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DNA synthesis and adenosine(S')tetraphosphate(S ')adenosine (Ap.A) levels decrease in cells treated with EDTA. The inhibitory effect of EDTA can be reversed with micro molar amounts of ZnCI2• ZnCh in micromolar concentrations also inhibits Ap.A hydrolase and stimulates amino acid-dependent Ap.A synthesis, suggesting that Zn2+ is modulating intracellular Ap.A pools. Serum addition to GI-arrested cells enhances uptake of Zn, whereas serum depletion leads to a fivefold decrease of the rates of zinc uptake. These results are discussed by regarding Zn2+ as a putative 'second messenger' of mitogenic induction and Ap.A as a possible 'third messenger' and trigger of DNA synthesis.
Circa 1% der Weltbevölkerung ist an schizophrenen Psychosen erkrankt. Durch Störung kognitiver und exekutiver Funktionen bedürfen diese Patienten regelmäßiger Untersuchung und Betreuung, was nicht nur für den einzelnen Betroffenen, sondern auch sozioökonomisch bedeutsam ist. Die Einteilung der endogenen Psychosen nach Karl Leonhard stellt eine hoch differenzierte, nosologisch orientierte Krankheitsklassifikation dar, die sich durch eine exakte Darstellung der diagnostischen Kriterien und durch eine Vielzahl von präzise voneinander abgegrenzten Krankheitsbildern mit spezifischer Verlaufscharakteristik auszeichnet. Der in dieser Arbeit vertretene Ansatz geht davon aus, dass es sich bei den schizophrenen Psychosen nicht um eine einzelne Erkrankung, sondern um verschiedene Krankheitsentitäten handelt, die wiederum unterschiedlichen pathogenentischen Prinzipien unterliegen. Ziel war es darzustellen, dass sich die zykloiden Psychosen mit immer wiederkehrenden Manifestationen im Vergleich zu den unsystematischen Schizophrenien mit überwiegend hereditärer Genese und im Vergleich zu den monomorph und monophasisch ablaufenden systematischen Schizophrenien hinsichtlich der Immunparameter deutlich unterschieden. Methode: Um eine mögliche Immunpathogenese bestimmter Formen endogener Psychosen belegen zu können, wurden in einer retrospektiven Untersuchung 61 Patienten aus dem schizophrenen Formenkreis nach Karl Leonhard (32 zykloide Psychosen, 21 unsystematische und 12 systematische Schizophrenien) gegenübergestellt und hinsichtlich ausgewählter Immunparameter aus Serum und Liquor, klinischer Verlaufsparameter und soziodemographischer Variablen untersucht. Ergebnisse: Die Analyse immunologischer Parameter aus Serum und Liquor erbrachte keine signifikanten Unterschiede zwischen den einzelnen Erkrankungsgruppen. Ebenso wurden bei der Verteilung auf beide Geschlechter, bei der Anzahl von Allergikern und bei der Anzahl der Patienten mit Gefäßrisikofaktoren keine signifikanten Unterschiede zwischen den Erkrankungsgruppen nach der Leonhard-Klassifikation ermittelt. Auch die Untersuchung peripherer Parameter und Serum- Liquorparametern bei Patienten mit Erstdiagnose ergab keine signifikanten Unterschiede. Im Rahmen einzelner klinischer Verlaufsparameter unterschieden sich jedoch die zykloiden Psychosen signifikant von den schizophrenen Psychosen. Konklusion: In einer Folgestudie könnte die Analyse speziellerer Immunparameter, wie beispielsweise Zytokine, wichtige Hinweise erbringen, um die zykloiden Psychosen auch auf paraklinischem Wege von chronisch schizophrenen Psychosen zu differenzieren und um neue, auf mögliche immunologische Prozesse abgestimmte Behandlungsalternativen prüfen zu können.
As critical steps in the life cycle oJ measles virus (Mfl), the e.fficiency of uptake into and replication in susceptible host cells are governed by cellular determinants. Measles virus infections of cells of the human CNS are characterized by particular constraints imposed on v1:ral transcription and translation attenuating viral gene Junctions and thus contributing to the pathogenesis oJ MV persistence in these cells.
The role of host dendritic cells during the effector phase of intestinal graft-versus-host disease
(2014)
Monocytes can be functionally divided in two subsets, both capable to differentiate into dendritic cells (DCs): CX3CR1loCCR2+ classical monocytes, actively recruited to the sites of inflammation and direct precursors of inflammatory DCs; and CX3CR1hiCCR2− non-classical monocytes, characterized by CX3CR1-dependent recruitment to non-inflamed tissues. Yet, the function of non-classical monocyte-derived DCs (nc-mo-DCs), and the factors, which trigger their recruitment and DC differentiation, have not been clearly defined to date. Here we show that in situ differentiated nc-moDCs mediate immunosuppression in the context of intestinal graft-versus-host disease (GVHD).
