Kurzfassung

IL-6 is instrumental for the priming of encephalitogenic T cells in organ specific autoimmunity. IL-6 needs to signal into T cells in order to (a) prevent the upregulation of Foxp3 and (b) to induce encephalitogenic properties in effector T cells including the expression of IL-17. While both events are required to induce clinical EAE, it is not completely resolved how these two events are linked in a molecular manner within a given T cell. In addition, the cellular sources that provide IL-6...IL-6 is instrumental for the priming of encephalitogenic T cells in organ specific autoimmunity. IL-6 needs to signal into T cells in order to (a) prevent the upregulation of Foxp3 and (b) to induce encephalitogenic properties in effector T cells including the expression of IL-17. While both events are required to induce clinical EAE, it is not completely resolved how these two events are linked in a molecular manner within a given T cell. In addition, the cellular sources that provide IL-6 to signal into T cells have not been investigated. Therefore, during the first funding period of this CRC, we have generated a number of tools to address the question which auxiliary cells are relevant for providing IL-6 in the process of priming encephalitogenic T cells. We have generated an IL-6 reporter/depleter construct that can be conditionally expressed in any cell lineage dependent on a distinct cre driver. We found that macrophages and dendritic cells (DCs) are the main sources of IL-6 in draining lymph nodes and spleens of MOG35-55 peptide induced EAE mice. Since genetic ablation of IL-6 in DCs completely abolished EAE, we conclude that DCs are the relevant source of IL-6 in priming encephalitogenic T cells. Notably, lack of IL-6 in DCs did not prevent the suppression of Foxp3 induction in antigen specific activated T cells. In addition, lack of IL-6Rα in DCs showed a similar phenotype. Thus, we propose that DCs – via their membrane bound IL-6Rα – are able to trans-present their own secreted IL-6 to T cells during antigen specific priming. While this mode of IL-6 signaling is indispensable for the induction of encephalitogenic properties in conventional T cells, classic membrane bound IL-6 signaling is sufficient to prevent the upregulation of Foxp3. Moreover, we could link IL-6 signaling by trans-presentation through DCs (cluster signaling) to enhanced Stat3 activation and show that this full activation of Stat3 is required to induce the encephalitogenic potential of conventional T cells. By contrast, suppression of Foxp3 in T cells is less dependent on Stat3 activation. In the follow-up project, we will first investigate the pathways downstream of the gp130/IL-6 receptor signaling complex in cluster signaling vs classic membrane bound IL-6 signaling. In functional terms, we will compare myelin antigen specific T cells generated under conditions of classic IL-6 signaling vs IL-6 cluster signaling. In a translational approach, we will analyse the IL-6 cluster signaling associated expression profile in T cells from healthy controls and from untreated and treated MS patients.
Second, using our IL-6 reporter mice, we will test the dynamics and anatomical compartments of IL-6 production in B cells during recombinant MOG protein induced EAE. While in MOG35-55 induced EAE, DCs and macrophages are major sources of IL-6, B cells play a crucial role as APCs and cytokine producers in EAE induced with recombinant hMOG protein. Thus, we will analyse IL-6- vs IL-6+ B cells in germinal centre reactions and functionally analyse B cell-derived IL-6 by B cell conditional ablation of Il6 and by anti-CD90.1 mediated depletion of IL-6 reporter (CD90.1) positive B cells in this model. Furthermore, IL-6Rα expression on B cell subsets will be assessed as well as the potential of B cells to undergo cluster signaling with distinct interaction partners. In a translational approach, the IL-6Rα status on B cells and the level of soluble IL-6Rα will be tested in healthy controls and MS patients.
Third, IL-6 has been proposed to be critically involved in chronic MS. Here, we will explore the role of astrocyte derived and microglia derived IL-6 during EAE by specifically expressing our IL-6 reporter or specifically ablating IL-6 in these glial cell types. In addition to ex vivo flow cytometric analysis of immune cell compositions, we will immune-monitor these animals by sequential CSF analysis.» weiterlesen» einklappen