The present COVID-19 pandemic has revealed that several characteristics render patients especially prone to developing severe COVID-19 disease, i.e., the male sex, obesity, and old age. An explanation for the observed pattern of vulnerability has been proposed which is based on the concept of low sensitivity of the TLR7-signaling pathway at the time of infection as a common denominator of vulnerable patient groups. We will discuss whether the concept of established TLR-tolerance in macrophages and dendritic cells of the obese and elderly prior to infection can explain not only the vulnerability of these two demographic groups towards development of a severe infection with SARS-CoV-2, but also the observed cytokine response in these vulnerable patients, which is skewed towards pro-inflammatory cytokines with a missing interferon signature.

<p>  </p> <p>The phosphatases of regenerating liver are a subfamily of protein tyrosine phosphatases that consist of PRL1, PRL2 and PRL3. The overexpression of PRLs promote cell proliferation, migration and invasion and contribute to tumorigenesis and metastasis to aggravate survival outcome. Although there is increasing interest in understanding the implication of these phosphatases in tumor development, currently, limited knowledge is available about their mechanism of action and the efficacy of PRL inhibition in <em>in vivo</em> tumor models, the tumor extrinsic role of PRLs that allow them to impact tumor development, as well as <em>in vivo</em> physiological function of PRLs that could implicate them in diseases other than cancer. The work presented here aims to address these limitations.</p> <p><br></p>

<p>Food allergies are immune system-driven diseases that lead to reproducible adverse reactions which can be fatal. These severe systemic reactions are primary mediated by immunoglobulin E (IgE) that is derived from B cells which have been activated by T helper type 2 (Th2) cells. While much work has advanced the clinical and pharmacological management of patients with allergic diseases, much remains to be elucidated about how individuals initially acquire allergy. This Thesis details a mechanism linking initial gastrointestinal exposure to peanut (PN) allergen, to the generation of Th2 cells: PN allergen activates epithelial cell secretion of interleukin (IL)-33 and eosinophil degranulation of eosinophil peroxidase, which causes CD103+ dendritic cell (DC) activation and migration to mesenteric lymph nodes where DC OX40L engages naïve T cells to secrete IL-4 in an autocrine/paracrine manner to promote and consolidate Th2 cell differentiation. These events are followed by B cell activation and PN-specific IgE production, which sensitizes mast cells to be hypersensitive to PN re-exposure by causing immediate allergic reactions including anaphylaxis. This is later followed by eosinophilic inflammation that is partially mediated by innate lymphoid cells. As food allergy also serves as a unique model to better understand mechanisms of adaptive immunity, especially Th2 immunobiology, both basic science and clinical implications are discussed in this Thesis. Major themes include Th2 and disease heterogeneity, identification of ‘the original source of IL-4’, an unprecedented <em>in vivo </em>requirement for eosinophils in priming adaptive immune responses, and the need to weigh basic science findings against the human disease <em>in natura </em>litmus test. Looking forward, many questions remain to be answered in the field of food allergy research, but the findings of this Thesis may be one step towards the prevention, management or cure of a disease with growing public concern, potentially fatal consequences, and an unmet need in understanding its pathogenesis.</p> / Doctor of Philosophy (Medical Science)

No / The ability of neurons to modulate synaptic strength underpins synaptic plasticity, learning and memory, and adaptation to sensory experience. Despite the importance of synaptic adaptation in directing, reinforcing, and revising the behavioral response to environmental influences, the cellular and molecular mechanisms underlying synaptic adaptation are far from clear. Brain-derived neurotrophic factor (BDNF) is a prime initiator of structural and functional synaptic adaptation. However, the signaling cascade activated by BDNF to initiate these adaptive changes has not been elucidated. We have previously shown that BDNF activates mitogen- and stress-activated kinase 1 (MSK1), which regulates gene transcription via the phosphorylation of both CREB and histone H3. Using mice with a kinase-dead knock-in mutation of MSK1, we now show that MSK1 is necessary for the upregulation of synaptic strength in response to environmental enrichment in vivo. Furthermore, neurons from MSK1 kinase-dead mice failed to show scaling of synaptic transmission in response to activity deprivation in vitro, a deficit that could be rescued by reintroduction of wild-type MSK1. We also show that MSK1 forms part of a BDNF- and MAPK-dependent signaling cascade required for homeostatic synaptic scaling, which likely resides in the ability of MSK1 to regulate cell surface GluA1 expression via the induction of Arc/Arg3.1. These results demonstrate that MSK1 is an integral part of a signaling pathway that underlies the adaptive response to synaptic and environmental experience. MSK1 may thus act as a key homeostat in the activity- and experience-dependent regulation of synaptic strength.

