Galactosaminogalactan, a New Immunosuppressive Polysaccharide of Aspergillus fumigatus

A new polysaccharide secreted by the human opportunistic fungal pathogen Aspergillus fumigatus has been characterized. Carbohydrate analysis using specific chemical degradations, mass spectrometry, 1H and 13C nuclear magnetic resonance showed that this polysaccharide is a linear heterogeneous galactosaminogalactan composed of α1-4 linked galactose and α1-4 linked N-acetylgalactosamine residues where both monosacharides are randomly distributed and where the percentage of galactose per chain varied from 15 to 60%. This polysaccharide is antigenic and is recognized by a majority of the human population irrespectively of the occurrence of an Aspergillus infection. GalNAc oligosaccharides are an essential epitope of the galactosaminogalactan that explains the universal antibody reaction due to cross reactivity with other antigenic molecules containing GalNAc stretches such as the N-glycans of Campylobacter jejuni. The galactosaminogalactan has no protective effect during Aspergillus infections. Most importantly, the polysaccharide promotes fungal development in immunocompetent mice due to its immunosuppressive activity associated with disminished neutrophil infiltrates

TSLP-activated dendritic cells induce human T follicular helper cell differentiation through OX40-ligand.

T follicular helper cells (Tfh) are important regulators of humoral responses. Human Tfh polarization pathways have been thus far associated with Th1 and Th17 polarization pathways. How human Tfh cells differentiate in Th2-skewed environments is unknown. We show that thymic stromal lymphopoietin (TSLP)-activated dendritic cells (DCs) promote human Tfh differentiation from naive CD4 T cells. We identified a novel population, distinct from Th2 cells, expressing IL-21 and TNF, suggestive of inflammatory cells. TSLP-induced T cells expressed CXCR5, CXCL13, ICOS, PD1, BCL6, BTLA, and SAP, among other Tfh markers. Functionally, TSLP-DC-polarized T cells induced IgE secretion by memory B cells, and this depended on IL-4Rα. TSLP-activated DCs stimulated circulating memory Tfh cells to produce IL-21 and CXCL13. Mechanistically, TSLP-induced Tfh differentiation depended on OX40-ligand, but not on ICOS-ligand. Our results delineate a pathway of human Tfh differentiation in Th2 environments

Régulation de la diversité des sous-populations de lymphocytes T auxiliaires humaines : des mécanismes in vitro dérivés des cellules dendritiques aux candidats biomarqueurs dans la dermatite atopique

