Editorial

Insights into the dynamics of immune responses in immune-privileged tissues such as the central nervous system (CNS) are critical to understanding the etiology of autoimmune diseases. Essential in this field is understanding the ways immune cells access and traffic across different types of the blood-brain barrier (BBB), and how the therapeutics alter these processes (see excellent review by Mapunda et al.). The current Research Topic brought into attention a diverse panel of original research papers and two reviews on the immune cells involved in CNS pathophysiology, including dendritic cells (DC), mucosal-associated invariant T (MAIT) cells, neutrophils, and pathogenic Th17 cells, as well as a different aspects of that pathophysiology, including molecular signaling pathways (PP2Cδ) and the role of signaling complexes, known as supramolecular organizing centers (SMOCs), therapeutic interventions (STAT3-specific nanobody, treatment of rheumatoid meningitis with intravenous immunoglobulin - IVIg), possible new forms of autoantigens (neutrophil extracellular traps (NETs) in neuropsychiatric systemic lupus erythematosus - NPSLE), and assessment of correlation between inflammatory markers and severity of autoimmune encephalitis (AE)

Caractérisation et évaluation thérapeutique d une nouvelle population de progéniteurs B régulateurs dans le diabète de type 1

PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Thérapie cellulaire des maladies autoimmunes avec des populations de progéniteurs hématopoïétiques (caractérisation et comparaison de leur mécanisme d'action dans le diabète de type I et encéphalomyélite autoimmune expérimentale)

Les infections et l activation du système immunitaire stimulent l hématopoïèse. L activation des récepteurs Toll-like (TLRs) des cellules souches hématopoïétiques, par leur reconnaissance de motifs moléculaires portés par des agents infectieux, en oriente la différenciation vers les voies myéloïdes, renforçant la capacité de notre organisme à lutter contre les infections. Ici, nous avons étudié si les agonistes TLRs peuvent, au contraire, induire au sein de la moelle osseuse l émergence de progéniteurs hématopoïétiques présentant des propriétés immunorégulatrices. Nous montrons que l incubation de moelle osseuse de souris en présence de l agoniste TRL-9, CpG-B, entraîne l émergence d une population de progéniteurs au stade pro-B (appelée CpG-proBs). Le transfert adoptif de seulement 60,000 CpG-proBs par receveur, à l apparition des premiers signes cliniques, confère une protection à long terme dans deux modèles expérimentaux de maladies auto-immunes, le Diabète de Type I (T1D) et l Encéphalomyélite Auto-immune Expérimentale (EAE). La migration, la différenciation, et les mécanismes cellulaires et moléculaires de cette population protectrice sont décrits et comparés entre ces deux modèles. Dans les deux modèles, les CpG-proBs migrent vers le tissu cible de la réponse auto-immune et se différencient en cellules B matures régulatrices. Dans le T1D, l interféron-g (IFN-g) produit par les cellules T s avère essentiel pour induire la surexpression de FasL à la surface des CpG-proBs, entraînant l apoptose des cellules T effectrices. De plus, l IFN-g produit par les CpG-proBs réduit la production par les cellules T de l IL-21, une cytokine pathogène majeure dans le T1D. La descendance des CpG-proBs est composée de précurseurs transitionnels B, de cellules B de la zone marginale et de cellules B folliculaires, exprimant de forts niveaux de FasL et toujours capables d induire l apoptose des cellules T, prolongeant ainsi le contrôle des cellules effectrices T auto-immunes in vivo. Dans l EAE, l IFNg est indirectement responsable de la rétention des cellules T, par l internalisation de CCR7, au sein des ganglions lymphatiques, inhibant ainsi leur migration au système nerveux central (SNC). Dans la moelle épinière, tissu cible de l EAE, les CpG-proBs se différencient en cellules B220+CD5+CD1dhiCD11b+, secrétant la cytokine anti-inflammatoire IL-10. Enfin, la mobilisation des progéniteurs hématopoïétiques par un cocktail de facteurs hématopoïétiques confère à une sous-population multipotente au stade MPP2 la propriété d augmenter l expansion des Foxp3+ Tregs et de prévenir la survenue du diabète de type 1. Nous montrons que les MPP2 mobilisés s avèrent également capables d exercer un effet protecteur envers l EAE. Leur capacité à induire l expansion de Treg Foxp3+ au sein du SNC et à la périphérie joue un rôle essentiel dans la protection des souris envers l EAE, puisque la déplétion des Treg abolit la protection déjà établie. Pour conclure, nous avons mis en évidence que diverses stimulations de l hématopoïèse induisent l émergence de nouvelles populations de progéniteurs hématopoïétiques qui présentent des propriétés immunorégulatrices et constituent de nouveaux outils de thérapie cellulaire des maladies auto-immunes.It is well known today that various infectious events or other stimuli of the immune system can trigger hematopoiesis. The hematopoeitic stem and/or progenitor cells express on their cell surface Toll-like receptors which can recognize molecular motifs of infectious agents. The stimulation of TLRs on hematopoietic stem cells favors their differentiation into myeloid lineages, reinforcing the capacity of our body to fight against the pathogens. Herein, we have investigated whether the stimulation of TLRs can induce, instead, the emergence within the bone marrow of selective progenitor cells with immunoregulatory properties. We show that incubation of bone marrow cells with the TLR-9 ligand CpG-B can induce a pro-B cell population (named CpG-proBs) whose adoptive transfer at low numbers of 60,000 cells provided long-lasting protection in two models of autoimmune diseases, Type I Diabetes (TID) and Experimental Autoimmune Encephalomyelitis (EAE) at the onset of clinical signs. The migration, differentiation and molecular mechanism of action of this protective population is described and compared between these two models. In both models, the CpG-proBs migrate to the target tissue of autoimmune responses and differentiate into more mature regulatory B cells. In TID, IFN-g produced by both T and CpG-proB cells is essential for the upregulation of FasL at the surface of CpG-proBs, inducing the apoptosis of the effector T cells. In addition, IFN-g reduced the T-cell production of IL-21, a major pathogenic cytokine in TID. The progeny of the adoptively transferred CpG-proBs, including transitional precursors B cells, marginal zone and follicular B cells, display high expression of FasL, promote apoptosis of effector T cells and prolong the control of autoimmune effector T cells in vivo. In EAE, IFN-g was responsible for the restriction of T cells to the lymph nodes, inhibiting their homing to the CNS. IFN-g indirectly induced the internalization of CCR7, a receptor required for the migration across the blood-brain barrier. In the spinal cord (target tissue in EAE), CpG-proBs differentiated into B220+CD5+CD1dhiCD11b+ cells secreting the anti-inflammatory cytokine IL-10. Finally, hematopoietic progenitor populations mobilized to the periphery by a cocktail of G-CSF and Flt3l, at the stage of MPP2, have already been shown to protect against TID by expanding the Foxp3+ Tregs. We evaluated them in the EAE model, showing that the ability of these mobilized progenitor cells to trigger the expansion of Foxp3+ Treg within the CNS and the periphery was necessary for providing protection to EAE mice since Treg depletion abrogated the protection once established. In conclusion, we provide evidence for the emergence of new populations of hematopoietic progenitor cells which can display immunoregulatory properties and might be used for cell therapy of autoimmune diseases.PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF

