<p>The existence of immune self-tolerance allows the immune system to mount responses against infectious agents, but not against self-molecular constitutes. Although self-tolerance is a robust phenomenon, in some individuals as well as in experimental models, the self-tolerance breaks down and as a result, a self-destructive autoimmune disease emerges. The underlying mechanisms for the development of autoimmune diseases are not known, but genetic, environmental and immunological factors are suggested to be involved. In this thesis, we used murine mercury-induced autoimmunity to test this suggestion.</p><p>In susceptible mice mercuric chloride induces a systemic autoimmune disease characterized by increased serum levels of IgG1 and IgE, production of anti-nucleolar autoantibodies (ANolA) and formation of renal IgG deposits. In contrast, in resistant DBA/2 (H-2^d) mice, none of these characteristics develop after exposure to mercury. By crossing and backcrossing mercury-resistant DBA/2 mice to mercury susceptible strains, we found that the resistance was inherited as a dominant trait in F1 hybrids and that one gene or a cluster of genes located in the H-2 loci determined the resistance to ANolA production, whereas resistance to the other characteristics was found to be controlled by two or three non-H-2 genes.</p><p>We further put forward the “cryptic peptide hypothesis” to investigate whether mercury and another xenobiotic metal use similar pathway(s) to induce the H-2 linked production of ANolA. We found that while mercury stimulated ANolA synthesis in all H-2 susceptible (H-2^s, H-2^q and H-2^f) mouse strains, silver induced only ANolA responses in H-2^s and H-2^q mice, but not in H-2^fmice. Further studies showed that the resistance to silver-induced ANolA production in H-2^fmice was inherited as a dominant trait.</p><p>We next tested the proposition that mercury induces more adverse immunological effects in mouse strains, which are genetically prone to develop autoimmune diseases, using tight-skin 1 mice, an animal model for human Scleroderma. It was found that in this strain, mercury induced a strong immune activation with autoimmune characteristics, but did not accelerate the development of dermal fibrosis, a characteristic in Tsk/1 mice.</p><p>Finally we addressed the Th1/Th2 cross-regulation paradigm by examining if a Th1-type of response could interact with a Th2-type of response if simultaneous induced in susceptible mice. Our findings demonstrated that mercury-induced autoimmunity (Th2-type) and collagen-induced arthritis (CIA) (Th1-type) can interact in a synergistic, antagonistic or additive fashion, depending on at which stage of CIA mercury is administered.</p>

Neonatal immune responses are typically deficient against a wide variety of antigens, including alloantigens, vaccine antigens, and infectious agents. These responses are characterized by Th2-skewed cytokine production, and deficient Th1 and cytotoxic responses. However, these deficient responses can be boosted to adult levels by the use of strong, Th1 promoting agents. This demonstrates that neonates are capable of developing mature immune responses under specific conditions. Using two different murine models, we have found that neonates develop robust Th and cytotoxic responses, which under some antigenic conditions significantly exceed those of adults. First, using a model of early life exposure to noninherited maternal antigens (NIMA), we found that murine neonates develop robust in vivo cytotoxic responses to low doses of alloantigens. Importantly, primary in vivo cytotoxic responses to alloantigen developed during the neonatal period, and persisted into adulthood. Neonates developed similar memory cytotoxic responses to donor spleen cells, bone marrow, and stem cell-enriched (Lin-) bone marrow cells, suggesting that the exposure dose is more important than the type of transplanted donor cell for the development of cytotoxicity. NIMA-exposed neonates also developed vigorous primary and memory allospecific Th1/Th2 responses which exceeded the responses of adults. These findings suggest that early exposure to low levels of NIMA may lead to long term immunological priming of all arms of T cell adaptive immunity. Second, we characterized the phenotype and function of neonatal recent thymic emigrants (RTE). RTE are the predominant cell type in murine neonates, and are present at higher frequencies within the neonatal CD4+ compartment than in adults. Our data demonstrate that RTE from murine neonates and adults are phenotypically and functionally distinct. In particular, although the magnitude of RTE cytokine responses from both age groups is dependent on the conditions of activation, neonatal RTE consistently exhibited higher levels of effector cytokine production than adult RTE. In particular, activation of neonatal RTE in the presence of IL-7 lead to greatly increased IFNgamma production, while adult responses were not altered. Overall, neonatal RTE responses were more plastic than those of adult RTE, as both Th1 and Th2 responses were altered in neonates using various activation conditions, while only Th2 responses were consistently changed in adults. Finally, in contrast to adult RTE, neonatal RTE proliferated in response to IL-7 stimulation at very early timepoints. This was associated with faster kinetics of IL-7Ralpha downregulation and higher levels of pSTAT5 in neonatal RTE. These quantitative and qualitative differences in neonatal RTE populations may largely explain the diverse responses that are elicited in neonates in response to different antigens, especially under those conditions in which Th1 responses are enhanced (i.e., exposure to NIMA alloantigens). Taken together, these data demonstrate that neonatal T cell responses are actually highly plastic, instead of intrinsically deficient. Furthermore, if given optimal stimulation conditions, neonatal responses can actually exceed those produced by adults.

