Diabetes mellitus represents a group of metabolic disorders caused by both environmental and genetic factors. The two most common forms of diabetes are type 2 diabetes (T2D) and type 1 diabetes (T1D). T2D is associated with obesity and the disease is caused by insulin resistance and pancreatic b-cell dysfunction. T1D is an autoimmune disease in which the insulin- producing b-cells in the pancreas are destroyed by infiltration of lymphocytes. The aim of this thesis was to identify genes conferring susceptibility to diabetes. This was approached using genetic methods, both linkage and association studies, within the population of northern Sweden. The northern Swedish population is well suited for genetic studies of familial forms of disease, since an internal expansion of the northern Swedish population, coupled with a low frequency of immigration and a high frequency of consanguineous marriages, has resulted in a relatively homogeneous gene pool. This simplified genetic background increases the probability of identifying genes contributing to disease. The family-based material used for the type 2 diabetes studies (papers I and II) consisted of 231 individuals from 59 families originating in northern Sweden. The type 2 diabetes case-control material (papers I and II) consisted of 872 cases and 857 matched controls, all from northern Sweden. In paper I we performed a genome-wide linkage scan, seeking T2D susceptibility loci. Linkage to the previously identified Calpain-10 region was found, however, association studies in the case-control material revealed no association to the CAPN10 gene. Using both the family-based and the case-control material, we were able to confirm the association of polymorphisms in the TCF7L2 gene to T2D in the population of northern Sweden (paper II). CTLA-4 is a negative regulator of T cell activity, belonging to the CD28 co-stimulatory receptor family. Numerous reports, including our own, have associated CTLA-4 variants with T1D as well as other autoimmune diseases, such as autoimmune thyroid disease (AITD). Allelic variation in the 3ÚTR of the CTLA-4 gene was associated to human T1D and this variant has also been suggested to affect the level of mRNA encoding the soluble form of the molecule (sCTLA-4). We confirmed the association of allelic variation in the 3ÚTR of the CTLA-4 gene in a T1D/AITD case-control material from northern Sweden, consisting of 104 individuals with ATID, 149 individuals with T1D and 865 matched controls. However, we were unable to identify any correlation between allelic variants in the 3ÚTR of the CTLA-4 gene and expression of sCTLA-4 (paper III). Based on recently published genome-wide association (GWA) scans, 33 single-nucleotide polymorphisms (SNPs) located within 16 genes were selected for an association analysis in T1D/AITD families from northern Sweden. The T1D/AITD family-based material consisted of 253 cases and 206 healthy individuals from 97 northern Swedish families. Analysis revealed association to T1D for SNPs in PTPN22, COL1A2, IL-2Ra and INS. In addition, SNPs in CTLA-4, IL-2 and C12orf30 were shown to be associated to AITD (paper IV). Together, these results underpin the notion that the population of northern Sweden is well suited for the detection of genes involved in complex diseases. The use of our more restricted patient material, compared to materials used in published GWA scans, enables the discovery of disease associated genes in a more cost effective manner and show that our population is capable of detecting general susceptibility genes.

