La dermatite atopique (DA) est une maladie inflammatoire et prurigineuse de la peau, très fréquente chez les enfants et dont la prévalence augmente dans les pays industrialisés. La physiopathologie complexe de cette maladie met en jeu un défaut de la barrière cutanée et/ou des défauts génétiques résultant en une hypersensibilité aux allergènes de l'environnement tels que ceux issus d'acariens. Récemment, des études sur les interactions entre le système immunitaire et les bactéries commensales et pathogènes de la peau ont révélé leur importance dans cette maladie. Pour étudier le rôle du microbiote cutané dans la réponse T CD4+, des cohortes de jeunes enfants, atteints de DA et sensibilisés aux allergènes d'acariens (Der p) ou non DA (population contrôle), ont été recrutées. L'analyse du microbiote (MALDI-TOF) et du profil transcriptomique cutanés, ainsi que la quantification des T CD4+ anti-Derp (ELISpot) ont montré que la présence de S. aureus sur la peau inflammatoire des sujets AD était associée à des taux élevés d'IgE, des transcrits caractéristiques d'une orientation Th2/Th22 et à une réponse périphérique Th2. Des cellules dendritiques dérivées de monocytes (moDC) de donneurs sains produisent respectivement de l'IFN-gamma et de l'IL-10 en présence de sécrétomes issus de souches de S. aureus et S. epidermidis provenant de patients. La prolifération de lymphocytes T CD4+ stimulés avec des moDC allogéniques traitées avec le sécrétome de S. aureus est atténuée par le traitement simultané des moDC avec le sécrétome de S. epidermidis. Les sécrétomes de S. aureus sont capables d'inhiber directement l'activité suppressive de lymphocytes T régulateurs en l'absence de cellule présentatrice d'antigène. L'ensemble de nos résultats nous permet de penser que S. aureus est un facteur pro-inflammatoire de la DA en exacerbant la prolifération de lymphocytes Th2 résidents et en inhibant la fonction des lymphocytes T régulateurs. Favoriser les effets anti-inflammatoires des bactéries commensales telles que S. epidermidis liés à l'induction d'une sécrétion d'IL-10 par les cellules dendritiques de la peau pourrait bénéficier aux patients atteints de DA. / Atopic dermatitis (AD) is an inflammatory and pruritic skin disease frequently affecting children. Its prevalence is increasing in industrialized countries. Its complex pathophysiology involves a skin barrier dysfunction and/or genetic abnormalities leading to sensitivity to environmental allergens such as house dust mites. Interactions between the immune system and skin bacteria, pathogens and commensals, appeared to be important in the disease. To study the influence of skin microbiota in the CD4+ T cell response, we designed a cohort of young AD children sensitized to house dust mite allergens (Der p) and their counterparts (controls). Analysis of skin microbiota (MALDI-TOF), transcripts profiling and quantification of anti-Der p CD4+ T cells showed that the presence of S. aureus on inflamed skin of AD subjects was associated with high IgE levels, Th2/Th22 transcripts and peripheral Th2 anti-Der p response. Monocyte-derived dendritic cells (moDC) were exposed to secretomes produced by S. aureus and S. epidermidis strains isolated from patients and released IFN-gamma and IL-10 respectively. Proliferation of CD4+ T cells induced by allogeneic moDC exposed to S. aureus secretome was blunted by concurrent exposure of moDC to S. epidermidis secretome. Regulatory T cells (Treg) lost their activity against conventional CD4+ T cells under the direct effect of S. aureus secretome. Overall, these results allow us to think that S. aureus is an important factor of the AD inflammation by inducing Th2 activation and silencing resident Treg. Commensals such as S. epidermidis could be used to counteract these effects by inducing IL-10 production by skin DC.