The existence of immune self-tolerance allows the immune system to mount responses against infectious agents, but not against self-molecular constitutes. Although self-tolerance is a robust phenomenon, in some individuals as well as in experimental models, the self-tolerance breaks down and as a result, a self-destructive autoimmune disease emerges. The underlying mechanisms for the development of autoimmune diseases are not known, but genetic, environmental and immunological factors are suggested to be involved. In this thesis, we used murine mercury-induced autoimmunity to test this suggestion. In susceptible mice mercuric chloride induces a systemic autoimmune disease characterized by increased serum levels of IgG1 and IgE, production of anti-nucleolar autoantibodies (ANolA) and formation of renal IgG deposits. In contrast, in resistant DBA/2 (H-2d) mice, none of these characteristics develop after exposure to mercury. By crossing and backcrossing mercury-resistant DBA/2 mice to mercury susceptible strains, we found that the resistance was inherited as a dominant trait in F1 hybrids and that one gene or a cluster of genes located in the H-2 loci determined the resistance to ANolA production, whereas resistance to the other characteristics was found to be controlled by two or three non-H-2 genes. We further put forward the “cryptic peptide hypothesis” to investigate whether mercury and another xenobiotic metal use similar pathway(s) to induce the H-2 linked production of ANolA. We found that while mercury stimulated ANolA synthesis in all H-2 susceptible (H-2s, H-2q and H-2f) mouse strains, silver induced only ANolA responses in H-2s and H-2q mice, but not in H-2f mice. Further studies showed that the resistance to silver-induced ANolA production in H-2f mice was inherited as a dominant trait. We next tested the proposition that mercury induces more adverse immunological effects in mouse strains, which are genetically prone to develop autoimmune diseases, using tight-skin 1 mice, an animal model for human Scleroderma. It was found that in this strain, mercury induced a strong immune activation with autoimmune characteristics, but did not accelerate the development of dermal fibrosis, a characteristic in Tsk/1 mice. Finally we addressed the Th1/Th2 cross-regulation paradigm by examining if a Th1-type of response could interact with a Th2-type of response if simultaneous induced in susceptible mice. Our findings demonstrated that mercury-induced autoimmunity (Th2-type) and collagen-induced arthritis (CIA) (Th1-type) can interact in a synergistic, antagonistic or additive fashion, depending on at which stage of CIA mercury is administered.

