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Two signaling pathways can increase fas expression in human thymocytes
N Moulian1, J Bidault, C Planché
1CNRS UPRESA, Hôpital Marie-Lannelongue, Le Plessis Robinson, France.
Blood
|August 8, 1998
Summary
Two pathways upregulate Fas expression on human thymocytes. Cytokine activation broadly increases Fas and apoptosis susceptibility, while anti-CD3 activation targets specific cells, revealing stimulus-dependent immune responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Fas is a cell surface receptor crucial for inducing apoptosis.
- Human thymocytes express low levels of Fas, with fewer than 3% showing strong expression.
- Understanding Fas regulation is key to modulating immune responses and cell death in the thymus.
Purpose of the Study:
- To investigate the differential upregulation of Fas antigen expression on human thymocytes by distinct signaling pathways.
- To compare the effects of anti-CD3 activation versus interleukin-7 + interferon-gamma activation on Fas expression and thymocyte apoptosis.
- To elucidate how different activation stimuli influence thymocyte susceptibility to Fas-mediated apoptosis.
Main Methods:
- In vitro analysis of human thymocytes.
- Stimulation using anti-CD3 antibodies and a combination of interleukin-7 (IL-7) and interferon-gamma (IFN-γ).
- Assessment of Fas antigen expression, inhibition studies with cyclosporin A and cycloheximide, and evaluation of Fas-induced apoptosis susceptibility.
Main Results:
- Both anti-CD3 and cytokine pathways upregulated Fas expression, but with distinct patterns across thymic subsets.
- Cytokine activation increased Fas in all subsets, while anti-CD3 primarily affected the CD4 lineage.
- Cyclosporin A inhibited anti-CD3-induced Fas upregulation, but not cytokine-induced upregulation.
- Cycloheximide inhibited cytokine-induced Fas upregulation, but not anti-CD3-induced upregulation.
- Cytokine-activated thymocytes, particularly CD4+ cells, exhibited greater susceptibility to Fas-induced apoptosis.
Conclusions:
- The nature of the activating stimulus significantly influences Fas expression levels and the susceptibility of human thymocytes to apoptosis.
- Distinct signaling pathways mediate Fas upregulation through different mechanisms, involving calcineurin and protein synthesis.
- These findings highlight the context-dependent regulation of thymocyte apoptosis and immune cell fate.