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Les tiques du genre Ixodes englobent un grand nombre d’espèces dont Ixodes ricinus, objet de cette étude. Ixodes ricinus peuple les sous-bois de nos régions et la plupart des grandes forêts de l’Europe centrale et de l’est. Au cours de leur cycle parasitaire, les tiques réalisent un repas sanguin au détriment de petits mammifères (mulots, lièvres,…), mais aussi de grands mammifères tels que le cerf, la biche ou le sanglier. Elles deviennent particulièrement voraces au début du printemps et en automne, c’est pourquoi à ces époques de l’année, les promeneurs et les animaux domestiques (principalement, le chien) peuvent en être infestés. Pour mener à bien leur repas sanguin, les tiques mettent en place une série de mécanismes les rendant non seulement indécelables par l’animal parasité mais aussi leur donnant la capacité de contrecarrer les défenses de l’hôte. En effet, lors de sa fixation et durant tout le repas sanguin, la tique injecte un cocktail de facteurs bioactifs qui inhibent la sensation de douleur au moment de l’ancrage dans le derme, mais également les défenses immunitaires de l’hôte parasité. De plus, certains de ces facteurs possèdent des propriétés anti-hémostatiques garantissant la fluidité du sang pendant tout le repas.<p><p>Le Service de Biologie Moléculaire des Ectoparasites (anciennement Service de Génétique Appliquée) a identifié un grand nombre de séquences d’ARNm induites spécifiquement dans les glandes salivaires de la tique au cours de son repas sanguin. Deux d’entres-elles ont servi de point de départ à ce travail :il s’agit de seq16 (renommée Metis1) et de seq7 (renommée Ir-CPI).<p><p>Le travail sur la séquence seq16 a conduit à l’identification d’une nouvelle famille de 5 métalloprotéases (nommée Metis pour Metalloprotease from Ixodes ricinus). L’analyse des séquences a permis de les associer à certaines métalloprotéases hémorragiques de venin de serpent. Bien que les 5 métalloprotéases décrites possèdent toutes les mêmes caractéristiques au niveau de leur séquence et de leur profil d’expression dans les glandes salivaires, les résultats d’analyse phylogénétique, d’étude de variation antigénique, de leur mode d’activation et de leur spécificité d’action permettent de les diviser en 3 sous-familles. L’utilisation de la technique d’ARN interférence en in vivo et l’analyse vaccinale soulignent le rôle essentiel de la famille Metis dans les premières heures du repas de la tique et de manière générale dans la réussite du repas sanguin. Enfin, des études d’activité ont montré que certains membres de la famille ont une activité fibrino(gèno)lytique ;plus particulièrement, la protéine Metis4 possède une activité protéolytique envers la gélatine, la caséine, la fibronectine et le fibrinogène. Ces études ont montré également un mode d’activation original ;plutôt que d’être activée par une pro-séquence en amino-terminal, Metis4 s’active spontanément en perdant un peptide à son extrémité carboxy-terminale. <p><p>Le travail sur la séquence seq7 a conduit à la caractérisation d’un nouvel inhibiteur de sérines protéases. Cette protéine, nommée Ir-CPI pour « Ixodes ricinus - Contact Phase Inhibitor », possède un motif kunitz et est capable d’inhiber de manière importante la voie intrinsèque de la coagulation et dans une moindre mesure la fibrinolyse. Grâce à la technique d’ARN interférence, l’activité de la protéine recombinante a été corrélée à l’activité de la protéine native exprimée dans les glandes salivaires. Ir-CPI inhibe dans un plasma humain l’activation réciproque du facteur XII, de la prékallikréine et du facteur XI, et se fixe spécifiquement à la forme activée de ces trois facteurs. De plus, Ir-CPI est capable de bloquer la fibrinolyse en inhibant spécifiquement la plasmine. Enfin, les résultats obtenus sur deux modèles animaux indépendants établissent l’effet d’Ir-CPI comme agent anti-thrombotique en empêchant la formation de caillot et de manière remarquable sans altérer l'équilibre hémostatique.<p><p>En conclusion, ce travail a identifié des protéines anti-hémostatiques qui agissent soit comme inhibiteur de protéases empêchant la coagulation soit comme protéases facilitant la lyse du caillot. Cette redondance de protéines anti-hémostatiques illustre remarquablement la capacité de la tique à agir en synergie sur des facteurs essentiels aux mécanismes de défense de l’hôte.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

"Ticks have already been studied in our country and abroad. Progress in the field of taxonomy has probably been the most rapid and has culminated in a large number of papers and excellent monographs, but much more remains to be done. To produce an overall picture of the factors influencing the behaviour of the tick under natural conditions, studies have to be conducted on tick ecology and experimental physiology. We still have a lack of knowledge of host specificity, the selection of feeding sites on hosts and the nature of resistance to attacks by ticks. Because of the varied habits of different species of ticks, the first essential prerequisite is an adequate knowledge of their biology." (Jansen 1969). The above words sum up the position of research on ticks in southern Africa at the present time.