Preeclampsia is one of the most feared pregnancy complications, with a risk of maternal and fetal death and with no ideal therapy readily available. The cause of this strictly pregnancyrelated disease is still unknown and is therefore a great challenge to all researchers in the field of pregnancy-related pathophysiology. Today, the dominating theory of the origin of preeclampsia is defective initial placentation with insufficient penetration of the trophoblasts, leading to impaired maternal blood flow through narrow spiral arteries. However, the cause of this defective trophoblast behavior is not known. The maternal immune system has been proposed to have an influence on both the placentation and the subsequent systemic reactions. Therefore, it is very interesting to study the maternal immune system during preeclampsia, in hope of achieving a better understanding of this puzzling disease. Earlier studies have suggested that normal pregnancy requires a shift to a Th2/antiinflammatory type of immunity, at least directed towards the fetus and placenta, while some pregnancy complications, such as preeclampsia, could be due to a skewed Th1/proinflammatory type of immunity. However, the results from earlier studies designed to test the Th1/Th2 hypothesis in preeclampsia have not been consistent. Therefore, the aim of this thesis was to examine if established preeclampsia is associated with increased innate inflammatory responses and a deviation of adaptive responses towards Th1 when compared with normal pregnancy. Enumerations of cytokine-producing cells from peripheral blood did not show any difference in the production of IFN-γ, IL-4, IL-10 and IL-12 between women with preeclampsia and normal pregnancies. However, a decrease in the spontaneously produced levels of IL-5 was detected in cell cultures on peripheral blood mononuclear cells in women with preeclampsia. Furthermore, a decreased production of IL-10 in response to paternal antigens, believed to represent the fetus, was also detected for the preeclamptic women. Serum analysis showed increased levels of the pro-inflammatory mediators IL-6 and IL-8 during preeclampsia. Also, preeclamptic women displayed increased serum levels of the soluble IL-4 receptor, but no difference in the levels of IL-4 compared to normal pregnant women. This was an elusive finding, since the receptor was originally thought to reflect the levels of IL-4, but has recently been shown to have both agonistic and antagonistic properties on the IL-4 levels. Further studies of the local immune responses in the placenta showed no difference in the immunohistochemical staining of IL-4 and TNF-α between women with preeclampsia and women with normal pregnancies. In general, there were no hallmarks of abnormal morphology in the placental sections examined, regardless of diagnosis. In conclusion, the decreased levels of IL-10 in response to paternal antigens and the systemically increased levels of IL-6 and IL-8 suggest a specific decrease in antiinflammatory responses towards fetal antigens, together with a systemic activation of proinflammatory mediators during preeclampsia. Furthermore, the decreased production of IL-5 also indicates, at least partly, decreased Th2 responses in the established preeclampsia. / Figure 1 on page 6 is republished in the Ph.D. thesis with the kind permisson of Blackwell Publishing (http://www.blackwellpublishing.com). Figure IX on page38, figure XB on page 41, figure XI on page 46 and figure XII on page 47 are all published in the Journal of Reproductive Immunology and republished with kind permisson from Elsevier (http://www.elsevier.com/) in the Ph.D. thesis.

Recent studies suggest that some cases of prenatal depression may be associated with reactivation of latent infections of the herpesvirus family. The possible relationships among stress, prenatal depression, and herpes viral reactivation in pregnancy are understudied and the molecular pathways such as the neuroimmune biogenic amine pathway are unidentified. Chronic stress shifts the T helper-1 cell (Th1) cytokine profile to a Th2 profile, which favors virus induced pathogenesis and survival. Pregnancy is also associated with a similar Th2 dominance. In non-pregnant individuals, exposure to psychological or physical stress may be associated with latent herpes viral reactivation and could result in behavioral deficits and depression. Normally, type-1 cytokines such as Interferon-gamma (IFN -gamma) and inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) induce indoleamine-2, 3-dioxygenase (IDO) activation which inhibits herpes virus replication and reactivation, decreases tryptophan production, and alters phenylalanine /tyrosine metabolism. Thus it is possible that prenatal depression may occur from tryptophan stealing through the IDO pathway which results in decreased serotonin as well as increased risk for latent herpes viral reactivation. The purpose of this study is to analyze the relationships among stress, herpes viral titers, depression, and metabolites of IDO activation, which involves tryptophan and guanosine-triphosphate-cyclohydrolase-1(GTP-CH1) pathways. This study builds on Influence of Lactation on Postpartum Stress and Immunity (Grant number: R01-NR05000) which investigated perinatal immune, endocrine, and inflammatory changes in pregnancy and the postpartum. A secondary data analysis was conducted on baseline data from women collected at 16 to 25 gestational weeks. This data set included some herpes viral titers, and additional ones were measured in stored plasma samples. The aim of this study is to examine relationships among stress, herpes viral reactivation, depression, and the IDO activation pathway. The results of this study provide information about the possible role of further relationships of prenatal stress, latent herpes viral reactivation, and depression mechanisms. The results will be important in health promotion and disease prevention during pregnancy.