Tesis Magister en Ciencias Odontológicas con Mención en Periodontología / Las periodontitis son un conjunto de enfermedades de naturaleza inflamatoria y etiología infecciosa. La biopelícula patogénica subgingival, constituida principalmente por bacterias anaerobias Gram-negativas, es el factor etiológico responsable del inicio y progresión de las periodontitis. Esta biopelícula está compuesta por una amplia variedad de bacterias, entre ellas, Aggregatibacter actinomycetemcomitans. Sobre la base de la antigenicidad del O-polisacárido componente del LPS, en A. actinomycetemcomitans se describen distintos serotipos bacterianos y se ha propuesto que entre ellos existe una virulencia y patogenicidad distinta. Las bacterias periodonto-patógenas son reconocidas por las células dendríticas periodontales. Una vez activadas, las células dendríticas expresan moléculas co-estimuladoras y liberan citoquinas pro-inflamatorias y quimioquinas, determinantes de la presentación antigénica a los linfocitos T. Durante esta presentación antigénica, las células dendríticas inducen la activación, proliferación y diferenciación selectiva de los linfocitos TCD4+ hacia los distintos fenotipos efectores, caracterizados por la expresión y secreción de un patrón específico de citoquinas que determina el tipo de respuesta inmune en el hospedero y, finalmente, el fenotipo clínico de las periodontitis. En este estudio, se evaluó la respuesta de células dendríticas estimuladas con los serotipos a, b o c de A. actinomycetemcomitans. Ante el serotipo b se detectaron mayores niveles de expresión y secreción de IL-1β, IL-12, IL-23, IFN-γ y TNF-α en comparación a las células dendríticas estimuladas con los serotipos a o c. Adicionalmente, se analizó la activación de los linfocitos TCD4+ naïve ante células dendríticas autólogas estimuladas con los serotipos a, b o c de A. actinomycetemcomitans y se cuantificaron los niveles de expresión de los factores de transcripción y de expresión y secreción de las citoquinas fenotipo-específicas. En los linfocitos TCD4+ naïve activados por células dendríticas estimuladas con el serotipo b de A. actinomycetemcomitans se detectaron mayores niveles de expresión de los factores de transcripción T-bet y RORC2 y de producción de las citoquinas IL-1β, IL-6, IL-12, IL-17, IL-23, IFN-γ, TNF-α y RANKL, característicos de un patrón de respuesta inmune tipo Th1 (pro-inflamatorio) y Th17 (osteo- destructivo), en comparación a las mismas células estimuladas con los serotipos a o c. En conjunto, estos datos permiten establecer un mayor potencial inmuno-estimulador del serotipo b de A. actinomycetemcomitans en las células dendríticas y linfocitos TCD4+ naïve. Los mayores niveles de secreción de citoquinas propias de un patrón de respuesta tipo Th1 y Th17 se correlacionaron positivamente con la expresión de T-bet y RORC2, factores de transcripción determinantes de los fenotipos linfocitarios Th1 y Th17, respectivamente. Estos resultados nos permiten especular una asociación entre la mayor frecuencia de detección del serotipo b en lesiones periodontales de pacientes con periodontitis y la mayor respuesta inducida en las células dendríticas y linfocitos TCD4+ naïve establecida en este estudio, con una mayor patogenicidad del microorganismo, en particular, con un fenotipo de enfermedad pro-inflamatorio y osteo-destructivo. / Financiamiento: Proyecto FONDECYT 11100298

A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg 2014 / Human receptor CD4 is a membrane-bound glycoprotein expressed on the surface of certain leukocytes where it plays a key role in the activation of immunostimulatory T cells. This function is diverted by the Human Immunodeficiency Virus (HIV) envelope glycoprotein (gp120), which uses CD4 as its primary receptor for cell entry. The requirement of CD4 for viral entry has rationalised the development of recombinant CD4-based proteins as competitive viral attachment inhibitors and immunotherapeutic agents. While growing evidence suggests that redox exchange reactions involving CD4 disulphides (potentially catalysed by cell surface-secreted oxidoreductases) play an essential role in regulating the activity of CD4, their mechanism(s), biological utility and structural consequences that may be applicable to the designs of novel antiviral therapies and vaccines remain incompletely understood. Herein, a novel recombinant CD4 protein designed to bind gp120 through a targeted disulphide-exchange mechanism is described. This molecule contains a conservative Ser60 to Cys mutation on the CD4 domain 1 α-helix which, according to theoretical crystal structure modelling, positions a thiol in close proximity of the gp120 V1/V2 loop disulphide (126Cys–Cys196) resulting in the formation of an interchain disulphide bond. Experimental evidence for this effect is provided by describing the expression, purification, refolding, receptor binding and antiviral activity analysis of a recombinant two-domain CD4 variant containing the S60C mutation (2dCD4-S60C). This 2dCD4-S60C binds HIV-1 gp120 with a significantly higher affinity than wild-type protein under conditions that facilitate disulphide exchange and this translates into a corresponding increase in the efficacy of CD4-mediated viral entry inhibition. To gain more insights into the importance of redox activity in the mechanism of HIV entry, a panel of recombinant 2-domain CD4 proteins (2dCD4), including wild-type and Cys/Ala variants, were used to show that Thioredoxin (Trx), an oxidoreductase found on the cell surface, reduces 2dCD4 highly efficiently, catalysing the formation of conformationally distinct monomeric 2dCD4 isomers, and a stable, disulphide-linked 2dCD4 dimer. HIV-1 gp120 was shown to be incapable of binding a fully oxidised, monomeric 2dCD4 in which both domain 1 and 2 disulphides are intact, but binds robustly to reduced equivalents that are the products of Trx-mediated isomerisation. This Trx-driven dimerisation of CD4, a process believed to be critical for the establishment of functional MHCII-TCR-CD4 antigen presentation complexes, is shown to be impaired when CD4 is bound to gp120. Finally, preliminary, low-resolution structural analysis of individual CD4 domains 1 and 2 are suggestive of intrinsic metastability in domain 2, and reduction of its resident allosteric disulphide bond likely underpins the structural rearrangements in CD4 that are required for efficient interaction with gp120. Overall, these findings emphasise the fundamental importance of redox pathways in the biochemical mechanism of HIV entry, and illustrate the feasibility of exploiting these for the development of novel antiviral ligands.