The MHC class I status of tumour cells during immunotherapy is often underestimated. It represents one of important tumour escape mechanisms and thus can contribute to the failure of most of the cancer clinical trials that are usually based on the induction of cytotoxic T cell responses. Epigenetic changes in the promoters of genes involved in the MHC class I Ag presentation can result in decreased expression of the cell surface MHC molecules on tumour cells. Thus, epigenetic modifiers can restore an expression of the MHC class I molecules and make tumours visible to the CD8+ effector cells. Besides the epigenetic changes on the tumour cells, epigenetic modulators affect cells of the immune system such as dendritic cells (DC). Tumour cells can escape from the immune response not only by changes in the cancer cells, but also by influencing, expanding and/or activating immunoregulatory cell populations, such as regulatory T cells (Treg). This thesis focuses on the potential of the DC-based vaccines against HPV-16-associated tumours with a different MHC class I expression, on the combination of cancer immunotherapy with the treatment using epigenetic modifiers, with special attention paid to their effects on DC, and, finally, on the impacts of the anti-CD25 antibody (used for Treg elimination) on Treg and NKT...

Das human pathogene Varicella-Zoster Virus (VZV) gehört zur Familie der Herpesviren und ist weltweit verbreitet. Die Primärinfektion verursacht Varicellen, welche durch einen bläschenartigen Hautausschlag charakterisiert ist. Im Anschluss daran etabliert VZV eine lebenslange Latenz und verursacht nach Reaktivierung Herpes Zoster. Seit 2004 ist der Lebendimpfstoff aus attenuierten Virionen des VZV-Stammes V-Oka in Deutschland empfohlen. Im Gegensatz zur Infektion mit zirkulierenden virulenten VZV Stämmen tritt nach Verimpfung des Vakzin-Stammes V-Oka kein Exanthem auf. Die Haut ist der Hauptreplikationsort von VZV und immunologische Unterschiede zwischen virulentem VZV und dem Vakzin-Stamm treten hier am deutlichsten auf. In der vorliegenden Arbeit konnte eine neue Immunevasionsstrategie virulenter VZV Stämme aufgedeckt werden, welche erklären könnte, wie virulente VZV Stämme frühe antivirale Immunantworten umgehen. In Hautläsionen von Herpes Zoster Patienten konnte eine massive Infiltration von myeloiden inflammatorischen Dendritischen Zellen beobachtet werden. In vitro Studien mit Monozyten abgeleiteten Dendritischen Zellen (DC), welche inflammatorische DC repräsentieren, zeigten, eine signifikant erhöhte Expression von CD1c Molekülen nach Infektion mit dem Vakzin-Stamm, sowie virulentem VZV. Funktionelle Untersuchungen mit intraepithelialen CD1c-restringierten gamma delta T Zellen zeigten, dass DC nach Infektion mit dem Vakzin-Stamm phänotypisch und funktionell reiften und somit die T Zellen zur IFN-gamma Sekretion stimulierten. Im Gegensatz dazu wurde die funktionelle Reifung von DC, die mit virulentem VZV infiziert waren, geblockt. Folglich wurde kein bioaktives IL-12 sezerniert, welches als entscheidendes Cytokin zum Aufbau einer antiviralen T-Helfer 1 Immunantwort beiträgt. Darüber hinaus konnte gezeigt werden, dass virulentes VZV die Signalkaskade des Toll-like Rezeptors 2 (TLR2) in DC inhibiert und somit die IL-12 Produktion verhindert. / Varicella-zoster virus (VZV) which belongs to the family of herpesviruses is restricted to humans and distributed worldwide. Primary infection of VZV causes chickenpox characterized by a disseminated rash. Thereafter, VZV establishes a lifelong latency and can be reactivated to cause herpes zoster. Since 2004 the attenuated strain V-Oka of VZV was licensed for Germany to immunize children against VZV infection. In contrast to infection by circulating virulent VZV strains, vaccination with V-Oka remains asymptomatic. The skin is the major replication site of VZV and immunological differences between virulent VZV and the vaccine should become most apparent within this immune organ. In summary, this study discovered a new immune evasion strategy of virulent VZV strains which might explain how virulent VZV strains overcome innate antiviral responses. A strong infiltration of myeloid-derived inflammatory DCs has been detected in skin lesions of herpes zoster patients. In vitro studies with monocyte-derived dendritic cells (DCs), reflecting inflammatory DCs, showed that they were efficiently infected by both, the vaccine and a virulent VZV strain. Intriguingly, a significant upregulation of CD1c molecules on VZV-infected DCs was observed. Functional investigations using intraepithelial CD1c-restricted gamma delta T cells revealed that DCs infected with the vaccine virus were fully instructed to mature, thereby promoting IFN-gamma secretion of gamma-delta T cells. In striking contrast, DCs infected with virulent VZV strains were efficiently blocked to mature functionally. In detail, they did not secrete bioactive IL-12 which is an instrumental cytokine for generation of antiviral T helper 1 responses. Moreover, virulent VZV blocked Toll-like receptor 2 (TLR2) signaling in DCs thereby preventing production of bioactive IL-12 which in turn inhibited IFN-gamma secretion by gamma-delta T cells.

