Modulation of CD4+ T-cell activation by CD95 co-stimulation.

Area of Science:

• Immunology
• Cell Biology
• Molecular Signaling

Background:

• CD95 (also known as Fas receptor) is a transmembrane protein involved in regulating cell death.
• Its function is context-dependent, mediating either pro-apoptotic or anti-apoptotic signals.
• The precise role of CD95 in T cell receptor (TCR)/CD3 signaling remains incompletely understood.

Purpose of the Study:

• To investigate the dual function of CD95 in modulating TCR/CD3-driven signaling in resting T lymphocytes.
• To elucidate the dose-dependent effects of CD95 engagement on T cell activation, proliferation, and survival.
• To analyze the co-stimulatory capacity of CD95 in human CD4(+) T cells.

Main Methods:

• Utilized immobilized CD95 agonists at varying concentrations to stimulate resting human CD4(+) T cells.
• Analyzed TCR/CD3 co-internalization with CD95.
• Assessed caspase activation, MAP kinase phosphorylation, antiapoptotic protein expression, transcription factor activation, and cell-cycle regulator activity.

Main Results:

• High doses of CD95 agonists silenced T cells, whereas low doses augmented activation and proliferation.
• Low-dose CD95 engagement promoted co-internalization of CD95 and TCR/CD3 complexes.
• This co-internalization led to non-apoptotic caspase activation, sustained MAP kinase signaling, increased antiapoptotic protein levels, and activation of transcription factors and cell-cycle regulators, ultimately inducing proliferation and cytokine production.

Conclusions:

• CD95 exhibits a dose-dependent co-stimulatory role in T cell activation.
• The level of CD95 ligand (CD95L) dictates whether CD95 signaling is inhibitory or co-stimulatory.
• This fine-tuning mechanism is critical for regulating primary T cell responses in vivo.