Stepwise Development of MAIT Cells in Mouse and Human

Mucosal-associated invariant T (MAIT) cells display two evolutionarily conserved features: an invariant T cell receptor (TCR)α (iTCRα) chain and restriction by the nonpolymorphic class Ib major histocompatibility complex (MHC) molecule, MHC-related molecule 1 (MR1). MR1 expression on thymus epithelial cells is not necessary for MAIT cell development but their accumulation in the gut requires MR1 expressing B cells and commensal flora. MAIT cell development is poorly known, as these cells have not been found in the thymus so far. Herein, complementary human and mouse experiments using an anti-humanVα7.2 antibody and MAIT cell-specific iTCRα and TCRβ transgenic mice in different genetic backgrounds show that MAIT cell development is a stepwise process, with an intra-thymic selection followed by peripheral expansion. Mouse MAIT cells are selected in an MR1-dependent manner both in fetal thymic organ culture and in double iTCRα and TCRβ transgenic RAG knockout mice. In the latter mice, MAIT cells do not expand in the periphery unless B cells are added back by adoptive transfer, showing that B cells are not required for the initial thymic selection step but for the peripheral accumulation. In humans, contrary to natural killer T (NKT) cells, MAIT cells display a naïve phenotype in the thymus as well as in cord blood where they are in low numbers. After birth, MAIT cells acquire a memory phenotype and expand dramatically, up to 1%–4% of blood T cells. Finally, in contrast with NKT cells, human MAIT cell development is independent of the molecular adaptor SAP. Interestingly, mouse MAIT cells display a naïve phenotype and do not express the ZBTB16 transcription factor, which, in contrast, is expressed by NKT cells and the memory human MAIT cells found in the periphery after birth. In conclusion, MAIT cells are selected by MR1 in the thymus on a non-B non-T hematopoietic cell, and acquire a memory phenotype and expand in the periphery in a process dependent both upon B cells and the bacterial flora. Thus, their development follows a unique pattern at the crossroad of NKT and γδ T cells

Rôle des lymphocytes T CD4+ et des lymphocytes T régulateurs dans l'immunothérapie et la physiopathologie de la maladie d'Alzheimer : études chez la souris

Cerebral accumulation of aggregated Aβ40-42 peptides is among the major pathological hallmarks of Alzheimer's disease (AD). In spite of encouraging results of Aβ vaccination in preclinical mouse models, the first human clinical trial had to be interrupted because of the occurence of meningoencephalitides in 6% of the cases, supposedly related to inappropriate T cell responses. Thus, a better understanding of vaccination-induced anti-Aβ CD4+ T cell responses seems essential for the optimisation of future immunotherapeutical approaches. We tried to identify the genetic factors that control the magnitude and the nature of vaccination-induced Aβ-specific CD4+ T cell responses in mice. Both MHC-dependent and MHC-independent genetic factors are critical parameters. Among MHC-independent genetic factors, those that determine the individual propensity of generating Aβ-specific regulatory T cell (Treg) responses are important. Moreover, the vaccination-induced CD4+ T cell responses analysis in an APPPS1 mouse model of AD suggest that Tregs may inhibit anti-Aβ CD4+ T cells responses that spontaneously arise in the course of AD. These observations led us to evaluate the impact of CD4+ effector and regulatory T cell responses in the pathophysiology of AD. Using Treg depletion experiments, we evidenced the anti-neuroinflammatory functions and beneficial effects of these cells on the amyloid pathology and cognition of APPPS1 mice. Altogether, our results suggest that Treg responses may both limit vaccination efficacy and have a neuroprotective role in the course of AD.L'accumulation des peptides Aβ40-42 au niveau cérébral est un élément physiopathologique majeur de la Maladie d'Alzheimer (MA) et une cible thérapeutique potentielle. A l'issue de résultats encourageants de vaccination par Aβ dans des modèles murins de la MA, un essai clinique a été entrepris chez l'Homme. Mais il a dû être interrompu en raison de la survenue de méningo-encéphalites chez 6% des patients, supposées liées à une activation inappropriée de lymphocytes T. Une meilleure compréhension des réponses T CD4+ induites par la vaccination semble donc primordiale pour l'optimisation des stratégies vaccinales. Nous avons cherché à identifier les facteurs génétiques qui pourraient avoir un rôle sur l'amplitude et la nature des réponses vaccinales T CD4+ anti-Aβ chez la souris. Nous avons mis en évidence que l'amplitude de la réponse variait en fonction des haplotypes H-2 mais aussi de facteurs génétiques indépendants du CMH et liés à la capacité de générer des réponses T régulatrices (Tregs) anti-Aβ. De plus, l'analyse des réponses vaccinales dans un modèle murin de MA (souris APPPS1) semble suggérer qu'une réponse Treg inhiberait des réponses T CD4 effectrices anti- Aβ spontanées. Ces observations nous ont conduits à rechercher l'impact de ces réponses effectrices et régulatrices dans la physiopathologie de la maladie. En inactivant les cellules Tregs, nous avons pu mettre en évidence les fonctions anti-neuroinflammatoires et les effets bénéfiques de ces cellules sur la pathologie amyloïde et la cognition. Ensemble, nos résultats suggèrent donc que les réponses Treg pourraient limiter l'efficacité vaccinale mais auraient une action neuroprotectrice dans la physiopathologie de la MA