No description available.

Sphingolipid metabolites play a role in the initiation and perpetuation of inflammatory responses. Since intestinal inflammation is a driving force in the development of colon cancer, in the present study, we investigated the suppression of dextran sodium sulfate (DSS)-induced colitis by dietary sphingomyelin in mice that lack functional peroxisome proliferator-activated receptor γ (PPAR-γ) in intestinal epithelial and immune cells. Dietary spingomyelin decreased colonic inflammation in mice of both genotypes but more efficiently in mice expressing PPAR-γ. Using a real-time polymerase chain reaction array, we detected an up-regulation in genes involved in Th1 (interferon γ) and Th17 (interleukin [IL]-17 and IL-23) responses despite the reduced inflammation. However, the genes involved in Th2 (IL-4, IL-13 and IL-13ra2) and Treg (IL-10rb) anti-inflammatory responses were up-regulated in a PPAR-γ-dependent manner. In order to direct mechanistic studies of how PPAR-γ expression is involved in SM-induced suppression of DSS colitis, we investigated the effect of dietary SM in DSS-treated mice that lack PPAR-γ in the CD4+ T-cells. While the pathogenesis of colitis was independent of PPAR-γ expression in CD4+ T-cells, dietary SM decreased disease activity and colonic inflammation in mice of both genotypes but more efficiently in mice expressing PPAR-γ, indicating both PPAR-γ dependent and independent signaling pathways. In conclusion, in contrast to endogenous sphingolipid metabolites, dietary SM modulated both pro- and anti-inflammatory responses at the early stages of the disease in a partially PPAR-γ dependent manner resulting in a suppression of inflammation that may be critical for the suppression of inflammation-driven colon cancer. / Master of Science

CD4+ T cells are a group of lymphocytes that play critical roles in the immune system. By releasing cytokines, CD4+ T cells regulate other immune cells for maximizing the efficiency of the system. Naive CD4+ T cells are activated and become mature upon engagement with antigens, and the mature CD4+ T cells have several subsets, which play diverse regulatory functions. For the past two decades, our understanding of CD4+ T cells has been advanced through the studies on the differentiation process and the lineage specification of various subsets of these cells. Although in most experimental studies of CD4+ T cells, researchers focused on how transcription factors and signaling molecules influence the differentiation of a particular subset of these cells, many evidence have shown that the differentiation of CD4+ T cells can be heterogeneous in terms of the phenotypes of the cells involved. This dissertation describes a framework that uses mathematical models of the dynamics of the signaling pathways to explain heterogeneous differentiation. We show that the mutual inhibitions among the master regulators govern the formation of multi-stability behavior, which in turn gives rise to heterogeneous differentiation. The framework can be applied to systems with two or more master regulators, and models based on the framework can make specific predictions about heterogeneous differentiations. In addition, this dissertation describes an experimental study on CD4+ T cell differentiation. Being part of the adaptive immune system, the differentiation of CD4+ T cells was previously known to be induced by the signals from the innate immune cells. However, the expression of Toll-like receptor in CD4+ T cells suggests that microbial products can also influence the differentiation directly. Using an in vitro cell differentiation approach, we show that the differentiation and proliferation of CD4+ T cells can be influenced by lipopolysaccharide under the condition that would favor the differentiation of induced regulatory T cells. These theoretical and experimental studies give novel insights on how CD4+ T cells differentiate in response to pathogenic challenges, and help to gain deeper understanding of regulatory mechanisms of the complex immune system. / Ph. D.

