Christelle Faveeuw

Peroxisome proliferator-activated receptor γ activators inhibit interleukin-12 production in murine dendritic cells

Peroxisome proliferator‐activated receptors (PPARs) are members of the nuclear receptor superfamily. They are divided into three subtypes (α, β or δ, and γ) and are involved in lipid and glucose homeostasis and in the control of inflammation. In this study, we analyzed the expression of PPARs in murine dendritic cells (DCs), the most potent antigen presenting cells. We find that immature as well as mature spleen‐derived DCs express PPARγ, but not PPARα, mRNA and protein. We also show that the PPARγ activator rosiglitazone does not interfere with the maturation of DCs in vitro nor modifies their ability to activate naive T lymphocytes in vivo. Finally, we present evidence that PPARγ activators down‐modulate the CD40‐induced secretion of interleukin‐12, a potent Th1‐driving factor. These data suggest a possible role for PPARγ in the regulation of immune responses.

Prostaglandin D2 Affects the Maturation of Human Monocyte-Derived Dendritic Cells: Consequence on the Polarization of Naive Th Cells

Among the factors produced at inflammatory sites and those capable of modulating dendritic cell (DC) functions, PGD2 may be important in the outcome of immune responses. The biological roles for PGD2 are in part effected through two plasma membrane G protein-coupled receptors: the D prostanoid (DP) receptor and the chemoattractant receptor-homologous molecule expressed on Th2 lymphocytes (CRTH2). In this report, we studied the effects of PGD2 and of its major physiological metabolite, 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2), on the functions of human monocyte-derived DC. First, we show that PGD2 exerts in vitro chemotactic effects on monocytes via CRTH2 activation while it inhibits the chemokine-driven migration of monocyte-derived DC through DP. We also report that PGD2 and 15d-PGJ2 alter the LPS- and allergen-induced DC maturation and enhance the CD80/CD86 ratio on mature DC in a DP- and CRTH2-independent manner. Moreover, PGD2 and 15d-PGJ2 strongly reduce the secretion of the Th1 promoting cytokine IL-12 and affect the synthesis of chemokines involved in Th1 cell chemotaxis, particularly CXCL10. Inhibition of cytokine/chemokine secretion implicates at least in part DP, but not CRTH2. The effects exerted by PGD2 are associated with the phosphorylation of CREB, but do not parallel with the deactivation of the NF-κB and mitogen-activated protein kinase pathways. In contrast, 15d-PGJ2 seems to target other cellular proteins. Finally, in a model of Th CD45RA+ differentiation induced by allergen- and superantigen-pulsed DC, PGD2 impacts on the orientation of the immune response by favoring a Th2 response.

Interleukin-22 Is Produced by Invariant Natural Killer T Lymphocytes during Influenza A Virus Infection POTENTIAL ROLE IN PROTECTION AGAINST LUNG EPITHELIAL DAMAGES

Background: Invariant natural killer T (iNKT) cells play a beneficial role during experimental influenza A virus (IAV) infection. Results: iNKT cells produce IL-22 during infection, and IL-22 prevents the IAV-triggered cell death of pulmonary epithelium. Conclusion: IL-22 produced by iNKT cells might be important during IAV infection. Significance: Understanding how iNKT cells function during IAV infection might be instrumental to control IAV-associated pathogenesis. Invariant natural killer T (iNKT) cells are non-conventional lipid-reactive αβ T lymphocytes that play a key role in host responses during viral infections, in particular through the swift production of cytokines. Their beneficial role during experimental influenza A virus (IAV) infection has recently been proposed, although the mechanisms involved remain elusive. Here we show that during in vivo IAV infection, mouse pulmonary iNKT cells produce IFN-γ and IL-22, a Th17-related cytokine critical in mucosal immunity. Although permissive to viral replication, IL-22 production by iNKT cells is not due to IAV infection per se of these cells but is indirectly mediated by IAV-infected dendritic cells (DCs). We show that activation of the viral RNA sensors TLR7 and RIG-I in DCs is important for triggering IL-22 secretion by iNKT cells, whereas the NOD-like receptors NOD2 and NLRP3 are dispensable. Invariant NKT cells respond to IL-1β and IL-23 provided by infected DCs independently of the CD1d molecule to release IL-22. In vitro, IL-22 protects IAV-infected airway epithelial cells against mortality but has no role on viral replication. Finally, during early IAV infection, IL-22 plays a positive role in the control of lung epithelial damages. Overall, IAV infection of DCs activates iNKT cells, providing a rapid source of IL-22 that might be beneficial to preserve the lung epithelium integrity.