Rôle des lymphocytes T CD4+ et des lymphocytes T régulateurs dans l immunothérapie et la physiopathologie de la maladie d Alzheimer (Etudes chez la souris)

L accumulation des peptides A 40-42 au niveau cérébral est un élément physiopathologique majeur de la Maladie d Alzheimer (MA) et une cible thérapeutique potentielle. A l issue de résultats encourageants de vaccination par A dans des modèles murins de la MA, un essai clinique a été entrepris chez l Homme. Mais il a dû être interrompu en raison de la survenue de méningo-encéphalites chez 6% des patients, supposées liées à une activation inappropriée de lymphocytes T. Une meilleure compréhension des réponses T CD4+ induites par la vaccination semble donc primordiale pour l optimisation des stratégies vaccinales. Nous avons cherché à identifier les facteurs génétiques qui pourraient avoir un rôle sur l amplitude et la nature des réponses vaccinales T CD4+ anti-A chez la souris. Nous avons mis en évidence que l amplitude de la réponse variait en fonction des haplotypes H-2 mais aussi de facteurs génétiques indépendants du CMH et liés à la capacité de générer des réponses T régulatrices (Tregs) anti-A . De plus, l analyse des réponses vaccinales dans un modèle murin de MA (souris APPPS1) semble suggérer qu une réponse Treg inhiberait des réponses T CD4 effectrices anti-A spontanées. Ces observations nous ont conduits à rechercher l impact de ces réponses effectrices et régulatrices dans la physiopathologie de la maladie. En inactivant les cellules Tregs, nous avons pu mettre en évidence les fonctions anti-neuroinflammatoires et les effets bénéfiques de ces cellules sur la pathologie amyloïde et la cognition. Ensemble, nos résultats suggèrent donc que les réponses Treg pourraient limiter l efficacité vaccinale mais auraient une action neuroprotectrice dans la physiopathologie de la MA.Cerebral accumulation of aggregated A 40-42 peptides is among the major pathological hallmarks of Alzheimer s disease (AD). In spite of encouraging results of A vaccination in preclinical mouse models, the first human clinical trial had to be interrupted because of the occurence of meningoencephalitides in 6% of the cases, supposedly related to inappropriate T cell responses. Thus, a better understanding of vaccination-induced anti-A CD4+ T cell responses seems essential for the optimisation of future immunotherapeutical approaches. We tried to identify the genetic factors that control the magnitude and the nature of vaccination-induced A -specific CD4+ T cell responses in mice. Both MHC-dependent and MHC-independent genetic factors are critical parameters. Among MHC-independent genetic factors, those that determine the individual propensity of generating A -specific regulatory T cell (Treg) responses are important. Moreover, the vaccination-induced CD4+ T cell responses analysis in an APPPS1 mouse model of AD suggest that Tregs may inhibit anti-A CD4+ T cells responses that spontaneously arise in the course of AD. These observations led us to evaluate the impact of CD4+ effector and regulatory T cell responses in the pathophysiology of AD. Using Treg depletion experiments, we evidenced the anti-neuroinflammatory functions and beneficial effects of these cells on the amyloid pathology and cognition of APPPS1 mice. Altogether, our results suggest that Treg responses may both limit vaccination efficacy and have a neuroprotective role in the course of AD.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Caractérisation fonctionnelle des MAITs (Musocal Associated Invariant T cells) chez l'homme et chez la souris

Les MAITs (Mucosal Associated invariant T cells) sont des cellules restreintes par MR1 (MHC class I related molecule) et qui, comme les NK-T, expriment une chaîne a du TCR invariante (iVa19 chez la souris, iVa7.2 chez l Homme). Très conservés entre espèces, ces lymphocytes T non conventionnels sont localisés principalement dans la lamina propria intestinale. Les LT (essentiellement les CD4) des souris transgéniques pour iVa19 ont un phénotype Th2, en partie lié à MR1. La caractérisation fonctionnelle de ces cellules chez l Homme montre, par contre, un profil pro-inflammatoire et suggère fortement qu elles sont dotées de propriétés cytotoxiques. Malgré les différences entre les deux espèces, dont les causes sont débattues, l ensemble de nos résultats positionne les MAITs comme des cellules ayant un rôle important dans l immunité intestinale. Leur implication possible dans diverses fonctions est discutée.CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Insights into anti‐D formation in carriers of RhD variants through studies of 3D intraprotein interactions

