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Positive and negative selection invoke distinct signaling pathways
J Alberola-Ila1, K A Hogquist, K A Swan
1Howard Hughes Medical Institute, Seattle, Washington, USA.
Abstract:
During T cell development, interaction of the T cell receptor (TCR) with cognate ligands in the thymus may result in either maturation (positive selection) or death (negative selection). The intracellular pathways that control these opposed outcomes are not well characterized. We have generated mice expressing dominant-negative Ras (dnRas) and Mek-1 (dMek) transgenes simultaneously, either in otherwise normal animals, or in animals expressing a transgenic TCR, thereby permitting a comprehensive analysis of peptide-specific selection. In this system, thymocyte maturation beyond the CD4+8+ stage is blocked almost completely, whereas negative selection, assessed using an in vitro deletion protocol, is quantitatively intact. This suggests that activation of the mitogen-activated protein kinase (MAPK) cascade is necessary for positive selection, but irrelevant for negative selection. Generation of gamma/delta and of CD4-8- alpha/beta T cells proceeds normally despite blockade of the MAPK cascade. Hence, only cells that mature via conventional, TCR-mediated repertoire selection require activation of the MAPK pathway to complete their maturation.
Insights
T cell development requires the mitogen-activated protein kinase (MAPK) cascade for positive selection, but not for negative selection. This pathway is essential for T cell receptor (TCR)-mediated maturation.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- T cell development in the thymus involves T cell receptor (TCR) signaling, leading to either positive selection (maturation) or negative selection (death).
- The intracellular signaling pathways governing these distinct outcomes, particularly the role of the mitogen-activated protein kinase (MAPK) cascade, remain incompletely understood.
Purpose of the Study:
- To investigate the specific role of the MAPK cascade in TCR-mediated positive and negative selection during T cell development.
- To elucidate the intracellular signaling requirements for thymocyte maturation beyond the CD4+8+ stage.
Main Methods:
- Generation of transgenic mice expressing dominant-negative Ras (dnRas) and Mek-1 (dMek) transgenes simultaneously.
- Analysis of T cell development and selection in these mice, including peptide-specific selection using transgenic TCR models.
- Assessment of negative selection via an in vitro deletion protocol.
Main Results:
- Simultaneous blockade of Ras and Mek signaling (MAPK cascade inhibition) almost completely blocked thymocyte maturation beyond the CD4+8+ stage.
- Negative selection, evaluated through in vitro deletion assays, remained quantitatively intact despite MAPK cascade blockade.
- Generation of gamma/delta and CD4-8- alpha/beta T cells proceeded normally under MAPK cascade blockade.
Conclusions:
- Activation of the MAPK cascade is a necessary but not sufficient component for TCR-mediated positive selection during T cell development.
- The MAPK pathway is dispensable for negative selection, indicating distinct signaling requirements for these two selection processes.
- Conventional TCR-mediated repertoire selection requires MAPK pathway activation for the maturation of conventional T cells.