Mouse syngenic in vitro blood-brain barrier model: a new tool to examine inflammatory events in cerebral endothelium

Although cerebral endothelium disturbance is commonly observed in central nervous system (CNS) inflammatory pathologies, neither the cause of this phenomenon nor the effective participation of blood–brain barrier (BBB) in such diseases are well established. Observations were mostly made in vivo using mouse models of chronic inflammation. This paper presents a new mouse in vitro model suitable for the study of underlying mechanistic events touching BBB functions during CNS inflammatory disturbances. This model consists of a coculture with both primary cell types isolated from mice. Mouse brain capillary endothelial cell (MBCEC)s coming from brain capillaries are in culture with their in vivo partners and form differentiated monolayers that retain endothelial markers and numerous phenotypic properties of in vivo cerebral endothelium, such as: (1) peripheral distribution of tight junction proteins (occludin, claudin-5, claudin-3 and JAM-1); (2) high trans-endothelium electrical resistance value; (3) attenuated paracellular flux of sucrose and inulin; (4) P-gp expression; (5) no MECA-32 expression. Furthermore, this endothelium expresses cell adhesion molecules described in vivo and shows intracellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 upregulation under lipopolysaccharide-treatment. Therefore, this well-differentiated model using autologous cells appears as a suitable support to reconstitute pathological in vitro BBB model.

Schistosome N‐glycans containing core α3‐fucose and core β2‐xylose epitopes are strong inducers of Th2 responses in mice

During murine schistosomiasis, egg‐derived glycoconjugates play a key role in skewing the immune response towards a Th2 phenotype. Among the candidates responsible for this effect, complex‐type N‐glycans containing the core α3‐fucose and core β2‐xylose determinants, two glycan epitopes found in some invertebrate‐ and plant‐derived allergens, may be important. Here, we show that core α3‐fucose and core β2‐xylose determinants are expressed in the different developmental stages of Schistosoma mansoni, particularly in the excretory‐secretory systems of schistosomula and adult worms and in eggs deposited in the liver. Glycosyltransferase assays confirmed the presence of core α3‐fucosyltransferase and core β2‐xylosyltransferase activities in egg extracts. Using a model of immunization with pulsed dendritic cells, we show that egg‐derived glycoproteins containing the core α3‐fucose and core β2‐xylose determinants generate a strong Th2‐biased cellular response in mice and that the glycan moieties of this extract are important in this effect. During murine infection, these complex‐type N‐glycans induce a glycan‐specific Th2 cellular response and elicit T‐dependent anti‐core α3‐fucose and anti‐core β2‐xylose IgG1 (a Th2‐associated isotype), but not IgG2b (a Th1‐associated isotype) Ab. Taken together, our results point out theimportance of core fucosylated/xylosylated N‐glycans in the Th2 immune response during murine schistosomiasis.

Antigen Presentation by CD1d Contributes to the Amplification of Th2 Responses to Schistosoma mansoni Glycoconjugates in Mice

During murine schistosomiasis, there is a gradual switch from a predominant Th1 cytokine response to a Th2-dominated response after egg laying, an event that favors the formation of granuloma around viable eggs. Egg-derived glycoconjugates, including glycolipids, may play a crucial role in this phenomenon. In this study, we used a model of dendritic cell sensitization to study the role of egg glycoconjugates in the induction of specific immune response to soluble egg Ag (SEA) and to investigate the possibility that CD1d, a molecule implicated in glycolipid presentation, may be involved in such a phenomenon. We show that, when captured, processed, and presented to naive T lymphocytes by dendritic cells, egg, but not larval, Ag skew the immune response toward a Th2 response. Periodate treatment reversed this effect, indicating that the sugar moiety of SEA is important in this phenomenon. Using DC treated ex vivo with a neutralizing anti-CD1d Ab or isolated from CD1d knockout mice, we show that CD1d is crucial in the priming of SEA-specific Th2 lymphocytes. We then evaluated the contribution of CD1d on the development of the SEA-specific immune response and on the formation of the egg-induced liver granuloma during murine schistosomiasis. We find that CD1d knockout mice have a reduced Th2 response after egg laying and develop a less marked fibrotic pathology compared with wild-type mice. Altogether, our results suggest that Ag presentation of parasite glycoconjugates to CD1d-restricted T cells may be important in the early events leading to the induction of Th2 responses and to egg-induced pathology during murine schistosomiasis.

Galectin-3 Modulates Immune and Inflammatory Responses during Helminthic Infection: Impact of Galectin-3 Deficiency on the Functions of Dendritic Cells

ABSTRACT Galectin-3 (Gal-3) is a multifunctional β-galactoside-binding lectin that senses self-derived and microbial glycoconjugates. Although Gal-3 is important in immune reactions and host defense in some experimental models, the function of Gal-3 during helminthic diseases (e.g., schistosomiasis) is still elusive. We show that, compared to wild-type Schistosoma mansoni-infected mice, infected Gal-3−/− mice have a reduced number of T and B lymphocytes in the spleen, develop reduced liver granulomas at 7 weeks (acute phase) and 14 weeks (chronic phase) postinfection, and mount a biased cellular and humoral Th1 response. In an attempt to understand this latter phenomenon, we studied the role of endogenous Gal-3 in dendritic cells (DCs), the most potent antigen-presenting cells, both in vitro and in vivo. Although Gal-3 deficiency in DCs does not impact their differentiation and maturation processes, it greatly influences the strength (but not the nature) of the adaptive immune response that they trigger, suggesting that Gal-3 deficiency in some other cell types may be important during murine schistosomiasis. As a whole, this study implies that Gal-3 is a modulator of the immune/inflammatory responses during helminthic infection and reveals for the first time that Gal-3 expression in DCs is pivotal to control the magnitude of T-lymphocyte priming.