CD4+ T cells mediate and orchestrate a tremendous panoply of lymphoid cell subsets in the human immune system. CD4+ T cells are able to differentiate into either effector pro-inflammatory or regulatory anti-inflammatory subsets depending on the cytokine milieu in their environment. This complex process is mediated through a variety of cytokines and soluble factors. Yet, the mechanisms of action underlying the process of differentiation and plasticity of this interesting immune subset are incompletely understood. To gain a better understanding of the CD4+ T cell differentiation and function, here we present an array of different strategies to model and validate CD4+ T cell differentiation and heterogeneity. The approaches presented here vary from ordinary-differential equation-based to agent-based simulations, from data-driven to theory-based approaches, and from intracellular mathematical to tissue-level or cellular modeling. The knowledge generated throughout this dissertation exemplifies how a combination of computational modeling with experimental immunology can efficiently advance the scene on CD4+ T cell differentiation. In this thesis I present i) an overview on CD4+ T cell differentiation and an introduction to which computational strategies have been adopted in the field to tackle with this problem, ii) ODE-based modeling and predictions on Th17 plasticity modulated by PPARγ, iii) ODE- and ABM-based cellular level modeling of immune responses towards Helicobacter pylori and the role of CD4+ T cell subsets on it, iv) Intracellular strategies to validate a potential therapeutic target within a CD4+ T cell to treat H. pylori infection, and finally v) data-driven strategies to model Th17 differentiation based on sequencing or microarray data to generate novel predictions on specific components. I present both mathematical and computational work as well as experimental work, in vitro and in vivo with animal models, to demonstrate how computational immunology and immunoinformatics can help, not only in understanding this complex process, but also in the development of immune therapeutics for infectious, allergic and immune-mediated diseases. / Ph. D.

Le syndrome de Sézary (SS) est un variant leucémique et érythrodermique de lymphomes T cutanés épidermotropes. Son diagnostic repose à la fois sur des critères cliniques, la présence de lymphocytes T à noyau atypique cérébriforme sur un frottis sanguin et la mise en évidence dans la peau, les ganglions et le sang d’un clone lymphocytaire T CD4+. Notre laboratoire a identifié KIR3DL2 comme premier marqueur membranaire spécifique des cellules tumorales de Sézary. KIR3DL2 peut ainsi être utilisé pour le diagnostic et le suivi des patients atteints du SS. Toutefois, aucune étude n’a démontré de lien entre sa structure de récepteur inhibiteur et sa fonction dans les lymphocytes tumoraux de Sézary, et plus particulièrement son implication possible dans les mécanismes régulant la prolifération et/ou la résistance à l’apoptose des cellules tumorales.Au cours de ce travail deux axes ont été développés :- Un premier axe visant à mieux comprendre la fonction de KIR3DL2 et les mécanismes de signalisation intracellulaire initiés lors de son engagement par l’anticorps AZ158 dans les lymphocytes T tumoraux de Sézary. Nos résultats mettent en évidence un rôle de corécepteur inhibiteur pour KIR3DL2 dans les cellules tumorales de Sézary. En effet, l’engagement de KIR3DL2 inhibe la prolifération et l’AICD induites par la stimulation CD3, cette inhibition étant corrélée à une modulation négative des signaux médiés par le TCR. Ainsi, KIR3DL2 ne se comporte pas comme une unité de signalisation indépendante dans les cellules tumorales de Sézary, contrairement à ce qui est observé dans les cellules NK.- Un second axe portant sur l’évaluation d’une nouvelle fonction de KIR3DL2 comme récepteur pour les ODN CpG. Ainsi, nous rapportons pour la première fois un effet direct de l’ODN CpG sur les cellules tumorales T CD4+ de Sézary. En effet, nous avons observé un effet apoptotique de l’ODN CpG-C caspases-dépendant sur les lignées et les cellules tumorales circulantes. De plus, le traitement des cellules tumorales de patients Sézary avec l’ODN CpG-C conduit à une inhibition de l’activation constitutive du facteur de transcription STAT3.La réalisation de cette étude a permis de mieux comprendre la fonction et les mécanismes initiés à partir de KIR3DL2 dans les cellules tumorales T CD4+ de Sézary. De