Dendritische Zellen (DZ) sind essentiell für die Aktivierung von Immunantworten. Drei Flt3-abhängige DZ Populationen aus dem Blut bestehend aus konventionellen (kDZ) BDCA1+ DZs und BDCA3+ DZs und plasmazytoide DZs wurden bereits beschrieben. Hier wurden zum ersten Mal sich aus Monozyten entwickelnde DZ (moDZ), genauer BDCA1+CD14+ pro-inflammatorische DZ (pro-iDZ) aus periphärem Blut unter homöostatischen Bedingungen identifiziert. Isolierte pro-iDZ sekretierten spontan große Mengen an pro-inflammatorischen Zytokinen, die kDZ reifen ließen und T Zell Proliferation unterstützten. Sie waren BDCA1+CD14- DZ und CD14+CD16- Monozyten in der TH17 Zell Induktion überlegen. Pro-iDZ ähnliche BDCA1+CD14+ Zellen konnten durch imaging cycler microscopy in Geweben von Patienten die an Psoriasis, Dermatomyositis oder entzündetem Halonävus erkrankt waren identifiziert werden. Ihr Fehlen in gesunder Haut deutete eine Rekrutierung von pro-iDZs in entzündetes Gewebe an. Eine Verwandtschaftsanalyse von pro-iDZ zwischen Monozyten, kDZ des Blutes und in vitro generierten moDZ auf genomweiter Ebene wies auf einen monozytären Ursprung hin. Anylse mittels funktioneller Annotation auf differentiell exprimierten Genen zwischen pro-iDZ und Monozyten zeigte eine DZ spezifische Gensignatur auf. Diese Gene waren insgesamt in der gleichen Weise wie in kDZ und moDZ reguliert, das eine Entwicklung von Monozyten nach DZ nahelegte. Dieses Entwicklungskonzept wurde insofern unterstützt, indem unter entzündlichen Bedingungen kultivierte CD14+CD16- Monozyten BDCA1 Expression und DZ Funktion erlangten. Da pro-iDZ sehr ähnlich zu BDCA1+CD14+ Zellen aus entzündeter Haut waren und beide große Konvergenz mit zuvor beschriebenen BDCA1+CD14+ inflammatorischen DZ (infDZ) aus entzündeten Geweben aufwiesen, können pro-iDZ als direkte infDZ Vorläufer angesehen werden. Dadurch und wegen ihrer monozytären Herkunft können pro-iDZ als Beweis für die humane Differenzierung von Monozyten nach DZ in vivo betrachtet werden. / Dendritic cells (DCs) are critical for the activation of immune responses. Three Flt3-dependent blood DC populations including conventional BDCA1+ DCs and BDCA3+ DCs (cDCs) and plasmacytoid DCs were described previously. This work identifies for the first time human peripheral blood monocyte derived BDCA1+CD14+ pro-inflammatory DCs (pro-iDCs) during steady state. Isolated pro-iDCs spontaneously secreted high amounts of pro-inflammatory cytokines, which matured cDCs and promoted T cell proliferation. They were superior in priming TH17 cells when compared to BDCA1+CD14- DCs and CD14+CD16- monocytes. BDCA1+CD14+ cells resembling blood pro-iDCs as identified by imaging cycler microscopy were found in samples from patients suffering from psoriasis, dermatomyositosis and inflamed halo nevus. Their absence in healthy donor’s skin indicated a recruitment of pro-iDCs to sites of inflammation. Analysis of the developmental relationship of pro-iDCs between monocytes, blood cDCs and in vitro generated monocyte derived DCs (moDCs) on whole genome level strongly suggested a monocytic origin. Functional annotation analysis of differentially regulated genes between monocytes and pro-iDCs revealed a DC specific gene signature. In addition, these genes were overall regulated in the same way in blood cDCs and moDCs, indicating an ongoing development of pro-iDCs from monocytes towards DCs. This developmental concept was supported as CD14+CD16- monocytes cultured under inflammatory conditions gained BDCA1 expression and DC function. Since pro-iDCs were highly similar to BDCA1+CD14+ cells found in inflamed skin and as both showed a marked convergence with BDCA1+CD14+ inflammatory DCs (infDCs) present in inflamed tissues described previously, pro-iDCs can be regarded as immediate precursors of infDCs. Thus, in respect of a monocytic origin and a presumably inflammatory DC fate, pro-iDCs may constitute a missing link to prove human moDC differentiation in vivo.