Employing multi-color confocal microscopy we observed a dramatic loss of steady state host-type CD103+ DC subset immediately after transplantation, followed by an enrichment of immune-regulatory CD11b+ nc-moDCs. Parabiosis experiments revealed that tissue-resident non-classical CX3CR1+ monocytes differentiated in situ into intestinal CD11b+ nc-moDCs after allogeneic hematopoietic cell transplantation (allo-HCT). Differentiation of this intestinal DC subset depended on CSF-1 but not on Flt3L, thus defining the precursors as monocytes and not pre-DCs. Importantly, CX3CR1 but not CCR2 was required for this DC subset differentiation, hence defining the precursors as non-classical monocytes. In addition, we identify PD-L1 expression by CX3CR1+ nc-moDCs as the major mechanism they employ to suppress alloreactive T cells during acute intestinal GVHD. All together, we demonstrate that host nc-moDCs surprisingly mediate immunosuppression in the context of murine intestinal GVHD – as opposed to classical “inflammatory” monocyte-derived dendritic cells (mo-DCs) – via coinhibitory signaling. This thorough study unravels for the first time a biological function of a - so far only in vitro and phenotypically described - DC subset. Our identification of this beneficial immunoregulatory DC subset points towards alternate future strategies in underpinning molecular pathways to foster their function. We describe an unexpected mechanism of nc-moDCs in allo-HCT and intestinal GVHD, which might also be important for autoimmune disorders or infections of the gastrointestinal tract.
Cutaneous leishmaniasis is an infectious disease that is endemic especially in tropical and desert regions with an incidence of 1.5 million cases per year and a prevalence of 12 million people infected worldwide. The infection can be caused by the intracellular parasite Leishmania major. The disease has been studied extensively in the murine model. It has become apparent that the induction of a class of interferon (IFN)--producing CD4+ T helper cells (TH1 cells) that activate macrophages to kill the parasites they harbor is desicive for the establishment of immunity. The redirection of the host’s immune response towards a protective TH1 phenotype will also be the key to an effective vaccine. Dendritic cells (DC) loaded with leishmanial antigens ex vivo were lately described as vaccines against L. major infections. One single recombinant Leishmania antigen, LeIF (Leishmania homologue of eukaryotic ribosomal initiation factor 4a), which was identified as a protein that stimulates DC to secrete interleukin (IL)-12 and discussed as a pattern-associated molecular pattern (PAMP), was found to mediate a protective TH1-dependent effect when used for pulsing of DC. The application of recombinant proteins is tied to many disadvantages, which is why other methods of antigen administration have been developed. RNA electroporation of DC has recently emerged from tumor research as a safe and versatile method of antigen delivery, by which a large number of RNA molecules encoding a specific antigen gains access to the cytosol of DC by an electrical impulse. The present study describes, for the first time, transfection of DC with RNA encoding a molecularly defined parasite antigen. Initially, a standardized protocol for RNA transfection was established, using the enhanced green fluorescent protein (EGFP) as reporter antigen. EGFP-RNA was well translatable in an in vitro translation system, and both a DC cell line (fetal skin-derived DC; FSDC) and murine primary bone marrow-derived DC (BMDC) could be transfected efficiently, with a yield of up to 90% and 75%, respectively. In both cell types, maximal transfection efficiency was attained with 20 µg RNA and could not be further increased with larger amounts of RNA. The level of antigen expression, measured as the mean fluorescence intensity (MFI) by flow cytometry, was directly proportional to the amount of RNA used for transfection. In FSDC, transfection efficiency and MFI were generally higher than in BMDC when the same amounts of RNA were used. Furthermore, the kinetics was shown to be sensitive to treatment with lipopolysaccharide (LPS): the expression peak was higher and was reached sooner, followed by a more rapid decline. In transfection experiments with LeIF, two variants of LeIF-RNA were used: LeIF(fl)-RNA, encoding the complete LeIF sequence, and LeIF(226)-RNA, encoding only the aminoterminal half of the LeIF sequence (226 amino acids), the immunogenic part of LeIF. Only LeIF(fl) was detectable by Western Blot in whole cell lysates of BMDC after LeIF(fl)-RNA transfection, whereas LeIF(226) could never be detected in LeIF(226)-transfected BMDC. However, as both constructs were well translatable in a cell-free system, the failure to detect LeIF(226) in BMDC lysates did not represent a failure in RNA translation, but rather a rapid antigen degradation. It was therefore expected that LeIF(226)-transfected BMDC should nevertheless be able to present LeIF(226)-derived antigenic peptides to T cells from BALB/c mice primed with recombinant LeIF (rLeIF). This hypothesis was confirmed by measuring IFN- production in BMDC-T cell co-incubation assays, showing that rLeIF-pulsed, LeIF(226)- and LeIF(fl)-transfected day 7 BMDC did indeed activate T cells from LeIF-immunized mice in an antigen-specific manner. In contrast, IL-4 was not produced, which was consistent with the fact that T cells found in lymph nodes from LeIF-primed mice are primarily of the TH1 type. In the supernatants of LeIF-transfected BMDC cultures, in contrast to rLeIF-pulsed BMDC, the proinflammatory cytokines IL-1β, IL-6, IL-10 and IL-12 were not detected. This effect was not due to the electroporation procedure, as cytokine production by BMDC electroporated with rLeIF was only partially impaired. Also, the expression levels of CD86 were lower upon LeIF transfection than after pulsing with rLeIF. Thus, LeIF transfection did not induce maturation of DC. In conclusion, LeIF-transfected BMDC may have acted as semi-mature antigen-specific tolerance inducers, with regulatory T cells as responders. The effect of LeIF transfection on the immunostimulatory capacity of BMDC was not significantly increased when day 8 or 9 BMDC were used. However, day 8, and even more day 9 BMDC pulsed with rLeIF mounted a vigorous T cell response. Day 9 BMDC were able to activate naïve T cells. In conclusion, before a strong T cell response against LeIF can be induced, DC need to – besides presenting antigen and expressing co-stimulatory molecules – exhibit a susceptibility to the innate signaling molecule LeIF which is linked to their maturation age. This third signal is provided by extracellular rLeIF, but it is not conveyed – or is suppressed – by intracellular LeIF after LeIF-RNA transfection. Furthermore, electroporation of rLeIF abrogated IL-12 production by BMDC completely, the production of IL-1 was reduced with higher antigen doses, and the production of IL-10 was partially increased. The IL-6 production was unaffected. This altered cytokine profile suggests that LeIF as a PAMP might have a bipartite nature: besides exhibiting the capacity to stimulate IL-12 production upon extracellular presence, thereby enhancing host resistance against L. major, LeIF could also contribute to parasitic host evasion mechanisms from intracellular compartments of DC, possibly by interfering with mitogen-activated protein (MAP) kinase signaling pathways. Thus, the adjuvant properties of LeIF depend both on its mode of delivery (transfection with RNA vs. pulsing with the recombinant protein) and the targeted compartment (extra- vs. intracellular). From this work, it can be summarized that BMDC are well transfectable with a parasite antigen. The antigen is processed and presented, but it is not recognized as a PAMP by DC. Hence, transfection with antigen-encoding mRNA by itself does not convey all necessary signals for the elicitation of a potent immune response.
