Effets de l'histamine sur l'activation et la polarisation des cellules dendritiques humaines (implication dans la réponse allergique)

Les maladies allergiques sont caractérisées par une réponse Th2 dominante spécifique de l'allergène. La différenciation des cellules Th est notamment induite par les cellules dendritiques (DC), et les signaux qui contrôlent la capacité des DC à induire préférentiellement une réponse Th2 (DC2) lors de la réaction allergique sont peu connus. Les mastocytes de sujets allergiques, stimulés par allergène, sécrètent de l'histamine, un médiateur impliqué dans la réaction immédiate d'hypersensibilité. Les mastocytes et les DC immatures étant en contact dans les tissus périphériques, mon projet de thèse était d'évaluer si l'histamine pouvait affecter la fonction des DC humaines. L'histamine induit la production par les DC immatures de cytokines et chimiokines pro-inflammatoires asociées à la phase tardives de la réaction allergique, et favorise l'activation des DC induite par le lipopolysaccharide (LPS). De plus, même en présence d'interféron..., un puissant facteur connu pour polariser les DC en DC1, l'histamine permet la polarisation des DC en cours de maturation en DC2 effectrices, qui ne produisent pas d'IL-12 après stimulation et induisent le développement d'une réponse Th2. Les deux récepteurs H1 et H2 sont impliqués dans les effets de l'histamine sur les DC. En conclusion, l'histamine, en activant les DC résidentes, participerait non seulement à la réaction inflammatoire tardive associée aux maladies allergiques, mais également à la polarisation Th2. Ces données mettent en évidence un nouveau mécanisme qui expliquerait l'initiation et le maintien d'une réponse Th2 dominante dans les maladies allergiques.LILLE1-BU (590092102) / SudocSudocFranceF

Early Emergence of Adaptive Mechanisms Sustaining Ig Production: Application to Antibody Therapy

International audienceAntibody therapy, where artificially-produced immunoglobulins (Ig) are used to treat pathological conditions such as auto-immune diseases and cancers, is a very innovative and competitive field. Although substantial efforts have been made in recent years to obtain specific and efficient antibodies, there is still room for improvement especially when considering a precise tissular targeting or increasing antigen affinity. A better understanding of the cellular and molecular steps of terminal B cell differentiation, in which an antigen-activated B cell becomes an antibody secreting cell, may improve antibody therapy. In this review, we use our recently published data about human B cell differentiation, to show that the mechanisms necessary to adapt a metamorphosing B cell to its new secretory function appear quite early in the differentiation process i.e., at the pre-plasmablast stage. After characterizing the molecular pathways appearing at this stage, we will focus on recent findings about two main processes involved in antibody production: unfolded protein response (UPR) and endoplasmic reticulum (ER) stress. We’ll show that many genes coding for factors involved in UPR and ER stress are induced at the pre-plasmablast stage, sustaining our hypothesis. Finally, we propose to use this recently acquired knowledge to improve productivity of industrialized therapeutic antibodies

CXCR4 expression functionally discriminates centroblasts versus centrocytes within human germinal center B cells.

International audienceThe human germinal center is a highly dynamic structure where B cells conduct their terminal differentiation and traffic following chemokine gradients. The rapidly dividing centroblasts and the nondividing centrocytes represent the two major B cell subsets present in germinal center and also the most common normal counterparts for a majority of lymphomas. CD77 expression was previously associated to proliferating centroblasts undergoing somatic hypermutation, but data from transcriptional studies demonstrate that CD77 is not a reliable marker to discriminate human centroblasts from centrocytes. Herein we were able for the first time to separate these two subpopulations based on the expression of the chemokine receptor CXCR4 allowing their characterization. Phenotypic and functional features were especially explored, giving an accurate definition of CXCR4(+) centroblasts compared with CXCR4(-) centrocytes. We show that CXCR4(+) and CXCR4(-) germinal center B cells present a clear dichotomy in terms of proliferation, transcription factor expression, Ig production, and somatic hypermutation regulation. Microarray analysis identified an extensive gene list segregating these B cells, including highly relevant genes according to previous knowledge. By gene set enrichment analysis we demonstrated that the centroblastic gene expression signature was significantly enriched in Burkitt's lymphomas. Collectively, our findings show that CXCR4 expression can properly separate human centroblasts from centrocytes and offer now the possibility to have purified normal counterparts of mature B cell-derived malignancies