Le diabète de type 1 (DT1) est une maladie auto-immune qui résulte en la destruction des cellules (ß des îlots de Langerhans par les cellules du système immunitaire. Des travaux précédents de notre laboratoire ont identifié la cytokine "Thymic Stromal Lymphopoietin" (TSLP) comme étant un stimulus tolérogénique pour les cellules dendritiques (DCs) chez le modèle murin du DT1, la souris "Non Obese Diabeiic" (NOD). Les DCs conditionnées à la TSLP (TSLP-DCs) présentent un phénotype semi-mature, sont capables d’induire une réponse Th2 ainsi qu’une conversion et une expansion des lymphocytes T régulateurs (Tregs) in vitro et protègent les souris NOD contre le DT1. Ces observations nous ont amené à investiguer les mécanismes qui entraînent cette protection contre le DT1. Les travaux décrits dans ce mémoire montrent que les TSLP-DCs injectées chez les souris NOD migrent vers la rate, de manière privilégiée. Ces observations nous ont amené à étudier l’influence des TSLP-DCs sur la réponse Th1/Th2 au niveau de la rate. Nous avons observé que les splénocytes CD4[indice supérieur +] et CD8[indice supérieur +] de souris injectées avec des TSLP-DCs exprimaient moins d’IFN? par rapport au souris témoins (splénocytes des souris injectées avec des LPS-DCs). Ces résultats suggèrent une diminution de la réponse Th1 chez ces splénocytes. Par contre, les résultats obtenus avec l’IL-10 ne nous ont pas permis de conclure quant à l’influence des TSLP-DCs sur la réponse Th2. Cependant, nous avons confirmé la capacité des TSLP-DCs à induire la conversion des lymphocytes T CD4[indice supérieur +]CD25[indice supérieur -] en Tregs CD4[indice supérieur +]CD25[indice supérieur +]Foxp3[indice supérieur +]. Nous avons aussi montré que ces Tregs partiellement convertis inhibent la prolifération de lymphocytes T 8.3-CD8[indice supérieur +] diabétogènes, et empêchent la production d’IFN?. Les Tregs convertis en présence de TSLP-DCs ou de LPS-DCs ont également été injectés à des souris 8.3-NOD.RAG2[indice supérieur -/-]. Les résultats ont révélé que seuls les Tregs différenciés en présence de TSLP-DCs ont la capacité d’empêcher le développement du DT1. Nos travaux suggèrent que la diminution de la réponse Th1 et l’induction d’une population efficiente de lymphocytes Tregs font partie des mécanismes utilisés par les TSLP-DCs pour protéger les souris NOD contre le DT1.

No description available.

