Ticks are blood feeding parasites transmitting a wide variety of pathogens to their vertebrate hosts. The transmitted pathogens apparently evolved efficient mechanisms enabling them to evade or withstand the cellular or humoral immune responses within the tick vector. Despite its importance, our knowledge of tick innate immunity still lags far beyond other well established invertebrate models, such as drosophila, horseshoe crab or mosquitoes. However, the recent release of the American deer tick, Ixodes scapularis, genome and feasibility of functional analysis based on RNA interference (RNAi) facilitate the development of this organism as a full-value model for deeper studies of vector-pathogen interactions.
- MeSH
- fagocytóza MeSH
- hmyz - vektory genetika imunologie MeSH
- hmyzí proteiny genetika imunologie MeSH
- klíště genetika imunologie mikrobiologie MeSH
- komplement genetika imunologie MeSH
- lektiny metabolismus MeSH
- molekulární sekvence - údaje MeSH
- přirozená imunita imunologie MeSH
- RNA interference MeSH
- sekvence aminokyselin MeSH
- sekvenční seřazení MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Ticks are important ectoparasites and vectors of multiple human and animal diseases. The obligatory hemophagy of ticks provides a formidable route for parasite transmission from one host to another. Parasite survival inside the tick relies on the ability of a pathogen to escape or inhibit tick immune defenses, but the molecular interactions between the tick and its pathogens remain poorly understood. Here we report that tick genomes are unique in that they contain all known classes of the α(2)-macroglobulin family (α(2)M-F) proteins: α(2)-macroglobulin pan-protease inhibitors, C3 complement components, and insect thioester-containing and macroglobulin-related proteins. By using RNA interference-mediated gene silencing in the hard tick Ixodes ricinus we demonstrated the central role of a C3-like molecule in the phagocytosis of bacteria and revealed nonredundant functions for α(2)M-F proteins. Assessment of α(2)M-F functions in a single organism should significantly contribute to the general knowledge on the evolution and function of the complement system. Importantly, understanding the tick immune mechanisms should provide new concepts for efficient transmission blocking of tick-borne diseases.
- MeSH
- alfa-makroglobuliny genetika MeSH
- Chryseobacterium imunologie patogenita MeSH
- fagocytóza genetika MeSH
- genom imunologie MeSH
- genomika MeSH
- hemocyty imunologie metabolismus mikrobiologie patologie MeSH
- hmyzí proteiny genetika metabolismus MeSH
- infekce bakteriemi čeledi Flavobacteriaceae genetika imunologie MeSH
- komplement C3 genetika metabolismus MeSH
- kultivované buňky MeSH
- lidé MeSH
- malá interferující RNA genetika MeSH
- molekulární evoluce MeSH
- sekvenční analýza DNA MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Ticks are blood feeding parasites transmitting a wide variety of pathogens to their vertebrate hosts. The vector competence of ticks is tightly linked with their immune system. Despite its importance, our knowledge of tick innate immunity is still inadequate and the limited number of sufficiently characterized immune molecules and cellular reactions are dispersed across numerous tick species. The phagocytosis of microbes by tick hemocytes seems to be coupled with a primitive complement-like system, which possibly involves self/nonself recognition by fibrinogen-related lectins and the action of thioester-containing proteins. Ticks do not seem to possess a pro-phenoloxidase system leading to melanization and also coagulation of tick hemolymph has not been experimentally proven. They are capable of defending themselves against microbial infection with a variety of antimicrobial peptides comprising lysozymes, defensins and molecules not found in other invertebrates. Virtually nothing is known about the signaling cascades involved in the regulation of tick antimicrobial immune responses. Midgut immunity is apparently the decisive factor of tick vector competence. The gut content is a hostile environment for ingested microbes, which is mainly due to the antimicrobial activity of hemoglobin fragments generated by the digestion of the host blood as well as other antimicrobial peptides. Reactive oxygen species possibly also play an important role in the tick-pathogen interaction. The recent release of the Ixodes scapularis genome and the feasibility of RNA interference in ticks promise imminent and substantial progress in tick innate immunity research.
Ticks are among the most important vectors of a wide range of human and animal diseases. During blood feeding, ticks are exposed to an enormous amount of free iron that must be appropriately used and detoxified. However, the mechanism of iron metabolism in ticks is poorly understood. Here, we show that ticks possess a complex system that efficiently utilizes, stores and transports non-heme iron within the tick body. We have characterized a new secreted ferritin (FER2) and an iron regulatory protein (IRP1) from the sheep tick, Ixodes ricinus, and have demonstrated their relationship to a previously described tick intracellular ferritin (FER1). By using RNA interference-mediated gene silencing in the tick, we show that synthesis of FER1, but not of FER2, is subject to IRP1-mediated translational control. Further, we find that depletion of FER2 from the tick plasma leads to a loss of FER1 expression in the salivary glands and ovaries that normally follows blood ingestion. We therefore suggest that secreted FER2 functions as the primary transporter of non-heme iron between the tick gut and the peripheral tissues. Silencing of the fer1, fer2, and irp1 genes by RNAi has an adverse impact on hatching rate and decreases postbloodmeal weight in tick females. Importantly, knockdown of fer2 dramatically impairs the ability of ticks to feed, thus making FER2 a promising candidate for development of an efficient anti-tick vaccine.
