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Human monocyte CD14 is upregulated by lipopolysaccharide
R Landmann1, H P Knopf, S Link
1Department of Research and Internal Medicine, University Hospital, Basel, Switzerland.
Abstract:
Membrane CD14 is involved in lipopolysaccharide (LPS)-induced monocyte activation; it binds LPS, and antibodies against CD14 block the effects of low-dose LPS. It is unknown how LPS regulates its own receptor CD14 in vitro. Therefore, we investigated the effects of LPS on CD14 mRNA and membrane and soluble CD14 (mCD14 and sCD14, respectively) in human monocytes and macrophages. No changes were observed during the first 3 h of LPS stimulation. After 6 to 15 h, LPS weakly reduced CD14 mRNA and mCD14 and transiently enhanced sCD14 release. A 2-day incubation with LPS caused increases in the levels of CD14 mRNA (2-fold), mCD14 (2-fold), sCD14 (1.5-fold), and LPS-fluorescein isothiocyanate binding (1.5-fold); a 5-h incubation with LPS was sufficient to induce the late effects on mCD14 and sCD14. The maximal effect on mCD14 and sCD14 was reached with > or = 1 ng of LPS per ml; the proportional distribution of the two sCD14 isoforms was not modified by LPS. Besides rough and smooth LPS, lipid A, heat-killed Escherichia coli, lipoteichoic acid, and Staphylococcus aureus cell wall extract (10 micrograms/ml) caused similar increases of mCD14. The LPS effect was blocked by polymyxin B but not by anti-tumor necrosis factor alpha, anti-interleukin-6, anti-gamma interferon, and anti-LPS-binding protein. LPS-induced tumor necrosis factor alpha production was abolished after a second 4-h challenge. In contrast, the LPS-induced increases CD14 mRNA, mCD14, and sCD14 were stronger and appeared earlier after a second LPS challenge. In conclusion, CD14 is transcriptionally upregulated by LPS and other bacterial cell wall constituents.
Insights
Lipopolysaccharide (LPS) upregulates CD14 receptor expression in human monocytes and macrophages. This transcriptional upregulation of CD14 mRNA and membrane CD14 (mCD14) occurs after prolonged LPS exposure and is mediated by bacterial cell wall components.
Area of Science:
- Immunology
- Cell Biology
Background:
- Membrane CD14 (cluster of differentiation 14) is crucial for monocyte activation by lipopolysaccharide (LPS).
- The in vitro regulation of CD14 by LPS remains largely uncharacterized.
Purpose of the Study:
- To investigate the effects of LPS on CD14 mRNA and protein levels (membrane-bound CD14 [mCD14] and soluble CD14 [sCD14]) in human monocytes and macrophages.
Main Methods:
- Human monocytes and macrophages were stimulated with LPS in vitro.
- CD14 mRNA and protein expression, as well as LPS binding, were analyzed over time.
- Effects of various bacterial components and blocking antibodies were assessed.
Main Results:
- LPS induced a late, transcriptional upregulation of CD14 mRNA and mCD14 after 2-day incubation.
- Soluble CD14 (sCD14) release was transiently enhanced.
- Other bacterial cell wall components also increased mCD14, and the LPS effect was blocked by polymyxin B.
Conclusions:
- CD14 is transcriptionally upregulated by LPS and other bacterial cell wall constituents.
- This upregulation is a late response and distinct from early inflammatory cytokine production.