Effet des immunoglobulines intraveineuses sur les lymphocytes B : mécanismes d'action et récepteurs impliqués

Le plasma récupéré des dons de sang est utilisé pour produire annuellement plusieurs milliers de kg de préparations thérapeutiques d'immunoglobulines pour injection intraveineuse (IglV) qui sont utilisées pour le traitement de patients souffrant d'immunodéficiences primaires ou secondaires. Depuis quelques années, de très fortes doses d'IglV sont également utilisées pour traiter un nombre croissant de maladies autoimmunes, augmentant grandement les risques de pénurie de ce produit pour lequel il n'existe à l'heure actuelle aucun substitut. Il a été rapporté que le traitement in vitro des lymphocytes B humains aux IgPV induit une baisse de leur prolifération ainsi qu'une augmentation de la sécrétion d'IgG. Mes travaux de thèse ont porté sur l'étude des mécanismes par lesquels les IglV agissent sur les lymphocytes B. Dans un premier temps, nous avons utilisé une approche d'immunoprecipitation suivie d'analyses par spectrométrie de masse afin d'identifier les molécules ciblées par les IgPV à la surface des lymphocytes B. Comme prévu, nous avons identifié plusieurs protéines membranaires ou associées à la membrane plasmique telles que le CD91, les molécules du CMH I et II ainsi que les prohibitines 1 et 2. Cependant, des protéines strictement intracellulaires ont aussi été identifiées, telles que l'endoplasmine et le LYST (Lysosomal-trafficking regulator). Ces résultats nous ont permis de démontrer que les IglV étaient internalisées de manière spécifique et spontanée par les lymphocytes B activés in vitro et par les cellules myéloïdes dans le sang total. L'identification de molécules impliquées dans le processus de la présentation antigénique, comme les complexes majeurs d'histocompatibilité (CMH) I et II, nous a conduit à émettre l'hypothèse que les IgPV pouvaient interférer avec ce processus. À l'aide d'un système in vitro de présentation antigénique dépendant du CMH H, nous avons démontré que les IglV inhibaient la présentation d'antigène dépendante et indépendante du récepteur antigénique (BCR). Il a aussi pu être établi que cet effet n'était pas dû à une modulation du niveau de CMH II exprimé à la surface des lymphocytes B ni dépendant du récepteur inhibiteur pour la partie constante des IgG, le FcyRIIb. Nous avons donc proposé un mécanisme dépendant de l'interaction avec des protéines intracellulaires impliquées dans le processus de la présentation antigénique afin d'expliquer cet effet des IglV. Par la suite, à l'aide d'une lignée cellulaire déficiente pour l'expression du CD91, il nous a été possible de démontrer l'implication de ce récepteur dans l'internalisation spontanée des IglV. De plus, nous avons observé que le traitement aux IglV induit une phosphorylation de la partie intracellulaire du CD91 sur la tyrosine 4507. Nos résultats suggèrent aussi que le CD91 pourrait permettre la transcytose des IglV à travers la barrière hémato-encéphalique. En résumé, mes travaux de thèse ont identifié le CD91 comme étant impliqué dans le processus d'internalisation spontanée des IglV et suggèrent que cette internalisation est impliquée dans un nouvel effet des IglV sur les lymphocytes B : l'inhibition de la présentation antigénique

T-Cell responses in individuals infected with Zika virus and in those vaccinated against dengue virus

Background: The outbreak of Zika virus (ZIKV) infection in Brazil has raised concerns that infection during pregnancy could cause microcephaly and other severe neurodevelopmental malformations in the fetus. The mechanisms by which ZIKV causes fetal abnormalities are largely unknown. The importance of pre-infection with dengue virus (DENV), or other flaviviruses endemic to Brazil, remains to be investigated. It has been reported that antibodies directed against DENV can increase ZIKV infectivity by antibody dependent enhancement (ADE), suggesting that a history of prior DENV infection might worsen the outcome of ZIKV infection. Methods: We used bioinformatics tools to design 18 peptides from the ZIKV envelope containing predicted HLA-I T-cell epitopes and investigated T-cell cross-reactivity between ZIKV-infected individuals and DENV-vaccinated subjects by IFNg ELISPOT. Results: Three peptides induced IFNg production in both ZIKV-infected subjects and in DENV-vaccinated individuals. Flow cytometry indicated that 1 ZIKV peptide induced a CD4+ T-cell response in DENV-vaccinated subjects. Conclusions: We demonstrated that vaccination against DENV induced a T-cell response against ZIKV and identified one such CD4+ T-cell epitope. The ZIKV-reactive CD4+ T cells induced by DENV vaccination and identified in this study could contribute to the appearance of cross-reactive antibodies mediating ADE

