A epidemia promovida pela infecção com o vírus da imunodeficiência humana tipo 1 (HIV-1) é um fator agravante de saúde pública mundial, representando altas taxas de morbidade, com perda de qualidade de vida e mortalidade. Uma vasta gama de fatores de resposta inata exercem atividade antiviral, sendo a maior parte deles regulados pelo interferon tipo I. Desta forma, a proposta de estudo foi avaliara expressão de fatores antivirais e fatores reguladores da resposta de interferon tipo I em especial o sensor de DNA viral STING em células mononucleares do sangue periférico e em células do lavado bucal, de indivíduos expostos ao HIV-1 e não infectados, seu parceiro infectado por HIV-1, de indivíduos infectados por HIV-1 com carga viral (CV) detectável (acima de 5000 cópias/µL) e indivíduos saudáveis. Os resultados obtidos até o momento mostram que a exposição ao HIV-1 não é capaz de induzir a expressão de fatores antivirais regulados por IFN tipo I, mostrando que é preciso a infecção ativa para indução dos fatores. / The quality of life and morbidity are the most important hallmarker or the HIV-1 infection on the worldwide. Some important factors has been connected with this protection, likewise genetic, viral and immune host factors. Thus, this study reviewed the expression profile of antivirals factors and INF-I production regulators, in special the DNA sensor STING. The type I Interferon (IFN-I) is the major factor in HIV-1 inflammatory response. Therefore, we investigate the expression levels of activation and regulation IFN-I factors expressed in peripheral mononuclear blood cells (PBMCs) and cells of buccal wash of Exposed non-infected subjects, your infected partner, high viremia subjects (under 5.000 copies/mL) and health controls Our results indicated na important control mechanism to avoid inflammation who provide the permissiviness and infection with HIV-1.

Este estudo consistiu em avaliar comparativamente se camundongos neonatos e adultos, quando expostos ao poluente 1,2-NQ exibiriam susceptibilidade aumentada à inflamação alérgica (ovalbumina; OVA). Camundongos adultos ou neonatos foram expostos à 1,2-NQ ou veículo (15 min por três dias). Os camundongos adultos, após 24 h, ou neonatos, após 59 dias, foram sensibilizados/desafiados com OVA e os parâmetros funcionais e inflamatórios foram avaliados 24 h após. Em animais expostos a 1,2-NQ na fase neonatal, o desafio alérgico na idade adulta causou potente influxo de leucócitos no pulmão, sangue periférico e maturação eosinofílica na medula óssea, mas não afetou a hiperresponsividade brônquica. Isto foi consistente com maior biossíntese de citocinas Th2 e apresentação de CD11c esplênica. Em animais adultos, a 1,2-NQ não amplificou a inflamação alérgica. Conclui-se que, a exposição de camundongos neonatos à 1,2-NQ aumentou a susceptibilidade destes à inflamação alérgica na idade adulta via maior apresentação de CD11c esplênica e da biossíntese de citocinas Th2. / We have comparatively investigated whether exposure of neonates and adults mice to 1,2-NQ increases their susceptibility to allergic inflammation evoked by ovalbumin (OVA). Adults or neonate mice were nebulized with 1,2-NQ or corresponding vehicle. Following 24 h or eight weeks, adult or neonate mice were sensitized and challenged with OVA and the functional and inflammatory parameters were evaluated 24 h later. The allergic challenge in mice exposed to 1,2-NQ as neonates caused a potent influx of leukocytes in bronchoalveolar lavage, peripheral blood and increased eosinophil maturation in the bone marrow, without affecting Penh response. This was correlated with increased presentation of splenic CD11c and biosynthesis of Th2 cytokines in the lung. Adult mice exposure to 1,2-NQ failed to significantly increase OVA-induced allergic responses. Exposure to 1,2-NQ during neonatal period is critical to enhance susceptibility of asthma at a later stage of life, and that increased expression of splenic CD11c and inflammatory mediators contribute to this effect.