International audienceBackground: Many RhD variants associated with anti-D formation (partial D) in carriers exposed to the conventional D antigen carry mutations affecting extracellular loop residues. Surprisingly, some carry mutations affecting transmembrane or intracellular domains, positions not thought likely to have a major impact on D epitopes.Study design and methods: A wild-type Rh trimer (RhD1 RhAG2 ) was modeled by comparative modeling with the human RhCG structure. Taking trimer conformation, residue accessibility, and position relative to the lipid bilayer into account, we redefine the domains of the RhD protein. We generated models for RhD variants carrying one or two amino acid substitutions associated with anti-D formation in published articles (25 variants) or abstracts (12 variants) and for RHD*weak D type 38. We determined the extracellular substitutions and compared the interactions of the variants with those of the standard RhD.Results: The findings of the three-dimensional (3D) analysis were correlated with anti-D formation for 76% of RhD variants: 15 substitutions associated with anti-D formation concerned extracellular residues, and structural differences in intraprotein interactions relative to standard RhD were observed in the others. We discuss the mechanisms by which D epitopes may be modified in variants in which the extracellular residues are identical to those of standard RhD and provide arguments for the benignity of p.T379M (RHD*DAU0) and p.G278D (RHD*weak D type 38) in transfusion medicine.Conclusion: The study of RhD intraprotein interactions and the precise redefinition of residue accessibility provide insight into the mechanisms through which RhD point mutations may lead to anti-D formation in carriers

MHC-Independent Genetic Factors Control the Magnitude of CD4+ T Cell Responses to Amyloid- Peptide in Mice through Regulatory T Cell-Mediated Inhibition

International audienceAccumulation of amyloid-β peptide (Aβ) is considered the triggering factor of pathogenic lesions in Alzheimer's disease (AD), and vaccines targeting Aβ are promising therapeutic options. However, the occurrence of meningoencephalitides attributed to T cell responses in 6% of Aβ-immunized patients underscores the need for a better understanding of T cell responses to Aβ. We characterized the parameters controlling the magnitude of Aβ-specific CD4(+) T cell responses in mice. T cell responsiveness to Aβ1-42 was highly heterogeneous between mouse strains of different H-2 haplotypes, with SJL/J (H-2(s)) mice displaying a strong response, mainly specific for Aβ10-24, and C57BL/6 (H-2(b)) mice displaying a weak response to Aβ16-30. Surprisingly, C57BL/6 mice congenic for the H-2(s) haplotype (B6.H-2(S)), which display a "permissive" MHC class II allele for presentation of the immunodominant Aβ10-24 epitope, showed a very weak CD4(+) T cell response to Aβ, suggesting that MHC-independent genes downmodulate Aβ-specific CD4(+) T cell responses in C57BL/6 background. Vaccine-induced CD4(+) T cell responses to Aβ were significantly enhanced in both C57BL/6 and B6.H-2(S) mice upon depletion of regulatory T cells (Tregs), whereas Treg-depleted SJL/J mice displayed unaltered Aβ-specific T cell responses. Finally, Treg depletion in C57BL/6 transgenic APPPS1 mice, a mouse model of AD, results in enhanced vaccine-induced CD4(+) T cell responses in AD compared with wild-type animals. We concluded that the magnitude of Aβ-specific CD4(+) T cell responses is critically controlled in both physiological and pathological settings by MHC-independent genetic factors that determine the overall potency of Aβ-specific Treg responses

Impact of red blood cell polymorphisms on the antibody response to Plasmodium falciparum in Senegal

The evidence of protection afforded by red blood cell polymorphisms against either clinical malaria or Plasmodium falciparum blood levels varies with the study site and the type of malaria transmission. Nevertheless, no clear implication of an antibody-related effect has yet been established in the protection related to red blood cell polymorphisms. We performed a prospective study, where plasma IgG and IgG subclasses directed to recombinant proteins from the merozoite surface protein 2 (MSP2/3D7 and MSP2/FC27) and the ring-infected erythrocyte surface antigen (RESA) were determined in a cohort of 413 Senegalese children before the annual malaria transmission season. The antibody response was dependent on age, and to a lesser extent, on the village of residence. IgG3 responders to all proteins, IgG responders to RESA and MSP2/3D7, as well as IgG2 to RESA and IgG1 responders to MSP2/3D7, presented enhanced mean values of parasite density, as evaluated during an 18-month follow-up. The levels of IgG and IgG3 to MSP2/3D7 were negatively associated with the risk of occurrence of a malaria attack during the following transmission season. Compared to normal children, sickle cell trait carriers presented lower levels of IgG to MSP2/3D7. Similarly, G6PD A- girls had lower levels of IgG and IgG3 to MSP2/FC27 than did G6PD normal girls. The impact of these particular genetic polymorphisms on the modulation of the antibody response is discussed. (c) 2006 Elsevier SAS. All rights reserved

Impact of red blood cell polymorphisms on the antibody response to Plasmodium falciparum in Senegal

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Red blood cell polymorphisms in relation to Plasmodium falciparum asymptomatic parasite densities and morbidity in Senegal

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