Graves¡¦ disease (GD), an organ specific autoimmune disease, requires two signals to activate the T cells. In addition to the specific binding of T cell receptor to the antigenic peptide-MHC complex, an antigen-independent costimulatory pathway reportedly require generate subsequent cytokines and cell surface molecules. This regulation of T-cell response is a highly-organized multiple step program. T cell costimulatory signals is found to regulate the magnitude and duration of various type of autoimmune diseases. This study is to test whether genetic polymorphism of these costimulatory genes is related with the disease susceptibility or progression. We anticipated that the candidate genetic makers are beneficial for importing GD management. We recruited 262 GD patients from the Outpatient Department of Endocrine and 200 healthy controls from the Health Screening Center of Chang Gung Memorial Hospital in Kaohsiung.The GD patients were divided into three groups: recurred within 9 months (n=91), between 10-36 months (n=65), and more than 36 months (n=106). Clinical and laboratory attributes included: the genotypes of CTLA-4, CD28, ICOS, PD-1 and CD40; serum levels of T4, T3 and TSH; goiter size and TSH-receptor antibodies at the beginning and end of treatment. Genomic DNA was extracted from peripheral blood leucocytes by kit. The single nuclotide polymorphisms of the candidate genes were genotyped by polymerase chain reaction- restriction fragment length polymorphism and TaqMan® SNP Genotyping Assays with specific primers. Linkage disequilibuium between pairs of polymorphism was estimated by Haploview software. Haplotype analyses were performed using the Hap-Clustering program. Variance and correlation of data was statistically analyzed by Chi-square, general liner model, multiple logistic regression analysis and Kaplan-Meier plot. A p value <0.01 was considered significant. The results showed:(1) Genetic polymorphism within the costimulatory molecules affected the susceptibility and progression of GD; (2) GD patients carried more risk alleles than the controls; (3) Within the GD group, patients harboring more risk alleles wound relapse earlier after drug withdrawal; (4) Number of risk alleles, goiter size and TBII levels at end of treatment were independent predictors of disease relapse; (5) A risk score calculation based on odds ratio of risk alleles correlated with patients¡¦ relapse time after drug withdrawal. We concluded that patients¡¦ genetic makers of costimulatory molecules may be helpful in choosing appropriate treatment for GD.

Submitted by Tatiana Oliveira (tsilva@icict.fiocruz.br) on 2012-06-06T12:23:16Z No. of bitstreams: 1 jorgenilce_s_sales_ioc_bp_0022_2010.pdf: 2120746 bytes, checksum: 319e0b7b0dce67008dbde7aeb9028520 (MD5) / Made available in DSpace on 2012-06-06T12:23:16Z (GMT). No. of bitstreams: 1 jorgenilce_s_sales_ioc_bp_0022_2010.pdf: 2120746 bytes, checksum: 319e0b7b0dce67008dbde7aeb9028520 (MD5) Previous issue date: 2010 / Fundação Oswaldo Cruz.Instituto Oswaldo Cruz. Rio de janeiro, RJ, Brasil / Os mecanismos que levam a ausência de resposta imune celular no pólo lepromatoso da hanseníase frente ao Mycobacterium leprae permanecem obscuros. Estudos anteriores mostraram que fatores secretados pelos macrófagos de pacientes lepromatosos inibem a proliferação de linfócitos de indivíduos saudáveis, sugerindo que fatores endógenos produzidos por células da linhagem mielóide podem exercer uma atividade supressora nas células T. Recentemente, diversos estudos têm demonstrado a participação da enzima indoleamina 2,3 dioxigenase (IDO) na supressão das células T, indicando que mudanças bioquímicas devido ao catabolismo do triptofano têm efeitos na proliferação dessas células. No presente trabalho nós demonstramos que os pacientes com a forma clínica lepromatosa apresentam uma maior expressão de IDO em biópsias de pele e maior atividade de IDO no soro quando comparados com pacientes com a forma tuberculóide e que o M. leprae induz a expressão e a atividade de IDO em monócitos de indivíduos saudáveis e de pacientes lepromatosos. Além disso, observamos que o M. leprae induz aumento na atividade de IDO nas células dendríticas derivadas de monócitos de indivíduos saudáveis e que esta atividade aumentada de IDO contribui para o aumento percentual de linfócitos expressando a molécula supressora CTLA-4, sugerindo que IDO participe na anergia T antígeno específico observada em pacientes com a forma lepromatosa da doença / The absence of cellular immune response to M. leprae in lepromatous pole of leprosy remains unclear. Previous studies showed that factors secreted by macrophages of lepromatous patients inhibit the proliferation of lymphocytes from healthy individuals, suggesting that endogenous factors produced by cells of myeloid lineage may have suppressive activity on T cells. Recently, several studies have been demonstrating the involvement of the enzyme indoleamine 2,3 dioxygenase (IDO) in the suppression of T cells, indicating that biochemical changes due to the catabolism of tryptophan affects on the proliferation of these cells. In this study we demonstrated that patients with lepromatous clinical form showed higher IDO expression in skin biopsies and increased IDO activity in serum when compared with patients with the tuberculoid form. In addition, M. leprae induces the expression and activity of IDO in monocytes of healthy subjects and lepromatous patients. Moreover, we observed that M. leprae induces increased activity of IDO in monocyte-derived dendritic cells of healthy individuals and that this increased IDO activity may contribute to the increase in percentage of T lymphocytes expressing CTLA-4, which suggest that IDO may play a role in T-specific anergy observed in lepromatous leprosy patients

No description available.