Antígenos de alta massa molecular (PI) do extrato de Ascaris suum exercem efeito supressor sobre a resposta imune a antígenos heterólogos. PI atua diretamente sobre as DCs, diminuindo a expressão das moléculas coestimuladoras, MHC de classe II e assim, a proliferação de linfócitos T. Esse efeito é independente de TLR2, TLR4 e da molécula MyD88. Nesse trabalho estudamos a participação dos receptores DC-SIGN e MR, na modulação da atividade das DCs. PI contém oligossacarídeos N-ligados com cadeias de alta manose e do tipo complexa e contém resíduos de fosforilcolina. Os componentes do PI contendo as cadeias glicosídicas N-ligadas inibem a maturação de DCs incubadas com LPS. Receptores DC-SIGN e MR estão envolvidos no reconhecimento e internalização dos componentes do PI pelas DCs. O bloqueio desses receptores foi capaz de abolir o efeito inibitório do PI sobre as DCs e a resposta proliferativa de linfócitos T in vitro. Portanto, os resultados mostram a participação do DC-SIGN e MR no reconhecimento de componentes glicosilados do PI e na sua ação imunomoduladora. / High molecular weight components (PI) of Ascaris suum extract exert suppressive effect on the immune response to OVA. PI exert direct effect on DCs, decreasing the T lymphocyte proliferation. This effect is independent of TLR2 and 4 as well as MyD88 molecule. In this work we studied the glycoconjugates in PI and the participation of DC-SIGN and MR, in the modulation of the functional activity of DCs. PI components contain high mannose- and complex-type N-linked oligosaccharides and phosphorylcholine residues. PI components containing N-linked glycans inhibited the DCs maturation induced by LPS. The previous incubation of DCs with mannan, anti-DC-SIGN and anti-MR antibodies abolished the modulatory effect of PI on the DCs maturation. It was also observed that the blockage of DC-SIGN and MR in DCs reversed the inhibitory effect of PI in the in vitro T cells proliferative response. Taking together these results show the involvement of DC-SIGN and MR in the recognition of glycosylated components of PI by DCs and in its modulatory effect.

O processo de apresentação antigênica realizado pelas células dendríticas (DC) aos linfócitos T constitui o passo inicial da geração da resposta imune anti-tumoral. As neoplasias interferem nesse processo alterando funcionalmente as DCs. Entre os fatores que influenciam a função das DCs, está a proteína C3 do sistema complemento. Assim, este trabalho investigou a influência de fatores solúveis dos sobrenadantes tumorais das linhagens de glioblastoma humano A172 e U87MG sobre a síntese de C3 pelas DCs derivadas de doadores saudáveis in vitro. A fenotipagem indicou que os sobrenadantes, especialmente da linhagem U87MG, parece estar modulando a expressão das moléculas CD14, CD80, CD86, CD83, CD274 e CD11b. Já a expressão do gene C3 parece sofrer uma modulação geralmente negativa pelo sobrenadante da linhagens U87MG enquanto a linhagem A172 tende a exercer o efeito inverso. / Antigen presentation by dendritic cells (DC) to T cells is the first step to generate an antitumor immune response. Tumors interfere in this process, affecting DCs function. One of the factors that affect DCs´s function is the complement system protein C3, which is produced by these cells. In this work, we investigated the influence of tumor supernatants derived from human glioma cells lines U87MG and A172 in the production of complement protein C3 by monocyte-derived dendritic cells from healthy donors in vitro. DC phenotyping indicated that the supernatants seem to modulate the expression of CD14,CD80,CD86, CD83, CD274 and CD11b. The expression of C3 gene, was negatively modulated by U87MG supernatant while the A172 supernatant seemed to exert the reverse effect.

