Résultat de la recherche
Estimated Lyme borreliosis incidence in the canton of Neuchâtel (Switzerland)
Ir-LBP, an Ixodes ricinus Tick Salivary LTB4-Binding Lipocalin, Interferes with Host Neutrophil Function
Background : During their blood meal, ticks secrete a wide variety of proteins that can interfere with their host's defense mechanisms. Among these proteins, lipocalins play a major role in the modulation of the inflammatory response.
Methodology/Principal Findings : We previously identified 14 new lipocalin genes in the tick Ixodes ricinus. One of them codes for a protein that specifically binds leukotriene B4 with a very high affinity (Kd: ±1 nM), similar to that of the neutrophil transmembrane receptor BLT1. By in silico approaches, we modeled the 3D structure of the protein and the binding of LTB4 into the ligand pocket. This protein, called Ir-LBP, inhibits neutrophil chemotaxis in vitro and delays LTB4-induced apoptosis. Ir-LBP also inhibits the host inflammatory response in vivo by decreasing the number and activation of neutrophils located at the tick bite site. Thus, Ir-LBP participates in the tick's ability to interfere with proper neutrophil function in inflammation.
Conclusions/Significance : These elements suggest that Ir-LBP is a “scavenger” of LTB4, which, in combination with other factors, such as histamine-binding proteins or proteins inhibiting the classical or alternative complement pathways, permits the tick to properly manage its blood meal. Moreover, with regard to its properties, Ir-LBP could possibly be used as a therapeutic tool for illnesses associated with an increased LTB4 production.
Discrete adrenergic influence on the skin response to pathogen-associated molecular pattern (PAMPs)
La neuroimmunologie est la science qui étudie les interactions entre le système nerveux central et le système immunitaire. Différentes études morphologiques ont démontré que le système nerveux sympathique innerve tous les organes lymphoïdes primaires et secondaires et que la plus grande partie des cellules immunitaires expriment à leur surface les récepteurs adrénergiques nécessaires à la transduction du signal de ce système. Dans ce travail, nous avons montré in vivo que le blocage des récepteurs β−adrénergiques influence la réponse immunitaire innée de la peau au peptidoglycanne (PGN), mais pas au lipopolysaccharide (LPS), en induisant l’expression génique des cytokines IL-23, IL-12 et IFN-γ. Le blocage de ces récepteurs influence aussi la réponse immunitaire adaptative qui est polarisée vers une réponse de type Th1. Celle-ci a été évaluée par la mesure de la réponse d’hypersensibilité retardée(DTH) et par la production de cytokines dans le ganglion drainant. Cette réponse est aussi caractérisée par une augmentation de la migration de cellules dendritiques plasmacytoides au ganglion drainant le site d’injection. La migration de ces cellules est aussi augmentée par l’utilisation de PGN en combinaison avec de l’extrait de glandes salivaires (EGS) des tiques Ixodes ricinus. Cette observation suggère que l’EGS contient des agonistes aux PRRs (pour Pattern Recognition Receptors) ou des chémokines qui pourraient agire en synérgie avec le PGN. Nous avons aussi démontré que le blocage simultané des récepteurs β1 et β2 adrénergiques est nécessaire pour influencer la réponse immunitaire in vivo. L’influence de l’activation des récepteurs β−adrénergiques par la norépinephrine (NE) sur la production des cytokines induites a aussi été analysée in vitro par l’activation de différents PRRs chez les cellules dendritiques (CDs). Nos résultats ont montré que, en accord avec les résultats obtenus in vivo, la NE possède des propriétés anti-inflammatoires et inhibe la production des cytokines IL-12, IL-23 et IL-6 chez les CDs incubées avec le PGN. La production de la cytokine anti-inflammatoire IL-10 est quant-à-elle induite. En outre, l’utilisation d’autres agonistes spécifiques pour les récepteurs TLR-2 et NOD2 ont montré que l’augmentation de la production d’IL-10 induite par la NE chez les CDs incubée avec du PGN est due à la modulation de la signalisation du récepteur TLR-2 mais pas à celle de NOD2. Cette production augmentée d’IL-10 a aussi un effet inhibiteur sur la production des cytokines caractéristiques des Th17, à savoir IL-6 et IL-23. Nous avons aussi démontré que la NE peut induire in vitro via les récepteurs β2-adrénergiques la production d’IL-6 chez le CDs dont le récepteur NOD2 est activé. Ce résultat est important pour la compréhension des mécanismes régulant la production de cette cytokine et de la pathogenèse de maladies où une augmentation de la concentration d’IL-6 est observée. Des résultats préliminaires ont aussi montré que l’injection chez les souris de CDs préalablement incubées avec les agonistes spécifiques des récepteurs β2-adrénergiques, TLR-2 et NOD2 en présence d’une protéine soluble, favorise le développement d’une réponse de type Th17 au détriment de celle de type Th1. Ceci a été évalué par l’analyse de la production des cytokines IL-17 et IFN-γ. Ces résultats aident à la compréhension du développement de la réponse Th17 et des maladies auto-immunitaires et des cancers qui en dépendent.
Does access to the bluestreak cleaner wrasse Labroides dimidiatus affect indicators of stress and health in resident reef fishes in the Red Sea?