Dans l'introduction, diverses voies de trafic intracellulaire et endocytose seront discutées. Je familiarise le lecteur avec des protéines inactivant les ribosomes, en mettant l'accent sur la structure, l'endocytose, et le trafic intracellulaire de la toxine bactérienne Shiga toxin (STX). STx et la ricine suivent la voie rétrograde pour exercer leur effet toxique sur les cellules. Ils sont respectivement, une menace maladie infectieuse pour la santé humaine et des outils potentiels pour le bioterrorisme pour lequel aucun antidote n’existe actuellement. D'un criblage à haut débit, Retro-1 et Retro-2 avaient déjà été identifiés comme de puissants inhibiteurs de la voie rétrograde à l'interface des endosomes précoces-TGN, et Retro-2 a été démontré pour protéger les souris contre la ricine. Parmi les facteurs de trafic analysés, seule la protéine SNARE syntaxine-5 a été ré- localisée dans les cellules traitées avec Rétro - 2. / In the introduction, various endocytic and intracellular trafficking pathways will be discussed. I acquaint the reader with ribosome-inactivating proteins, with emphasis on the structure, endocytosis, and intracellular trafficking of the bacterial toxin Shiga toxin (STx). STx and ricin follow the retrograde route to exert their toxic effect on cells. They are respectively, an infectious disease threat to human health and potential tools for bioterrorism for which no antidote currently exists. From a high throughput screening, Retro-1 and Retro-2 had previously been identified as potent inhibitors of the retrograde route at the early endosomes-TGN interface, and Retro-2 was demonstrated to protect mice against ricin. Of the trafficking factors analyzed, only the SNARE protein syntaxin-5 was re-localized in Retro-2 treated cells. Yet, whether syntaxin-5 is the direct target of Retro-2 and whether its re-localization was directly responsible for retrograde transport inhibition remained to be established.

In this work, the influence of the second messenger cAMP on the functional plasticity of M-DC8+ dendritic cells (DC) was examined. The marker M-DC8 defines a population of native DC first described in blood. After their isolation, M-DC8+ DC acquire a mature CD83+ phenotype during a short culture ex vivo. After a challenge with LPS and IFN-g, M-DC8+ DC secrete large amounts of the proinflammatory cytokines IL-12(p70) and TNF-a surpassing by far other DC populations and monocytes. Due to their preferential induction of TH1-dominated T cell responses, M-DC8+ DC might play a role in the pathogenesis of inflammatory diseases. Different cAMP-elevating agents suppressed the proinflammatory cytokine production and enhanced the secretion of anti-inflammatory IL-10. Activity of phosphodiesterase (PDE) 4, the most important cAMP-hydrolysing enzyme in immune cells, was detected and RT-PCR revealed the expression of PDE4 subtypes 4A, 4B and 4D in M-DC8+ DC, whereas 4C was not detectable. The PDE4-specific inhibitors AWD12-281 and Roflumilast were then used to elevate cAMP concentrations. These substances have been proven to be efficient in anti-inflammatory therapies. In the presence of PDE4 inhibitors, the LPS/IFN-g-induced production of IL-12 and TNF-a was decreased by 90 % and 60 %, respectively, whereas the IL-10-release was doubled. These effects were only observed, if the PDE4 inhibitors where present from the beginning of the culture. The inhibition of the IL-12 secretion was reverted using an a-IL-10-receptor antibody. PDE4 inhibitor-treated M-DC8+ DC showed a reduced capacity to polarize TH1-cells, which was demonstrated analysing culture supernatants by ELISA and by single-cell analysis detecting intracellular IFN-g und IL-4. These