Toxoplasma gondii, an obligate intracellular protozoan parasite, establishes a latent, chronic infection by forming cysts preferentially in the brain after replication of tachyzoites in various organs during the acute stage of infection. Chronic infection with T. gondii is one of the most common parasitic diseases in humans. The immune system is required for maintaining the latency of chronic infection. Reactivation of infection can occur in immunocompromised individuals, such as AIDS patients, which results in the development of life-threatening toxoplasmic encephalitis (TE). IFN-gamma-dependent, cell mediated immune responses play an essential role in preventing the reactivation of chronic infection of T. gondii in the brain. In my dissertation study, we examined the mechanisms of IFN-gamma-mediated prevention of TE by using models of reactivation of chronic infection in BALB/c mice. This strain of mouse is genetically resistant to T. gondii infection and establishes a latent chronic infection as do immunocompetent humans, and therefore provides an excellet model for this purpose. Our laboratory previously demonstrated that both T cells and IFN-gamma-producing non-T cells are required for genetic resistance of BALB/c mice against development of TE. However, the function of T cells required for the resistance is still unclear. Therefore, in the present study, we examined whether IFN-gamma production or perforin-mediated cytotoxicity of T cells play an important role in their protective activity against TE. Immune T cells were obtained from infected IFN-gamma-knockout (IFN-g-/-), perforin-knockout (PO), and wild-type (WT) BALB/c mice, and transferred into infected, sulfadiazine-treated athymic nude mice which lack T cells but have IFN-gamma-producing non-T cells. Control nude mice that had not received any T cells developed severe TE due to reactivation of infection and died after discontinuation of sulfadiazine treatment. Animals that had received immune T cells from either PO or WT mice did not develop TE and survived. In contrast, nude mice that had received immune T cells from IFN-gamma-/- mice developed severe TE and died as early as control nude mice. T cells obtained from spleens of the animals that had received either PO or WT T cells both produced large amounts of IFN-gamma following stimulation with T. gondii antigens in vitro. In addition, the amounts of IFN-gamma mRNA expressed in the brains of PO T-cell recipients did not differ from those of WT T-cell recipients. These results indicate that IFN-gamma production, but not perforin-mediated cytotoxic activity, by T cells is required for prevention of TE in genetically resistant BALB/c mice. In our attempt to identify a T cell population(s) that produces IFN-gamma in the brain and plays an important role for prevention of TE, we analyzed T cell receptor (TCR) Vb chain usage in T cells expressing IFN-gamma in the brains of infected BALB/c mice. We found T cells bearing TCR V beta8 chain to be the most frequent IFN-g-producing population in the brains of infected animals. To examine the role of IFN-gamma production by this T cell population for prevention of TE, V beta8+ immune T cells purified from spleens of infected BALB/c and IFN-g-/- mice were transferred into infected, sulfadiazine-treated athymic nude mice. After discontinuation of sulfadiazine treatment, control nude mice that had not received any T cells and animals that had received Vb8+ T cells from IFN-g-/- mice all died due to reactivation of infection (TE). In contrast, animals that had received the cells from WT mice survived. These results indicate that IFN-gamma production by Vb8+ T cells in the absence of any other T cell population can prevent reactivation of infection. Thus, V beta8+ T cells play a crucial role in genetic resistance of BALB/c mice to TE through their production of IFN-gamma. When V beta8+ immune T cells were divided into CD4+ and CD8+ subsets, a potent protective activity was observed only in the CD8+ subset whereas a combination of both subsets provided greater protection than did the