Jean Kanellopoulos

P2 receptors and immunity.

Immune cells express receptors for extracellular nucleotides named P2 receptors. P2 receptors transduce signals delivered by nucleotides present in the extracellular environment. Accruing evidence shows that purinergic signalling has a profound effect on multiple immune cell responses such as T lymphocyte proliferation, chemotaxis, cytokine release, phagocytosis, Ag presentation and cytotoxicity. This makes P2 receptors an attractive target for the therapy of immuno-mediated disease and cancer.

Is the inflammasome relevant for epithelial cell function

Inflammasomes are intracellular protein complexes that sense microbial components and damage of infected cells. Following activation by molecules released by pathogens or injured cells, inflammasomes activate caspase-1, allowing secretion of the pro-inflammatory cytokines IL-1β and IL-18 from innate immune cells. Inflammasomes are also expressed in epithelial cells, where their function has attracted less attention. Nonetheless, depending on the tissue, epithelial inflammasomes can mediate inflammation, wound healing, and pain sensitivity. We review here recent findings on inflammasomes found in epithelial tissues, highlighting the importance of these protein complexes in the response of epithelial tissues to microbial infections.

Natural killer T cells.

This issue of Biomedical Journal includes two review articles on natural killer T cells. The first review article has been written by Drs. Birkholz and M. Kronenberg: « Antigen Specificity of Invariant Natural Killer T Cells » [1]. The second review is from Dr Agn es Lehuen and her colleagues on « Regulatory Role of Natural Killer T Cells in Diabetes » [2]. Dr Kronenbergs review principally describes the ligands of natural killer T-cells (iNKT) bearing a T cell receptor (TCR) comprising an invariant TCR alpha-chain associated with a limited number of V-beta chains. It analyzes in depth the lipid antigens which are presented by the weakly polymorphic CD1d molecule, structurally similar to MHC class I molecules. The mode of interactions of alpha-galactosylceramide (alphaGalCer) with CD1d and the invariant TCR are described. Several head group modifications of the alphaGalCer sugarmoiety have been shown to alter TCR binding and iNKT responses. Indeed, some synthetic compounds related to alphaGalCer were inactive while others were shown to preferentially trigger Th1 or Th2 iNKT responses. Modifications of lipid chains of CD1d agonists lead to the synthesis of new antigens with Th2 or Th1 profiles. Stronger interactions of these modified agonists with CD1d and/or prolonged presentation of them by dendritic cells triggered higher IFN-gamma production in vivo. This resulted in a stronger adjuvant effect when compared to regular alphaGalCer. Other parts of this review are devoted to the structural analyses of endogenous ligands and foreign antigens from bacteria, fungi and parasites. Isoglobotrihexosylceramide, the first self-ligand to be identified, is shown complexed to mouse CD1d and mouse iNKT TCR in a crystal structure. Numerous microbial antigens recognized by iNKTTCRs are glycolipids capable of stimulating protective immune responses against pathogens. This very interesting review clearly shows that deciphering the biochemical rules of interactions in the various tri-molecular CD1d-antigen-INKT TCR complexes, is likely to lead to the synthesis of agonists with therapeutic values.

A New Marker on Chicken Hematopoietic Cells isDefined by a Monoclonal Antibody Raised Against a V ßChain of the Human TCR

In this paper, we show that a mouse monoclonal antibody, 111-427, specific for the V ß 5.3 chain of the human T-cell receptor (TCR) for antigen, also reacts with chicken hematopoietic cells. Our data indicate that the majority of 111-427 positive cells among peripheral blood leucocytes (PBL) are thrombocytes. This antibody also recognizes two in vitro cell lines, III-C5, an IL-2-dependent T-cell-line and HD11, a macrophage cell line. In addition, erythrocytes and a minor subpopulation of thymus and spleen cells are also stained by the monoclonal antibody (mAb). No specific immunoprecipitation could be detected from 125I radiolabeled cell lysates. By Western blotting techniques, the 111- 427 mAb identifies a single band of apparent molecular weight 91 kD, unaffected by reduction, from III-C5 and HD11 cell lysates. This band is absent in negative cell control lysates. On thrombocytes, the apparent molecular weight of the band is shifted to 87 kD. These results indicate that the mAb does not recognize the chicken T-cell receptor for antigen, but a cell surface marker shared primarily between thrombocytes and erythrocytes. This new chicken cell marker is compared to other cell surface markers in avian or mammalian species that present some analogies in their tissue distribution.