plus, ce travail ouvre de nouvelles perspectives thérapeutiques basées sur le ciblage direct et spécifique des cellules tumorales de Sézary pouvant être associé à une stimulation des acteurs immuns grâce à l’action des ODN CpG. / Sézary syndrome (SS) is an aggressive leukemic and erythrodermic variant of cutaneous T-cell lymphoma. It is characterized by the presence of a clonal CD4+ T lymphocyte population in the skin, lymph nodes and peripheral blood. Our laboratory has previously identified the NK cell receptor KIR3DL2 as a valuable diagnostic and prognostic marker for the detection of the tumoral T cell burden of Sézary syndrome patients. However, the function of this receptor on the malignant T lymphocyte population remained unexplored. The specific expression of KIR3DL2 by SS patients malignant cells prompted us to investigate its possible influence on mechanisms regulating the tumoral cells outgrowth and apoptosis process.To this aim, two axes were developed. The first axis aimed to highlight the function of KIR3DL2 on the malignant T lymphocyte population and to elucidate the intracellular signaling mechanisms initiated by engagement of the receptor with the monoclonal antibody AZ158. Our results show that KIR3DL2 can exert an inhibitory co-receptor function in malignant Sézary cells. Indeed, triggering of KIR3DL2 inhibits the CD3-mediated proliferation and cell death of the CD4+ KIR3DL2+ cells, this inhibition being correlated to a down-modulation of the TCR-mediated signals. Thus, KIR3DL2 does not behave as an independent signaling unit in Sézary cells, unlike NK cells.The second axis aimed to evaluate a new function of KIR3DL2 as CpG ODN receptor. We show for the first time a direct effect of CpG ODN on tumoral CD4+ T Sézary cells. Thus, we observed a caspase-dependent apoptotic effect of CpG ODN-C on Sézary cell lines and circulating malignant T cells. This process of cellular death is correlated to a dephosphorylation of the transcription factor STAT3, which is found constitutively phosphorylated and activated in Sézary cells.This study has provided new insights into the function and the intracellular signaling pathways initiated by KIR3DL2 in malignant Sézary T cells. Furthermore, this work opens new therapeutic perspectives based on the direct and specific targeting of tumor cells that could be associated to immune cell stimulation through the use of ODN CpG.

O vírus linfotrópico de células T humanas (HTLV-1) foi o primeiro retrovírus descrito e está etiologicamente ligado a duas principais doenças: a leucemia/linfoma de célula T do adulto (ATLL) e a mielopatia associada ao HTLV-1/paraparesia espástica tropical (HAM/TSP). Apenas 0,3 a 5% dos indivíduos infectados desenvolvem essas doenças associadas, enquanto a maioria permanece assintomática. A HAM/TSP é uma manifestação inflamatória do sistema nervoso central e o mecanismo pelo qual o HTLV-1 induz o surgimento de HAM/TSP ainda não está totalmente esclarecido. Atualmente, uma abordagem promissora no entendimento de mecanismos, bem como na fisiopatogênese das infecções virais tem sido a avaliação da função de microRNAs (miRNAs). Há poucos dados na literatura envolvendo estas moléculas na infecção pelo HTLV-1 em linfócitos T CD4+ bem como no estabelecimento da doença HAM/TSP. No presente estudo, foi avaliada a expressão de miRNAs dos linfócitos T CD4+ isolados de portadores sem HAM/TSP (HAC), pacientes HAM/TSP e indivíduos sadios (CT) por meio de PCR em tempo real. A análise do perfil de expressão dos miRNAs nessas células revelou que 56 e 10 miRNAs apresentavamse mais 1,5 vezes aumentados no grupo HAM/TSP e HAC, respectivamente. O miR- 125b-1-1 apresentou expressão significamente maior no grupo HAC e o miR-146a, no grupo HAM/TSP. A análise in silico de predição de alvo demonstrou que o gene IFNG era potencialmente alvo do miR-125b-1-1 e os genes IRAK1 e TRAF6 do miR- 146a. Foi demonstrado que a expressão do IFNG no grupo HAC era 1,3 vezes mais elevado que o grupo CT e 1,8 vezes mais elevado no grupo HAM que no grupo CT. Houve um aumento na expressão de TRAF6 de 15,7 e 1,5 vezes nos grupos HAM/TSP e HAC, respectivamente. Não foi observada diferença na expressão de IRAK1 entre os três grupos. O ensaios de superexpressão do miR-125b-1-1 alterou a expressão do IFNG e do miR-146a alterou a expressão do gene IRAK1 e sua proteína. Os resultados evidenciados neste trabalho ressaltam a importância dos miRNAs na modulação de genes e proteínas importantes durante a