The Emerging Role of MAIT Cell Responses in Viral Infections.

Mucosal-associated invariant T (MAIT) cells are unconventional T cells with innate-like antimicrobial responsiveness. MAIT cells are known for MR1 (MHC class I-related protein 1)-restricted recognition of microbial riboflavin metabolites giving them the capacity to respond to a broad range of microbes. However, recent progress has shown that MAIT cells can also respond to several viral infections in humans and in mouse models, ranging from HIV-1 and hepatitis viruses to influenza virus and SARS-CoV-2, in a primarily cognate Ag-independent manner. Depending on the disease context MAIT cells can provide direct or indirect antiviral protection for the host and may help recruit other immune cells, but they may also in some circumstances amplify inflammation and aggravate immunopathology. Furthermore, chronic viral infections are associated with varying degrees of functional and numerical MAIT cell impairment, suggesting secondary consequences for host defense. In this review, we summarize recent progress and highlight outstanding questions regarding the emerging role of MAIT cells in antiviral immunity

MAIT cells are activated in acute Dengue virus infection and after in vitro Zika virus infection.

Dengue virus (DENV) and Zika virus (ZIKV) are members of the Flaviviridae and are predominantly transmitted via mosquito bites. Both viruses are responsible for a growing number of infections in tropical and subtropical regions. DENV infection can cause lethargy with severe morbidity and dengue shock syndrome leading to death in some cases. ZIKV is now linked with Guillain-Barré syndrome and fetal malformations including microcephaly and developmental disorders (congenital Zika syndrome). The protective and pathogenic roles played by the immune response in these infections is unknown. Mucosal-associated invariant T (MAIT) cells are a population of innate T cells with potent anti-bacterial activity. MAIT cells have also been postulated to play a role in the immune response to viral infections. In this study, we evaluated MAIT cell frequency, phenotype, and function in samples from subjects with acute and convalescent DENV infection. We found that in acute DENV infection, MAIT cells had elevated co-expression of the activation markers CD38 and HLA-DR and had a poor IFNγ response following bacterial stimulation. Furthermore, we found that MAIT cells can produce IFNγ in response to in vitro infection with ZIKV. This MAIT cell response was independent of MR1, but dependent on IL-12 and IL-18. Our results suggest that MAIT cells may play an important role in the immune response to Flavivirus infections

Dynamic MAIT cell response with progressively enhanced innateness during acute HIV-1 infection.

Mucosa-associated invariant T (MAIT) cell loss in chronic HIV-1 infection is a significant insult to antimicrobial immune defenses. Here we investigate the response of MAIT cells during acute HIV-1 infection utilizing the RV217 cohort with paired longitudinal pre- and post-infection samples. MAIT cells are activated and expand in blood and mucosa coincident with peak HIV-1 viremia, in a manner associated with emerging microbial translocation. This is followed by a phase with elevated function as viral replication is controlled to a set-point level, and later by their functional decline at the onset of chronic infection. Interestingly, enhanced innate-like pathways and characteristics develop progressively in MAIT cells during infection, in parallel with TCR repertoire alterations. These findings delineate the dynamic MAIT cell response to acute HIV-1 infection, and show how the MAIT compartment initially responds and expands with enhanced function, followed by progressive reprogramming away from TCR-dependent antibacterial responses towards innate-like functionality

Innate immune cell activation after HIV-1 vaccine administration is associated with increased antibody production