Host-parasite interactions are complex, involving host behaviour, host condition, and possible antagonism or mutualism between co-occurring parasites. The white-footed mouse (Peromyscus leucopus) is a small, abundant, generalist rodent, and the primary host for the black-legged tick (Ixodes scapularis) in its larval stage. Since larval ticks do not actively pursue their hosts (they wait for possible hosts to come to them), individual differences in mouse exploratory behaviour might be expected to correlate with tick burden. However, mice may also prevent tick attachment with defensive behaviour such as grooming. Yet, the relationships between tick parasitism and host exploratory and grooming behaviours have never been assessed. I analysed data from a capture-mark-recapture study conducted over 5 summers (2016-2020) in eastern Ontario, Canada, in which 1,035 mice were captured a total of 4,333 times. The probability of tick parasitism occurring and being more intense was significantly higher when the mouse was also parasitized by fleas, suggesting co-occurrence of these two parasites on host mice. A total of 510 mice were subjected to an open-field test to quantify exploratory and grooming behaviours. Exploration had a negative relationship with tick presence and a positive relation with flea presence. Most interestingly, there was a significant “tick × flea” interaction on exploratory behaviour such that fleas were positively associated with exploration only when ticks were absent. Surprisingly, there was no relationship between grooming behaviour in the open-field test and parasite presence, although grooming increased with mouse activity. This study shows that co-occurring parasite species (ticks and fleas) may interact to affect their host’s exploratory behaviour. Alternatively, individual differences in exploratory behaviour of hosts may differentially affect their susceptibility to being infested with ticks, fleas, or both. Future manipulative studies should use experimental design to determine the causality of the parasitism-behaviour relationships observed.

Les interactions intimes et répétées entre hôtes et parasites peuvent engendrer la spécialisation d’un parasite à son hôte, grâce à des adaptations comportementales, morphologiques et/ou génétiques, combinées avec un flux de gènes limité. C’est un processus clef car il participe à l’évolution de la biodiversité parasitaire et peut ainsi permettre de mieux comprendre l’émergence d’organismes pathogènes. Encore peu étudié, une spécialisation d’hôtes a néanmoins été démontré lors de précédentes études chez deux espèces de tiques nidicoles : chez Ixodes uriae une tique dure, parasite des oiseaux marins coloniaux en zone arctique, et dans un complexe de tiques molles Ornithodoros capensis sensu lato, parasitant aussi de nombreuses espèces d’oiseaux marins, mais cette fois-ci en zones tempérées et tropicales. Ces deux espèces sont vectrices d’une grande diversité d’agents pathogènes incluant des virus, des bactéries et des protozoaires. Cependant, les facteurs impliqués dans le phénomène de spécialisation d’hôte restent inconnus. Dans ce cadre, le but de ma thèse était donc de déterminer 1) si l’évolution des divergences en fonction des hôtes est toujours accompagnée par les mêmes changements phénotypiques et 2) si ces changements pourraient permettre d’identifier les facteurs de sélection sous-jacents. Dans ce contexte, des campagnes d’échantillonnage de tiques ont été menées durant la période de reproduction des hôtes oiseaux dans les différentes zones de leur répartition et nous avons réalisé des analyses morphométriques, basées sur l’utilisation de landmarks et de contours sur chaque individu tique et des analyses phylogénétiques et génétiques des populations sur les mêmes individus. L’ensemble de ces résultats suggère la présence de convergences morphologiques au sein de ces systèmes et souligne un rôle de la sélection dans ce processus de divergence. En effet, les caractéristiques écologiques des hôtes mais aussi le micro-habitat exercent des pressions sélectives importantes dans ces deux