Interleukin-4 (IL-4) und Interleukin-13 (IL-13) sind bedeutende Regulatorproteine des Immunsystems. Sie spielen eine entscheidende Rolle bei der Entstehung und dem Verlauf von allergischen Erkrankungen, wie z.B. Asthma. Um ihre Signale in die Zielzelle zu transduzieren, kann von beiden Zytokinen der gleiche Zelloberflächenrezeptor verwendet werden, wodurch sich die überlappenden, biologischen Funktionen erklären lassen. Dieser gemeinsam genutzte Rezeptor ist aus den beiden Untereinheiten IL-4Ralpha; und IL-13Ralpha1 aufgebaut. Da IL-4 und IL-13 auf Aminosäureebene nur etwa 25% Sequenzidentität besitzen und stark unterschiedliche Affinitäten zu den beiden Rezeptorketten besitzen, stellt sich die Frage, durch welchen molekularen Erkennungsmechanismus, die Affinität und die Spezifität der Ligand-Rezeptor-Interaktion unabhängig voneinander reguliert werden kann. In dieser Arbeit gelang es, rekombinante Expressions- und Aufreinigungsstrategien für IL-13 und die extrazellulären Domänen der Rezeptorketten IL-13Ralpha1 und IL-13Ralpha2 zu entwickeln. Dadurch war es mögliche, eine breite Mutations-/Interaktionsanalyse der IL-13Ralpha1-Kette durchzuführen.Es konnte gezeigt werden, dass die N-terminale FnIII-ähnliche Domäne von IL-13Ralpha1 sowohl an der Bindung von IL-13 als auch an der Interaktion mit IL-4 beteiligt ist. Im funktionellen Bindeepitop der IL-13Ralpha1-Kette wurden die Aminosäurereste Arg84, Phe253 und Tyr321 als Hauptbindungsdeterminanten für die Interaktion mit IL-13 identifiziert. Durch die Interaktionsstudien der IL-13Ralpha1-Varianten mit IL-4 wurde gezeigt, dass diese Hauptbindungsdeterminanten auch für die niederaffine Bindung von IL-4 von größter Bedeutung sind. Die funktionellen Bindeepitope für IL-4 und IL-13 auf der IL-13Ralpha1-Kette sind nahezu identisch und überlappen in einem großen Bereich. Aufgrund der Ergebnisse aus der Mutagenesestudie war es möglich, ein Strukturmodell der extrazellulären Domäne der IL-13Ralpha1-Kette zu erstellen. Darin wird eine neuartige Orientierung der N-terminalen FnIII-Domäne und deren Beteiligung an der Ligandeninteraktion dargestellt. Mit Hilfe des Strukturmodells gelang es, neue Aminosäurerest auf der Oberfläche von IL-13 zu identifizieren, die an der Bindung zu IL-13Ralpha1 beteiligt sind, was die Relevanz des Strukturmodells weiter unterstreicht. In einem weiteren Teil dieser Arbeit wurde versucht, den molekularen Mechanismus aufzuklären, durch den es den superagonistischen IL-4-Varianten T13D und F82D gelingt, mit dreifach höherer Affinität an die IL-4Ralpha-Kette zu binden, als wildtypischer Ligand. Durch strukturelle und funktionelle Untersuchungen wurde gezeigt, dass der Affinitätssteigerung ein indirekter Mechanismus zugrunde liegt, bei dem eine Konformationsänderung und die Fixierung der Arg85-Seitenkette von IL-4 zur Ausbildung von zusätzlichen Ligand-Rezeptor-Interaktionen führt. Das Bindeepitop zwischen IL-4 und der IL-4Ralpha-Kette besitzt eine modulare Architektur aus drei unabhängig voneinander agierenden Interaktionsclustern. Bei der Interaktion von wildtypischem IL-4 mit IL-4Ralpha tragen nur zwei dieser Cluster in signifikanter Weise zur freien Bindeenergie bei. Im Falle der superagonistischen IL-4-Varianten ist jedoch auch das dritte Cluster an der Generierung von zusätzlicher, freier Bindeenergie beteiligt, wodurch die Affinität zwischen Ligand und Rezeptor erhöht wird. Damit stellt der modulare Aufbau der Interaktionsfläche zwischen IL-4 und der IL-4Ralpha-Kette möglicherweise einen Mechanismus dar, über den Proteine die Affinität von Wechselwirkungen über einen großen Bereicht variieren können, ohne dabei Spezifität einzubüssen. Da IL-4 und IL-13 als interessante Zielmoleküle für die Therapie von allergischen und asthmatischen Erkrankungen erkannt worden sind, können die in der vorliegenden Arbeit gewonnenen Informationen über den Bindemechanismus und die Einblicke in den molekularen Charakter der Interaktion zwischen den beiden Zytokinen und ihren spezifischen Rezeptorketten dabei helfen, neuartige und hoch spezifische, inhibitorische Moleküle zu entwickeln.