Immunotherapy has emerged as one of the four “standard” cancer therapies, alongside surgery, chemotherapy, and radiotherapy. Immune checkpoint inhibitor (ICI) therapy is an immunotherapy that blocks inhibitory immune checkpoint interactions, allowing T cells and other immune cells to kill tumor cells. In the tumor microenvironment, there is often overexpression of immune checkpoint proteins, whose binding interaction with cytotoxic T cells and other immune cells results in the dampening of the antitumor response. Programmed cell death protein 1 (PD-1) and T-lymphocyte-associated protein 4 (CTLA-4) are the two most targeted immune checkpoint proteins. Antibodies against PD-1 and CTLA-4, as well as other checkpoint proteins, are approved for clinical use as well as in clinical trials. While ICIs have changed the treatment landscape for many cancers, particularly those with significant immunogenicity, only 20-40% of patients respond to ICI therapy. Many factors are behind the lack of response and resistance, and significant efforts are aimed at improving the response to ICI therapy. One major area is modulating the gut microbiome, as it is well-established that microbial dysbiosis is associated with various human diseases. The concept is that by modulating the microbiome, we might be able to return it to a composition more similar to that seen in healthy individuals or provide microorganisms beneficial to clinical response. In the case of ICI therapy, it is proposed that there is a connection between certain microbial species and the immune system via metabolites and other signaling effects. The microbiome can be manipulated through many methods, including fecal microbiota transplantation (FMT), transferring bacterial isolates or consortia, probiotics, antibiotics, and soluble dietary fiber. For clinical insights, it is important to consider how the pre-treatment microbiome of patients may affect their response to ICI therapy, as well as how their microbiomes can be manipulated to enhance their response. Initial clinical trials have been promising, but this is an emerging field with additional work to be done. Particularly, a better understanding of the microorganisms involved in the response to ICI therapy and the mechanism by which they communicate with the immune system is essential. Future studies will need to be much larger to reduce noise between studies and to allow for emerging computational techniques to be applied.

No description available.

La maladie du greffon contre l’hôte (GVHD) est la principale cause de mortalité et de morbidité suite aux greffes de cellules souches hématopoïétiques. Plusieurs patients demeurent réfractaires aux traitements actuels ce qui rend nécessaire le développement de nouvelles stratégies afin de combattre cette maladie. Dans l’étude qui suit, nous avons utilisé un nouvel agent thérapeutique, le TH9402, une molécule photosensible et démontré qu’elle permet, lorsqu’exposée à la lumière visible (514 nm), d’éliminer sélectivement les cellules T activées in vivo tout en préservant les cellules T au repos et les cellules T régulatrices (Tregs). Les Tregs ainsi préservés peuvent abroger la réponse alloréactive par la sécrétion d’IL-10 ou par contact cellule-cellule via un mécanisme impliquant le CTLA-4. Nous avons découvert que la signalisation du CTLA-4 était associée à une hausse de la population Treg in vitro. Cette hausse est due à la conversion de cellules T CD4+CD25- en Tregs et non à une prolifération sélective des Tregs. Dans la deuxième partie de cette étude, nous avons démontré que la signalisation de CTLA-4 était associée à une augmentation de l’expression de la protéine Indoleamine 2,3 dioxygenase (IDO). Ces effets nécessitent la déplétion du tryptophane ainsi que de la protéine de phase aigue GCN2. Finalement, nous avons observé que l’infusion de cellules traitées au TH9402 chez des patients souffrant de GVHD chronique est associée à une augmentation de la population Treg chez ces patients sans causer de lymphopénie ni de diminution de la réponse immunitaire dirigée contre les antigènes viraux. Ces résultats suggèrent que le traitement au TH9402 pourrait représenter une approche particulièrement