Facteurs de croissance et progéniteurs hématopoïetiques autologues (de nouveaux outils pour la restauration de la tolérance au soi dans le diabète auto-immun)

La rupture de la tolérance au soi s'accompagne d'un déséquilibre fonctionnel entre cellules T régulatrices et pathogènes. Les stratégies thérapeutiques visent soit à limiter la progression des cellules T effectrices soit à expandre les Treg. Nous avons fait l'hypothèse que la stimulation de l'hematopoïèse favoriserait l'émergence de Treg. Un traitement par le G-CSF prévient en effet la survenue du diabète de type 1 chez la souris NOD par l'émergence de cellules dendritiques tolérogènes semi-matures qui recrutent des Treg. En outre, associé au Flt-3ligand, le G-CSF engendre le développement de progéniteurs hématopoïetiques tolérogènes dont l'expression de Jagged-2 favorise l'expansion directe des Treg en augmentant leur expression membranaire du récepteur Notch3. L'émergence de cellules T régulatrices par la greffe de cellules souches hématopoïétiques mobilisées autologue pourrait jouer un rôle crucial dans les rémissions observées dans les maladies auto-immunes.Expansion of regulatory T cells in vivo is a promising strategy to cure auto-immune diseases. Here we demonstrate that stimulation of hematopoiesis either by the growth factor G-CSF or by transplantation of mobilised hematopoietic progenitors (HPC), but not of medullary hematopoietic stem cells, increases CD4+CD25+Foxp3+ regulatory T cell (Treg) numbers in peripancreatic lymph nodes and provides protection against type 1 diabetes in the NOD mouse. Protection is based on the following mechanisms : G-CSF promotes the differentiation of semi-mature plasmacytoid dendritic cells which in turn recruit Treg whereas HPC directly expand Treg. The HPC-Treg interaction requires cell contact and activates the Notch signalling pathway via Jagged2, selectively expressed on HPC, which increases Notch3 expression on Treg. This selective expression of jagged2 on mobilised progenitors needs to be confirmed in human and could represent a novel way to distinguish immunogenic from tolerogenic progenitors.PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