Natural killer (NK) cells are non-specific killer cells of the innate immune system that eliminate target cells based on discrimination between self and non-self. Activation is carefully regulated through integration of signals received through both activating and inhibitory receptors. During the course of a herpes simplex virus type-1 (HSV-1) infection, NK cells can influence host susceptibility to infection with severe infections occurring in individuals with genetic defects in the NK cell response. In response to HSV infection, NK cells are recruited to the inflammatory tissue where ensuing reciprocal interactions with accessory cells and proinflammatory cytokines induce NK cell activation, cytolytic activity, and cytokine production, contributing to innate immune response and ultimately influencing the adaptive immune response. The objective of this study was to elucidate the multiple roles of NK cells during the numerous steps in anti-HSV immune induction. Accordingly, we have demonstrated that NK cells are novel helpers that assist and influence an anti-HSV immune response via the secretion of cytokines that enhance HSV-specific CD8+ T cell effector function and cytokine production. Taken together, data from this study presented the critical importance of NK cells in mounting an essential and efficient anti-HSV immunity. The key findings of our study were: 1. In the absence of NK cells, dendritic cells have decreased capacity to prime HSV-specific T cells. 2. HSV infected NK cells can be directly activated via toll-like receptor (TLR) in a MyD88-dependent mechanism; however, interaction with HSV infected dendritic cells yields optimal NK cell activation and function (CD69 and IFNγ). 3. TRAIL-expressing NK cells eliminate antigen-bearing immature dermal DCs (CD11c+CD8α-DR5+), that migrate to draining lymphoid organs, to facilitate antigen transfer to lymphoid resident CD8α+ DC for T cell cross priming. 4. 'Helpless' CD8+ T cell function, generated in the absence of CD4+ T cells, can be partially restored to wild-type levels by NK cell supplementation. 5. Treatment of NK cells with anti-CD69 antibody results in a heightened NK activated state and augments the adaptive immune response, without increasing NK cell numbers. These findings may contribute to the potential revelation of avenues to manipulate NK cells for anti-viral therapies.

Les cellules dendritiques (DC) tiennent une place centrale dans l'initiation des réponses immunitaires et dans le contrôle du développement des tumeurs. La sous-population cDC1 suscite aujourd'hui en grand intérêt de par ses fonctions d'activation de réponses cytotoxiques par présentation croisée d'Ag aux lymphocytes T (LT) CD8+ ainsi que son implication dans l'immunité antitumorale et la réponse aux immunothérapies chez la souris. Le rôle des cDC1 chez l'Homme est cependant peu décrit. Les cDC1 murines et humaines sont aussi connues pour produire de larges quantités d'interféron (IFN) de type III (IFN-III), aussi appelés IFN-λ. Tout comme les IFN-I avec lesquels ils partagent la même voie de signalisation, les IFN-III ont un rôle antiviral bien décrit. Des modèles murins ont également suggéré un rôle antitumoral, mais ces IFN n'ont jamais été étudiés dans un contexte de cancer chez l'Homme. Il est donc crucial de comprendre les mécanismes expliquant l'impact pronostique positif des cDC1 ainsi que le rôle des IFN-III dans l'immunité antitumorale, en particulier pour le développement de nouvelles approches thérapeutiques. Nous avons démontré pour la première fois l'infiltration des tumeurs humaines de sein et d'ovaire par diverses sous-populations de DC. Les cDC1 sont particulièrement enrichies par rapport au sang des patientes et forment de nombreuses interactions avec les LT CD8+ dans les tumeurs. Une approche de bio-informatique a permis de révéler que les cDC1 représentent l'unique population de DC associée à une meilleure survie des patients dans la majorité des cancers du TCGA. De façon intéressante, la signature de réponses aux IFN-I et III est enrichie dans les tumeurs de sein fortement infiltrées par les cDC1 mais pas par les autres sous-populations. L'expression des gènes codant pour l'IFN-λ1 ou le récepteur aux IFN-III est également associée à une meilleure survie sans rechute dans le cancer du sein. De plus, nous avons démontré la capacité des cDC1 à produire de l'IFN-III sans aucune réactivation ex vivo. Ce résultat indique clairement que dans un contexte de réponse immunitaire antitumorale chez l'Homme, la synthèse d'IFN-III est une spécificité des cDC1 comparées aux autres sous-populations. La présence d'IFN-III dans les surnageants tumoraux