intéressante pour le traitement de la GVHD chronique réfractaire aux traitements actuels. De plus, l’augmentation de l’expression d’IDO pourrait être utilisée comme valeur prédictive de la réponse du patient au traitement. Ceci pourrait permettre d’améliorer la qualité de soins ainsi que de la qualité de vie des patients souffrant de GVHD chronique. / Graft versus host disease (GVHD) is the primary cause of mortality and morbidity following hematopoietic stem cell transplantation. Many patients remain refractory to current treatments, emphasizing the need to develop new therapeutic strategies. In the present study, we have used a novel therapeutic agent, TH9402, and shown that once activated by visible light (514 nm), this photosensitizer becomes specifically cytotoxic toward activated T cells while preserving resting T cells and regulatory T cells (Tregs). Preserved Tregs can display anti GVHD activity through IL-10 and CTLA-4 dependent mechanisms. Furthermore, CTLA-4 signaling was associated with an increased Treg population. This increase resulted from FOXP3 induction in CD4+CD25- cells and not selective proliferation of Tregs. In the second part of this study, we showed that CTLA-4 signaling was associated with enhanced expression of indoleamine 2,3 dioxygenase (IDO). The expression of IDO results in the generation of anti GVHD activity and an increase in the Treg population following TH9402 treatment. This increased Treg population was mediated by tryptophan degradation and implied acute phase protein GCN2 activity. Finally, we show that the infusion of TH9402 treated cells in patients suffering from chronic GVHD resulted in an increase of the Treg population as early as 8 weeks after treatment initiation without causing lymphopenia or hyporesponsiveness toward viral antigens. Furthermore, the increase of IDO corresponded to patient response to treatment. These results suggest that TH9402 represents a most interesting therapeutic approach for patients with refractory chronic GVHD. IDO expression could also be used to predict patient responsiveness to the treatment. This could increase the quality of the treatment as well as the quality of life of patients suffering from refractory chronic GVHD.

A predisposição de recém-nascidos às doenças infecciosas é atribuída, em parte, a falta da memória imunológica pré-existente. Em recém-nascidos pré-termo, é presumido que o sistema imune seja menos desenvolvido ao nascimento, mas pouco se sabe sobre o tamanho e as características das subpopulações de linfócitos. Células T reguladoras (Treg) possuem papel crucial no controle do desenvolvimento de um sistema imune saudável incluindo a manutenção da autotolerância e, sua ausência, é responsável pela gama de manifestações inflamatórias e autoimunes observadas em pacientes com IPEX (Immunodeficiency, Poliendocrinopathy and Enteropathy X-linked Syndrome). Essas células são fenotipicamente caracterizadas pela presença do fator de transcrição Foxp3 (forkhead box P3) e pela alta expressão da cadeia ? do receptor de IL-2 (CD25), já que esta citocina é essencial para a geração, manutenção e funcionamento das células Treg. Pouco se sabe sobre a frequência destas células em recém-nascidos, particularmente em recém-nascidos muito prematuros ou moderados e recém-nascidos prematuros tardios, estudados como grupos separados. Resultados preliminares do nosso grupo revelaram uma maior capacidade dos recém-nascidos de produzir resposta pró-inflamatória em comparação aos adultos, a qual foi ainda mais acentuada pela diminuição da produção de IL-10, o que sugere uma função reguladora reduzida. Diante disso, o objetivo deste trabalho foi caracterizar fenotipicamente e quantificar a população de células Treg, por meio de citometria de fluxo, em sangue de cordão umbilical de 15 recém-nascidos pré-termo nascidos entre 30-336/7 semanas de gestação (Grupo 1), 19 recém-nascidos pré-termo nascidos entre 34-366/7 semanas de gestação (Grupo 2) e 20 recém-nascidos a termo nascidos entre 37-41 semanas de gestação (Grupo 3), todos clinicamente saudáveis e com peso adequado para a idade gestacional, em comparação com 26 adultos saudáveis. Os resultados demonstraram que existe uma