Human immunity is essentially driven by dendritic cells and T helper cells. When dendritic cells detect a pathogen, they will instruct T helper cells to adopt the adapted phenotype for the specific threat encountered. T helper cells are subdivided in multiple subsets, characterized by particular sets of cytokines. Each T helper subset has specific functions and is involved in the clearance of distinct pathogens. If T helper responses are not precisely regulated, they can become pathogenic, in this case T helper pathways can be considered as potential targets for therapy. In this context, I focused my PhD work on studying T helper cell subset diversity and regulation. First, I demonstrated the ability of TSLP-activated dendritic cell to induce T follicular helper cell polarization. Then I participated in building a mathematical model capable of predicting T helper cell response to dendritic-cell derived signals. This model allowed us to identify the specific role of IL-12p70, in an IL-1 context, to induce IL-17F without IL-17A. Finally, I monitered eight T helper and T follicular helper cell populations in peripheral blood from atopic dermatitis patients treated with Dupilumab, an immunotherapy targeting the IL-4 receptor alpha subunit, and was able to show a correlation between decrease of Th17 cell percentage and improvement of EASI clinical score. Overall, my work on Th phenotype diversity provides key mechanistic insight with potential application in immunotherapy.Le système immunitaire humain est majoritairement commandé par les cellules dendritiques et les lymphocytes T auxiliaires. Lorsque les cellules dendritiques détectent un pathogène, elles vont instruire les lymphocytes T auxiliaires afin qu’ils adoptent le phénotype approprié à la menace rencontrée. Les lymphocytes T auxiliaires peuvent être divisés en plusieurs sous-populations, caractérisées par la production de cytokines spécifiques. Chaque sous-population de lymphocyte T auxiliaire possède des fonctions propres et est impliquée dans l’élimination de pathogènes distincts. Si les réponses des lymphocytes T auxiliaires ne sont pas finement régulées, ils peuvent devenir pathogéniques, et dans ce cas, considérés comme cibles potentielles pour des thérapies. Dans ce contexte, j’ai concentré mon travail de doctorat sur l’étude de la diversité des sous- populations de lymphocytes T auxiliaires et de leur régulation. Premièrement, j’ai démontré que les cellules dendritiques activées par la TSLP sont capables d’induire la polarisation de lymphocytes T folliculaires. Ensuite, j’ai participé à la construction d’un modèle mathématique capable de prédire la réponse lymphocytaire T auxiliaire en fonction de signaux dérivés des cellules dendritiques. Ce modèle nous a permis d’identifier un rôle spécifique pour l’IL-12p70, dépendant du contexte IL-1, dans l’induction d’IL-17F sans IL-17A. Enfin, j’ai monitoré huit populations de lymphocytes T auxiliaires et folliculaires dans le sang périphérique de patients atteints de dermatite atopique traités par Dupilumab, une immunothérapie ciblant la sous-unité alpha du récepteur de l’IL-4 et j’ai pu montré que la diminution du pourcentage de lymphocytes Th17 correlait avec l’amélioration du score clinique EASI. Globalement, mon travail sur la diversité de phénotypes Th apporte une ressource mécanistique importante, avec une potentielle application en immunothérapie

TLR1/2 orchestrate human plasmacytoid predendritic cell response to gram+ bacteria

International audienceGram+ infections are worldwide life-threatening diseases in which the pathological role of type I interferon (IFN) has been highlighted. Plasmacytoid predendritic cells (pDCs) produce high amounts of type I IFN following viral sensing. Despite studies suggesting that pDCs respond to bacteria, the mechanisms underlying bacterial sensing in pDCs are unknown. We show here that human primary pDCs express toll-like receptor 1 (TLR1) and 2 (TLR2) and respond to bacterial lipoproteins. We demonstrated that pDCs differentially respond to gram+ bacteria through the TLR1/2 pathway. Notably, up-regulation of costimulatory molecules and pro-inflammatory cytokines was TLR1 dependent, whereas type I IFN secretion was TLR2 dependent. Mechanistically, we demonstrated that these differences relied on diverse signaling pathways activated by TLR1/2. MAPK and NF-κB pathways were engaged by TLR1, whereas the Phosphoinositide 3-kinase (PI3K) pathway was activated by TLR2. This dichotomy was reflected in a different role of TLR2 and TLR1 in pDC priming of naïve cluster of differentiation 4+ (CD4+) T cells, and T helper (Th) cell differentiation. This work provides the rationale to explore and target pDCs in bacterial infection

A Quantitative Multivariate Model of Human Dendritic Cell-T Helper Cell Communication

International audienceCell-cell communication involves a large number of molecular signals that function as words of a complex language whose grammar remains mostly unknown. Here, we describe an integrative approach involving (1) protein-level measurement of multiple communication signals coupled to output responses in receiving cells and (2) mathematical modeling to uncover input-output relationships and interactions between signals. Using human dendritic cell (DC)-T helper (Th) cell communication as a model, we measured 36 DC-derived signals and 17 Th cytokines broadly covering Th diversity in 428 observations. We developed a data-driven, computationally validated model capturing 56 already described and 290 potentially novel mechanisms of Th cell specification. By predicting context-dependent behaviors, we demonstrate a new function for IL-12p70 as an inducer of Th17 in an IL-1 signaling context. This work provides a unique resource to decipher the complex combinatorial rules governing DC-Th cell communication and guide their manipulation for vaccine design and immunotherapies