CpG-Activated Regulatory B-Cell Progenitors Alleviate Murine Graft-Versus-Host-Disease

International audienceDevelopment of Graft Versus Host Disease (GVHD) represents a major impediment in allogeneic hematopoietic stem cell transplantation (HSCT). The observation that the presence of bone marrow and circulating hematogones correlated with reduced GVHD risks prompted us to evaluate whether B-cell progenitors, which provide protection in various autoimmune disease models following activation with the TLR-9 agonist CpG (CpG-proBs), could likewise reduce this allogeneic disorder. In a murine model of GVHD that recapitulates an initial phase of acute GVHD followed by a phase of chronic sclerodermatous GVHD, we found that CpG-proBs, adoptively transferred during the initial phase of disease, reduced the diarrhea score and mostly prevented cutaneous fibrosis. Progenitors migrated to the draining lymph nodes and to the skin where they mainly differentiated into follicular B cells. CpG activation and IFN-γ expression were required for the protective effect, which resulted in reduced CD4 + T-cell-derived production of critical cytokines such as TGF-β, IL-13 and IL-21. Adoptive transfer of CpG-proBs increased the T follicular regulatory to T follicular helper (Tfr/Tfh) ratio. Moreover, CpG-proBs privileged the accumulation of IL-10-positive CD8 + T cells, B cells and dendritic cells in the skin. However, CpG-proBs did not improve survival. Altogether, our findings support the notion that adoptively transferred CpG-proBs exert immunomodulating effect that alleviates symptoms of GVHD but require additional anti-inflammatory strategy to improve survival

Fas receptor signaling is requisite for B cell differentiation

International audienceThe Fas/Fas ligand (FasL) pathway has been largely implicated in the homeostasis of mature cells. However, it is still unclear whether it plays a role at the progenitor level. To address this issue, we created chimeric mice by transferring C57BL/6 bone marrow (BM) cells of the lpr (Fas−FasL+) or gld (Fas+FasL−) genotype into Rag‐2−/− hosts of the same genetic background. In this model, the consequences of a deficient Fas/FasL pathway on lymphoid differentiation could be evaluated without endogenous competition. Analysis of the chimerism revealed a differential sensitivity of hematopoietic lineages to the lack of Fas receptor signaling. While donor‐derived myelo‐monocytic cells were similarly distributed in all chimeric mice, mature B cells were deleted in the BM and the spleen of lpr chimera, leading to the absence of the marginal zone (MZ) as detected by immunohistology. In contrast, B cell hematopoiesis was complete in gld chimera but MZ macrophages undetectable. These defects suggest a direct and determinant dual role of FasL regulation in negative selection of B cells and in maintenance of the MZ

Effects of peripheral administration of LPS on the expression of immunoreactive interleukin-1α, β, and receptor antagonist in rat brain

The cytokine interleukin-1 (IL-1) appears to play a pivotal role in the orchestration of brain-mediated, nonspecific illness symptoms during an infection. In the present study, we examine the possibility that IL-1 is produced in the central nervous system itself, which may be responsible for the induction of brain-mediated responses. Using immunocytochemical techniques, we demonstrated that peripheral administration of bacterial endotoxin to rats caused a time- (1.5-24 hr) and dose-dependent (4 μg/kg-2.5 mg/kg) induction of IL 1β immunoreactivity in cells identified as macrophages in meninges and choroid plexus and microglial cells in various brain regions. At 8 hr after endotoxin (2.5 mg/kg), immunoreactive IL-1α was observed in the same areas and cell types as IL-1β. Although no quantitative measurements have been performed, it appears that fewer cells express immunoreactive IL-1α than IL-1β. Furthermore, IL 1ra was found to be constitutively expressed in neurons in the paraventricular nucleus and supraopic nucleus, which is in accordance with mRNA data. After administration of endotoxin, we observed no additional cells that expressed immunoreactive IL-1ra. We conclude that IL-1α and IL-1β production in the brain is induced in the same cell types, whereas IL-1ra is expressed consititutively by a different cell type - probably neurons