New role of P2X7 receptor in an Alzheimer’s disease mouse model

Extracellular aggregates of amyloid β (Aβ) peptides, which are characteristic of Alzheimer’s disease (AD), act as an essential trigger for glial cell activation and the release of ATP, leading to the stimulation of purinergic receptors, especially the P2X7 receptor (P2X7R). However, the involvement of P2X7R in the development of AD is still ill-defined regarding the dual properties of this receptor. Particularly, P2X7R activates the NLRP3 inflammasome leading to the release of the pro-inflammatory cytokine, IL-1β; however, P2X7R also induces cleavage of the amyloid precursor protein generating Aβ peptides or the neuroprotective fragment sAPPα. We thus explored in detail the functions of P2X7R in AD transgenic mice. Here, we show that P2X7R deficiency reduced Aβ lesions, rescued cognitive deficits and improved synaptic plasticity in AD mice. However, the lack of P2X7R did not significantly affect the release of IL-1β or the levels of non-amyloidogenic fragment, sAPPα, in AD mice. Instead, our results show that P2X7R plays a critical role in Aβ peptide-mediated release of chemokines, particularly CCL3, which is associated with pathogenic CD8+ T cell recruitment. In conclusion, our study highlights a novel detrimental function of P2X7R in chemokine release and supports the notion that P2X7R may be a promising therapeutic target for AD.

Variations in Cellular Responses of Mouse T Cells to Adenosine-5′-Triphosphate Stimulation Do Not Depend on P2X7 Receptor Expression Levels but on Their Activation and Differentiation Stage

A previous report has shown that regulatory T cells (Treg) were markedly more sensitive to adenosine-5′-triphosphate (ATP) than conventional T cells (Tconv). Another one has shown that Tregs and CD45RBlow Tconvs, but not CD45RBhigh Tconvs, displayed similar high sensitivity to ATP. We have previously reported that CD45RBlow Tconvs expressing B220/CD45RABC molecules in a pre-apoptotic stage are resistant to ATP stimulation due to the loss of P2X7 receptor (P2X7R) membrane expression. To gain a clearer picture on T-cell sensitivity to ATP, we have quantified four different cellular activities triggered by ATP in mouse T cells at different stages of activation/differentiation, in correlation with levels of P2X7R membrane expression. P2X7R expression significantly increases on Tconvs during differentiation from naive CD45RBhighCD44low to effector/memory CD45RBlowCD44high stage. Maximum levels of upregulation are reached on recently activated CD69+ naive and memory Tconvs. Ectonucleotidases CD39 and CD73 expression levels increase in parallel with those of P2X7R. Recently activated CD69+ CD45RBhighCD44low Tconvs, although expressing high levels of P2X7R, fail to cleave homing receptor CD62L after ATP treatment, but efficiently form pores and externalize phosphatidylserine (PS). In contrast, naive CD45RBhighCD44low Tconvs cleave CD62L with high efficiency although they express a lower level of P2X7, thus suggesting that P2X7R levels are not a limiting factor for signaling ATP-induced cellular responses. Contrary to common assumption, P2X7R-mediated cellular activities in mouse Tconvs are not triggered in an all-or-none manner, but depend on their stage of activation/differentiation. Compared to CD45RBlow Tconvs, CD45RBlowFoxp3+ Tregs show significantly higher levels of P2X7R membrane expression and of sensitivity to ATP as evidenced by their high levels of CD62L shedding, pore formation and PS externalization observed after ATP treatment. In summary, the different abilities of ATP-treated Tconvs to form pore or cleave CD62L depending on their activation and differentiation state suggests that P2X7R signaling varies according to the physiological role of T convs during antigen activation in secondary lymphoid organs or trafficking to inflammatory sites.

Experimental autoimmune encephalomyelitis

This issue of Biomedical Journal includes three review articles on experimental autoimmune encephalomyelitis (EAE), an animal model of mul‐ tiple sclerosis (MS). EAE shares several pathological aspects with MS: Inflammation, demyelination, and neuronal death, even though EAE is not the same disease. In addition, EAE proved to be an excellent model to characterize pathogenic T lymphocytes and to test drugs with therapeutic potential in MS. The first review article is written by Dr. Florian C. Kurschus on “T cell‐mediated pathogenesis in EAE: Molecular mechanisms”. The second review is from Dr. Jean–Charles Guery and colleagues on “Es‐ trogen‐mediated protection of EAE: Lessons from the dissection of estrogen receptor (ER)‐signaling in vivo”. The third one is by Dr. Stephen Anderton: “Peptide immunotherapy (PIT) in EAE”. Dr. Kurschus’s review article describes the dif‐ ferent populations of CD4 + T lymphocytes capable of triggering and maintaining EAE. The complex role of Th17 lymphocytes is discussed and the major role of IL‐23 and granulocyte‐macrophage colo‐ ny‐stimulating factor (GM‐CSF) is presented, even though the exact mechanism of action of GM‐CSF is still unknown. Finally, several models of EAE in‐ duced by CD8 + T cells are analyzed and discussed. Overall, this very interesting article reviews the different encephalitogenic T lymphocytes and the effector mechanisms leading to demyelination and inflammation in the central nervous system (CNS). The second article, by Dr. Guery and col‐ leagues, presents and analyzes the studies show‐ ing that estrogens are the hormones mediating the protective effect of pregnancy on MS. Furthermore, the authors analyze the experimental evidence demonstrating the anti‐inflammatory effects of estrogens on EAE. The potential cellular targets of Experimental Autoimmune Encephalomyelitis

Studying host-microbiota interactions in Drosophila melanogaster.