The expression of measles virus (MV) in six different permanent human glioma cell lines (D-54, U-251, U-138, U-105, U-373, and D-32) was analyzed. Although all celllines were permissive for productive replication of all MV strains tested, U-251, D-54, and D-32 cells spontaneously revealed restrictions of MV transcription similar to those observed for primary rat astroglial cells and brain tissue. In vitro differentiation of D-54 and U-251 cells by substances affecting tbe intracellular cyclic AMP Ievel caused a significant reduction of tbe expression of tbe viral proteins after 18, 72, and 144 b of infection. This pronounced restriction was not paralleled to a comparable Ievel by an inhibition of tbe syntbesis and biological activity in vitro of virus·specific mRNAs as sbown by quantitative Northem (RNA) blot analyses and in vitro translation. The block in viral protein syntbesis could not be attributed to tbe induction of type I interferon by any of tbe substances tested. Our findings indicate tbat down-regulation of MV gene expression in human brain cells can occur by a cell type-rlependent regulation of tbe viral mRNA transcription and a differentiation-dependent regulation of translation, botb of wbicb may be crucial for the establisbment of persistent MV infections in tbe centrat nervous system.
Leishmaniasis is a neglected tropical disease that can be manifested through different clinical forms, ranging from cutaneous to visceral. The host response against Leishmania spp. is greatly dependent on T cell-mediated immunity, in which T helper 1 responses are associated with macrophage activation and elimination of the parasite, while regulatory T cells and T helper 2 responses are correlated with parasite survival and persistence of infection. Leishmania uses different virulence factors as strategies for evading the immune response of the host. One of them are cathepsin-like cysteine proteases, which are currently under extensive investigation as targets for drug development. Previous studies with inhibitors of cathepsins B and L in vivo revealed an outstanding modulation of the host T helper cell response. However, the mechanisms behind these observations were not further investigated. Given the urgent need for better treatments against leishmaniasis, the aim of this study was to investigate the effects that the lack of cathepsin B and L activity have on the signals that dendritic cells use to instruct T helper cell polarization in response to infection with Leishmania major.
The cathepsin inhibitors tested showed low or no cytotoxicity in bone marrow-derived dendritic cells, and dendritic cells and macrophages could be generated from cathepsin B and cathepsin L-deficient mice without apparent alterations in their phenotype in comparison to wild-type controls. Furthermore, lack of cathepsin B and L activity showed no impact in the rate of promastigote processing by dendritic cells. Cathepsin B and cathepsin L-deficient macrophages showed no differences in parasite proliferation and capacity to produce nitric oxide in comparison to wild-type macrophages. In response to the parasite, dendritic cells treated with a cathepsin B inhibitor and dendritic cells from cathepsin B-deficient mice showed higher levels of expression of major histocompatibility complex (MHC) class II molecules than dimethyl sulfoxide (DMSO) or wild-type controls, but it was not accompanied by changes in the expression of costimulatory molecules. Wild-type dendritic cells and macrophages are not able to express the pro-inflammatory cytokine interleukin (IL)-12 in response to promastigotes. However, cells treated with a cathepsin B inhibitor or cells deficient for cathepsin B were able to express IL-12, whilethe expression of other cytokines -including IL-6 and tumor necrosis factor (TNF)-alpha-remained unchanged. These characteristics point towards a more “pro-Th1” profile of dendritic cells in the absence of cathepsin B.
This data is the first report on IL-12 regulation depending on cathepsin B. The IL-12 up-regulation observed was already present at the transcriptional level. Furthermore, it was also present in macrophages and dendritic cells in response to LPS, and the latter had a higher capacity to induce T cell helper 1 polarization in vitro than wild-type dendritic cells. The activation of different signaling pathways was analyzed, but the up-regulation of IL-12 could not be attributed to modulation of nuclear factor-kappaB (NFkappaB), p38 mitogen activated protein kinase (MAPK) and extra-cellular signal-regulated kinase (ERK)1/2 pathways. Thus, the mechanism behind IL-12 regulation by cathepsin B remains to be elucidated, and the impact of these effects is yet to be confirmed in vivo. Altogether it is tempting to speculate that cathepsin B, in addition to its role in processing endocytosed material, is involved in the modulation of the pro-inflammatory cytokine IL-12.