correlação inversa entre a frequência de Treg e a idade gestacional, com frequências significativamente maiores de células Treg CD4+CD25hiCD127loFoxp3+ no Grupo 1 quando comparado aos Grupos 2 e 3 e no Grupo 2 comparado ao Grupo 3, assim como frequências e números de Treg mais elevados em todos os recém-nascidos comparados aos adultos. Todos os recém-nascidos exibiram maior frequência de células Treg com fenótipo naïve comparados aos adultos. A expressão de CTLA-4 nas células Treg naïve foi reduzida nos dois grupos de pré-termo comparados aos grupos de recém-nascidos a termo e adultos, assim como nas células Treg de memória do Grupo 1 comparado aos demais grupos. As frequências de Tregs alfa4beta7+ e alfa4beta1+ foram maiores em ambos os grupos de pré-termo, mas significativamente diferentes somente no Grupo 1, quando comparado aos recém-nascidos a termo e adultos. Em conclusão, foram observadas altas frequências de células Treg em recém-nascidos pré-termo e a termo, e essas frequências mostraram correlação inversa com a idade gestacional. Essas células exibiram um perfil naïve quando comparadas às dos adultos, com alta expressão de CD45RA e alfa4beta7+ e menor expressão de CTLA-4, sugerindo uma menor função, particularmente em recém-nascidos muito prematuros / The predisposition of newborn infants to infectious diseases is attributed, in part, to the lack of pre-existing immunological memory. In preterm newborns, it is assumed that the immune system is less developed at birth, but little is known about the size and characteristics of lymphocyte subpopulations. Regulatory T cells (Tregs) have a crucial role in controlling the development of a healthy immune system including the maintenance of self-tolerance and, their absence, is responsible for the range of inflammatory and autoimmune manifestations observed in patients with IPEX (Immunodysregulation Polyendocrinopathy Enteropathy X-linked Syndrome). These cells are phenotypically characterized by the presence of the transcription factor Foxp3 (forkhead box P3) and by the high expression of the ? chain of the IL-2 receptor (CD25), as this cytokine is essential for the generation, maintenance and function of Treg cells. Little is known about the frequency of these cells in neonates, particularly in very and moderate preterm newborns and late preterm newborns studied as separate groups. Preliminary results from our group revealed greater ability of newborns to produce proinflammatory response compared to adults, which was further accentuated by the decreased production of IL-10, which suggests a reduced regulatory function. Thus, the aim of this study was to phenotypically characterize and quantify the population of Treg cells, by flow cytometry, in the cord blood of 15 preterm newborns born at 30-336/7 gestation weeks (Group 1), 19 preterm newborns born at 34-366/7 gestation weeks (Group 2) and 20 term newborns born at 37-41 gestation weeks (Group 3), all clinically healthy and adequate-for-gestational-age, compared to 26 healthy adults. The results demonstrated that there is an inverse correlation of the Treg frequency and gestational age, with significantly higher frequencies of CD4+CD25hiCD127loFoxp3+ Treg cells in Group 1 compared to Groups 2 and 3 and in Group 2 compared to Group 3, as well as significantly higher Treg frequencies and numbers in all the neonates compared to the adults. All of the newborns exhibited increased Treg frequencies with a naive phenotype compared to the adults. CTLA-4 expression in the naive Tregs was decreased in both preterm groups compared with those from term newborns and adults, as well as in the memory Treg cells from Group 1 compared with the other groups. The frequencies of alfa4beta7+ and alfa4beta1+ Tregs were higher in both preterm groups, but significantly different only in Group 1, when compared with those from the term newborns and the adults. In conclusion, high frequencies of Tregs were observed in term and preterm newborns, and these frequencies showed an inverse correlation with gestational age. These cells exhibited a naive profile when compared with adults, with high expression of CD45RA and alfa4beta7+ and lower expression of CTLA-4, implying a decreased function, particularly in very preterm newborns

