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For a long time, the nervous system and the immune system have been studied as isolated entities, but a growing body of evidence shows that there is an extensive crosstalk between both systems. In fact, neurons and immune cells share certain functional features and reside in close proximity within the tissues, enabling them to effectively communicate. T cells are crucial for mounting and controlling almost any kind of immune response. However, when dysregulated, T cells fail to protect the host from invading pathogens or can cause damage to surrounding tissues, leading to autoimmunity-related pathology. In the first part of this cumulative thesis, we aimed at identifying novel genes regulating CD4 T cell responses and identified VIMP, one of the 25 human proteins containing the 21st amino acid selenocysteine, as a gene having anti-inflammatory functions. Furthermore, T cells express various neurotransmitter receptors allowing the integration of neuronal signal for an appropriate response. In the second part, we showed a CD4-T-cell-intrinsic mechanism through which stress hormones mediate their control over the immune system. We identified a previously unrecognized pathway regulating CD4 T cell differentiation that involves the circadian clock gene Per1 and mTORC1 signalling. Finaly, T cells involvement in different neuropathologies has been reported in the past few decades. Emerging evidence indicates the involvement of the immune system and in particular T cells in the pathogenesis of Parkinson’s disease (PD), the 2nd most common neurodegenerative disease. In the 3rd part of the thesis we systematically characterized the immunological status of early-to-mid stage PD patients and matched healthy controls, and identified a distinct peripheral immunological fingerprint in PD patients, especially in the CD8 T-cell compartment. The findings of the studies described in this cumulative thesis advance our understanding of the regulatory nodes of CD4 T cells during a stress response and fill the knowledge gap on the early involvement of CD8 T cells and other immune subsets in neurodegenerative diseases in the case of PD.

Decline in immune function during aging increases susceptibility to different aging related diseases. However, the underlying molecular mechanisms, especially the genetic factors contributing to imbalance of naïve/memory T-cell subpopulations, still remain largely elusive. Here we show that loss of DJ-1 encoded by PARK7 /DJ-1, causing early-onset familial Parkinson’s disease (PD), unexpectedly delayed immunoaging in both human and mice. Compared with two gender-matched unaffected sibling carriers of similar ages, the index PD patient with DJ-1 deficiency showed a decline in many critical immunoaging features, including almost doubled frequencies of non-senescent T cells. The observation of a ‘younger’ immune system in the index patient was further consolidated by the results in aged DJ-1 knockout mice. Our data from bone marrow chimera models and adoptive transfer experiments demonstrated that DJ-1 regulates several immunoaging features via hematopoietic-intrinsic and naïve-CD8-intrinsic mechanisms. Our finding suggests an unrecognized critical role of DJ-1 in regulating immunoaging, discovering a potent target to interfere with immunoaging- and aging-associated diseases.

Das angeborene Immunsystem ist die erste Verteidigungslinie gegen eindringende Krankheitserreger. Aufspürung von konservierten „pathogen-associated molecular patterns“ (PAMP) durch „pattern recognition receptors“ (PRR), initiiert die angeborene Immunantwort. Abhängig vom Rezeptor und der Art des PAMP, werden eine Vielzahl von Signalkaskaden aktiviert, was zu einer transkriptionellen Aktivierung von verschiedenen Genen führt. Diese Gene regulieren die Entzündungsreaktion und die angeborenen Wirtsabwehr. Listeria monocytogenes ist ein fakultativ intrazelluläres Bakterium, welches in der Lage ist, dem Phagosom ins Cytoplasma zu entweichen, wo es replizieren kann. L. monocytogenes wird zuerst durch PRR an der Zelloberfläche erkannt, was den „nuclear factor κB“ (NFκB) Signalweg und die Expression von NFκB-abhängigen Genen aktiviert. Nachdem der Erreger dem Phagosom entkommen ist, wird er durch cytoplasmatische Sensoren erkannt, welche die „interferon response factor 3“ (IRF3) -abhängige Expression und Sekretion von Typ-I-Interferone (IFN) induziert. Typ I Interferone binden wiederrum IFN-α Rezeptorkomplexe (IFNAR), die den „Janus kinase/signal transducers and activators of transcription“ (JAK/STAT) Signalweg aktivieren. Dies führt zur Bildung des „interferon-stimulated gene factor 3“ (ISGF3) komplex und zur Expression von Interferon-abhängigen Genen (ISG). Hier erzeugen und charakterisieren wir einen monoklonalen Antikörper gegen eine der Untereinheiten von ISGF3, nämlich IRF9. Wir zeigen, dass dieser Antikörper ein wertvolles Werkzeug ist um ISGF3 Interaktion mit Chromatin zu studieren. Im Gegensatz zu klassischen NFκB- oder IFN-abhängigen Genen, brauchen koregulierte Gene, einschließlich jenes Gen das für die „Nitric oxide synthase 2“ (Nos2), eine koordinierte Zusammenführung der Transkriptionsmaschinerie die sowohl von NFκB als auch von ISGF3 abhängig ist. Die Behandlung von Knochenmark Makrophagen (BMDMs) mit Hitze-inaktivierten Listerien (hkL) und IFN-β, aktiviert den NFκB und IFN-Signalweg. Diese Kostimulierung ähnelt einer Infektion mit lebenden Listerien. In dieser Studie wurde die Ausführbarkeit dieser Herangehensweise für das Studieren transkriptioneller Aktivierung von koregulierten Genen gezeigt. Sowohl hkL als auch der klassische NFκB Aktivator „tumor necrosis factor α“ (TNF-α), synergieren mit Typ I IFN bei der Expression von koregulierten Genen, obwohl hkL höhere Induktionsraten im Vergleich zu TNF-α hervorrief. Die Rekrutierung des allgemeinen Transkriptionsfaktors TFIIH, inklusive seiner CDK7 („cyclin-dependant kinase 7) Kinase Untereinheit, an den Nos2 Promotor ist abhängig von NFκB. Im Zuge dieser Arbeit wurden CDK7 und p65 ko-immunpräzipitiert. Dies ist ein Hinweis darauf, dass die Rekrutierung von TFIIH/CDK7 zum Nos2 Promotor das Ergebnis einer direkten Interaktion zwischen der NFκB Untereinheit p65 und CDK7 ist. Weitere Experimente werden benötigt um dies zu bestätigen. Unerwarteter Weise konnte eine Interaktion zwischen IRF9 und p65 gezeigt werden. Die Funktion dieser Wechselwirkung ist jedoch unklar., The innate immune system represents the first line of defence against invading path-ogens. Recognition of evolutionary conserved pathogen-associated molecular pat-terns (PAMP) by pattern recognition receptors (PRR) expressed on specialized cells of the innate immune system, initiates the innate immune response. Depending on the receptor and the nature of PAMP, a variety of signaling cascades are activated, leading to the transcriptional activation of distinct genes regulating inflammation and innate host defence. Listeria monocytogenes is a facultative intracellular pathogen able to evade the phagosome into the cytoplasm, where it replicates. L. monocyto-genes is first sensed by PRR at the cell surface, which activates the nuclear factor κB (NFκB) pathway to induce the expression of inflammatory genes. After phagoso-mal evasion, the pathogen is recognized by cytosolic sensors, which induce the inter-feron response factor 3 (IRF3) -dependent expression and secretion of type I Inter-ferons (IFN). In turn, type I interferons bind the IFN-alpha receptor (IFNAR) to further activate the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway, resulting in the assembly of the interferon-stimulated gene factor 3 (ISGF3) complex and thus to the expression of interferon stimulated genes (ISGs). Here we generate and characterize a monoclonal antibody against one of the ISGF3 subunits, IRF9. We demonstrate that this antibody is a valuable tool to study the ISGF3 interaction with chromatin. Unlike classical NFκB- or IFN-dependent genes, coregulated genes, including the gene coding for the Nitric oxide synthase 2 (Nos2), need a coordinated assembly of the transcription machinery dependent on both NFκB and ISGF3. Treating bone mar-row derived macrophages (BMDMs) with heat-killed Listeria (hkL) and IFN-β, acti-vates the NFκB and the IFN pathway respectively, mimicking the signaling profile of macrophages infected with L. monocytogenes. Here we demonstrate the feasibility of this approach for studying the transcriptional activation of coregulated genes. Both hkL and the classical NFκB activator, tumor necrosis factor α (TNF-α) synergized with type I IFN in stimulating expression of coregulated genes, although hkL gener-ated higher induction rates compared to TNF-α. Recruitment of the general transcription factor TFIIH and its kinase subunit CDK7 (cyclin-dependant kinase 7) to the Nos2 promoter during transcriptional activation is dependent on NFκB, hence hkL alone is sufficient to enrich TFIIH/CDK7 at the DNA. In the course of this thesis, CDK7 and p65 were co-immunoprecipitated after over-expression in HEK293 cells. Although needing further investigation, this is an indica-tion that the recruitment of TFIIH/CDK7 to the Nos2 promoter is the result of a direct interaction between NFκB p65 and CDK7. Although the implications of this interaction are unclear, IRF9 was also co-immunoprecipitated with p65.