CD8+Vb8+ population alone. These results indicate that CD8+ subset of V beta8+ T cells is a major afferent limb of IFN-gamma-mediated resistance of BALB/c mice against TE, although the CD4+ subset of the T cell population works additively or synergistically with the CD8+V beta8+ population. T cells need to enter into the brains of infected mice to demonstrate their protective activity against TE. This migration is mediated, in part, by endothelial adhesion molecules. Since IFN-gamma is essential for preventing reactivation of chronic infection with this parasite in the brain, we examined whether this cytokine plays an important role in expression of lymphocyte and endothelial adhesion molecules and recruitment of T cells into the brain during chronic infection with T. gondii using IFN-g-/- and WT BALB/c mice. Although the number of cerebral vessels expressing intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) increased in both WT and IFN-g-/- mice following infection, there were more VCAM-1+ vessels in brains of infected WT than infected IFN-g-/- mice; in contrast, numbers of ICAM-1+ vessels did not differ between strains. We did not detect endothelial E-selectin, P-selectin, MAdCAM-1 or PNAd in any of the brains. Significantly fewer CD8+ T cells were recruited into brains of infected IFN-g-/- than WT mice. Treatment of infected IFN-g-/- mice with recombinant IFN-gamma restored the expression of VCAM-1 on their cerebral vessels and recruitment of CD8+ T cells into their brains, confirming an importance of this cytokine for up-regulation of VCAM-1 expression and CD8+ T cell trafficking. In infected WT and IFN-g-/- animals, almost all cerebral CD8+ T cells had an effector/memory phenotype (LFA-1high, CD44high and CD62Lneg) and approximately 38% were positive for a4b1 integrin (the ligand for VCAM-1). In adoptive transfer of immune spleen cells, pre-treatment of the cells with a monoclonal antibody against a4 integrin markedly inhibited recruitment of CD8+ T cells into the brain of chronically infected wild-type mice. These results indicate that IFN-g-induced expression of endothelial VCAM-1 and its binding to a4b1 integrin on CD8+ T cells is important for recruitment of the T cells into the brain during the chronic stage of T. gondii infection. Since we found strong expression of ICAM-1 on endothelia and LFA-1 on T cells in the brains of infected mice, LFA-1/ICAM-1 interaction, in addition to a4b1 integrin/VCAM-1 interaction, may also be involved in this process. As mentioned earlier, CD8+ T cells are crucial for prevention of TE in BALB/c mice. Therefore, IFN-gamma-mediated expression of VCAM-1 and its binding to a4b1 integrin for recruitment of CD8+ T cells may play a critical role in genetic resistance of BALB/c mice to development of TE. / Ph. D.

Bei Autoimmunkrankheiten wie der Multiplen Sklerose (MS) kommt es zu einer fehlgesteuerten Immunantwort mit Aktivierung und Persistenz autoreaktiver T-Zellen. Apoptose-regulierende Mechanismen wie das CD95-Rezeptor/CD95-Ligand- und TRAIL-Rezeptor/TRAIL-System könnten dabei eine wichtige Rolle spielen. Die lösliche Form des CD95-Rezeptor (sCD95) kann an CD95L binden und so die Apoptose aktivierter T-Zellen verhindern. Die systemische Blockade von TRAIL führt zur Exazerbation von Autoimmunerkrankungen in Tierversuchen. In der vorliegenden Arbeit wurden deshalb die Expression, Regulation und Bedeutung sowohl von sCD95 als auch von löslichem TRAIL (sTRAIL) und membranständigem TRAIL bei gesunden Probanden und Patienten mit schubförmig remittierender MS (RRMS) untersucht. Zytokine wurden mit ELISAs, Zelloberflächenproteine sowie Apoptose im Durchflusszytometer gemessen. Die Untersuchungen mit magnetisch gereinigten humanen Leukozytensubpopulationen und Zelllinien zeigten, dass sCD95 lediglich von zelltyp-spezifisch aktivierten humanen T-Zellen, sezerniert wird. TRAIL wurde vor allem von Monozyten, die mit IFN-beta stimuliert waren, sezerniert und auf der Zelloberfläche exprimiert. Zellkulturüberstände, die sTRAIL enthielten, lösten Apoptose in suszeptiblen Tumorzellen aus. TRAIL führte zu