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Ulaganathan, Vijay Kumar (2010): Gene Expression Profiling of Encephalitogenic CD4+ T cells: Identification of Genes Controlling Migration of Effector T cells into the CNS. Dissertation, LMU München: Faculty of Biology
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Abstract

T cells directed against brain antigens are generally held to play a crucial role in the initiation of multiple sclerosis (MS). This was deduced from experimental autoimmune encephalomyelitis (EAE). In this model for MS, T cells reactive for myelin antigens induced a severe paralytic disease upon transfer to healthy syngeneic recipients. Intriguingly, the disease does not start immediately upon transfer of the pathogenic effector T cells. Instead, as earlier studies have shown, the effector T cells attack their target organ only after having migrated in the periphery through secondary lymphoid organs. The aim of the project was to characterize the functional properties of these migrating encephalitogenic T cells during the course of EAE and to identify biological pathways which determine their migratory behaviour and pathogenic potential. To this end, average linkage hierarchical clustering, pathway and gene ontology (GO) analyses of transcriptomes from cultured and ex vivo-isolated myelin basic protein-reactive T cells (TMBP cells) were performed. At the time of transfer, encephalitogenic T cells in vitro are maximally activated, i.e. they exhibit a prominent upregulation of cell cycle genes such as cyclin A2 (CCNA2) and cyclin B2 (CCNB2) among others. In contrast, T cells isolated from spleen 3 days post transfer, downregulated activation markers such as interleukin 2 receptor (IL2R) and interferon γ (IFNγ), and at the same time upregulated migration specific genes such as CC-chemokine receptor 1 (CCR1), CC-chemokine receptor 2 (CCR2) and CC-chemokine receptor 5 (CCR5). Hierarchical cluster analysis revealed that several transcription regulators known for inhibiting cell cycle progression such as krüppel-like factor 4 (KLF4), B-cell translocation gene 2 (BTG2) and transducer of ERBB2, 1 (TOB1) were clustered together with cell cycle and migration genes. Overexpression of KLF4 in T cells not only inhibited G1/S phase progression of the cell cycle but additionally induced upregulation of CCR2 and CCR5. A novel tetraspan membrane protein called epithelial membrane protein (EMP1), was found to be up regulated in ex vivo-isolated effector T cells. Overexpression of EMP1 in encephalitogenic T cells influenced the migratory behaviour of effector T cells both in vitro and in vivo. EMP1 enhanced T cell motility within the extracellular matrix milieu in vitro and promoted T cell migration from the connective tissue to lymph nodes in vivo resulting in an accelerated onset of EAE. In conclusion, gene expression profiling of encephalitogenic T cells revealed interesting genome wide transcriptomic changes and established a correlation between cell cycle progression and cell migration. As a result, in silico analysis put forth several interesting candidate genes that hold promise as potential targets for therapeutic intervention.