systèmes pouvant être à l’origine de la divergence observée entre les populations. De plus, les caractéristiques biologiques de chaque espèce de tiques, telle que la capacité de dispersion, entrent également en jeu et peuvent fortement modifier l’épidémiologie des agents infectieux dont elles sont vectrices.Mots clés : Argasidae, écologie de la transmission, évolution convergente, interactions hôte-parasite, Ixodidae, oiseaux marins. / Intimate and repeated interactions between hosts and parasites can lead to parasite specialization to a given host via behavioral, morphological and/or genetic adaptations that act in combination with restricted gene flow. Specialization is a key process leading to the generation of parasite biodiversity and can help us understand the emergence of pathogenic organisms. Although little studied, host specialization has already been demonstrated to occur in previous studies of two nidicolous tick species: Ixodes uriae a hard tick parasitizing colonial seabirds in polar regions, and soft ticks of the complex Ornithodoros capensis sensu lato, that also exploit colonial seabirds, but this time in temperate and tropical zones. Both of these species act as vector to a wide variety of pathogenic organisms, including viruses, bacteria and protozoa. However, the factors involved in host specialization remain unknown. In this context, the aim of my thesis was to determine 1) whether the evolution of host specialization is always accompanied by the same phenotypic changes and 2) whether these changes could help to identify the selective factors that influence this phenomenon. In this context, tick collections were conducted during the breeding period of the host birds in different areas of their distribution and morphometric analyses, based on landmark and contour methods, were performed on each individual tick. Phylogenetic and population genetic analyses were also carried out using the same individuals. Overall, the results demonstrate that morphological convergence occurs within these systems, highlighting the role of selection in the divergence process. Indeed, the ecological characteristics of the hosts, but also their micro-habitat, may exert significant selective pressures on ticks and may cause the observed divergence among populations. Likewise, the biological characteristics of each tick species, particularly in relation to dispersal capacity, may also come into play and will greatly modify the epidemiology of associated infectious agents.Keywords: Argasidae, convergent evolution, host-parasite interactions, Ixodidae, transmission ecology, seabirds.

Thesis (MTech (Horticulture))--Cape Peninsula University of Technology, 2018. / Ticks and tick-borne diseases are important limiting factors to the attainment of sustainable animal and human health, affecting livelihood of resource poor farming communities in developing countries. Rhipicephalus appendiculatus and Amblyomma variegatum (Ixodidae) are among the most troubling tick species in Africa. While ticks can be controlled by applying chemical acaricides, these chemicals are quite expensive, especially, for small-scale famers in developing countries. Hence, the quest for alternative tick control over the years have revealed that entomopathogenic fungi (EPF) and plant extracts have huge prospects as sustainable alternatives for tick control. Beauveria bassiana (Hypocreales) is a fungal entomopathogen with the ability to colonize plants endophytically and induce secondary metabolite production in plants, and it has been found to be a potential biological control agent against a wide range of arthropods. Several plant species including plant species belonging to the family Alliaceae possess anti-tick activities (repellent and toxic); therefore, integrating the two strategies by inoculating Tulbaghia violacea with B. bassiana could enhance secondary metabolite contents in extracts obtained from the plant and increase medicinal materials. The primary purpose of the present study was to evaluate the effect of indigenous endophytic entomopathogens inoculation of T. violacea on the