Doctoral theses
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| Identifier |
uch.biology.phd//2002chatzidakis |
| Title |
Ομοιοστατικοί μηχανισμοί κυτταροτοξικών Τ λεμφοκυττάρων σε μοντέλα διαγονιδιακών και ελλειμματικών ποντικιών |
| Alternative Title |
Homeostasis of cytotoxic T lumphocytes in transgenic and knock - out mouse models |
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Author
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Χατζηδάκης, Ιωάννης
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Thesis advisor
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Παπαματθαιάκης, Ι.
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| Abstract |
Vertebrates have developed complex immune systems comprised of cells, molecules and mechanisms capable to cope with invading microorganisms. It is equally important that mechanisms assuring immune system homeostasis and protection of self-tissues from immune reactivity are developed too. The latter group of mechanisms is collectively called immunologigal tolerance. T cell tolerance can be established either in the thymus (central tolerance) or/and in the peripheral lymphoid organs (peripheral tolerance). To study the peripheral CD8 T cell tolerance we used transgenic mice expressing the NP nucleoprotein of an influenza virus. We also used TCR transgenic mice expressing the F5 T cell receptor, which is able to recognize an NP epitope in the context of the Db MHC I molecule, and double transgenic F5/NP mice. There is no negative selection (central tolerance) observed in F5/NP thymocytes. However, there is a marked clonal deletion of F5 CD8 T cells in the periphery of F5/NP mice. Moreover, F5 cells that escaped clonal deletion have become severely hyporeactive to a second challenge with antigen in vitro, a state that is termed T cell anergy. F5/NP CD8 T cells hyporeacivity is at least partly due to low IL-2 receptor expression following stimulation and that probably explains the partial reversion of the anergic phenotype after addition of exogenous IL-2, since anergic F5/NP T cells can not properly utilize this cytokine. More evidence that tolerance induction in F5/NP mice takes place in the periphery is the fact that na?ve F5 T cells transferred to NP expressing recipients are soon rendered anergic in hosts tissues. Using the models described above, we showed that anergy induction of F5 T cells is preceded by activation as judged by high expression of surface activation markers and clonal expansion of F5 T cells in transfer experiments. This indicates that in our models anergy is induced by chronic exposure to antigen presented by APCs and not by lack of costimulation. We tried to identify novel genes that are involved in the induction and/or the persistence of anergy in F5/NP CD8 T cells. To do so we used the mRNA Differential Display technology on RNA populations from purified na?ve F5 and anergic F5/NP CD8 T cells. After an extensive pursuit we ended up with one differentially expressed transcript corresponding to the SLP-65 gene, which is upregulated in the anergic F5/NP T cells compared to the na?ve F5. In this study, we also tried to assess the role of TNF and Fas, two members of the TNF/TNFR superfamily, on the adaptive immune system and specifically on CD8 T cells. In particular, we showed that lack of endogenous TNF results to lower numbers of peripheral F5 cells as well as to reduced homeostatic proliferation after adoptive transfer to lymphopenic hosts. It is of interest that T cell derived rather than host derived TNF has the major contribution to homeostatic expansion of transferred F5 T cells. Furthermore we showed that F5/TNF-/- CD8 T cells respond to the antigen, in vitro and in vivo, in a lesser extent compared to F5 ones. Namely, they exhibit a lower division rate and express lower levels of surface activation markers after encountering the antigen. The lower degree of activation is accompanied and can be correlated with lower activation induced cell death (AICD). This influence of TNF mutation is not restricted to the F5 T cell clone but is rather polyclonal since a-CD3 activation of TNF-/- T cells results to less activation and AICD compared to TNF+/+ T cells. These defective TNF-/- T cell responses can be well attributed, at least partly, to defective NF-κB and NF-ATp activation that we have identified in F5/TNF-/- T cells. Our results showed that TNF plays a non-compensatory role in CD8 T lymphocyte tolerance. Potentially autoreactive F5/NP T cells undergo decreased clonal deletion in a TNF-/- background. In addition F5/NP/TNF-/- cells that escaped clonal deletion are considerably reactive after rechallenge with NP antigen in vitro compared to F5/NP. On top of that, anergy induction is compromised when transferring na?ve F5 CD8 T cells in NP recipients the absence of TNF. Overall our results point out to a pivotal role of TNF on modulating CD8 T cell functions by enhancing TCR signaling for both low and high affinity ligands. Our results with lpr mice (a mutation that renders fas gene inactive) showed that Fas has a minor role in the maintenance of normal populations of peripheral na?ve F5/CD8 T cells in young mice. Moreover, there is an additive effect of the Fas mutation to the TNF mutation as far as it concerns numbers of peripheral F5 CD8 T cells. There is no obvious participation of Fas to activation induced apoptosis of F5 T cells in vivo as judged by transfer experiments in NP expressing mice. In addition, there was no discernible role of Fas in this type of experiments even if F5 T cells were unable to produce both TNF and Fas. There is also not an apparent role of endogenous Fas either to F5/NP CD8 T cells clonal deletion or to the establishment of their anergic phenotype.
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| Language |
Greek |
| Subject |
Τ κύτταρα; Ανέργεια; Ελλειματικά ποντίκια; Κλωνική ανταλοιφή; Αυτοαντιγόνα |
| Issue date |
2002-09-16 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Biology--Doctoral theses
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Type of Work--Doctoral theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/7/9/7/metadata-dlib-2002chatzidakis.tkl
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| Views |
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