The RV144 Thai phase III clinical trial’s canarypox–protein HIV vaccine regimen showed modest efficacy in reducing infection. We therefore sought to determine the effects of vaccine administration on innate cell activation and subsequent associations with vaccine-induced immune responses. RV306 was a randomized, double-blind clinical trial in HIV-uninfected Thai adults that tested delayed boosting following the RV144 regimen. PBMC collected from RV306 participants prior to and 3 days after the last boost were used to investigate innate immune cell activation. Our analysis showed an increase in CD38+ mucosal associated invariant T (MAIT) cells, CD38+ invariant natural killer T (iNKT) cells, CD38+ γδ T cells, CD38+, CD69+ and HLA-DR+ NK cells 3 days after vaccine administration. An increase in CD14-CD16+ non-classical monocytes and CD14+CD16+ intermediate monocytes accompanied by a decrease in CD14+CD16- classical monocytes was also associated with vaccine administration. Inclusion of ALVAC-HIV in the boost did not further increase MAIT, iNKT, γδ T, and NK cell activation or increase the proportion of non-classical monocytes. Additionally, NK cell activation 3 days after vaccination was positively associated with antibody titers of HIV Env-specific total IgG and IgG1. Vδ1 T cell activation 3 days after vaccine administration was associated with HIV Env-specific IgG3 titers. Finally, we observed trending associations between MAIT cell activation and Env-specific IgG3 titers and between NK cell activation and TH023 pseudovirus neutralization titers. Our study identifies a potential role for innate cells, specifically NK, MAIT, and γδ T cells, in promoting antibody responses following HIV-1 vaccine administration

Persistent Immune Activation in CVID and the Role of IVIg in Its Suppression

Common variable immunodeficiency (CVID) is one of the most common and clinically important primary immune deficiencies. CVID patients have poor humoral immunity resulting in recurrent infections of the gastrointestinal and upper respiratory tracts, as well as increased incidence of some forms of cancers and autoimmune diseases. The treatment for CVID is IgG replacement, often given as intravenous immunoglobulins (IVIg). IVIg consists of monomeric IgG purified from pooled plasma from healthy donors and is used to treat an increasing number of conditions including autoimmune diseases. In the case of CVID, IVIg has mainly been seen as reconstitution therapy, providing patients with pathogen-specific antibodies. Recent evidence shows that IVIg has diverse effects on the immune system of CVID patients, and one important component is that IVIg alleviates the state of chronic immune activation. In this review we will discuss causes and consequences of persistent immune activation in CVID, possible underlying mechanisms for how IVIg treatment reduces immune activation, and implications for our understanding of primary as well as acquired immune deficiencies

Colony-stimulating factor-1- and interleukin-34-derived macrophages differ in their susceptibility to Mycobacterium marinum

© 2019 Society for Leukocyte Biology Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), remains the leading global cause of death from an infectious agent. Mycobacteria thrive within their host Mϕs and presently, there is no animal model that permits combined in vitro and in vivo study of mycobacteria-host Mϕ interactions. Mycobacterium marinum (Mm), which causes TB in aquatic vertebrates, has become a promising model for TB research, owing to its close genetic relatedness to Mtb and the availability of alternative, natural host aquatic animal models. Here, we adopted the Xenopus laevis frog-Mm surrogate infection model to study host Mϕ susceptibility and resistance to mycobacteria. Mϕ differentiation is regulated though the CSF-1 receptor (CSF-1R), which is activated by CSF-1 and the unrelated IL-34 cytokines. Using combined in vitro and in vivo approaches, we demonstrated that CSF-1-Mϕs exacerbate Mm infections, are more susceptible to mycobacterial entry and are less effective at killing this pathogen. By contrast, IL-34-Mϕs confer anti-Mm resistance in vivo, are less susceptible to Mm entry and more effectively eliminate internalized mycobacteria. Moreover, we showed that the human CSF-1- and IL-34-Mϕs are likewise, respectively, susceptible and resistant to mycobacteria, and that both frog and human CSF-1-Mϕs are more prone to the spread of mycobacteria and to being infected by Mm-laden Mϕs than the respective IL-34-Mϕ subsets. This work marks the first report describing the roles of these Mϕ subsets in mycobacterial disease and may well lead to the development of more targeted anti-Mtb approaches