plant growth, tissue nutrient contents and secondary metabolites, and anti-tick activities of extracts of T. violacea. The specific objectives were: (i) to carry out a study on the effects of inoculating T. violacea with fungal strains of B. bassiana and Clonostachys rosea on plant growth and tissue nutrient contents in extracts of T. violacea with the view of selecting one of the two fungi for further investigation (ii) to compare secondary metabolite profiles of extracts obtained from plants exposed to fungus (EPF) inoculum and control treatment during cultivation, and (iii) to determine whether exposure of T. violacea to an endophytic fungus (B. bassiana) during cultivation affects the repellent and acaricidal activities of extracts of T. violacea on A. variegatum and R. appendiculatus. The study had two experiments, presented in chapters two and three. In the first experiment, eight weeks old potted seedlings of T. violacea were inoculated separately with B. bassiana (strain SM3) and C. rosea (strain SM8) conidia suspended at concentrations of 1 x 106 conidia mL-1. Plant growth parameters, such as number of leaves, plant height (aerial part), fresh weights of aerial parts, and tissue nutrient contents were assessed. Results indicated that B. bassiana induced higher growth of plants than C. rosea. Inoculation with B. bassiana did not significantly (P ˃ 0.05) influence most of the growth parameters, number of leaves, fresht weight of roots and of fresh weight aerial parts (leaves) of T. violacea assessed in the current study. However, mean plant heights and root lengths were significantly (P < 0.05) higher in favour of B. bassiana treated plants compared to those in C. rosea. Fe contents in the roots (1416.3 ± 305.10 mg/kg) were found to be positively influenced (P < 0.05) by the fungal inoculation. There was a significant difference in roots (P < 0.05) on the uptake of Mn in C. rosea treated plants (243 ± 19 mg/kg) compared to the control group (169 ± 16.37 mg/kg) and B. bassiana treated roots (161.3 ± 14.44 mg/kg). Macro nutrients up take did not differ significantly among treatments on both leaves and roots (P > 0.05).

Made available in DSpace on 2016-04-28T20:16:32Z (GMT). No. of bitstreams: 1 1997 - Armando de Lemos Ribeiro.pdf: 1637429 bytes, checksum: 67368e92ac3e601a127f511f61aef35b (MD5) Previous issue date: 1997-12-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The first experiment was set up to measure the drop-off rhythm of larvae and nymphs of Amblyomma cajennense feeding on the rabbits as experimental hosts. Infestations were carried out with unfed larvae and nymphs aging 15 and 45 days post eclosion and host larval moulting, respectively. Three rabbits were infested with approximately 825 larvae (50 mg of eggs) and 100 nymphs for each age totaling 12 rabbits. Each host were examined at 8, 12, 16 and 24 hours and the dropped larvae and nymphs collected. Regardless of age and instar higher drop-off rhythm were observed from 8 to 16 hours: 73,6 and 72,8% larvae with 15 and 45 days post eclosion and 69,6 and 57,5 nymphs with 15 and 45 days post larval moulting, respectively. The second experiment was set up to evaluate the effect of age on the attachment of larvae and nymphs of Amblyomma cajennense using the rabbit as experimental host. Infestations were carried out with unfed larvae aging from 0-4 to 150 days post-eclosion and unfed nymphs aging from 0-2 to 165 days post-larval moulting. A total of 11 and 12 infestations respectively for larvae and nymphs with 15 days interval were monitored. Three rabbits were infested with 825 larvae and 100 nymphs per rabbit at each interval. Larvae and nymphs with 0-2 day post-eclosion and post larval moulting were able to attach and feed at rates of 45 and 77%. Higher attachment rates for larva (> 70%) were observed from days 15 to 60 post eclosion. Then, start to decrease until 25% at 150 days post-eclosion. Higher attachment rates for nymphs were observed from days 15 to 90 post moulting (> 80%). Then, start to decrease until 36% at 165 days. The periods of attachment and ecdisis, and the percentage of ecdisis were similar for both stages regardless the age prior attachment. When the period of pre-ecdisis is analyzed one might note a shortening as the nymphs because older whereas it was similar for larvae in ali evaluated ages. This third experiment was conduct as an attempt to correlate the weight pre-ecdisis period and timing of drop-off of nymphs with the forecast of the sexes in adults of Rhipicephalus sanguineus. The mean weight of nymphs that moulted to males (n = 96) was 1,97 ? 