The role of Zap70 in thymocyte development.
Doctoral thesis, UCL (University College London).
CD4+CD8+ double positive (DP) precursors undergo positive selection in the thymus, and subsequently commit to either the CD4 or CD8 single positive (SP) lineage. Mice lacking Zap70, a crucial kinase involved in T-cell receptor (TCR) signal transduction are developmentally arrested at the DP stage, showing that this process depends on TCR signalling. Furthermore, the resultant SP populations are major histocompatibility (MHC) matched, as CD4 lineage cells recognise MHC-II whereas CD8 lineage T cells recognise MHC-I. There are currently two favoured models describing how the MHC restriction of the TCR correlates with lineage choice. These suggest that differences in either the TCR signalling strength or signalling length underlie the CD4/CD8 lineage decision during the DP stage. Both models posit that differences in signalling strength/length are properties that are conferred by the different signalling capacities of the CD4/CD8 coreceptors. However, questions remain over the mechanisms behind this process, including how the selecting cell interprets the proximal differences in TCR activation and whether the quality of this signal impacts on its future homeostatic survival potential. A major obstacle in addressing these questions is the lack of tools to facilitate understanding of the kinetic regulation of positive selection. We therefore sought to examine the kinetics of T-cell development using a tetracycline inducible Zap70 mouse model (TetZap70 hereon). In the absence of the tetracycline derivative doxycycline (dox), T-cells were arrested at the DP stage, prior to positive selection. However, the administration of dox induced positive selection of a synchronized wave of positively selecting thymocytes, enabling the resolution of intermediate populations of positively selecting DPs. We found that CD4 and CD8 lineage development occurred with temporal distinction, from phenotypically disparate populations of DP thymocytes. Furthermore, we found that endogenous Zap70 was developmentally regulated in different DP populations of WT mice, and loss of this regulation in TetZap70 mice corresponded to an impairment in CD8 lineage generation. Thus we suggest that temporal regulation of T-cell signalling sensitivity during thymic development facilitates the resolution of strong/consistent signals versus weak/intermittent signals. Finally we find evidence that the quality of the positive selection signal not only controls the CD4/CD8 lineage decision, but also impacts on the future homeostatic survival potential of T-cells by influencing levels of the prosurvival interleukin-7 receptor alpha chain (IL7rα).
|Title:||The role of Zap70 in thymocyte development|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Medical Sciences > Infection and Immunity (Division of)|
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