Broad antiretroviral defence by human APOBEC3G through lethal editing of nascent reverse transcripts

Viral replication usually requires that innate intracellular lines of defence be overcome, a task usually accomplished by specialized viral gene products. The virion infectivity factor (Vif) protein of human immunodeficiency virus (HIV) is required during the late stages of viral production to counter the antiviral activity of APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G; also known as CEM15), a protein expressed notably in human T lymphocytes. When produced in the presence of APOBEC3G, vif-defective virus is non-infectious. APOBEC3G is closely related to APOBEC1, the central component of an RNA-editing complex that deaminates a cytosine residue in apoB messenger RNA. APOBEC family members also have potent DNA mutator activity through dC deamination; however, whether the editing potential of APOBEC3G has any relevance to HIV inhibition is unknown. Here, we demonstrate that it does, as APOBEC3G exerts its antiviral effect during reverse transcription to trigger G-to-A hypermutation in the nascent retroviral DNA. We also find that APOBEC3G can act on a broad range of retroviruses in addition to HIV, suggesting that hypermutation by editing is a general innate defence mechanism against this important group of pathogens

IL-2 requirement for human plasma cell generation: coupling differentiation and proliferation by enhancing MAPK-ERK signaling.

International audienceMature B cell differentiation involves a well-established transcription factor cascade. However, the temporal dynamics of cell signaling pathways regulating transcription factor network and coordinating cell proliferation and differentiation remain poorly defined. To gain insight into the molecular processes and extrinsic cues required for B cell differentiation, we set up a controlled primary culture system to differentiate human naive B cells into plasma cells (PCs). We identified T cell-produced IL-2 to be critically involved in ERK1/2-triggered PC differentiation. IL-2 drove activated B cell differentiation toward PC independently of its proliferation and survival functions. Indeed, IL-2 potentiated ERK activation and subsequent BACH2 and IRF8 downregulation, sustaining BLIMP1 expression, the master regulator for PC differentiation. Inhibition of the MAPK-ERK pathway, unlike STAT5 signaling, impaired IL-2-induced PC differentiation and rescued the expression profile of BACH2 and IRF8. These results identify IL-2 as a crucial early input in mature B cell fate commitment

Plasmablasts derive from CD23-negative activated B cells after the extinction of IL-4/STAT6 signaling and IRF4 induction

International audienceThe terminal differentiation of B cells into antibody-secreting cells (ASCs) is a critical component of adaptive immune responses. However, it is a very sensitive process, and dysfunctions lead to a variety of lymphoproliferative neoplasias including germinal center-derived lymphomas. To better characterize the late genomic events that drive the ASC differentiation of human primary naive B cells, we used our in vitro differentiation system and a combination of RNA sequencing and Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC sequencing). We discovered 2 mechanisms that drive human terminal B-cell differentiation. First, after an initial response to interleukin-4 (IL-4), cells that were committed to an ASC fate downregulated the CD23 marker and IL-4 signaling, whereas cells that maintained IL-4 signaling did not differentiate. Second, human CD23- cells also increased IRF4 protein to levels required for ASC differentiation, but they did that independently of the ubiquitin-mediated degradation process previously described in mice. Finally, we showed that CD23- cells carried the imprint of their previous activated B-cell status, were precursors of plasmablasts, and had a phenotype similar to that of in vivo preplasmablasts. Altogether, our results provide an unprecedented genomic characterization of the fate decision between activated B cells and plasmablasts, which provides new insights into the pathological mechanisms that drive lymphoma biology