Regulation of B lymphocyte terminal differentiation and death by the transcription factor Blimp-1
(2005)
B lymphocyte induced maturation protein-1 (Blimp-1) and X-box-binding protein-1 (XBP-1) are indispensible transcription factors required for B lymphocyte terminal differentiation into Ig secreting plasma cells. Occurrence of an unfolded protein response (UPR) and XBP-1 splicing, due to elevated Ig levels, are critical events during plasma cell generation. However, the upstream molecule sufficient to trigger these events remain elusive. Because ectopic expression of Blimp-1 in B cells is sufficient to generate plasma cells, it is plausible that Blimp-1 might be the upstream molecule, sufficient for the induction of UPR and XBP-1 splicing. The results from the current study indicate that ectopic expression of Blimp-1 or its N-terminal domain, in B cells, is sufficient to induce XBP-1 splicing, UPR and Ig (immunoglobulin) secretion. Further more Blimp-1 is able to directly repress the antiapoptotic gene A1, by binding to specific DNA elements in A1 promoter. This repression of A1 by Blimp-1 seems to be an important prerequisite for Plasma cell differentiation because ectopic expression of A1 in primary B cells resulted in reduced immunoglobulin secretion.
Macrophages are important effector cells of the innate and adaptive immune response and exert a wide variety of immunological functions which necessitates a high level of plasticity on the chromatin level. In response to pathogen-associated molecular patterns (PAMPs) or inflammatory signals macrophages undergo a process of cellular activation which is associated with morphologic, functional and biochemical changes. Toll-like receptors (TLR) are able to sense many different PAMPs. TLR4 is an important sensor for lipopolysaccharide (LPS) which elicits a major portion of the host’s inflammatory response through the activation of many different signaling pathways such as the NF-κB and the MAPK protein kinase pathways RASRAF- MEK-ERK, p38 and JNK. Polycomb group (PcG) proteins are well known chromatin modifiers which function in large complexes and are required to maintain chromatin structure in a transcriptionally repressed state. It has previously been shown that the PcG protein Bmi1 is phosphorylated by 3pK, a downstream effector kinase of the MAPK protein kinase pathways RAS-RAF-MEK-ERK, p38 and JNK. In this work I analyzed the role of Bmi1 as a downstream effector of MAPK signaling during macrophage activation. Unexpectedly a rapid up-regulation on the Bmi1 protein level was observed in bone marrow derived macrophages (BMDMs) after LPS treatment. The Bmi1 induction was associated with transient protein phosphorylation that occured downstream of MAPK signaling. LPS treatment of BMDMs in the absence of Bmi1 resulted in a pronounced increase of IL-10 secretion. This secretion of the anti-inflammatory cytokine IL-10 was associated with increased IL-10 mRNA levels. Furthermore, siRNA mediated knock down of Bmi1 in J774A.1 macrophages also resulted in elevated IL-10 mRNA levels in response to LPS. ChIP analysis revealed that Bmi1 binds to throughout the il-10 locus. Alternative activation of wild type BMDMs via concomitant TLR4 and FcγR activation which triggers high IL-10 expression is paralleled by an attenuated Bmi1 protein expression. These results identify Bmi1 as a repressor of IL-10 expression during activation of macrophages.
Die Unterscheidung zwischen körpereigenen und körperfremden Strukturen ist eine grundlegende Herausforderung der spezifischen Immunantwort. Pathologische Veränderungen dieser Abgrenzung können zu schwerwiegenden Autoimmunerkrankungen wie beispielsweise Diabetes Mellitus, Rheumatischer Arthritis oder Multipler Sklerose führen. Um unerwünschte (Auto-) Immunreaktionen zu verhindern, existieren verschiedene Formen von peripheren Toleranzmechanismen, die durch viele Transkriptionsfaktoren wie z. B. ICER (inducible cAMP early repressor), NFAT (nuclear factor of activated T cells) und Foxp3 (forkhead box protein p3) kontrolliert werden. Foxp3+ regulatorische T-Zellen (Tregs) sind spezialisierte immun-suppressive Lymphozyten, welche die Aktivierung anderer Immunzellen unterdrücken können. Einer der möglichen Mechanismen ist der Transfer zyklischen Adenosin-Monophosphats (cAMP) von Tregs in konventionelle T- und B-Lymphozyten. Die erhöhte intrazelluläre Konzentration an cAMP führt in Effektorzellen zur Induktion und Kerntranslokation von ICER. Der transkriptionelle Repressor ICER supprimiert die Expression vieler NFAT-regulierter Gene und hemmt darüber hinaus die Induktion der NFATc1/αA-Isoform selbst. Diese Isoform wird speziell in pro-inflammatorischen Effektorzellen hochreguliert und ist maßgeblich an deren spezifischem transkriptionellen Programm beteiligt. Foxp3 ist ein zentraler Faktor für die Bildung und Funktion sowohl Thymus-generierter nTregs als auch peripher (TGFβ-) induzierter iTregs. Die Kontrolle des Foxp3-Gens wird in iTregs – überraschenderweise aber nicht in nTregs – durch NFAT-Faktoren reguliert. Allerdings hemmt Foxp3 durch eine negative Rückkopplung wiederum die Induktion und Aktivität von NFATc1/αA. Dies stellt somit ein weiteres Regulativ dar, wobei Foxp3 nicht nur die Plastizität, sondern auch die Funktion von immun-suppressiven T-Zellen steuert. Zusätzlich regulieren die verschiedenen NFAT-Faktoren auch die Antigen präsentierenden dendritischen Zellen (DCs). Während NFATc1 und NFATc2 die Differenzierung und Proliferation von DCs beeinflussen, reguliert NFATc3 deren Zytokinexpression und steuert indirekt auch die nachfolgende T-Zell-Immunantwort. Die Kontrolle der Genregulation in Immunzellen durch die Transkriptionsfaktoren ICER, NFAT und Foxp3 erfüllt somit spezifische Funktionen der Immunität, reguliert aber gleichzeitig wichtige Aspekte der peripheren Toleranz, um schädliche (Auto-) Immunreaktionen zu verhindern.