a été confirmée au niveau protéique et démontrée comme étant fortement corrélée avec l'IL-12p40, les CXCR3-L, le CX3CL1 et le TNF-α. Ces données soulèvent alors l'hypothèse de l'association entre l'IFN-III, produit dans le microenvironnement tumoral par les cDC1, et la présence de cytokines et chimiokines impliquées dans le recrutement et l'activation de lymphocytes cytotoxiques tels que les LT CD8+ ou cellules NK. Notre étude apporte des informations détaillées quant à la nature des différentes sous-populations de DC infiltrant les tumeurs humaines de sein et d'ovaire et démontrent pour la première fois la production d'IFN-III par les cDC1. L'association de ces cellules et des IFN qu'elles produisent avec une meilleure survie des patientes confirme l'intérêt de développer de nouvelles immunothérapies ciblant les cDC1, en particulier dans le cancer du sein / Dendritic cells (DCs) represent a promising target for the development of new immunotherapies because of their central role in the initiation and the control of immunity. The rare cDC1 population is under considerable scrutiny because their murine counterparts called CD8α+ DCs are essential for cross-presentation to CD8+ T cells, antitumor immunity and response to immunotherapies. In contrast, the role of human cDC1 in cancer has not been investigated as extensively as in mice. They were identified in several tumors and transcriptomic analyses revealed their association with a favorable patient outcome. They also represent a major source of type III interferon (IFN-III), also called IFN-λ, playing a crucial role in viral infections, similarly to IFN-I that share the same signaling pathway. Its antitumor activity was also reported in mouse models, therefore raising questions regarding the use of IFN-IIl in clinical oncology. We believe that understanding the underlying mechanisms of cDC1 favorable prognostic impact and the role of IFN-III in antitumor immunity will be central to design new therapeutic approaches. Here, we demonstrated the infiltration of human primary breast and ovarian tumors by several DC populations and the enrichment of cDC1 compared with patient blood. We also showed for the first time close contacts between cDC1 and T cells in breast tumors. An in silico approach using MCPcouter on the TCGA data sets revealed that cDC1 represented the only DC subset associated with a prolonged overall survival in the majority of solid tumors. Interestingly, type I/III signature was strongly enriched in tumors highly infiltrated only with cDC1. Furthermore, we observed by feature intracytoplasmic flow cytometry analysis a spontaneous production of IFN-λ1 that is restricted to cDC1 in the absence of any ex vivo stimulation in one third of tumors. This result clearly indicates that IFN-λ1 production is a distinct of cDC1 compared with other DC subsets, even in a human tumor context. Notably, a high expression level of genes coding for IFN-III or its receptor was correlated with an increased relapse-free survival in breast cancer. We confirmed the presence of the IFN-λ1 protein in more than 50% of tumors and observed its abundancy compared with other IFN subtypes. IFN-λ1 was strongly correlated with IL-12p40, CXCL9, CXCL10, CXCL11, CX3CL1 and TNF-α. These results raised the hypothesis that IFN-λ1, produced by cDC1 in the TME, could be associated with the production of cytokines and chemokines involved in the recruitment and activation of cytotoxic lymphocytes (NK cells and CD8+ T cells). Our study provides detailed information about the DC compartment infiltrating human breast and ovarian tumors, revealing their potential implication in the antitumor immunity. By focusing on the pathways associated with each DC subset, our findings shed new light on the link between DC population called cDC1 and IFN-I/III signature in tumors. Our clear demonstration of IFN-III production by cDC1 and of its positive impact on the prognosis of cancer patients provides valuable evidences to support the development of new therapeutic strategies targeting cDC1 to amplify the response to immunotherapies, especially in breast cancer