Experiências vivenciadas durante o período pré-natal são determinantes para a saúde do feto. A ocorrência de infecções maternas e a consequente ativação do sistema imune da mãe ocasionam uma série de alterações estruturais e funcionais no cérebro da prole, podendo predispor o indivíduo a transtornos psiquiátricos na vida pós-natal, como esquizofrenia e autismo. No entanto, estudos que investigam as alterações imunes na prole ainda são escassos na literatura. Dessa forma, o objetivo do presente estudo foi avaliar, na prole, o impacto da ativação imune materna sobre a atividade imune periférica, a resposta imune-inflamatória no sistema nervoso central (SNC), e sobre o desenvolvimento da encefalomielite autoimune experimental (EAE), o modelo murino de Esclerose Múltipla. Camundongos fêmeas prenhes receberam uma administração de salina ou lipopolissacarídeo (LPS) ao final da gestação (dia gestacional 17) e, quando adulta, a prole foi submetida a 3 experimentos principais, analisando: (1) produção de citocinas, atividade de células da periferia e desenvolvimento da hipersensibilidade do tipo tardia; (2) produção de mediadores inflamatórios por células residentes do SNC e; (3) desenvolvimento dos sintomas clínicos e da resposta imune no decorrer da EAE. Nossos resultados mostraram que a ativação imune materna provocou na prole alterações imunes periféricas, como aumento da produção de Interleucina(IL)- 12 e exacerbação da resposta de hipersensibilidade do tipo tardia; potencialização da produção das citocinas IL-1&#946; e IL-6 em cultura primária de células residentes do SNC e; piora na severidade dos sintomas clínicos causados pela EAE, que coincide com aumento do infiltrado de linfócitos e macrófagos no SNC e ativação imuneinflamatória das células da glia. Tomados em seu conjunto, os dados do presente trabalho sugerem que condições inflamatórias durante a gestação, particularmente durante o final da gestação, podem predispor o feto a distúrbios autoimunes e neurodegenerativos na vida adulta. / Prenatal period experiences are crucial for the fetal health. The occurrence of maternal infections and subsequent maternal immune system activation cause a number of structural and functional changes in the brain of the offspring that may predispose individuals to psychiatric disorders in post-natal life, such as schizophrenia and autism. However, studies investigating offspring´s immune alterations are still scarce in the literature. The aim of this study was to evaluate, in mice offspring taken from LPS-treated dams, the impact of maternal immune activation on peripheral immune cell activity, central nervous system (CNS) inflammatory response, and development of experimental autoimmune encephalomyelitis (EAE), the murine model of multiple sclerosis. Pregnant female mice received a dose of either saline or lipopolysaccharide (LPS) during late gestation (gestational day 17), and offspring were used in three experiments to analyze: (1) cytokine production and activity by peripheral immune cells and development of delayed type hypersensitivity, (2) production of inflammatory mediators by resident CNS cells and, (3) development of clinical symptoms and immune response during the course of EAE. Our results showed that maternal immune activation resulted in immune alterations in the offspring, such as increased peripheral production of interleukin (IL) -12 and exacerbated response of delayedtype hypersensitivity; enhancement of IL-1&#946; and IL-6 productions in primary CNS resident cells culture and; increased severity of EAE clinical symptoms, which is positively correlated with the increased lymphocytes and macrophages infiltration within the CNS and also with the immune-inflammatory activation of glial cells. Taken together, the data from this study suggest that inflammatory conditions during pregnancy, especially during the late pregnancy, may predispose the fetus to autoimmune and neurodegenerative disorders in adulthood.