To probe into the functional properties of the major peripheral myelin cell surface glycoprotein P 0 , its ability to confer adhesion and neurite outgrowth-promoting properfies was studied in cell culture. Tothis aim, Po was expressed as integral membrane glycoprotein at the surface of CV -1 cells with the help of a recombinant vaccinia virus expression system. Furthermore, the immunoglobulin-like extracellular domain of P0 (P0 -ED) was expressed as soluble profein in a bacterial expression system and used as substrafe coated to plastic dishes or as competitor in cell adhesion and neurite outgrowth-promoting assays. The adhesion of P0 -expressing CV-1 cells to P0 -ED substrafe was specifically inhibitable by polyclonal Po antibodies (54% :t 6% ). In addition, the specific interaction between Po molecules could be reduced ( 49% ± 8%) by adding soluble P0 -ED to the culture medium, demonstrating that the homophilic inter~ction between recombinant Po molecules can be mediated, at least on one partner of interacting molecules, by the unglycosylated Ig-like domain. Substrate-coated p -ED also conferred adhesion and neurite outgrowth ability to dorsal root ganglion neurons with neurites of a mean length of about 150 ,_..m. This neurite outgrowth was specifically inhibitable by soluble P" (74% ± 14%) and P 0 antibodies (65% ± 9% ). These observations indicate that Po is capable of displaying two different types of functional roles in the myelination process of . peripheral nerves: The heterophilic interaction with neurons may be responsible for the recognition between axon and myelinating Schwann cell at the onset of myelination, whereas the homophilic interacton may indicate its roJe in the selfrecognition of the apposing loops of Schwann cell surface membranes during the myelination process and in the mature compact myelin sheath.
iNKT cells are a population of T cells with unique characteristics. In contrast to most αβ T cells which recognize peptides presented by highly polymorphic MHC molecules, iNKT cells are reactive to glycolipids presented by CD1d, a non-polymorphic MHC-I like molecule. Moreover, whereas MHC-restricted αβ T cells bear highly variable receptors (TCRs) formed after somatic recombination of the V(D)J gene segments, the TCR of iNKT cells is formed by an invariant α chain, which always contains the same gene segments: AV14 and AJ18; and a β chain of limited BV gene usage: BV8S2, BV7 or BV2, in the mouse. This invariant α chain is the reason for which these cells are named “i” and the NK part of their name refers to the expression of receptors typical of natural killer (NK) cells. iNKT cells recognize glycolipids of endogenous and microbial origin. After activation they secrete large amounts of very different cytokines such as IFN-γ and IL-4 and thus influence immune responses and pathological conditions. One of the most potent iNKT cell agonists, recognized by the semi-invariant TCR, is the synthetic glycolipid α-Galactosylceramide (α-Gal). iNKT cells can be visualized using CD1d-multimeric complexes loaded with α-Gal and flow cytometry, since this reagent has enough avidity to stain these cells. Interestingly, mouse iNKT cells can be stained with human α-Gal-loaded CD1d oligomers and human iNKT cells can also be visualized with mouse α-Gal-loaded CD1d oligomers, indicating a high degree of conservation of the recognition of α-Gal presented by CD1d through evolution. Previous studies showed that rats have the genes necessary to build semi-invariant TCRs: They have a CD1d homologue; one or two BV8S2 homologues and interestingly, up to ten AV14 gene segments, which are highly conserved when compared to the mouse genes. Importantly, it has been shown at least for two of these AV14 gene segments that they can produce invariant TCRα chains which, when coexpressed with BV8-containing β chains, react to α-Gal presented by rat CD1d. Furthermore, ex vivo stimulation of primary splenocytes with α-Gal results in the secretion of IL-4 and IFN-γ. Surprisingly, rat semi-invariant TCRs do not recognize α-Gal presented by mouse CD1d and accordingly, mouse α-Gal-loaded CD1d tetramers failed to stain a discrete population of rat iNKT cells. Taking all together, despite that strong evidence suggested that iNKT cells are present in the rat, the direct identification of such population and the analysis of CD1d-restricted immune responses were still pending for this species. Hence the work presented in this doctoral thesis was aimed to identify iNKT cells, to analyze their phenotype and also to study the distribution and function of CD1d in the rat. For these purposes, we produced essential reagents which were still lacking such as rat specific anti-CD1d monoclonal antibodies and rat CD1d oligomers. Importantly, two of three anti-rat CD1d monoclonal antibodies (all of them generated in our laboratory before this thesis was initiated) also recognized mouse CD1d and therefore allowed a direct comparison of CD1d expression between rat and mouse. Whereas CD1d distribution in the hematopoietic system was found to be extremely similar between these two species; in non-lymphatic tissues important differences were observed. Interestingly, CD1d protein was detected at not yet described sites such as the rat exocrine pancreas and rat and mouse Paneth cells. These monoclonal antibodies did not only allowed the analysis of CD1d expression, but also the first demonstration of the function of rat CD1d as an antigen presenting molecule, since cytokine release in response to α-Gal was blocked when they were added to ex vivo cultures of rat