Activation of Invariant NKT Cells by the Helminth Parasite Schistosoma mansoni

Mouse CD1d-restricted NKT cells, including invariant (i)NKT cells, are innate cells activated by glycolipid Ags and play important roles in the initiation and regulation of immune responses. Through their ability to promptly produce large amounts of Th1 and/or Th2 cytokines upon TCR engagement, iNKT cells exert crucial functions in the immune/inflammatory system during bacterial, protozoan, fungal, and viral infections. However, their roles during metazoan parasite infection, which are generally associated with strong Th2 responses, still remain elusive. In this study, we show that during the course of murine schistosomiasis, iNKT cells exhibit an activated phenotype and that following schistosome egg encounter in the liver, hepatic iNKT cells produce both IFN-γ and IL-4 in vivo. We also report that schistosome egg-sensitized dendritic cells (DCs) activate, in a CD1d-dependent manner, iNKT cells to secrete IFN-γ and IL-4 in vitro. Interestingly, transfer of egg-sensitized DCs promotes a strong Th2 response in recipient wild-type mice, but not in mice that lack iNKT cells. Engagement of TLRs in DCs is not necessary for iNKT cell stimulation in response to egg-sensitized DCs, suggesting an alternative pathway of activation. Finally, we propose that self, rather than parasite-derived, CD1d-restricted ligands are implicated in iNKT cell stimulation. Taken together, our data show for the first time that helminths can activate iNKT cells to produce immunoregulatory cytokines in vivo, enabling them to influence the adaptive immune response.

Interleukin-22 reduces lung inflammation during influenza A virus infection and protects against secondary bacterial infection

ABSTRACT Interleukin-22 (IL-22) has redundant, protective, or pathogenic functions during autoimmune, inflammatory, and infectious diseases. Here, we addressed the potential role of IL-22 in host defense and pathogenesis during lethal and sublethal respiratory H3N2 influenza A virus (IAV) infection. We show that IL-22, as well as factors associated with its production, are expressed in the lung tissue during the early phases of IAV infection. Our data indicate that retinoic acid receptor-related orphan receptor-γt (RORγt)-positive αβ and γδ T cells, as well as innate lymphoid cells, expressed enhanced Il22 transcripts as early as 2 days postinfection. During lethal or sublethal IAV infections, endogenous IL-22 played no role in the control of IAV replication and in the development of the IAV-specific CD8+ T cell response. During lethal infection, where wild-type (WT) mice succumbed to severe pneumonia, the lack of IL-22 did not accelerate or delay IAV-associated pathogenesis and animal death. In stark contrast, during sublethal IAV infection, IL-22-deficient animals had enhanced lung injuries and showed a lower airway epithelial integrity relative to WT littermates. Of importance, the protective effect of endogenous IL-22 in pulmonary damages was associated with a more controlled secondary bacterial infection. Indeed, after challenge with Streptococcus pneumoniae, IAV-experienced Il22 −/− animals were more susceptible than WT controls in terms of survival rate and bacterial burden in the lungs. Together, IL-22 plays no major role during lethal influenza but is beneficial during sublethal H3N2 IAV infection, where it limits lung inflammation and subsequent bacterial superinfections.

Pivotal roles of the parasite PGD2 synthase and of the host D prostanoid receptor 1 in schistosome immune evasion

Prostaglandins (PG) are important modulators of immune and inflammatory responses. We recently demonstrated that the production of PGD2 by the helminthic parasite Schistosoma mansoni inhibits the migration of epidermal Langerhans cells (LC) to the draining lymph nodes (DLN). Here, we identify the responsible parasite enzyme as being a 28‐kDa glutathione‐S‐transferase (termed Sm28GST). Intradermal injection of Sm28GST in wild‐type (WT), but not in D prostanoid receptor (DP) 1‐deficient mice abrogates the departure of LC from the epidermis after TNF‐α or FITC treatment. During infection, DP1 deficiency restores LC migration, but does not enhance the rate of T cell proliferation in the skin DLN. However, relative to WT mice, DLN cells from DP1‐deficient infected mice produce dramatically less IFN‐γ and IL‐10, but equal amount of IL‐4. Interestingly, infected DP1‐deficient mice develop a more Th2‐biased humoral immune response, a significantly reduced parasitemia and a decreased egg‐induced inflammatory response in the liver and intestines. Taken together, we propose that DP1 activation by the Sm28GST‐derived PGD2 could represent a strategy for the schistosome to evade host immune defenses. We also suggest that DP1 is important in the Th1/Th2 balance of the immune response and in inflammatory reactions during infection.