Impact des agonistes des TLR sur les réponses B dépendantes des lymphocytes T

Les vaccins protéiques favorisent une immunité à long terme grâce à la différenciation de cellules B mémoires spécifiques de l'antigène et des plasmocytes à longue durée de vie. Pour être efficace, les vaccins doivent induire la différenciation de lymphocytes T auxilaires spécifiques de l'antigène qui sont nécessaires au contrôle des lymphocytes B activés. Il est maintenant clair que cette aide implique une lignée distincte de cellules T auxiliaires nommées lymphocytes T CD4+ folliculaires (Tfh). Puisque la combinaison d'adjuvants semble améliorer de façon synergique la réponse immunitaire, nous avons testé si l'addition d'agonistes des récepteurs Toll (TLR) à d'autres adjuvants vaccinaux contribue aux réponses humorales spécifiques de l'antigène dépendantes des T in vivo. Nous avons constaté que l'addition d'agonistes des TLR dépendants de MyD88 comme le CpG, agoniste de TLR9 utilisé en clinique, ou le LPS, agoniste du TLR4, augmente la différenciation des cellules Tfh spécifiques de l'antigène sans modifier la réponse globale des lymphocytes T spécifiques de l'antigène. Ce phénomène est observé quel que soit l'adjuvant complémenté par un agoniste de TLR: l'adjuvant de Freund incomplet, l'alum ou un adjuvant à base de squalène. En revanche, aucun des agonistes de TLR dépendants de TRIF ont un rôle promoteur sur la différenciation Tfh. L'effet sur les Tfh observé après addition de CpG ou de LPS corrèle avec une augmentation de la réaction du centre germinatif, des plasmocytes spécifiques de l'antigène et des anticorps circulants. Nous avons également démontré que cet effet activateur, en réponse à la signalisation des TLR via MyD88, est orchestré in vivo par la présentation antigénique et l'IL-6 sécrétée par les cellules dendritiques dérivées de monocytes. En revanche, ni les cellules B ni les cellules dendritiques plasmacytoïdes qui sécrètent également de l'IL-6 en réponse aux agonistes de TLR4 et TLR9, sont impliqués dans ce phénomène. Ainsi, alors que les cellules dendritiques conventionnelles initient les réponses des lymphocytes T CD4+ dans les ganglions lymphatiques drainants, le ciblage des cellules dendritiques dérivées de monocytes peut promouvoir le programme Tfh nécessaire au contrôle des cellules B de haute affinité B in vivo.Protein vaccines can promote long-term immunity through the differentiation of Ag-specific high-affinity memory B cells and long-lived plasma cells. To be effective, vaccine priming must induce Ag-specific helper T cells that are required to regulate the emerging B cell response. It is now clear that this cognate T cell help involves a distinct lineage of CD4+ T cells named T Follicular Helper cells (Tfh). Because adjuvant combinations could result in synergistic enhancement of the immune response, we tested whether addition of Toll-like Receptor (TLR) agonists to other vaccine adjuvant contributes to antigen-specific T cell-dependent B cell responses in vivo. We found that MyD88-dependent such as CpG, the TLR9 agonist used in clinics, or LPS, the TLR4 agonist, increased the differentiation of antigen-specific Tfh cells without changing the overall magnitude of the T cell response. This phenomenon was observed irrespective of the adjuvant used: Incomplete Freund's Adjuvant, Alum or squalene-based adjuvant. In contrast, no TRIF-dependent TLR agonists were able to promote Tfh differentiation. The enhancing effect after CpG or LPS addition correlated with an enhancement of germinal center reaction, antigen-specific plasma cells and circulating antibodies. We comprehensively demonstrated that this promoting effect in response to MyD88-dependent TLR signaling was orchestrated in vivo by antigen presentation and IL-6 secreted by monocyte-derived dendritic cells. In contrast, neither B cells nor plasmacytoid dendritic cells that also secreted IL-6 in response to TLR4 and TLR9 agonist were involved in this phenomenon. Thus, while conventional dendritic cells prime and initiate CD4+ T cell responses in the draining lymph nodes, we show that targeting monocyte-derived dendritic cells can specifically enhance the Tfh program needed to regulate high-affinity B cell protection in vivo

Unsupervised High-Dimensional Analysis Aligns Dendritic Cells across Tissues and Species.