0,97 and 2,52 ? 0,90 to females (n = 103) (P > 0,05) between the weight of nymphs can not be used to forecast the sexes due to overlapping of to weight ranges. The pre-ecdisis periods were 15,13 ? 0,94 and 14,60 ? 0,77 days for nymphs that moulted to males (n = 96) and females (n = 103) (P > 0,05) respectively. Nymphs (n = 50) that dropped-off on both third and fourth day (mode) post-infestation moulted to 29 females and 21 males whereas those (n = 50) that dropped-off on the fifth day post-infestation moulted to 30 females and 20 males (x2 > 0,05). Although there are numerical differences in ali evaluated parameters none can be used to forecast the sexes in R. sanguineus due to an extensive overlapping. / O primeiro experimento foi montado para avaliar o ritmo de queda de larvas e ninfas de Amblyomma cajennense alimentadas em coelhos. Infesta??es foram feitas com larvas e ninfas em jejum com idades de 15 e 45 dias ap?s eclos?o e ecdise larval respectivamente. Tr?s coelhos foram infestados com aproximadamente 825 larvas (50 mg de ovos) e 100 ninfas para cada idade totalizando 12 coelhos. Cada hospedeiro foi examinado nos hor?rios de 8, 12, 16 e 24 horas e as larvas e ninfas desprendidas foram coletadas. Independente da idade e do instar, o maior n?mero se desprendeu entre 8 e 16 horas: 73,6% e 72,8% para larvas com 15 e 45 dias ap?s eclos?o e 69,6% e 57,5% para ninfa. Com 15 e 45 dias ap?s ecdise larval, respectivamente. O segundo experimento teve como objetivo avaliar o efeito da idade sobre a fixa??o de larvas e ninfas de Amblyomma cajennense, usando o coelho como hospedeiro. Infesta??es foram feitas com larvas com per?odos de jejum de zero a 4 at? 150 dias ap?s eclos?o e ninfas em jejum variando de zero a 2 at? 165 dias ap?s ecdise larval. Um total de 11 e 12 infesta??es para larvas e ninfas respectivamente, com intervalos de 15 dias foram acompanhados. Tr?s coelhos foram infestados com 825 larvas e 100 ninfas por coelhos e para cada tratamento. Larvas e ninfas com zero a 4 dias ap?s eclos?o e zero a 2 dias ap?s ecdise larval se fixaram e se alimentaram, com taxas de recupera??o de 45 e 77% respectivamente. Taxas de recupera??o alta para larvas (> 70%) foi observado para 15 at? 60 dias ap?s eclos?o. Entretanto a partir da? come?ou a decrescer para 25% at? 150 dias p?s-eclos?o. As taxas de recupera??o foram altas para ninfas com 15 at? 90 dias p?s-ecdise (> 80%). Ent?o, come?ou a decrescer para 36% at? 165 dias. Os per?odos de pr?-ecdise, de ecdise e as percentagens de ecdise foram est?veis para todas as idades estudadas. Quando o per?odo de pr?-ecdise ? analisado nota-se um encurtamento conforme as ninfas se tornam mais velhas; ao contr?rio este per?odo foi similar para larvas de todas as idades. Esse terceiro experimento foi conduzido para se observar a correla??o entre o peso, o per?odo de pr?-ecdise e o per?odo de queda de ninfas ingurgitadas com a previs?o do sexo dos adultos de Rhipicephalus sanguineus. A m?dia do peso de ninfas que originaram machos (n = 96) foi de 1,97 ? 0,97 e 2,52 ? 0,90 para f?meas (n = 103) (P > 0,05). O peso das ninfas n?o pode ser usado para a previs?o dos sexos devido ? superposi??o dos pesos. O per?odo de pr?-ecdise foi de 15,13 ? 0,94 e 14,60 ? 0,77 dias par ninfas que originaram machos (n = 96) e f?meas (n = 103) (P > 0,05), respectivamente. Ninfas (n = 50), dos per?odos de queda, inicial (3? dia) e modal (4? dia), desprenderam-se 29 f?meas e 21 machos, em ambos per?odos. No per?odo final (5? dia) (n = 50) desprenderam-se 30 f?meas e 20 machos (x2 > 0,05). Embora exista diferen?as num?ricas em todos os par?metros avaliados, tais par?metros n?o podem ser utilizados para a previs?o dos sexos em R. sanguineus devido a amplitude da superposi??o.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xv, 126 p.; also includes graphics (some col.). Includes bibliographical references (p. 96-107). Available online via OhioLINK's ETD Center