- MeSH
- analýza přežití MeSH
- biologické modely MeSH
- ferritin genetika MeSH
- financování organizované MeSH
- fylogeneze MeSH
- hmyzí geny MeSH
- hmyzí proteiny genetika metabolismus MeSH
- intracelulární prostor metabolismus MeSH
- klíšťata fyziologie genetika růst a vývoj MeSH
- klonování DNA MeSH
- messenger RNA genetika metabolismus MeSH
- morčata MeSH
- proteosyntéza MeSH
- regulace genové exprese MeSH
- rozmnožování MeSH
- stanovení celkové genové exprese MeSH
- stravovací zvyklosti MeSH
- umlčování genů MeSH
- western blotting MeSH
- železo metabolismus MeSH
- zvířata MeSH
- Check Tag
- morčata MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
The universal protease inhibitors of the alpha(2)-macroglobulin (alpha(2)M) family are evolutionarily conserved constituents of innate immunity, presumably because they guard organisms against undesired proteolytic attacks of a different origin. Here, we determined the primary structure of alpha(2)-macroglobulin from the hard tick Ixodes ricinus (IrAM) by sequencing of overlapping PCR products. Predicted disulfide and glycosylation patterns, post-translational cleavage and alternative splicing within its 'bait region' demonstrate that IrAM is closely related to the alpha(2)-macroglobulin from the soft tick Ornithodoros moubata. The IrAM message is expressed in all tick developmental stages and tissues, except for the gut, and the protein was detected to be mainly present in the hemolymph. Silencing of IrAM by dsRNA interference markedly reduced the phagocytosis of a potential pathogen, Chryseobacterium indologenes, by tick hemocytes both in vitro and in vivo. In contrast, phagocytosis of the Lyme disease spirochete Borrelia burgdorferi or a commensal bacteria Staphylococcus xylosus was not affected by the IrAM knock-down. Similar results were obtained upon deactivation of all thioester proteins in tick hemolymph by methylamine. We have further demonstrated that phagocytosis of C. indologenes is dependent on an active metalloprotease secreted by the bacteria. These data indicate that interaction of tick alpha(2)-macroglobulin with a protease of an invading pathogen is linked with cellular immune response.
- MeSH
- alfa-makroglobuliny farmakologie genetika chemie imunologie MeSH
- Chryseobacterium imunologie MeSH
- fagocytóza imunologie MeSH
- fenantroliny farmakologie MeSH
- financování organizované MeSH
- hemocyty imunologie mikrobiologie účinky léků MeSH
- hemolymfa imunologie MeSH
- klíště genetika imunologie mikrobiologie MeSH
- metaloproteasy metabolismus účinky léků MeSH
- methylaminy farmakologie MeSH
- molekulární sekvence - údaje MeSH
- RNA interference MeSH
- sekvence aminokyselin MeSH
- sekvence nukleotidů MeSH
- sekvenční seřazení MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
Ticks are ectoparasitic blood-feeders and important vectors for pathogens including arboviruses, rickettsiae, spirochetes and protozoa. As obligate blood-feeders, one possible strategy to retard disease transmission is disruption of the parasite's ability to digest host proteins. However, the constituent peptidases in the parasite gut and their potential interplay in the digestion of the blood meal are poorly understood. We have characterised a novel asparaginyl endopeptidase (legumain) from the hard tick Ixodes ricinus (termed IrAE), which we believe is the first such characterisation of a clan CD family C13 cysteine peptidase (protease) in arthropods. By RT-PCR of different tissues, IrAE mRNA was only expressed in the tick gut. Indirect immunofluorescence and EM localised IrAE in the digestive vesicles of gut cells and within the peritrophic matrix. IrAE was functionally expressed in Pichia pastoris and reacted with a specific peptidyl fluorogenic substrate, and acyloxymethyl ketone and aza-asparagine Michael acceptor inhibitors. IrAE activity was unstable at pH > or = 6.0 and was shown to have a strict specificity for asparagine at P1 using a positional scanning synthetic combinatorial library. The enzyme hydrolyzed protein substrates with a pH optimum of 4.5, consistent with the pH of gut cell digestive vesicles. Thus, IrAE cleaved the major protein of the blood meal, hemoglobin, to a predominant peptide of 4kDa. Also, IrAE trans-processed and activated the zymogen form of Schistosoma mansoni cathepsin B1 -- an enzyme contributing to hemoglobin digestion in the gut of that bloodfluke. The possible functions of IrAE in the gut digestive processes of I. ricinus are compared with those suggested for other hematophagous parasites.
- MeSH
- cysteinové endopeptidasy genetika chemie izolace a purifikace MeSH
- financování organizované MeSH
- fluorescenční protilátková technika nepřímá MeSH
- fylogeneze MeSH
- hemoglobiny metabolismus MeSH
- kathepsin B metabolismus MeSH
- klíště enzymologie genetika MeSH
- klonování DNA MeSH
- messenger RNA biosyntéza genetika MeSH
- molekulární sekvence - údaje MeSH
- Pichia genetika metabolismus MeSH
- polymerázová řetězová reakce s reverzní transkripcí MeSH
- sekvence aminokyselin MeSH
- sekvence nukleotidů MeSH
- sekvenční seřazení MeSH
- transmisní elektronová mikroskopie MeSH
- trávicí systém MeSH
- zvířata MeSH
- Check Tag
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- abstrakt z konference MeSH