infeção pelo HTLV-1. A correlação entre o miR-125b-1-1 e gene IFNG sugere que este miRNA esteja envolvido nos mecanismos de desenvolvimento de HAM/TSP. Além disso, a interação entre o miR-146a e os genes IRAK1 e TRAF6 sugerem que este miRNA esteja relacionado a mecanismos de persistência viral da infecção pelo HTLV-1 em linfócitos T CD4+. / Human T-cell lymphotropic vírus type 1 (HTLV-1) was the first human retrovirus discovered and it is related with two major diseases: adult T cell lymphoma/leukaemia (ATLL) and HTLV-1 -associated myelopathy/tropical spastic paraparesis (HAM/TS). About 0.3 to 5% of infected individuals will develop HTLV-1 related diseases, while the majority will remain life-long asymptomatic carriers of the virus. HAM/TSP is an inflammatory manifestation of central nervous system and the mechanism involved in HAM/TSP development is noy well elucidated. Currently, a promising approach on understanding the mechanisms as well as physiopathogenesis of viral infections has been the evaluation of the role of microRNAs (miRNAs) roles. There are few data involving CD4+ T cells miRNA expression in HTLV-1 infection as well as HAM/TSP establishment. To identify miRNAs differentially expressed in CD4+ T cells among non-infected individuals (CT), asymptomatic (HAC) and HAM/TSP patients we applied quantitative real time PCR. The analysis of miRNA expression profile in these cells showed 56 and 10 miRNAs upregulated 1.5 times in HAM/TSP and HAC groups, respectively. miR- 125b-1-1 was upregulated in HAC group and miR-146a in HAM/TSP. In silico analysis of target prediction showed that IFNG was a potentially miR-125b-1-1 target and IRAK1 and TRAF6 were miR-146a targets. IFNG expression was 1.3 higher in HAC than CT group and 1.8 higher in HAM/TSP than CT group. It was observed that TRAF6 expression was 15.7 and 1.5 times higher in HAM/TSP and HAC groups, respectively. There was no difference of IRAK1 expression among the three groups. Overexpression assays of miR-125b-1-1 altered IFNG expression and overexpression of miR-146a altered IRAK1 gene and protein expression. The results revealed that miRNAs modulate genes and proteins during HTLV-1 infection. miR- 125b-1-1 and IFNG gene correlation suggests that miR-125b-1-1 seems to contribute to HAM/TSP development. Besides, miR-146a and IRAK1 and TRAF6 interaction suggests that miT-146a seems to contribute to HTLV-1 establishment in CD4+ T cells.

Linfócitos T CD4+ (LTCD4) sofrem morte pelo reestímulo do TCR em um processo chamado de AICD (activation-induced cell death) no fim de uma resposta imune. Resultados prévios de nosso grupo de pesquisa mostraram que melatonina foi capaz de inibir o processo de AICD em LTCD4 em experimentos in vitro. Portanto, o objetivo deste trabalho é verificar se a melatonina é capaz de agir como estimulador, aumentando a resposta imune mediada pelos LTCD4 in vivo. Nós observamos que 3 e 9mg/Kg de melatonina aumentaram a resposta de DTH (Delayed-type Hypersensitivity), de forma diretamente proporcional à dose utilizada. O tratamento com melatonina estimulou um aumento da proliferação e do numero absoluto de LTCD4 específicos de antígeno. Em experimentos de diferenciação linfocitária in vitro, nós observamos que o tratamento com melatonina estimulou a produção de LTCD4 do perfil Th1 e Th2, no entanto inibiu a produção de linfócitos Th17. Em conclusão, nossos resultados sugerem um efeito estimulador da melatonina sobre a função de linfócitos T CD4+. / CD4+ T lymphocytes (LTCD4+) suffer cell death by a process known as activation-induced cell death (AICD) at the end of immune response. Previous results from our group showed that melatonin can inhibits AICD process in LTCD4 at in vitro experiments. Therefore, the aim of this work is verify if a melatonin can act as immune stimulator increasing a LTCD4-mediated immune response in vivo. We showed that 3 and 9 mg/Kg of exogenous melatonin added during immunization resulted in potentiation dose-dependent of Delayed-type hypersensitivity (DTH) response. The treatment with melatonin increased the absolute number LTCD4 antigen-specific, probably by increment of its proliferation. In experiment of T cell differentiation, we observed that the treatment with melatonin stimulated LTCD4 production of Th1 and Th2 profile however blocked the Th17 lymphocytes production. In conclusion, our results support the idea about a regulator role of melatonin on LTCD4 lymphocytes function for development of an immune response.