Les cellules T folliculaires helper (Tfh) jouent un rôle central dans la mise en place de réponses humorales efficaces. En effet, les Tfh participent à la sélection des lymphocytes B permettant le développement de lymphocytes B mémoires et d’anticorps de haute affinité. Les Tfh représentent ainsi une cible prometteuse pour la mise en place de nouvelles stratégies thérapeutiques, notamment pour augmenter l’efficacité de la vaccination. Ainsi, il apparaît crucial de mieux comprendre les étapes menant à leur développement, en particulier chez l’Homme. L’initiation de la polarisation Tfh se déroule dans les organes lymphoïdes secondaires et met en jeu les cellules myéloïdes mononucléaires (MMC). Les MMC présentes dans les organes lymphoïdes comprennent les macrophages résidents et trois sous populations de DC résidentes : les cDC1 (CD141+), les cDC2 (CD1c+) et les pDC. Nous nous sommes plus particulièrement intéressés au rôle respectif des sous populations de MMC humaines dans l’induction de la polarisation Tfh. Ainsi, les travaux effectués au cours de ma thèse avaient pour objectifs dans un premier temps d’analyser la capacité des différentes populations de MMC à induire la polarisation Tfh, afin de mettre en évidence de potentielles spécialisations fonctionnelles. Dans un second temps, nous nous sommes concentrés sur les mécanismes moléculaires impliqués dans l’induction par les MMC de la polarisation Tfh. Nous avons montré une spécialisation fonctionnelle des cDC2 et des macrophages des amygdales pour la polarisation Tfh. Toutefois, des différences ont été observées entre les cDC2 et macrophages, puisque les macrophages induisent la sécrétion par les lymphocytes T d’une grande quantité de CXCL13 par rapport au cDC2, qui sont plus efficaces pour induire la production d’IL21. Nous avons pu également montrer que les cDC2 et macrophages sécrétaient des cytokines précédemment identifiées comme ayant un rôle dans l’induction des Tfh telles que IL12p70, ActivinA et TGFβ. Afin de confirmer le rôle de ces cytokines dans la polarisation induite par les MMC d’amygdales, nous avons utilisé des anticorps bloquants dans nos expériences de polarisation T helper. Ainsi, nous avons confirmé le rôle de l’IL12p70, de l’Activin A et du TGFβ dans l’induction des Tfh humains. Nos résultats suggèrent également un rôle de l’Activin A et de TGFβ dans l’induction de la sécrétion de CXCL13, alors que l’IL12p70 serait impliqué dans l’induction de la sécrétion d’IL21. Nos résultats suggèrent aussi l’existence de deux sous populations de Tfh caractérisées soit par l’expression d’IL21 soit par l’expression de CXCL13. Les travaux réalisés au cours de ma thèse enrichissent ainsi les connaissances sur la spécialisation fonctionnelle des sous populations de DC et des macrophages humains, et apportent de nouveaux éléments pour la compréhension de la différenciation des Tfh humains. / T follicular helper cells (Tfh) play a key role in the establishment of efficient humoral responses. Indeed, Tfh are involved in B lymphocyte selection allowing the development of high affinity memory B cells and antibodies. Tfh are promising targets for new therapeutic strategies, especially to increase the effectiveness of vaccination. Thus, it is crucial to better understand the stages leading to their development, especially in human. Initiation of Tfh polarisation occurs in secondary lymphoid organs and involves mononuclear myeloid cells (MMC). MMC from secondary lymphoid organs include resident macrophages and three subsets of resident Dendritic Cells (DC): cDC1 (CD141+), cDC2 (CD1c+) and pDC. We were particularly interested in human MMC subsets respective roles in the induction of Tfh polarisation. Thus, the work carried out during my thesis aimed first at analysing the ability of different populations of MMC to induce Tfh polarisation, in order to highlight potential functional specialisations. In a second step, we focused on the molecular mechanisms involved in Tfh polarisation by MMC. We have shown a functional specialisation of cDC2 and tonsillar macrophages for Tfh polarisation. However, differences have been observed between cDC2 and macrophages, since macrophages induce secretion by T cells of a large amount of CXCL13 compared to cDC2, which are more effective in inducing IL21 production. We have also been able to show that cDC2 and macrophages secreted cytokines previously shown to play a role in Tfh induction such as IL12p70, ActivinA and TGFβ. In order to confirm the role of these cytokines in Tfh polarisation induced by tonsil MMCs, we used blocking antibodies in our T helper polarisation experiments. Thereby, we confirmed the role of IL12p70, Activin A and TGFβ in the induction of human Tfh. Our results also suggest a role for Activin A and TGFβ in inducing secretion of CXCL13, whereas IL12p70 would be involved in the induction of IL21 secretion. Besides, our results suggest the existence of two Tfh subsets characterised by expression of either IL21 or CXCL13. The work performed during my thesis broadens the knowledge on the functional specialisation of human DC subsets and macrophages, and provides new insight into the differentiation of human Tfh.

