3-D-glucans occur as a principal component of microbial cell walls or can be secreted from both, nonpathogenic and pathogenic fungi such as S. cerevisae and C. albicans [1]
Simultaneous co-treatment of peripheral blood mononuclear cells (PBMC) with glucan phosphate (GP) did not change the LPS-induced NFκB binding to oligos from the TNFα promoter significantly (Fig. 1B), but substantially decreased the toxic shock syndrome toxin 1 (TSST-1)-induced NFκB binding when compared to TSST-1 or GP (100 μg) and differed completely from the theoretical value of GP/TSST-1 calc. (n = 4; p < 0.05 vs. GP/TSST-1 calc. and p = 0.07 vs. TSST-1; Fig. 1B)
For GP + TSST-1 we found a significant reduction in IL-1β from 18 h – 24 h, for the latter by about 40% when compared to TSST-1 or the theoretical value of GP/TSST-1 calc. (n = 6; both p = 0.01)
Summary
Background β-1→3-D-glucans occur as a principal component of microbial cell walls or can be secreted from both, nonpathogenic and pathogenic fungi such as S. cerevisae and C. albicans [1]. These β-1→3-D-linked glucose polymers are characterized as a fungal pathogen-associated molecular pattern (PAMP) [2]. In the murine system, binding of zymosan to Dectin-1 resulted in production of TNFα through Toll-like receptor 2 and the adaptor protein MyD88 [12] Another water-soluble β1→3-D-glucan (PGG-glucan) has been described to activate NFκB and NFIL-6 in murine cell lines [13,14]. Three other investigations have reported that human leukocytes and human vascular endothelial cells produce IL8 in response to zymosan [18] or a water-soluble β-1→3D-glucan [6,19]
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