Experiências vivenciadas durante o período pré-natal são determinantes para a saúde do feto. A ocorrência de infecções maternas e a consequente ativação do sistema imune da mãe ocasionam uma série de alterações estruturais e funcionais no cérebro da prole, podendo predispor o indivíduo a transtornos psiquiátricos na vida pós-natal, como esquizofrenia e autismo. No entanto, estudos que investigam as alterações imunes na prole ainda são escassos na literatura. Dessa forma, o objetivo do presente estudo foi avaliar, na prole, o impacto da ativação imune materna sobre a atividade imune periférica, a resposta imune-inflamatória no sistema nervoso central (SNC), e sobre o desenvolvimento da encefalomielite autoimune experimental (EAE), o modelo murino de Esclerose Múltipla. Camundongos fêmeas prenhes receberam uma administração de salina ou lipopolissacarídeo (LPS) ao final da gestação (dia gestacional 17) e, quando adulta, a prole foi submetida a 3 experimentos principais, analisando: (1) produção de citocinas, atividade de células da periferia e desenvolvimento da hipersensibilidade do tipo tardia; (2) produção de mediadores inflamatórios por células residentes do SNC e; (3) desenvolvimento dos sintomas clínicos e da resposta imune no decorrer da EAE. Nossos resultados mostraram que a ativação imune materna provocou na prole alterações imunes periféricas, como aumento da produção de Interleucina(IL)- 12 e exacerbação da resposta de hipersensibilidade do tipo tardia; potencialização da produção das citocinas IL-1&#946; e IL-6 em cultura primária de células residentes do SNC e; piora na severidade dos sintomas clínicos causados pela EAE, que coincide com aumento do infiltrado de linfócitos e macrófagos no SNC e ativação imuneinflamatória das células da glia. Tomados em seu conjunto, os dados do presente trabalho sugerem que condições inflamatórias durante a gestação, particularmente durante o final da gestação, podem predispor o feto a distúrbios autoimunes e neurodegenerativos na vida adulta. / Prenatal period experiences are crucial for the fetal health. The occurrence of maternal infections and subsequent maternal immune system activation cause a number of structural and functional changes in the brain of the offspring that may predispose individuals to psychiatric disorders in post-natal life, such as schizophrenia and autism. However, studies investigating offspring´s immune alterations are still scarce in the literature. The aim of this study was to evaluate, in mice offspring taken from LPS-treated dams, the impact of maternal immune activation on peripheral immune cell activity, central nervous system (CNS) inflammatory response, and development of experimental autoimmune encephalomyelitis (EAE), the murine model of multiple sclerosis. Pregnant female mice received a dose of either saline or lipopolysaccharide (LPS) during late gestation (gestational day 17), and offspring were used in three experiments to analyze: (1) cytokine production and activity by peripheral immune cells and development of delayed type hypersensitivity, (2) production of inflammatory mediators by resident CNS cells and, (3) development of clinical symptoms and immune response during the course of EAE. Our results showed that maternal immune activation resulted in immune alterations in the offspring, such as increased peripheral production of interleukin (IL) -12 and exacerbated response of delayedtype hypersensitivity; enhancement of IL-1&#946; and IL-6 productions in primary CNS resident cells culture and; increased severity of EAE clinical symptoms, which is positively correlated with the increased lymphocytes and macrophages infiltration within the CNS and also with the immune-inflammatory activation of glial cells. Taken together, the data from this study suggest that inflammatory conditions during pregnancy, especially during the late pregnancy, may predispose the fetus to autoimmune and neurodegenerative disorders in adulthood.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-05-17T14:40:56Z No. of bitstreams: 1 anaclaudiacarvalhogouveia.pdf: 2060044 bytes, checksum: a2757483182ff953fdffbf86f346380b (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-28T14:35:33Z (GMT) No. of bitstreams: 1 anaclaudiacarvalhogouveia.pdf: 2060044 bytes, checksum: a2757483182ff953fdffbf86f346380b (MD5) / Made available in DSpace on 2016-06-28T14:35:33Z (GMT). No. of bitstreams: 1 anaclaudiacarvalhogouveia.pdf: 2060044 bytes, checksum: a2757483182ff953fdffbf86f346380b (MD5) Previous issue date: 2012-08-30 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A asma alérgica é uma doença inflamatória crônica das vias aéreas, caracterizada por uma resposta de hipersensibilidade