einer signifikanten Inhibition der Proliferation und der Produktion von Th1- und Th2-spezifischen Zytokinen bei humanen (auto)antigenspezifischen T-Zellen. Weder für die sCD95- noch für die TRAIL-Expression wurden Unterschiede zwischen RRMS-Patienten und gesunden Probanden nachgewiesen. Die Ergebnisse dieser Arbeit zeigen ein komplexes Regulations- und Expressionsmuster von sCD95 und TRAIL, ohne jedoch Anhaltspunkte für Unterschiede zwischen MS-Patienten und Gesunden zu liefern. Es ergaben sich wichtige Hinweise darauf, dass der protektive immunomodulatorische Effekt einer systemischen IFN-beta-Therapie bei MS durch TRAIL vermittelt werden könnte. / Autoimmune disorders such as Multiple Sclerosis (MS) are characterized by an aberrant immune response with activation and persistence of autoreactive T-cells. Apoptosis-regulating mechanism such as the CD95-Rezeptor/CD95-Ligand- and the TRAIL-Rezeptor/TRAIL-System may play a major role in this process. The soluble CD95 receptor (sCD95) can bind to CD95L and subsequently inhibit apoptosis of activated T-cells. The systemic blockade of TRAIL leads to the exacerbation of autoimmune disease in animal experiments. In this work I investigated the expression, regulation and significance of sCD95, soluble TRAIL (sTRAIL) and membrane-bound TRAIL in patients with remitting-relapsing MS (RRMS), and in healthy controls. Cytokines were measured by ELISA, membrane bound proteins and apoptosis were measured by flow cytometry. The experiments with magnetically sorted human leucocyte subpopulations and cell lines showed, that only cell-type specific activated human T-cells secrete sCD95. Both forms of TRAIL were expressed by monocytes stimulated with IFN-beta. Cell supernatants containing sTRAIL induced apoptosis in susceptible tumour cells. Furthermore TRAIL inhibited proliferation of (auto)antigen-specific T cells and the production of Th-1 and Th-2 specific cytokines. There were no differences in the expression of sCD95 and TRAIL between RRMS patients and healthy controls. This work shows a complex regulation pattern of sCD95 and TRAIL without being able to detect differences between MS patients and healthy controls. However, results point out that TRAIL could be an important mediator of the immunomodulatory effects of systemic IFN-beta therapy in MS.

No description available.

La barrière hémo-encéphalique (BHE) est formée des cellules endothéliales microvasculaires cérébrales reliées entre elles par des jonctions serrées. Grâce à sa perméabilité restreinte et sélective, la BHE entrave le passage des molécules et cellules du sang vers le système nerveux central (SNC). Chez les patients atteints de sclérose en plaques (SEP), une maladie inflammatoire du SNC, la rupture de la BHE permet aux cellules immunes actives d'infiltrer le tissu cérébral. Il s'ensuit une réaction inflammatoire excessive au cours de laquelle d'autres leucocytes sont recrutés dans le cerveau et qui culmine par la formation des plaques de démyélinisation caractéristiques de la SEP. On dénote au niveau de ces lésions une présence importante de lymphocytes T CD4⁺ activés et de cytokines pro-inflammatoires propres à une réponse de type TH1, tels l’IFN-γ et l’IL-1. Curieusement cependant, l’inhibition de la voie TH1 n’empêche pas l’apparition de la maladie dans le modèle murin de la SEP et en aggrave même les symptômes. On attribue maintenant aux lymphocytes TH17, nommées en raison de leur capacité à produire de l’IL-17, un rôle clé dans le développement de la maladie. L’objectif de ce travail de thèse visait à caractériser les lymphocytes TH17 chez l’humain et définir leur contribution exacte dans la fragilisation de la BHE, une étape décisive dans la formation des lésions de SEP. Pour ce faire, nous avons mis au point une méthode expérimentale permettant l’expansion in vitro de populations de lymphocytes TH17 à partir de cellules mononuclées du sang de donneurs sains. Nos travaux démontrent que l’IL-23 induit la production d’IL-17, d’IL-22 et de granzyme B par les lymphocytes T CD4⁺CD45RO⁺ mémoires humains et qu’une proportion des cellules