primary cells. Staining of primary rat iNKT cells (possible now with the newly generated rat CD1d oligomers) revealed interesting similarities with human iNKT cells. First, we observed that rat iNKT cells are only a minority among all NKR-P1A/B positive T cells. Human iNKT cells constitute also a very small proportion of NKR-P1A (CD161) expressing T cells, whereas in mice inbred strains which express NKR-P1C (NK1.1), most of NKRP1C expressing T cells are iNKT cells. Second, the majority of rat iNKT cells are either CD4 or DN and only a small proportion expresses CD8β. These findings are similar to humans and different to mice which lack CD8+ iNKT cells. Third, analysis of various inbred rat strains demonstrated different iNKT cell frequencies which correlated with cytokine secretion after α-Gal stimulation of primary cells. In comparison to mice, iNKT cell numbers are markedly reduced in rats. In F344 rats, inbred rat strain which released the highest cytokine amounts after α-Gal stimulation, approximately 0.25% and 0.1% of total liver and spleen lymphocytes, respectively, are iNKT cells. In contrast, in LEW rats iNKT cells were practically absent and neither IL-4 nor IFN-γ were detected after stimulation of primary cells with α-Gal. Once more, these frequencies are very close to those observed in humans. Last, as reported for human peripheral blood cells, rat iNKT cells could be easily expanded in vitro by adding α-Gal to cultures of intrahepatic lymphocytes, whereas the expansion of mouse iNKT cells was not possible using the same protocol. The presence of a multimember AV14 gene segment family in the rat is an intriguing characteristic. These AV14 gene segments are extremely homologous except in the CDR2α region. Based on the amino acid sequence of this region they have been divided into two different types: Type I and II. A specific tissue distribution of the different types was proposed in the first study where the presence of several AV14 gene segments was described. We also analyzed the AV14 gene segment usage in F344 and LEW inbred rat strains. In F344 rats we found no preferential usage of either AV14 gene segment type in the spleen and the liver but type II AV14 gene segments appeared more frequently in the thymus. In contrast, LEW rats show a preferential usage of type I AV14 gene segments in all three compartments analyzed: Thymus, spleen and liver. Taken all together, the usage of newly generated reagents allowed to gain novel insights into CD1d expression in the rat and in the mouse and to directly identify rat iNKT cells for the first time. The phenotypic and functional analysis of rat iNKT cells revealed numerous similarities with human iNKT cells. These are of special interest, since rats serve to investigate several pathological conditions including models for autoimmune diseases. The possibility now to analyze iNKT cells and CD1d-restricted T cell responses in the rat might help to understand the pathogenesis of such diseases. In addition, the uncomplicated in vitro expansion and culture of rat iNKT cells should facilitate the analysis of the immunomoldulatory capacities of these cells.
We have assessed the role of tumour necrosis factor-a (TNF) during cutaneous leishmaniasis and demonstrated that significant levels of TNF were released by spleen cells from infected mice after in cirro restimulation with Leishmania major promastigotes. Spleen cells from both genetically resistant and genetically susceptible mice were equally capable of producing TNF. After challenge with bacterial endotoxin, TNF activity could also be demonstrated in the serum of L. mujor-infected mice and the titres correlated with the course of cutaneous disease in susceptible and resistant mice. TNF did not exert a direct leishmanicidal effect in uitro. Furthermore, our study indicated that macrophages are the source of L. major-induced TNF activity and that its elicitation is dependent on the presence of T cells. These findings suggest that TNF acts in concert with other cytokines produced during L. major infection and that its role depends on the composition of T cell subsets and cytokines present.
Seven monoclonal antibodies were raised against the immunoglobulin-like extracellular domain of PO (POED), the major protein of peripheral nervous system myelin. Mice were immunized with purified recombinant rat PO-ED. After fusion, 7 clones (POI-P07) recognizing either recombinant, rat, mouse, or human PO-ED were selected by ELlS A and were characterized by Western blot, immunohistochemistry, and a competition assay. Antibodies belonged to the IgG or IgM class, and P04-P07, reacted with PO in fresh-frozen and paraffin-embedded sections of human or rat peripheral nerve, but not with myelin proteins of the central nervous system of either species. Epitope specificity of the antibodies was determined by a competition enzyme-linked immunosorbent assay (ELISA) and a direct ELlS A using short synthetic peptides spanning the entire extracellular domain of PO. These assays showed that POl and P02 exhibiting the same reaction pattern in Western blot and immunohistochemistry reacted with different distant epitopes of PO. Furthermore, the monoclonal antibodies P05 and P06 recognized 2 different epitopes in close proximity within the neuritogenic extracellular sequence of PO. This panel of monoclonal antibodies, each binding to a different epitope of the extracellular domain of PO, will be useful for in vitro and in vivo studies designed to explore the role of PO during myelination and in demyelinating diseases of the peripheral nervous system.