imediata, obstrução brônquica, inflamação pulmonar e níveis elevados de IgE. A doença é mediada principalmente por uma resposta imunológica alérgeno-específica tipo Th2. Nas últimas décadas, a prevalência da asma alérgica tem aumentado significativamente, sobretudo nos países desenvolvidos. A Hipótese da Higiene atribui este aumento a uma menor exposição a determinados microrganismos durante a infância, quando o amadurecimento adequado do sistema imunológico requer estímulos que induzam respostas imunológicas de perfil Th1, fundamentais para o equilíbrio de respostas Th2 exacerbadas. Diversos trabalhos epidemiológicos parecem comprovar esta hipótese, evidenciando a existência de uma relação inversa entre o contato com microrganismos indutores de uma resposta Th1 e o desenvolvimento de asma alérgica. Paralelamente, estudos em modelos murinos constataram que o tratamento com Mycobacterium bovis BCG (BCG) reduz respostas Th2 alérgenoespecíficas. No entanto, os mecanismos pelos quais a micobactéria inibe o desenvolvimento da resposta alérgica são ainda pouco conhecidos. Este estudo avaliou o efeito da administração do BCG sobre a resposta imunológica ocorrida na alergia pulmonar em camundongos BALB/c previamente sensibilizados e desafiados com OVA. Vinte e quatro horas após o último desafio, o sangue e o lavado broncoalveolar foram coletados para análises de imunoglobulinas e contagem de células, respectivamente. Adicionalmente, os pulmões foram submetidos à análise histológica, avaliação da atividade de EPO e dosagens de citocinas e quimiocinas, assim como avaliação da expressão de CTLA-4, Foxp3 e IL-10 por citometria de fluxo. Os resultados obtidos indicam que o tratamento com BCG melhorou o processo alérgico através da redução dos principais parâmetros relacionados à resposta Th2, como o infiltrado eosinofílico pulmonar, a atividade de EPO, IL-4, IL-13, CCL11, além de IgE e IgG1 específicas anti-OVA. Por outro lado, a administração da micobactéria aumentou os níveis de IFN-γ, IL-10 e TGF-β, além das expressões de Foxp3 e CTLA-4 pelos linfócitos T CD4+. Paralelamente, houve um aumento na produção de IL-10 pelos linfócitos T CD8+. Esses dados sugerem que, além da indução de uma resposta imune Th1, a ação imunomoduladora do BCG está relacionada também à indução de mecanismos reguladores. / Atopic asthma is a chronic respiratory disease characterized by airway hyperresponsiveness, reversible airway obstruction, lung inflammation, and high levels of allergen-specific IgE, driven by allergen-specific Th2 cells. The increasing prevalence of allergic diseases, particularly in industrialized countries, has led to the hygiene hypothesis, which states that the newborn infant’s immune system is skewed toward Th2 responses and needs timely and appropriate environmental stimulus to create a balanced immune response. Supporting this hypothesis, epidemiological and experimental evidence has shown an inverse correlation between Th1-induced microbial infections and atopic asthma. Similarly, some animal studies have demonstrated that exposure to Mycobacterium tuberculosis or to environmental mycobacteria is able to protect against the development of allergic responses. However the exact mechanism underlying this inhibition still remains poorly understood. This study aimed to evaluate the ability of BCG to suppress an established allergic response in a mouse model of OVA-induced airway inflammation. To achieve this, OVA sensitized and challenged BALB/c mice were twice treated with BCG via nasal and 21 days after the first treatment, mice were rechallenged with OVA. Twenty-four hours after the last challenge, blood samples were collected to detect anti-OVA immunoglobulin isotypes, and bronchoalveolar lavage (BAL) was harvested for cell count. Additionally, lungs were collected for histological analysis, detection of EPO activity and measurement of cytokines and chemokines. The expression of CTLA-4, Foxp3 and IL-10 was also determined in lung tissue by flow cytometry. The data indicated that BCG treatment was able to inhibit an established allergic Th2-response by decreasing the allergen-induced eosinophilic inflammation, EPO activity, levels of IL-4, IL-13, CCL11 and serum levels of IgE and IgG1. Mycobacteria treatment increased lung levels of IFN-γ, IL-10 and TGF-β, and expressions of Foxp3 and CTLA-4 in CD4+T cells. Additionally, an increased production of IL-10 by CD8+ T cells was observed, even though no detectable changes in CD4+IL-10+ was noticed. Altogether, these results suggest that the mechanism underlying the down-regulatory effects of BCG on OVA-induced airway inflammation appear to be associated with the induction of both Th1 and T regulatory immune responses.