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IL-13 down-regulates CD14 expression and TNF-alpha secretion in normal human monocytes
G Cosentino1, E Soprana, C P Thienes
1Molecular Immunoregulation Unit, DIBIT/San Raffaele Scientific Institute, Milan, Italy.
Abstract:
CD14, a glycosylphosphatidylinositol (GPI)-linked protein expressed on monocytes and neutrophils, regulates monocyte-lymphocyte interactions and serves as the LPS receptor. We showed previously that IL-4 down-regulates the expression of human CD14 by acting at the transcriptional level. We now investigate whether CD14 expression could also be regulated by IL-13, another member of the chromosome 5 cytokine gene family. IL-13 dose-dependently inhibited CD14 expression on human monocytes. By contrast, expression of CD23 and CD11b was enhanced strongly. Down-regulation of CD14 involved neither shedding nor activation of endogenous GPI anchor-cleaving enzymes. Indeed, soluble CD14 was not increased in the supernatants of IL-13-stimulated monocytes, and expression of CD55/DAF, another GPI-linked protein, was unaffected by IL-13. CD14 transcript levels were reduced sixfold in IL-13-treated monocytes. These results suggest that IL-13 down-regulates membrane CD14 by suppressing CD14 RNA expression. IL-13-dependent down-regulation of CD14 resulted in the inhibition of CD14-mediated events. Indeed, CD14-mediated release of TNF-alpha was inhibited markedly (approximately 75%) in monocytes stimulated with LPS (100 ng/ml) after a 72-h preincubation with IL-13. However, IL-13 also directly inhibited monokine secretion, because it blocked PMA-induced, CD14-independent TNF-alpha release. Down-regulation of CD14 and TNF-alpha secretion may play a major role in the anti-inflammatory effects of IL-13 on LPS-stimulated monocytes.
Insights
Interleukin-13 (IL-13) reduces CD14 protein expression on monocytes by decreasing CD14 gene transcription. This IL-13 effect inhibits lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha release, suggesting anti-inflammatory roles.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- CD14 is a glycosylphosphatidylinositol (GPI)-linked protein on monocytes and neutrophils, crucial for lipopolysaccharide (LPS) recognition and monocyte-lymphocyte interactions.
- Interleukin-4 (IL-4) previously demonstrated to down-regulate CD14 expression transcriptionally.
- IL-13, a related cytokine, warrants investigation for its potential role in regulating CD14 expression.
Purpose of the Study:
- To investigate the effect of Interleukin-13 (IL-13) on CD14 expression in human monocytes.
- To determine the mechanism by which IL-13 affects CD14 expression.
- To assess the functional consequences of IL-13-mediated CD14 down-regulation on monocyte responses.
Main Methods:
- Human monocytes were treated with varying doses of IL-13.
- CD14, CD23, and CD11b expression levels were measured.
- CD14 transcript levels were quantified using RT-PCR.
- Monocyte responses, including TNF-alpha release, were assessed following LPS or PMA stimulation.
Main Results:
- IL-13 dose-dependently inhibited CD14 expression on human monocytes.
- IL-13 significantly reduced CD14 mRNA levels, indicating transcriptional regulation.
- IL-13 enhanced CD23 and CD11b expression.
- IL-13 pre-treatment inhibited CD14-mediated LPS-induced TNF-alpha release but also directly suppressed PMA-induced TNF-alpha release.
- No evidence of CD14 shedding or increased GPI anchor-cleaving enzyme activity was observed.
Conclusions:
- IL-13 down-regulates membrane CD14 expression primarily by suppressing CD14 gene transcription.
- The observed down-regulation of CD14 by IL-13 contributes to the inhibition of LPS-stimulated monocyte responses.
- IL-13 exhibits anti-inflammatory effects on LPS-stimulated monocytes through CD14 down-regulation and direct inhibition of cytokine secretion.