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Activation of microglial cells by the CD40 pathway: relevance to multiple sclerosis
1The Roskamp Institute, Department of Psychiatry, University of South Florida, Tampa 33613, USA. jtan@coml.med.usf.edu
Abstract:
It is well known that microglial cells perform a key role in mediating inflammatory processes, which are associated with neurodegenerative diseases such as multiple sclerosis (MS). In this study, we report that CD40 expression on microglia is greatly enhanced by a low dose (10 U/ml) of IFN-gamma. We also find that ligation of microglial CD40 by CD40L triggers a significant production of TNF-alpha. Activation of microglia by ligation of CD40 in the presence of IFN-gamma results in cultured cortical neuronal injury, which is markedly attenuated by blockade of the CD40 pathway or neutralization of TNF-alpha. Finally, we find significant levels of IFN-gamma and TNF-alpha in the medium of co-cultured activated CD4+ T cells and microglial cells, showing that microglia can supply the CD40 receptor to activated CD4+ T cells and suggesting that this cellular interaction is a key event in MS pathophysiology.
Insights
Interferon-gamma (IFN-gamma) boosts CD40 on microglia, triggering TNF-alpha release and neuronal injury. Blocking this CD40 pathway or TNF-alpha protects neurons, suggesting a key role in multiple sclerosis (MS).
Area of Science:
- Neuroimmunology
- Neuroinflammation
- Cellular and Molecular Neuroscience
Background:
- Microglial cells are central to inflammatory processes in neurodegenerative diseases like multiple sclerosis (MS).
- The role of microglial CD40 and its interaction with T cells in MS pathogenesis requires further elucidation.
Purpose of the Study:
- To investigate the effect of interferon-gamma (IFN-gamma) on microglial CD40 expression.
- To determine the impact of CD40 ligation on microglial activation and subsequent neuronal injury.
- To explore the relevance of microglial-T cell interactions in the context of MS.
Main Methods:
- Treatment of primary microglia with a low dose of IFN-gamma to assess CD40 expression.
- Stimulation of microglial CD40 with CD40L and measurement of Tumor Necrosis Factor-alpha (TNF-alpha) production.
- Co-culture of activated microglia with cortical neurons, with and without CD40 pathway blockade or TNF-alpha neutralization.
- Analysis of cytokine levels in co-cultures of activated CD4+ T cells and microglia.
Main Results:
- A low dose of IFN-gamma significantly enhances CD40 expression on microglia.
- CD40 ligation on microglia triggers substantial TNF-alpha production.
- Microglial activation via CD40 ligation in the presence of IFN-gamma causes neuronal injury, which is reduced by CD40 pathway blockade or TNF-alpha neutralization.
- Elevated levels of IFN-gamma and TNF-alpha are detected in co-cultures of activated CD4+ T cells and microglia.
Conclusions:
- IFN-gamma upregulates microglial CD40, promoting TNF-alpha release and neurotoxicity.
- The CD40-CD40L interaction involving microglia and T cells is a critical mechanism contributing to MS pathophysiology.
- Targeting the CD40 pathway or TNF-alpha may offer therapeutic strategies for MS.