A predisposição de recém-nascidos às doenças infecciosas é atribuída, em parte, a falta da memória imunológica pré-existente. Em recém-nascidos pré-termo, é presumido que o sistema imune seja menos desenvolvido ao nascimento, mas pouco se sabe sobre o tamanho e as características das subpopulações de linfócitos. Células T reguladoras (Treg) possuem papel crucial no controle do desenvolvimento de um sistema imune saudável incluindo a manutenção da autotolerância e, sua ausência, é responsável pela gama de manifestações inflamatórias e autoimunes observadas em pacientes com IPEX (Immunodeficiency, Poliendocrinopathy and Enteropathy X-linked Syndrome). Essas células são fenotipicamente caracterizadas pela presença do fator de transcrição Foxp3 (forkhead box P3) e pela alta expressão da cadeia ? do receptor de IL-2 (CD25), já que esta citocina é essencial para a geração, manutenção e funcionamento das células Treg. Pouco se sabe sobre a frequência destas células em recém-nascidos, particularmente em recém-nascidos muito prematuros ou moderados e recém-nascidos prematuros tardios, estudados como grupos separados. Resultados preliminares do nosso grupo revelaram uma maior capacidade dos recém-nascidos de produzir resposta pró-inflamatória em comparação aos adultos, a qual foi ainda mais acentuada pela diminuição da produção de IL-10, o que sugere uma função reguladora reduzida. Diante disso, o objetivo deste trabalho foi caracterizar fenotipicamente e quantificar a população de células Treg, por meio de citometria de fluxo, em sangue de cordão umbilical de 15 recém-nascidos pré-termo nascidos entre 30-336/7 semanas de gestação (Grupo 1), 19 recém-nascidos pré-termo nascidos entre 34-366/7 semanas de gestação (Grupo 2) e 20 recém-nascidos a termo nascidos entre 37-41 semanas de gestação (Grupo 3), todos clinicamente saudáveis e com peso adequado para a idade gestacional, em comparação com 26 adultos saudáveis. Os resultados demonstraram que existe uma correlação inversa entre a frequência de Treg e a idade gestacional, com frequências significativamente maiores de células Treg CD4+CD25hiCD127loFoxp3+ no Grupo 1 quando comparado aos Grupos 2 e 3 e no Grupo 2 comparado ao Grupo 3, assim como frequências e números de Treg mais elevados em todos os recém-nascidos comparados aos adultos. Todos os recém-nascidos exibiram maior frequência de células Treg com fenótipo naïve comparados aos adultos. A expressão de CTLA-4 nas células Treg naïve foi reduzida nos dois grupos de pré-termo comparados aos grupos de recém-nascidos a termo e adultos, assim como nas células Treg de memória do Grupo 1 comparado aos demais grupos. As frequências de Tregs alfa4beta7+ e alfa4beta1+ foram maiores em ambos os grupos de pré-termo, mas significativamente diferentes somente no Grupo 1, quando comparado aos recém-nascidos a termo e adultos. Em conclusão, foram observadas altas frequências de células Treg em recém-nascidos pré-termo e a termo, e essas frequências mostraram correlação inversa com a idade gestacional. Essas células exibiram um perfil naïve quando comparadas às dos adultos, com alta expressão de CD45RA e alfa4beta7+ e menor expressão de CTLA-4, sugerindo uma menor função, particularmente em recém-nascidos muito prematuros / The predisposition of newborn infants to infectious diseases is attributed, in part, to the lack of pre-existing immunological memory. In preterm newborns, it is assumed that the immune system is less developed at birth, but little is known about the size and characteristics of lymphocyte subpopulations. Regulatory T cells (Tregs) have a crucial role in controlling the development of a healthy immune system including the maintenance of self-tolerance and, their absence, is responsible for the range of inflammatory and autoimmune manifestations observed in patients with IPEX (Immunodysregulation Polyendocrinopathy Enteropathy X-linked Syndrome). These cells are phenotypically characterized by the presence of the transcription factor Foxp3 (forkhead box P3) and by the high expression of the ? chain of the IL-2 receptor (CD25), as this cytokine is essential for the generation, maintenance