Made available in DSpace on 2016-12-08T16:24:11Z (GMT). No. of bitstreams: 1 PGCA10MA065.pdf: 574095 bytes, checksum: 57eb26bddb6a6d197fe88cd5d25475f2 (MD5) Previous issue date: 2010-10-08 / The present study was intended to characterize Rickettsia spp. circulating in arthropod vectors in Santa Catarina, Brazil, utilizing to technical of Reaction of Chain of the Polimerase (PCR) and sequencing genetic and investigate the presence of antibodies against the spotted fever Rickettsiae group (SFRG) in horses. 288 arthropods were collected and taxonomically identified in the Laboratório de Parasitologia e Doenças Parasitárias do Centro de Ciências Agroveterinárias da Universidade do Estado de Santa Catarina (CAV/UDESC) and, subsequently prosecuted by the PCR and sequencing in the Laboratório de Doenças Parasitárias do Departamento de Medicina Preventiva e Saúde Animal (VPS) of the Faculdade de Medicina Veterinária e Zootecnia (FMVZ) of the Universidade de São Paulo (USP). Amblyomma ovale, A. aureolatum, A. longirostre, Rhipicephalus sanguineus and Dermacentor nitens showed sequences homology with R. parkeri cepa Mata Atlântica e R. amblyommi cepa AL. Equine (150) serum samples were tested by indirect fluorescent antibody (IFA) using R. rickettsii, R. parkeri, R. amblyommi, R. rhipicephali, R. belli and R. felis antigen. Only two of the equine sera tested (1.33%) had conclusive results of antibody titers. Molecular detection of rickettsiae species potentially pathogenic to humans in arthropod vectors and the presence of seroreactivity to SFRG in horses show the risk of transmission of rickettsiosis in this area and the need to maintain continuous epidemiological surveillance for rickettsial diseases / O presente trabalho foi realizado com objetivo de investigar as espécies de Rickettsia spp. que ocorrem no estado de Santa Catarina, por meio de pesquisa em ixodídeos coletados de diversas espécies animais, utilizando a Reação em Cadeia da Polimerase (PCR) e sequenciamento genético, e detectar anticorpos contra Rickettsia spp. em equinos, pela Reação de Imunofluorescência Indireta (RIFI). Os carrapatos coletados foram encaminhados para o Laboratório de Parasitologia e Doenças Parasitárias do Centro de Ciências Agroveterinárias da Universidade do Estado de Santa Catarina (CAV/UDESC) para identificação taxonômica e, posteriormente processados pela PCR e sequenciamento no Laboratório de Doenças Parasitárias do Departamento de Medicina Veterinária Preventiva e Saúde Animal (VPS) da Faculdade de Medicina Veterinária e Zootecnia (FMVZ) da Universidade de São Paulo (USP). Os carrapatos (n=288) foram analisados para os genes rickettsiais gltA, presente possivelmente em todas as espécies do gênero Rickettsia, e ompA, comum às rickettsias do grupo da febre maculosa. Para o gene gltA, 14 amostras foram positivas, infectando os vetores das espécies Rhipicephalus sanguineus, Amblyomma aureolatum, A. ovale, A. longirostre, A. tigrinum e Anocentor nitens. Nove amostras foram positivas para o gene ompA (A. aureolatum, A. ovale, A. longirostre, R. sanguineus). As amostras positivas para ompA foram sequenciadas. O resultado do sequenciamento indica que em Santa Catarina circulam os agentes Rickettsia parkeri cepa Mata Atlântica e Rickettsia amblyommii cepa AL. Além dos carrapatos, 150 amostras de sangue foram colhidas de equinos de duas mesorregiões de Santa Catarina (Serra Catarinense e Vale do Itajaí) para análise de anticorpos contra Rickettsia spp. Foram considerados positivos animais com RIFI &#8805;1:64. A soroprevalência para Rickettsia spp. observada em equinos do estado de Santa Catarina foi de 18,66%, ocorrendo reações cruzadas em todas as amostras para, no mínimo, duas das espécies testadas. Somente dois animais resultaram em um sorodiagnóstico conclusivo para R. bellii e R. rickettsii nas diluições máximas de 1:4096 e 1:512, respectivamente. Os resultados obtidos comprovam a importância do estudo da febre maculosa no estado de Santa Catarina e indicam a circulação de agentes da febre maculosa brasileira (FMB), tanto nos reservatórios como em seus vetores, e sugere que esta doença possa estar ocorrendo neste estado