exprime de manière concomitante de l’IL-17 et de l’IFN-γ. La fréquence des lymphocytes T CD4⁺ IL17⁺, IL-22⁺ et des doubles positifs IL-17⁺IFN-γ⁺ est significativement plus élevée dans les lignées de lymphocytes TH17 provenant de patientes en poussée que dans celles de contrôles. Nos analyses démontrent que les cellules endothéliales de la BHE expriment de faibles niveaux des récepteurs de l’IL-17 et de l’IL-22 à l’état basal mais que leur présence est accrue dans le cerveau de patients atteints de SEP. L’activation du récepteur de l’IL-17 entraîne une augmentation de la perméabilité de la BHE et une perturbation de l’organisation des protéines de jonction occludine et ZO-1. Finalement, nous démontrons que la migration des lymphocytes TH17 à travers la BHE est régie en grande partie par la molécule d’adhérence ICAM-1 et que les lymphocytes qui co-expriment l’IL-17 et l’IFN-γ sont plus aptes à franchir la BHE que ceux qui produisent uniquement l’une ou l’autre de ces cytokines. Nous retrouvons d’ailleurs des cellules qui expriment simultanément les facteurs de transcription T-bet et RORC, associés respectivement aux lymphocytes TH1 et aux TH17, au sein des infiltrats péri-vasculaires des lésions actives de SEP. Les travaux présentés dans cette thèse auront permis d’affiner nos connaissances sur les mécanismes d’entrée des lymphocytes TH17 dans le SNC et les propriétés délétères des cytokines qu’ils sécrètent, notamment dans l’activation et la déstabilisation de l’endothélium cérébral. / The blood-brain barrier (BBB) plays a crucial role in protecting the central nervous system (CNS) by restricting entry of cells and molecules into the brain. In the CNS disorder multiple sclerosis (MS), breakdown of the BBB allows activated leukocytes to infiltrate the brain parenchyma, leading to the formation of the characteristic demyelinated lesions. For decades, MS was viewed as a TH1-mediated disease, a notion that was largely supported by studies in its animal model and by the abundance of prototypical TH1-associated cytokines within active MS lesions. However, over the years, accumulating evidence has highlighted the involvement of another subset of CD4⁺ T cells that express IL-17, therefore named TH17 lymphocytes, in the pathology of the disease. The goal of the work presented herein was to characterize the human TH17 lymphocyte population and define their contribution to the disruption of the BBB and leukocyte infiltration into the CNS, both important early events in the formation of MS lesions. To do so, we developed and optimized a method to successfully generate human TH17 lines in vitro from peripheral blood mononuclear cells of healthy donors. We demonstrate that in response to IL-23, human memory CD4⁺CD45RO⁺ but not naïve CD4⁺CD45RA⁺ T lymphocytes produce IL-17, IL-22, and granzyme B, with a subset of cells simultaneously expressing IL-17 and IFN-γ. Interestingly, we measure a significant increase in the percentage of T CD4⁺ IL17⁺, of IL-22⁺, and of IL-17⁺IFN-γ⁺ dual producers in TH17 cell lines expanded from the peripheral blood of acutely relapsing MS women as compared to those generated from healthy controls and remitting MS patients. We show that both IL-17 and IL-22 receptors are upregulated on BBB endothelial cells in situ during inflammation and that IL-17 enhances BBB permeability by disrupting the integrity of tight junction proteins occludin and ZO-1. Finally, we provide evidence that TH17 lymphocytes transmigrate efficiently across human brain endothelial cells via the adhesion molecule ICAM-1 and show that IL-17⁺IFN-γ⁺ double producers have an increased propensity to do so. Accordingly, we detect lymphocytes that display immunoreactivity against both the TH1- and TH17-associated transcription factors T-bet and RORC within perivascular infiltrates of active MS lesions. The work presented in this thesis has refined our understanding of the mechanisms that drive TH17 lymphocyte recruitment into the CNS and shed light on the deleterious effect of TH17-secreted cytokines, specifically in the activation and breakdown of the BBB.