results suggest that PDE4 inhibitors may not only be useful in the therapy of TH2-mediated diseases but also in TH1-dominated indications such as multiple sclerosis and Crohn´s disease. Despite the shift of the cytokine profile, the in vitro maturation of M-DC8+ DC was not affected by PDE4 inhibitors. The expression of CD83, CD80, CD86, MHC-molecules as well as CD54 and CD58, was assessed by FACS analysis. Correspondingly, in the presence of AWD12-281, M-DC8+ DC efficiently stimulated the proliferation of allogeneic CD4+CD45RA+ T-cells. In the second part of this study, the effects of an inhibition of cAMP-synthesis in M-DC8+ DC were analyzed. Two adenylyl cyclase (AC) inhibitors, 2,5-Dideoxyadenosine and SQ22536, clearly hampered the in vitro maturation of M-DC8+ DC. The expression of the DC maturation marker CD83 could be reconstituted using the stable cAMP-analogon 8-Br-cAMP. Measuring the intracellular cAMP concentration in M-DC8+ DC, initially low cAMP-levels were observed, but within 30 min the concentration raised and returned to original levels within 2 hrs. Blocking the cAMP synthesis by AC inhibitors, the LPS/IFN-g-induced production of IL-12, TNF-a and IL-10 was strongly reduced. Furthermore, it was demonstrated that M-DC8+ DC can only release IL-12 after a transient elevation of cAMP, i.e. they acquire a &amp;quot;license&amp;quot;. Such a regulation of the IL-12 production has not been described before. Protein kinase A is an important effector molecule of cAMP. Inhibiting its activity resulted in a reduced expression of the DC maturation marker CD83 and a lower cytokine production underlining the importance of cAMP-signalling for the activation of M-DC8+ DC. In conclusion, this study provides evidence for a new concept of the immune-regulatory function of cAMP. Here, cAMP is essentially involved in the initial activation and maturation of DC and enables them to secrete large amounts of IL-12 and TNF-a upon stimulation with a TLR ligand. Conversely, a long-term elevation of cAMP-concentrations inhibits the proinflammatory effector functions of M-DC8+ DC and can induce anti-inflammatory responses by enhancing the secretion of IL-10. / In dieser Arbeit wurde der Einfluss des second messengers cAMP auf die funktionelle Plastizität von M-DC8+ dendritischen Zellen (DC) untersucht. Der Oberflächenmarker M-DC8 definiert eine zunächst im Blut beschriebene Population nativer DC. Nach ihrer Isolation erlangen M-DC8+ DC während einer kurzen Kultur einen maturen CD83+ Phänotyp. Nach Stimulation mit LPS und IFN-g produzieren native M-DC8+ DC deutlich höhere Mengen der proinflammatorischen Zytokine IL-12(p70) und TNF-a als andere DC-Populationen oder Monozyten. Dies resultiert in einer Programmierung TH1-dominierter T-Zellantworten. M-DC8+ DC könnten daher an der Pathogenese entzündlicher Krankheiten beteiligt sein. Unterschiedliche cAMP-erhöhende Substanzen supprimierten die proinflammatorische Zytokinproduktion und verstärkten gleichzeitig die Sekretion des anti-inflammatorischen IL-10. In M-DC8+ DC konnte die Aktivität von Phosphodiesterase (PDE) 4, dem wichtigsten cAMP-hydrolysierenden Enzym in Immunzellen, nachgewiesen werden. Durch RT-PCR wurde die Expression der PDE4-Subtypen 4A, 4B und 4D gezeigt, nicht aber 4C. Zur Erhöhung der cAMP-Konzentration wurden dann die PDE4-spezifischen Inhibitoren AWD12-281 und Roflumilast eingesetzt, deren klinische Effizienz bei anti-inflammatorischen Therapien belegt ist. Auch diese Substanzen verringerten die LPS/IFN-g-induzierte Produktion von IL-12 und TNF-a durch M-DC8+ DC um 90 % bzw. 60 %, während die IL-10-Freisetzung etwa verdoppelt wurde. Diese starken Effekte konnten nur erzielt werden, wenn