and function of Treg cells. Little is known about the frequency of these cells in neonates, particularly in very and moderate preterm newborns and late preterm newborns studied as separate groups. Preliminary results from our group revealed greater ability of newborns to produce proinflammatory response compared to adults, which was further accentuated by the decreased production of IL-10, which suggests a reduced regulatory function. Thus, the aim of this study was to phenotypically characterize and quantify the population of Treg cells, by flow cytometry, in the cord blood of 15 preterm newborns born at 30-336/7 gestation weeks (Group 1), 19 preterm newborns born at 34-366/7 gestation weeks (Group 2) and 20 term newborns born at 37-41 gestation weeks (Group 3), all clinically healthy and adequate-for-gestational-age, compared to 26 healthy adults. The results demonstrated that there is an inverse correlation of the Treg frequency and gestational age, with significantly higher frequencies of CD4+CD25hiCD127loFoxp3+ Treg cells in Group 1 compared to Groups 2 and 3 and in Group 2 compared to Group 3, as well as significantly higher Treg frequencies and numbers in all the neonates compared to the adults. All of the newborns exhibited increased Treg frequencies with a naive phenotype compared to the adults. CTLA-4 expression in the naive Tregs was decreased in both preterm groups compared with those from term newborns and adults, as well as in the memory Treg cells from Group 1 compared with the other groups. The frequencies of alfa4beta7+ and alfa4beta1+ Tregs were higher in both preterm groups, but significantly different only in Group 1, when compared with those from the term newborns and the adults. In conclusion, high frequencies of Tregs were observed in term and preterm newborns, and these frequencies showed an inverse correlation with gestational age. These cells exhibited a naive profile when compared with adults, with high expression of CD45RA and alfa4beta7+ and lower expression of CTLA-4, implying a decreased function, particularly in very preterm newborns

La réponse immune représente une réponse complexe à laquelle correspond une succession d’événements orchestrés finement. Parmi les mécanismes qui régulent la réponse immune, les lymphocytes T régulateurs (Tregs) assurent le maintien de la tolérance en périphérie et le contrôle des réponses immunes adaptatives. Ils représentent une population hétérogène et leurs mécanismes de suppression sont toujours l’objet d’intenses recherches. Suivant le contexte de suppression et leur nature, les lymphocytes Tregs réalisent une inhibition de l’activation des lymphocytes Th, soit directement, soit via la modulation de la fonction des cellules dendritiques (DC). Dans un modèle d’immunisation par des cellules dendritiques chargées de KLH, les lymphocytes Tregs naturels contrôlent sélectivement l’initiation des réponses de type Th1/CTL spécifiques de l’antigène. Le but de ce travail était de définir quels sont les acteurs potentiels du contrôle de cette réponse. A l’aide de l’anticorps PC61 dirigé contre le récepteur CD25 et éliminant les lymphocytes Tregs naturels, nous avons montré que le ligand de costimulation CD70 joue un rôle clé dans leur régulation de la réponse Th1/CTL (Article 1). Ainsi, dans des conditions normales, la cytokine IL-12 induit principalement l’initiation de la réponse Th1 in vivo, tandis qu’en l’absence de lymphocytes Tregs naturels, la voie CD70/CD27 est une voie alternative d’induction de l’IFN-γ. Cette voie d’activation pourrait être opérationnelle dans certains contextes infectieux lorsque les lymphocytes Tregs sont déstabilisés voire éliminés, par exemple lors d’infections par Toxoplasma gondii ou par les virus HTLV1, SIV ou HIV. Nous avons montré que les lymphocytes Tregs naturels diminuent l’expression du ligand CD70 sur les DC, de manière dépendante de son récepteur CD27. Ensuite, nous nous sommes intéressés à une deuxième population de lymphocytes T régulateurs, les lymphocytes Tregs ICOShigh induits in vivo par le traitement avec l’anticorps anti-CTLA-4. Dans le cadre d’une colite induite par l’agent alkylant TNBS et mettant en jeu une réponse Th1, cette population