Plasmacytoid dendritic cells (pDC) represent innate immune cells capable to detect viruses in their endosomal environment via Toll-like receptors (TLRs). Viral nuclear acid recognition leads to the massive production of type I interferon (IFN I) and induction of the antiviral state in uninfected cells. Crosslinking of the surface regulatory receptors, such as BDCA-2, with monoclonal antibodies or with some viruses leads to the activation of MEK1/2- ERK signaling pathway and inhibition of IFN I production in pDC. In this study, the role of MEK1/2 kinase has been highlighted. Its inhibition reversed the inhibitory effect of BDCA-2 crosslinking and its direct activation with PMA led to the inhibition of IFN-α production. Yet an unclear role of pDC in sensing of BK polyomavirus virus (BKV) responsible for kidney transplant rejection was investigated as a major topic of this thesis. Experiments with the pDC cell line Gen2.2 and HRPTEC primary cell line showed that pDCs were not able to detect BKV particles, however, exposure of activated Gen2.2 cells to BKV inoculum dramatically upregulated production of IFN-α. Most importantly, coculture of Gen2.2 cells with BKV- infected HRPTEC cells resulted in IFN-α and TNF-α production, which was prevented by Bafilomycin. These results suggest that BKV-infected...

Plasmacytoid dendritic cells (pDC) are a highly specialized subset of immune cells that sense viral nucleic acids by endosomal toll-like receptors 7 and 9 (TLR7/9). Activation of TLR7/9 leads to the production of type I interferons (IFN-I). Moreover, pDC contribute to the antiviral response by presenting viral antigens to T lymphocytes and link innate and adaptive immunity. pDC need to be properly regulated in order to limit excessive production of IFN-I that is associated with autoimmune diseases. Therefore, pDC possess a battery of regulatory receptors (RR) that limit TLR7/9-mediated cytokine production. This thesis focuses on the mechanism of RR-mediated inhibition of IFN-I production in pDC and explores interactions between pDC and two enveloped viruses, that possess the ability to hijack RR in pDC: hepatitis B virus (HBV) and human immunodeficiency virus (HIV). We showed, that MEK-ERK signaling pathway plays an active role in RR-mediated inhibition of IFN-I in pDC. Our results indicate that in line with other studies of our group, pharmacological targeting of MEK1/2-ERK signaling could be a strategy to re-establish immunogenic activity of pDC. Then, we investigated whether antiretroviral therapy (ART) in a cohort of 21 treatment-naive chronic HIV-infected patients has restored the number and...

Plasmacytoid dendritic cells (pDC) represent innate immune cells capable to detect viruses in their endosomal environment via Toll-like receptors (TLRs). Viral nuclear acid recognition leads to the massive production of type I interferon (IFN I) and induction of the antiviral state in uninfected cells. Crosslinking of the surface regulatory receptors, such as BDCA-2, with monoclonal antibodies or with some viruses leads to the activation of MEK1/2- ERK signaling pathway and inhibition of IFN I production in pDC. In this study, the role of MEK1/2 kinase has been highlighted. Its inhibition reversed the inhibitory effect of BDCA-2 crosslinking and its direct activation with PMA led to the inhibition of IFN-α production. Yet an unclear role of pDC in sensing of BK polyomavirus virus (BKV) responsible for kidney transplant rejection was investigated as a major topic of this thesis. Experiments with the pDC cell line Gen2.2 and HRPTEC primary cell line showed that pDCs were not able to detect BKV particles, however, exposure of activated Gen2.2 cells to BKV inoculum dramatically upregulated production of IFN-α. Most importantly, coculture of Gen2.2 cells with BKV- infected HRPTEC cells resulted in IFN-α and TNF-α production, which was prevented by Bafilomycin. These results suggest that BKV-infected...