Le tropisme cellulaire des prions infectieux diffère selon lespèce animale, celui-ci est corrélé à la souche infectieuse et à des facteurs spécifiques de lhôte. Par exemple, certains prions infectieux sont lymphotropiques, notamment en cas de scrapie chez les moutons et de variant de la maladie de Creutzfeldt-Jakob (vMCJ) chez lhomme. Par opposition, certains prions se caractérisent par un neurotropisme comme observé chez des patients Creutzfeldt-Jakob atteints de la forme sporadique ou chez des bovins atteints dencéphalopathies spongiformes bovines (ESB). Lhypothèse de notre travail repose sur les observations suivantes : dans le cas du variant de la maladie de Creutzfeldt-Jakob et des encéphalopathies spongiformes bovines, lagent responsable est identique, la voie dinoculation et les lésions neurologiques le sont également, seul le tropisme de cette souche pour les organes lymphoïdes diffère. En effet, les amygdales, la rate et lappendice sont infectieux chez lhomme. Par contre, linfectiosité est surtout confinée au niveau du système nerveux chez le bovin. Lors dune inoculation expérimentale par voie orale de lagent responsable de lESB chez les bovins, les plaques de Peyer iléales sont les seuls tissus lymphoïdes infectieux. Notre hypothèse de travail est que des propriétés de lhôte interviennent dans le tropisme de lagent infectieux. Deux axes de recherche ont été envisagés afin de vérifier cette hypothèse :  Lanalyse de la distribution des fibres nerveuses au sein des tissus lymphoïdes associés aux muqueuses (MALT) des espèces bovine et humaine  Létude de lexpression de PrPc et de ses isoformes au sein des tissus lymphoïdes et nerveux des espèces bovine et humaine. Pour atteindre au mieux nos objectifs, il nous manquait un outil essentiel permettant la caractérisation spécifique des FDC bovines. En effet, aucun marqueur spécifique de ces cellules nétait commercialisé. Nous avons donc produit, en collaboration avec le Centre dEconomie Rural de Marloie, un anticorps monoclonal spécifiquement dirigé contre les cellules folliculaires dendritiques (FDC) bovines. Cet anticorps nous a permis détudier la distribution des FDC au sein des organes lymphoïdes bovins. Une attention particulière a été portée aux FDC isolées à partir des plaques de Peyer jéjunales (PPJ) et iléales (PPI). Lapparente différence dinfectivité de ces tissus lymphoïdes chez des bovins atteints expérimentalement dESB nous a conduit à comparer les capacités fonctionnelles des FDC isolées à partir de PPJ et de PPI. Ces observations sont décrites et discutées dans le chapitre 1. Dans le chapitre 2, nous avons établi une cartographie des fibres nerveuses au sein des amygdales, des plaques de Peyer iléales et jéjunales bovines de plusieurs catégories dâge et ensuite comparé ce pattern dinnervation à celui des amygdales humaines; ceci permettra de pister les voies potentielles de neuro-invasion. Une attention particulière a été portée à linterface cellules folliculaires dendritiques fibres nerveuses. En effet, les FDC matures jouent un rôle prépondérant dans la pathogenèse des maladies à prion puisquen leur absence, une infection périphérique na pas lieu. De plus, la proximité entre fibres nerveuses et FDC est un paramètre intervenant dans la neuro-invasion; nous avons dès lors aussi analysé les contacts entre les FDC et les éléments nerveux. Lexpression de la PrPc est une condition sine qua non pour la formation de PrPres. Cette protéine cellulaire sert probablement de récepteur pour son homologue infectieux mais sert surtout de substrat pour lamplification de PrPres ; toute modification au niveau de sa synthèse pourrait entraîner un changement de la cinétique dinfection et pourrait expliquer lapparente absence dinfectivité constatée au niveau du système immunitaire chez les bovins. Lexpression tissulaire et cellulaire spécifique disoformes de la PrPc représente un facteur de lhôte potentiellement capable dinfluencer le tropisme cellulaire de lagent infectieux chez lhumain et le bovin. Cette expression a été étudiée dans les systèmes MALT bovins et humains. Pour affiner notre étude, nous avons analysé, par des techniques de western-blotting, le glycopattern de la PrPc ainsi que lexpression de ses formes tronquées dans les tissus lymphoïdes humains et bovins mais également dans des populations cellulaires spécifiques, les lymphocytes et les FDC. Afin de vérifier si les isoformes de PrPc sont spécifiques aux tissus lymphoïdes, nous avons effectué une étude comparative du pattern de glycosylation et du ratio des formes clivées de PrPc, exprimés au sein de différentes régions du système nerveux central bovin et humain. Les résultats de ces travaux sont repris dans le chapitre 3.