Dendritic cells (DCs) are professional antigen-presenting cells that hold great therapeutic potential. Multiple DC subsets have been described, and it remains challenging to align them across tissues and species to analyze their function in the absence of macrophage contamination. Here, we provide and validate a universal toolbox for the automated identification of DCs through unsupervised analysis of conventional flow cytometry and mass cytometry data obtained from multiple mouse, macaque, and human tissues. The use of a minimal set of lineage-imprinted markers was sufficient to subdivide DCs into conventional type 1 (cDC1s), conventional type 2 (cDC2s), and plasmacytoid DCs (pDCs) across tissues and species. This way, a large number of additional markers can still be used to further characterize the heterogeneity of DCs across tissues and during inflammation. This framework represents the way forward to a universal, high-throughput, and standardized analysis of DC populations from mutant mice and human patients

Microbial exposure during early human development primes fetal immune cells

Human fetal immune system begins to develop early during gestation, however factors responsible for fetal immune-priming remain elusive. We explored potential exposure to microbial agents in-utero and their contribution towards activation of memory T cells in fetal tissues. We profiled microbes across fetal organs using 16S-rRNA gene sequencing and detected low but consistent microbial signal in fetal gut, skin, placenta and lungs, in 2nd trimester of gestation. We identified several live bacterial strains including Staphylococcus and Lactobacillus in fetal tissues, which induced in vitro activation of memory T cells in fetal mesenteric lymph-node, supporting the role of microbial exposure in fetal immune-priming. Finally, using SEM and RNA-ISH, we visualised discrete localisation of bacteria-like structures and eubacterial-RNA within 14th week fetal gut lumen. These findings indicate selective presence of live-microbes in fetal organs during 2nd trimester of gestation and have broader implications towards establishment of immune competency and priming before birt

Unravelling the sex-specific diversity and functions of adrenal gland macrophages

Despite the ubiquitous function of macrophages across the body, the diversity, origin, and function of adrenal gland macrophages remain largely unknown. We define the heterogeneity of adrenal gland immune cells using single-cell RNA sequencing and use genetic models to explore the developmental mechanisms yielding macrophage diversity. We define populations of monocyte-derived and embryonically seeded adrenal gland macrophages and identify a female-specific subset with low major histocompatibility complex (MHC) class II expression. In adulthood, monocyte recruitment dominates adrenal gland macrophage maintenance in female mice. Adrenal gland macrophage sub-tissular distribution follows a sex-dimorphic pattern, with MHC class IIlow macrophages located at the cortico-medullary junction. Macrophage sex dimorphism depends on the presence of the cortical X-zone. Adrenal gland macrophage depletion results in altered tissue homeostasis, modulated lipid metabolism, and decreased local aldosterone production during stress exposure. Overall, these data reveal the heterogeneity of adrenal gland macrophages and point toward sex-restricted distribution and functions of these cells.</p

Deletion of a Csf1r enhancer selectively impacts CSF1R expression and development of tissue macrophage populations.

The proliferation, differentiation and survival of mononuclear phagocytes depend on signals from the receptor for macrophage colony-stimulating factor, CSF1R. The mammalian Csf1r locus contains a highly conserved super-enhancer, the fms-intronic regulatory element (FIRE). Here we show that genomic deletion of FIRE in mice selectively impacts CSF1R expression and tissue macrophage development in specific tissues. Deletion of FIRE ablates macrophage development from murine embryonic stem cells. Csf1r mice lack macrophages in the embryo, brain microglia and resident macrophages in the skin, kidney, heart and peritoneum. The homeostasis of other macrophage populations and monocytes is unaffected, but monocytes and their progenitors in bone marrow lack surface CSF1R. Finally, Csf1r mice are healthy and fertile without the growth, neurological or developmental abnormalities reported in Csf1r rodents. Csf1r mice thus provide a model to explore the homeostatic, physiological and immunological functions of tissue-specific macrophage populations in adult animals

Tracking by Flow Cytometry Antigen-Specific Follicular Helper T Cells in Wild-Type Animals After Protein Vaccination

International audienc

Monocyte‐derived dendritic cells promote T f ollicular h elper cell differentiation

Comment inMonocyte-derived dendritic cells identified as booster of T follicular helper cell differentiation. [EMBO Mol Med. 2014]International audienceTo be effective, protein priming must induce the development of a distinct lineage of CD4(+) T cells named T follicular helper (Tfh) cells, which regulate the differentiation of high-affinity memory B cells and long-lived plasma cells. In this context, we tested how adjuvantation with CpG, the Toll-like receptor 9 agonist used in clinics, contributes to antigen-specific T-cell-dependent B-cell responses in vivo. We found that addition of CpG to other vaccine adjuvant increased the differentiation of antigen-specific Tfh cells without changing the overall magnitude of the T-cell response. This phenomenon correlated with an enhancement of the germinal centre reaction, antigen-specific plasma cells and circulating antibodies. We comprehensively demonstrated that, in addition to the classical Tfh-cell differentiation mediated by conventional DC, the promoting effect due to CpG was orchestrated in vivo by antigen presentation and IL-6 secreted by monocyte-derived dendritic cells (DC) as shown in their absence. Thus, while conventional DC initiate T-cell responses, targeting monocyte-derived DC specifically enhances the Tfh programme needed to regulate high-affinity B-cell protection in vivo

A lung-resident Ly6c+ monocyte proliferates to give rise to immunosuppressive lung macrophages

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CpG-DNA expand immunosuppressive interstitial macrophages from Ly6c+ local precursors

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