die PDE4-Inhibitoren von Beginn der Kultur an eingesetzt wurden. Die Hemmung der IL-12-Sekretion wurde in Gegenwart eines a-IL-10-Rezeptor-Antikörpers aufgehoben. Unter dem Einfluss von PDE4-Inhibitoren war die TH1-Programmierung durch M-DC8+ DC deutlich reduziert, was sowohl durch die Analyse der Zellüberstände mittels ELISA als auch auf Einzelzell-Ebene durch intrazelluläre Detektion von IFN-g und IL-4 nachgewiesen wurde. Diese Ergebnisse legen nahe, dass PDE4-Inhibitoren nicht nur für TH2-vermittelte Erkrankungen sondern auch für TH1-dominierte Indikationen wie Multiple Sklerose oder Morbus Crohn von Nutzen sein könnten. Trotz der starken Modulation des Zytokinprofils blieb die in vitro-Ausreifung M-DC8+ DC unbeeinflusst von PDE4-Inhibitoren. Untersucht wurde die Expression von CD83, CD80, CD86, MHC-Molekülen, CD54 und CD58 mittels FACS-Analyse. Entsprechend induzierten M-DC8+ DC auch in Anwesenheit von AWD12-281 die Proliferation allogener CD4+CD45RA+ T-Zellen. Im zweiten Teil der Arbeit wurde untersucht, wie sich die Blockade der cAMP-Synthese auf M-DC8+ DC auswirkt. Zwei Adenylatcyclase-Inhibitoren, 2,5-Dideoxyadenosine und SQ22536, hemmten die in vitro-Maturation von M-DC8+ DC deutlich. Die CD83-Expression wurde mit 8-Br-cAMP rekonstituiert. Messungen der intrazellulären cAMP-Konzentration in unbehandelten M-DC8+ DC zeigten initial niedrige cAMP-Spiegel, die innerhalb von 30 min anstiegen und nach 2 h wieder auf das Ausgangsniveau abfielen. Die LPS/IFN-g-induzierte Produktion von IL-12, TNF-a und IL-10 wurde durch AC-Inhibitoren deutlich vermindert. M-DC8+ DC erhalten nur nach einer transienten cAMP-Erhöhung die &amp;quot;Lizenz&amp;quot; IL-12 freizusetzen. Eine derartige Regulation der IL-12-Sekretion ist bisher nicht beschrieben. Eine Hemmung des cAMP-Effektormoleküls Proteinkinase A resultierte in der reduzierten Expression des DC-Maturationsmarkers CD83 und einer verringerten Zytokinproduktion. Dies unterstreicht die Bedeutung von cAMP für die Aktivierung M-DC8+ DC. Zusammenfassend gibt diese Arbeit am Beispiel nativer humaner DC Anhalt für ein neues Konzept der immunregulatorischen Funktion von cAMP. Hierbei ist cAMP wesentlich an der Ausreifung von M-DC8+ DC beteiligt, woraufhin diese große Mengen IL-12 und TNF-a sekretieren können. Dagegen wirkt eine langfristige cAMP-Erhöhung durch die Induktion von IL-10 anti-inflammatorisch.

Albert Font Haro ABSTRACT Modulation of plasmacytoid dendritic cell function: role of immunoreceptors TIM-3 and BDCA-2 Plasmacytoid dendritic cells (pDCs) are key players in the antiviral response as well as in linking innate and adaptive immune response. They express endosomal toll-like receptors 7 and 9, which can detect ssRNA and unmethylated CpG DNA, respectively. Due to the constitutive expression of the transcription factor IRF7, pDCs are able to rapidly produce massive quantities of type I (α, β, ω) and type III (1, 2, 3, 4) interferons (IFN-I and IFN-III) as well as pro- inflammatory cytokines such as IL-1, IL-6 and TNF-α. After maturation, they also function as antigen-presenting cells. Despite intense research, the mechanisms of IFN and pro-inflammatory cytokines production and regulation are still poorly understood. Using the pDC cell line GEN2.2 and also primary human pDCs, we shed light on the role of kinases MEK and SYK in IFN-I production and regulation. We found that SYK is not only involved in the regulatory receptor (RR)-mediated BCR-like pathway that represents the negative regulation of IFN-I and IFN-III secretion but also in the positive TLR7/9-mediated signal transduction pathway that leads to IFN-I production, representing the immunogenic function. We also found that MEK plays a...