A family of putative metalloproteases in the salivary glands of the tick Ixodes ricinus
Ticks are obligate blood-feeding arachnids. During their long-lasting blood meal, they have to counteract the protective barriers and defense mechanisms of their host. These include tissue integrity, pain, hemostasis, and the inflammatory and immune reactions. Here, we describe a multigene family coding for five putative salivary metalloproteases induced during the blood meal of Ixodes ricinus. The evolutionary divergence inside the family was driven by positive Darwinian selection. This came together with individual variation of expression, functional heterogeneity, and antigenic diversification. Inhibition of the expression of some of these genes by RNA interference prevented completion of the tick blood meal and affected the ability of the tick saliva to interfere with host fibrinolysis. This family of proteins could therefore participate in the inhibition of wound healing after the tick bite, thereby facilitating the completion of the blood meal.
Ixodes ricinus Tick Lipocalins: Identification, Cloning, Phylogenetic Analysis and Biochemical Characterization
Background : During their blood meal, ticks secrete a wide variety of proteins that interfere with their host's defense mechanisms. Among these proteins, lipocalins play a major role in the modulation of the inflammatory response.
Methodology/Principal Findings : Screening a cDNA library in association with RT-PCR and RACE methodologies allowed us to identify 14 new lipocalin genes in the salivary glands of the Ixodes ricinus hard tick. A computational in-depth structural analysis confirmed that LIRs belong to the lipocalin family. These proteins were called LIR for “Lipocalin from I. ricinus” and numbered from 1 to 14 (LIR1 to LIR14). According to their percentage identity/similarity, LIR proteins may be assigned to 6 distinct phylogenetic groups. The mature proteins have calculated pM and pI varying from 21.8 kDa to 37.2 kDa and from 4.45 to 9.57 respectively. In a western blot analysis, all recombinant LIRs appeared as a series of thin bands at 50–70 kDa, suggesting extensive glycosylation, which was experimentally confirmed by treatment with N-glycosidase F. In addition, the in vivo expression analysis of LIRs in I. ricinus, examined by RT-PCR, showed homogeneous expression profiles for certain phylogenetic groups and relatively heterogeneous profiles for other groups. Finally, we demonstrated that LIR6 codes for a protein that specifically binds leukotriene B4.
Conclusions/Significance : This work confirms that, regarding their biochemical properties, expression profile, and sequence signature, lipocalins in Ixodes hard tick genus, and more specifically in the Ixodes ricinus species, are segregated into distinct phylogenetic groups suggesting potential distinct function. This was particularly demonstrated by the ability of LIR6 to scavenge leukotriene B4. The other LIRs did not bind any of the ligands tested, such as 5-hydroxytryptamine, ADP, norepinephrine, platelet activating factor, prostaglandins D2 and E2, and finally leukotrienes B4 and C4.
Variability and Action Mechanism of a Family of Anticomplement Proteins in Ixodes ricinus
Background : Ticks are blood feeding arachnids that characteristically take a long blood meal. They must therefore counteract host defence mechanisms such as hemostasis, inflammation and the immune response. This is achieved by expressing batteries of salivary proteins coded by multigene families.
Methodology/Principal Findings : We report the in-depth analysis of a tick multigene family and describe five new anticomplement proteins in Ixodes ricinus. Compared to previously described Ixodes anticomplement proteins, these segregated into a new phylogenetic group or subfamily. These proteins have a novel action mechanism as they specifically bind to properdin, leading to the inhibition of C3 convertase and the alternative complement pathway. An excess of non-synonymous over synonymous changes indicated that coding sequences had undergone diversifying selection. Diversification was not associated with structural, biochemical or functional diversity, adaptation to host species or stage specificity but rather to differences in antigenicity.
Conclusions/Significance : Anticomplement proteins from I. ricinus are the first inhibitors that specifically target a positive regulator of complement, properdin. They may provide new tools for the investigation of role of properdin in physiological and pathophysiological mechanisms. They may also be useful in disorders affecting the alternative complement pathway. Looking for and detecting the different selection pressures involved will help in understanding the evolution of multigene families and hematophagy in arthropods.
The impact of gene knock-down and vaccination against salivary metalloproteases on blood feeding and egg laying by Ixodes ricinus
Two cDNAs coding homologous putative metalloproteases (Metis 1 and Metis 2, expected molecular weights of 55.6 and 56.0 kDa, respectively) were identified from the hard tick Ixodes ricinus. The expression of Metis genes was induced in salivary glands during tick blood meal. RNA interference was used to assess the role of both Metis 1 and Metis 2 in tick feeding. It was found that salivary gland extracts lacking Metis 1–2 had a restricted ability to interfere with fibrinolysis. RNAi against Metis 1–2 also induced a high mortality rate. An immune reaction was raised in repeatedly bitten animals against Metis 1 and 2. Vaccination of hosts with the recombinant Metis 1 protein produced in a eukaryotic system partially interfered with completion of the blood meal. Although vaccination did not alter the survival rate or feeding time of ticks, their weight gain and oviposition rate were reduced. This will affect their reproductive fitness in the field. We believe this is the first report of an anti-tick vaccine trial using a metalloprotease derived from I. ricinus.