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CTLA-4 ligation blocks CD28-dependent T cell activation
T L Walunas1, C Y Bakker, J A Bluestone
1Department of Pathology, Ben May Institute for Cancer Research, University of Chicago, Illinois 60637, USA.
Abstract:
CTLA-4 is a CD28 homologue believed to be a negative regulator of T cell function. However, the mechanism of this downregulatory activity is not well understood. The present study was designed to examine the effect of CTLA-4 ligation on cytokine production, cell survival, and cell cycle progression. The results demonstrate that the primary effect of CTLA-4 ligation is not the induction of apoptosis. Instead, CTLA-4 signaling blocks IL-2 production, IL-2 receptor expression, and cell cycle progression of activated T cells. Moreover, the effect of CTLA-4 signaling was manifested after initial T cell activation. Inhibition of IL-2 receptor expression and cell cycle progression was more pronounced at late (72 h) time points after initial activation. The effects of anti-CTLA-4 mAbs were most apparent in the presence of optimal CD28-mediated costimulation consistent with the finding that CTLA-4 upregulation was CD28-dependent. Finally, the addition of exogenous IL-2 to the cultures restored IL-2 receptor expression and T cell proliferation. These results suggest that CTLA-4 signaling does not regulate cell survival or responsiveness to IL-2, but does inhibit CD28-dependent IL-2 production.
Insights
Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) signaling inhibits T cell activation by blocking Interleukin-2 (IL-2) production, not by inducing cell death. This mechanism impacts T cell proliferation and IL-2 receptor expression.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) is a homologue of CD28 and is thought to negatively regulate T cell function.
- The precise mechanism by which CTLA-4 exerts its downregulatory activity remains incompletely understood.
Purpose of the Study:
- To investigate the effects of CTLA-4 ligation on T cell cytokine production, cell survival, and cell cycle progression.
- To elucidate the specific molecular pathways modulated by CTLA-4 signaling in activated T cells.
Main Methods:
- Analysis of cytokine production following CTLA-4 ligation.
- Assessment of cell survival and apoptosis markers.
- Monitoring of cell cycle progression in activated T cells.
- Evaluation of IL-2 receptor expression and T cell proliferation.
- Investigation of CTLA-4 effects under varying CD28-mediated costimulation conditions.
- Assessment of exogenous IL-2 addition on T cell responses.
Main Results:
- CTLA-4 ligation does not primarily induce apoptosis in activated T cells.
- CTLA-4 signaling significantly blocks Interleukin-2 (IL-2) production and IL-2 receptor expression.
- Inhibition of IL-2 receptor expression and cell cycle progression is more pronounced at later time points (72h) post-activation.
- The inhibitory effects of CTLA-4 were most evident with optimal CD28 costimulation, indicating a CD28-dependent upregulation of CTLA-4.
- Addition of exogenous IL-2 rescued IL-2 receptor expression and T cell proliferation, suggesting CTLA-4 does not affect IL-2 responsiveness.
Conclusions:
- CTLA-4 signaling primarily inhibits CD28-dependent IL-2 production in activated T cells.
- CTLA-4 does not regulate T cell survival or responsiveness to IL-2.
- The findings clarify the mechanism of CTLA-4-mediated T cell regulation, focusing on IL-2 production inhibition.