La transmission mère-enfant (TME) du VIH-1 est un des enjeux majeurs de la pandémie. Une meilleure compréhension de la réponse des lymphocytes T cytotoxiques CD8+ (LTC) VIH-spécifiques lors de la grossesse facilitera le design de stratégies optimales pour diminuer la TME. Notre objectif est donc de caractériser l’amplitude et la diversité de la reconnaissance antigénique des LTC VIH-spécifiques avant, pendant et après la grossesse chez des femmes infectées par le VIH-1. Nos résultats montrent pour la première fois que l’initiation et la progression de la grossesse, à elles seules, n'ont que peu d’influence sur l’amplitude et la diversité de la reconnaissance antigénique des réponses LTC en termes de production d’IFN‐. Ces résultats indiquent que les femmes infectées par le VIH conservent une immunocompétence durant leur grossesse, du moins dans le contexte d’un traitement antirétroviral efficace. Ceci pourrait éventuellement aider à promouvoir l’immunisation comme stratégie pour prévenir la TME du VIH‐1. / Mother-to-child transmission (MTCT) of HIV-1 is one of the major issues of the pandemic. Characterization of HIV-specific immunity during pregnancy, especially cytotoxic CD8+ T lymphocytes (CTL), will lead to a better understanding of HIV pathogenesis and facilitate design of optimal strategies to prevent MTCT. Our objective is to describe the magnitude and the breadth of antigen recognition of HIV-specific CTL responses before, throughout and after pregnancy in a group of HIV-infected women. Our results revealed for the first time that initiation of pregnancy by itself doesn’t change the magnitude of CTL responses in terms of IFN- production. These findings support the fact that HIV-infected women maintain immunocompetence throughout gestation, at least in the context of effective antiretroviral treatment. These results provide a novel understanding of the dynamics of HIV-specific CTL responses during pregnancy and may help to promote maternal immunization as a strategy to prevent MTCT of HIV-1.

Le Streptocoque de groupe B (GBS) est un important agent d’infection invasive pouvant mener à la mort et demeure la cause principale de septicémie néonatale à ce jour. Neuf sérotypes ont été officiellement décrits basés sur la composition de la capsule polysaccharidique (CPS). Parmi ces sérotypes, le type III est considéré le plus virulent et fréquemment associé aux maladies invasives graves, telle que la méningite. Malgré que plusieurs recherches aient été effectuées au niveau des interactions entre GBS type III et les cellules du système immunitaire innées, aucune information n’est disponible sur la régulation de la réponse immunitaire adaptative dirigée contre ce dernier. Notamment, le rôle de cellules T CD4+ dans l’immuno-pathogenèse de l’infection causée par GBS n’a jamais été étudié. Dans cet étude, trois différents modèles murins d’infection ont été développé pour évaluer l’activation et la modulation des cellules T CD4+ répondantes au GBS de type III : ex vivo, in vivo, et in vitro. Les résultats d’infections ex vivo démontrent que les splénocytes totaux répondent à l’infection en produisant des cytokines de type-1 pro-inflammatoires. Une forte production d’IL-10 accompagne cette cascade inflammatoire, probablement dans l’effort de l’hôte de maintenir l’homéostasie. Les résultats démontrent aussi que les cellules T sont activement recrutées par les cellules répondantes du système inné en produisant des facteurs chimiotactiques, tels que CXCL9, CXCL10, et CCL3. Plus spécifiquement, les résultats obtenus à partir des cellules isolées T CD4+ provenant des infections ex vivo ou in vivo démontrent que ces cellules participent à la production d’IFN-γ et de TNF-α ainsi que d’IL-2, suggérant un profil d’activation Th1. Les cellules isolées T CD4+ n’étaient pas des contributeurs majeurs d’IL-10. Ceci indique que cette cytokine immuno-régulatrice est principalement produite par les cellules de l’immunité innée de la rate de souris infectées. Le profil Th1 des cellules T CD4+ a été confirmé