The events that trigger an autoimmune disease remain largely unknown. To study these events animal models are necessary because symptoms of autoimmune diseases are preceded by a long asymptomatic period in humans. Experimental autoimmune encephalomyelitis (EAE) is the best characterized model for cell mediated autoimmunity and an animal model for the human disease multiple sclerosis. EAE is induced in rodents by immunization with myelin antigens (Ags) together with adjuvants. After immunization, T cells are primed in the periphery by Ag presenting cells and subsequently invade the central nervous system where they mediate parenchymal inflammation, resulting in demyelination and clinical symptoms of an ascending paralysis. It is now generally recognised that the main cell type mediating EAE is the T helper type 17 (Th17) cell. Tolerance to EAE can be attained by DNA vaccination, but how the immune response against the myelin Ags is abrogated after DNA vaccination is not known. By employing short interfering RNA technology, induction of the innate immune signalling molecule interferon (IFN) -β was found to be necessary for the protective effect of DNA vaccination in EAE. In addition, DNA vaccination inhibited subsequent autoimmune Th17 cell responses. The Toll-like receptors (TLRs) of the innate immune system have evolved to recognise conserved molecular structures on microbes and signalling through them almost exclusively converge on the molecule MyD88. Signalling via MyD88 was found to be required for induction of EAE since mice deficient in this molecule did not develop disease. Upstream signalling via TLR4 and TLR9 had tolerogenic properties. In studies of Ag presentation in EAE, two major subtypes of dendritic cells (DCs) were examined. Plasmacytoid DCs were found to have a promoting role in the induction of EAE, partly via type 1 IFNs. Myeloid DCs had a redundant role in the induction phase of EAE, neither disease severity nor encephalitogenic Th17 responses were affected by their absence during priming. These studies further demonstrate that the cells and molecules of the innate immune system exhibit a crucial role in controlling the adaptive immune system which mediates tissue damage in autoimmune diseases.

According to WHO, leishmaniasis is endemic in 98 countries, and has been placed ninth in a global analysis of infectious diseases. Treatment of leishmaniasis is based on pentavalent antimonials but toxicity and developing resistance have been reported. Traditional medicine and scientific studies have shown that the extract of Galipea longiflora Krause (Evanta) exhibits antileishmanial activity. We hypothesized that the healing observed when using this plant might not only be due to the direct action on the parasite, but possibly to a parallel effect on the host immune response. We found that an alkaloid extract of Evanta (AEE) inhibited the growth of Leishmania braziliensis promastigotes while viability of eukaryotic cells was practically not affected. We also found that AEE interfered with polyclonal activation or Leishmania-specific re-stimulation of lymphocytes, as revealed by a reduction of in vitro cellular proliferation and IFN-g production. More important, AEE treatment of mice hosting L. braziliensis showed that AEE is able to control both inflammation and parasite load. Additionally, the healing process was improved when AEE and meglumine antimoniate were administered simultaneously. Dendritic cells (DCs) play a pivotal role in T-cell stimulation and polarization of naïve T cells. Therefore, we investigated if AEE could alter the activation of DCs and if allostimulatory DCs properties were altered if activated in the presence of AEE. DCs activated in the presence of AEE reduced the production of IL-12p40 and IL-23. When we analyzed the allostimulatory capacity of AEE-treated DCs, we found that allogeneic CD4+ T-cells secreted lower levels of IFN-γ. In conclusion, this thesis provides valuable insight into the effects of Evanta derived extract. The dual effect found for AEE, on Leishmania parasite and on the immune response, suggests that AEE may be useful in controlling the parasite burden and preventing over-production of inflammatory mediators and subsequently avoiding tissue damage. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Submitted.</p>