de lymphocytes Tregs amplifiée par le traitement à l’anticorps anti-CTLA-4 régule la réponse immune via la cytokine anti-inflammatoire IL-10 et l’enzyme immunosuppressive IDO (Article 2). Ainsi, les résultats obtenus nous ont permis de répondre à notre objectif et de définir certains mécanismes de suppression des lymphocytes Tregs naturels et des lymphocytes Tregs induits. Dans la dernière partie de ce travail, nous avons cherché à comparer les populations de lymphocytes Tregs naturels et ICOShigh présentes dans l’intestin d’une souris naïve. Une analyse transcriptomique a révélé que ces deux populations s’opposent sur les plans phénotypique et fonctionnel. Nous proposons un modèle dans lequel les deux populations de lymphocytes Tregs agiraient en synergie pour maintenir l’homéostasie intestinale. Les lymphocytes Tregs ICOShigh différenciés au niveau local et continuellement activés contrôleraient la réponse inflammatoire associée à la présence de la flore commensale. Les lymphocytes Tregs naturels, en quiescence dans les ganglions mésentériques, n’interviendraient qu’en cas d’infection par des pathogènes. L’étude des lymphocytes T régulateurs soulève un certain nombre de concepts clés de l’immunité : la spécificité des réponses, la distinction des microorganismes commensaux et pathogènes… Mieux connaître les lymphocytes Tregs dans un modèle murin permettra de mieux comprendre les réponses inflammatoires intestinales chroniques observées chez l'homme et d’envisager, à terme, de nouveaux traitements. / An immune response is complex and implies numerous sequential events. It is regulated by different mechanisms, among which regulatory T cells maintain peripheral tolerance and control adaptive immune responses. Regulatory T cells are very heterogeneous and suppress immune responses through different mechanisms, still under investigation. They can inhibit T cell activation directly or through the modulation of dendritic cell function, depending on their nature and the tissular context. In a dendritic cell-mediated immunization model, naturally occurring regulatory T cells selectively control the priming of antigen-specific Th1/CTL responses. Our goal was to define the potential actors of this control, targeted by natural regulatory T cells. Using the PC61 antibody which targets and depletes these cells, we showed that the costimulation ligand CD70 plays a key role in their control of Th1/CTL responses (first article). We showed that mainly IL-12 provokes Th1 development in normal conditions, wheras CD70 plays a major role in priming Th1 responses in the absence of natural Tregs. This pathway can be operational if regulatory T cells are destabilized or even depleted, for example during infection with Toxoplasma gondii or with HTLV1, SIV or HIV. We showed that natural Tregs downregulate CD70 expression on the surface of DCs. Next, we focused on another regulatory T cell population, induced in vivo by the anti-CTLA-4 mAb treatment. In a model of pro-Th1 colitis, induced by the alkylating agent TNBS, these ICOShigh regulatory T cells exert an IL-10 and IDO-dependant control over the immune response (second article). Thus, we succeeded in determining some control mechanisms of the immune response targeted by two populations of regulatory T cells. Finally, we compared two regulatory T cell populations: naturally occurring regulatory T cells and ICOShigh regulatory T cells from the intestines of naïve mice. A transcriptional analysis revealed two populations phenotypically and functionally distinct. We proposed a model in which these populations act synergistically and both maintain intestinal homeostasis. ICOShigh regulatory T cells might control commensal gut flora-specific inflammatory responses and quiescent natural regulatory T cells from mesenteric lymph nodes might control potential pathogen infections. As a conclusion, this study raises some immunological issues: specificity of immune responses, distinction between commensal and pathogenic microorganisms… A better knowledge of these regulatory populations will lead to a better understanding of human intestinal responses and in the medium term will lead to new therapeutic approaches and tools.