In this issue of Biomedical Journal, two reviews show the power of Drosophila melanogaster as an animal model to study the complex relationships between host and gut microbiota. The first review has been written by Dr. Jean‐Marc Reihhart and colleagues on “The multilayered innate immune de‐ fense of the gut.” The second one was contributed by Dr. François Leulier and his collaborators on “Study‐ ing host‐microbiota mutualism in Drosophila: Har‐ nessing the power of gnotobiotic flies.” The first review article by El‐Chamy et al. describes and analyzes the Drosophila gut anatomy and the induction of antimicrobial peptides (AMP), as well as the production of reactive oxygen spe‐ cies (ROS). The organization of the physical barrier in Drosophila gut is made of a single epi‐ thelial cell layer sealed tightly and protected by a peritrophic matrix (PM) which allows the transfer of digestive enzymes and nutrients but blocks bac‐ teria. The role of PM in the struggle against bacteria is established clearly because mutations affecting some components of the PM increase the sensitivity of flies to infections. In addition, various mutants increasing the permeability of the epithelial barrier become highly sensitive to infections by pathogenic bacteria. In the second part of this review, the au‐ thors describe the biochemical pathways involved in AMP production and the regulation of ROS production in the Drosophila gut lumen. The second review by Ma et al. presents the early scientific works leading to the production Studying Host‐microbiota Interactions in Drosophila Melanogaster

Mammalian gut microbiota and immunity

This issue of Biomedical Journal includes two review articles on gut microbiota and the immune system. The enormous and recent interest in this scientific topic is attested by a large surge in publications. The first review article is written by Professor Vijay-Kumar and his colleagues and is entitled “Mammalian gut immunity”. [1] The second review article is written by Professor Lai and his colleagues with the title “Impact of the gut microbiota, prebiotics, and probiotics on human health and disease”. [2] Professor Vijay-Kumar’s review article describes the tremendous complexity of the mucosal immune system, which has the ability to eliminate pathogens while tolerating the commensal bacteria needed for the production of nutrients, among other functions. The authors describe the role of the intestinal epithelium as a physical and chemical barrier. The epithelium also consists of cells capable of secreting numerous cytokines and chemokines that modulate the chemotaxis of various hematopoietic cells. The role of intestinal macrophages, dendritic cells, T lymphocytes, and innate lymphoid cells is also analyzed. The impact of microbiota and bacterial metabolites on the development of the host mucosal immune system is described. The second article, by Professor Lai, summarizes recent studies on gut microbiota and their potential role in several human diseases such as obesity and liver disease, and lung immunity. The role of microbiota on nutrient metabolism and fermentation products is analyzed, and the production of beneficial or harmful compounds by intestinal bacteria is critical for maintaining host homeostasis. Interestingly, in the section on prebiotics, the authors summarize their unpublished results on prebiotics found in fungi that are used in traditional Chinese medicine. As gut microbiota are featured prominently in both articles, it is tempting to speculate that after diverging for many centuries, Eastern and Western science may be converging again through the unexpected role played by gut microbes in immunity, health, and disease.

Hfe : une molécule à l’interface entre immunité et métabolisme du fer ?

24 mentaires entre EAT-2 ou ERT et d’autres récepteurs activateurs car, tout comme SAP, EAT-2 et ERT sont associées uniquement à 2B4 dans les cellules NK murines. La fonction inhibitrice d’EAT-2 et ERT est causée par la phosphorylation de deux tyrosines carboxy-terminales qui sont présentes dans ces molécules, mais pas dans SAP (Figure 2). Nous postulons que la phosphorylation de ces tyrosines permet le recrutement d’effecteurs intracellulaires capables d’inhiber la fonction des récepteurs NK activateurs. L’identité de ces effecteurs demeure pour l’instant inconnue. La présence d’EAT-2 dans les cellules dendritiques et les macrophages suggère que cette molécule pourrait avoir un rôle analogue dans ces cellules. Nos résultats démontrent l’importance de la famille SAP dans la réponse immunitaire normale. Bien qu’ERT n’existe pas chez l’humain, nous avons confirmé la fonction inhibitrice d’EAT-2 dans les cellules NK humaines [9]. Cette conservation de fonction suggère que des inhibiteurs chimiques pourraient être utilisés pour réprimer l’activité d’EAT-2 chez les patients atteints de cancers ou d’infections virales systémiques, permettant ainsi d’augmenter l’activité cytotoxique de leurs cellules NK. En combinaison avec des traitements anticancéreux ou antiviraux conventionnels, des inhibiteurs d’EAT-2 pourraient aider à endiguer les effets de ces maladies souvent dévastatrices. De tels inhibiteurs pourraient agir en bloquant l’interaction du domaine SH2 d’EAT-2 avec 2B4 ou l’association des tyrosines d’EAT-2 avec ses effecteurs intracellulaires. Nous proposons aussi que des altérations dans l’expression d’EAT-2 pourraient accroître la susceptibilité à des maladies comme le cancer, les infections virales ou les maladies autoimmunes. ◊ EAT-2 : a novel regulator of natural killer cell functions RÉFÉRENCES