en utilisant un modèle in vitro. Nos résultats démontrent aussi que la CPS de GBS a une role immuno-modulateur dans le développement de la réponse Th1. En résumé, cette étude adresse pour la première fois, la contribution des cellules T CD4+ dans la production d’IFN-γ lors d’une infection à GBS et donc, dans le développement d’une réponse de type Th1. Ces résultats renforcent d’avantage le rôle central de cette cytokine pour un control efficace des infections causées par ce pathogène. / Group B Streptococcus (GBS) is an important agent of life-threatening invasive infections and remains the leading cause of neonatal sepsis to this day. Nine serotypes have been officially described based on capsular polysaccharide (CPS) composition. Among them, capsular type III is considered one of the most virulent and frequently associated with severe invasive diseases, such as meningitis. Although extensive research has been done on the interactions between GBS type III and various cells of the innate immune system, no information is available on the regulation of the adaptive immune response against this pathogen. In particular, the role of CD4+ T cells in the immuno-pathogenesis of the infection caused by GBS has never been assessed. In this study, three different models of murine infection were developed to evaluate activation and modulation of responding CD4+ T cells against GBS type III: ex vivo, in vivo, and in vitro. Ex vivo analysis of total splenocytes showed that GBS induces the release of type-1 pro-inflammatory cytokines. A strong IL-10 production follows this inflammatory cascade, indicating the host effort to maintain homeostasis. Results also indicate that T cells were actively recruited by responding innate immune cells via the release of chemotactic factors such as CXCL9, CXCL10, and CCL3. More specifically, results obtained from isolated CD4+ T cells from ex vivo or in vivo infections showed that they actively participate in the production of IFN-γ and TNF-α, as well as IL-2, suggesting a Th1 profile of activation. On the other hand, isolated CD4+ T cells were not main sources of IL-10. This observation suggests that this immuno-regulatory cytokine is produced mainly by cells of the spleen innate immune system of infected animals. The CD4+ Th1 cell profile was confirmed using an in vitro model of infection. Our results also suggest that the GBS CPS plays an immuno-modulatory role in the development of a Th1 response. In summary, this study addresses for this first time the contribution of CD4+ T cells in IFN-γ production during GBS infection, and thus, in the development of a Th1 response. Our data further highlight the central role of this cytokine for effective control of GBS infections.

Hepatitis B virus (HBV) infection is one of the major causes of chronic and cancerous liver disease. Elimination of HBV from chronically infected patients by recombinant interferon α (IFNα) monotherapy shows that the mechanisms of the innate immunity play an important role in suppressing viral infection. However, the mechanisms of recognition of the HBV genome and its escape from the mechanisms of natural immunity are still little known. One of the principal factors enabling the virus to escape from cellular restriction mechanisms is the HBx viral protein. HBx is a 154 amino acid pleiotropic multifunctional protein affecting transcription, signal transduction, cell cycle, protein degradation, apoptosis, and chromosomal stability in the host cell. Previous results from our laboratory have shown that activation of the MEK1/2-ERK signaling pathway in plasmacytoid dendritic cells leads to inhibition of IFNα production. The aim of my work was to determine whether HBx activates the MEK1/2-ERK pathway and thus inhibits IFN type I production also in hepatocytes. For this purpose, I monitored HBx production in the Huh7 hepatoma cell line by transfecting the bicistronic plasmid pHBx- IRES-EGFP and Western blotting. Using the same method, I monitored activation of the MEK1/2-ERK signaling pathway by ERK...