Cutaneous leishmaniasis is initiated by the bite of an infected sandfly and inoculation of Leishmania major parasites into the mammalian skin. Macrophages are known to playa central role in the course of infection because they are the prime host cells and funetion as antigen-presenting eells (APC) for induetion of the eell-mediated immune response. However, in addition to maerophages in the dermis. the skin eontains epidermal Langerhans eells (LC) which ean present antigen (Ag) to T cells. Therefore, using a murine model of cutaneous leishmaniasis, we analyzed the ability of epidermal cells to induce a T eell response to L.major. The results demonstrated that freshly isolated LC, but not cuItured LC, are highly active in presenting L.major Ag in vitro to T cells from primed mice and to a L.major-specific T cell clone. Furthermore, freshly isolated LC had the ability to retain L.major Ag in immunogenic form for at least 2 days. Their efficiency was much greater than that of irradiated spleen cells, a standard population of APC. LC stimulated both T cell proliferation and production of the Iymphokines interleukin (IL)-2 and IL-4. The response was Ag specific and could be induced by lysate of L. major parasites and by live organisms. The data suggest that epidermal LC are important APC in eutaneous leishmaniasis. They may perform a critical funetion by eapturing L.major Ag in the skin and presenting it either to quiescent T eells circulating through the draining lymph node or locally to T effector cells infiltrating the cutaneous lesion.
Die Aktivierung der T Zelle bedarf der spezifischen Interaktion zwischen T Zelle und Antigen-präsentierender Zelle unter Ausbildung einer engen Anlagerung beider Zellmembranen („immunologische Synapse“) für Rezeptoren-Interaktionen und konsekutive Signaltransduktion. In dreidimensionaler Kollagenmatrix zeigte sich ein stereotypes, dynamisches Muster bei der Interaktion zwischen CD45RO-positiven humanen T Zellen und antigenpräsentierenden dendritischen Zellen. i) Die Kontaktaufnahme wurde stets über das Leading edge der T Zelle initiiert. ii) Beim dynamischen Kontakt wanderte die T Zelle polarisiert, mit vielen Richtungsänderungen und mit reduzierter Geschwindigkeit auf der DC-Oberfläche, nur unterbrochen von kurzen Stopp- und Abrundungsphasen. Der Uropod der T Zelle stand während der dynamischen Kontakts in kontinuierlicher Verbindung zur DC. iii) Die Loslösung der T Zelle von der DC war ein aktiver Prozess, der durch Interaktion der Vorderfront der T Zelle zu benachbarten Kollagenfasern eingeleitet wurde, gefolgt von der Lösung des Zellkörpers und des Uropods. Alternativ wurden Kontakte durch Uropod-mediierte Retention der T Zelle auf der DC-Oberfläche verlängert. Zur dynamischen molekularen Charakterisierung der Kontaktfläche wurde eine Methode zur Darstellung von Lipid-Rafts an lebenden Zellen in der 3D ECM mit BTRITC etabliert. Die Ergebnisse zeigen ein neues 3-Schritt-Konzept dynamischer und produktiver Interaktionen zwischen T Zelle und DC in vitro. Die assymetrische Kontaktzone impliziert distinkte Funktionen von Vorderfront und Uropod der T Zelle und definiert eine neuartige dynamische Kontaktform für die Signalübertragung zwischen beweglichen Zellen.
MDSCs are suppressive immune cells with a high relevance in various pathologies including cancer, autoimmunity, and chronic infections. Surface marker expression of MDSCs resembles monocytes and neutrophils which have immunostimulatory functions instead of suppressing T cells. Therefore, finding specific surface markers for MDSCs is important for MDSC research and therapeutic MDSC manipulation. In this study, we analyzed if the integrin VLA-1 has the potential as a novel MDSC marker. VLA-1 was expressed by M-MDSCs but not by G-MDSCs as well as by Teff cells. VLA-1 deficiency did not impact iNOS expression, the distribution of M-MDSC and G-MDSC subsets, and the suppressive capacity of MDSCs towards naïve and Teff cells in vitro. In mice, VLA-1 had no effect on the homing capability of MDSCs to the spleen, which is a major reservoir for MDSCs. Since the splenic red pulp contains collagen IV and VLA-1 binds collagen IV with a high affinity, we found MDSCs and Teff cells in this area as expected. We showed that T cell suppression in the spleen, indicated by reduced T cell recovery and proliferation as well as increased apoptosis and cell death, partially depended on VLA-1 expression by the MDSCs. In a mouse model of multiple sclerosis, MDSC injection prior to disease onset led to a decrease of the disease score, and this effect was significantly reduced when MDSCs were VLA-1 deficient. The expression of Sema7A by Teff cells, a ligand for VLA-1 which is implicated in negative T cell regulation, resulted in a slightly stronger Teff cell suppression by MDSCs compared to Sema7A deficient T cells. Live cell imaging and intravital 2-photon microscopy showed that the interaction time of MDSCs and Teff cells was shorter when MDSCs lacked VLA 1 expression, however VLA-1 expression had no impact on MDSC mobility. Therefore, the VLA-1-dependent interaction of MDSC and Teff cells on collagen IV in the splenic red pulp is implicated MDSC-mediated Teff cell suppression.