Les tiques sont des arthropodes ectoparasites obligatoires qui se nourrissent sur une grande variété de vertébrés sur une large partie du globe. Au cours de leur repas, les tiques sécrètent dans leur salive de nombreux facteurs leur permettant de contourner bon nombre des défenses de l’hôte. Bien que la littérature rapporte beaucoup d’informations au sujet des effets du repas de la tique sur l’hôte, la nature des facteurs actifs exprimés par les glandes salivaires de la tique est peu connue. Au cours d’anciens travaux au sein du laboratoire, le crible de deux banques d’ADN complémentaires - issues de la rétro-transcription des ARN messagers synthétisés par les glandes salivaires de la tique Ixodes ricinus – a permis l’identification de 27 protéines dont l'expression est spécifiquement induite ou régulée positivement pendant le repas sanguin de la tique I. ricinus. Parmi ces protéines, la protéine Seq24, induite au cours du repas sanguin, présente la capacité de moduler les immunités innée et acquise de l’hôte. En conséquence, la protéine Seq24 a été nommée Iris pour « Ixodes ricinus Immunosuppressor ». Au cours de la présente étude, notre but fût de caractériser le rôle d’Iris et de déterminer son importance dans le repas sanguin de la tique I. ricinus.<p>La protéine Iris appartient à la famille des inhibiteurs de sérine protéases et présente une homologie significative avec l’inhibiteur d’élastase de leucocytes. Une analyse in silico a confirmé qu’Iris présentait la structure des serpines, et notamment le RCL (Reactive Center Loop), boucle responsable de l’activité anti-protéasique. Comme attendu (sur base de l’analyse in silico), Iris inhibe de manière spécifique l’activité de plusieurs sérine protéases, et en particulier l’élastase de leucocyte. Ces tests effectués, nous avons essayé de comprendre quel(s) pouvai(en)t être le(s) rôle(s) d’Iris dans l’accomplissement du repas sanguin de la tique, c’est à dire dans la lutte contre les différents systèmes de défenses de l’hôte.<p>Tout d’abord, des tests ont démontré la capacité d’Iris à inhiber les mécanismes de l’hémostase. Des tests sur du plasma et du sang complet ont montré qu’Iris allonge le temps de fibrinolyse, la voie intrinsèque de la coagulation et l’adhésion plaquettaire. L’utilisation de mutants a également démontré que si les deux premières activités sont dépendantes du RCL, et donc d’un mode de fonctionnement anti-protéolytique, l’adhésion plaquettaire est indépendante de ce système. Ce résultat met en évidence l’existence d’autres sites actifs, isolés par analyse in silico, nommés Receptor Binding Domain (RBD).<p>Un travail antérieur du laboratoire avait permis d’indiquer la capacité de la protéine recombinante Iris semi-purifiée à inhiber la production de TNF-a, d’IL-6, et d’IL-8 (cytokines pro-inflammatoires) ainsi que l’IFN-g par des PBMCs (Peripherical Blood Mononuclear Cells) humaines. Ces résultats ont été confirmés avec de la protéine purifiée. Des analyses complémentaires ont démontré qu’un mutant d’Iris - dépourvu d’activité anti-protéasique - conserve l’activité pro-inflammatoire. Là encore, ce mécanisme semble impliquer un ou plusieurs RBD. L’utilisation d’anticorps dirigés contre ces zones a permis de déterminer le domaine d’interaction (aa :105-120) impliqué dans cette fonction. D’autre part, une analyse par FACS a permis de démontrer qu’Iris interagit uniquement avec les cellules d’origine monocytaire.<p>Enfin, nous avons également analysé l’importance d’Iris au cours du repas sanguin de la tique par une approche vaccinale. Les résultats observés indiquent que 30 % des tiques nourries sur des lapins immunisés par la protéine rIris ne survivent pas au repas. / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished