Toxoplasma gondii est un eucaryote unicellulaire appartenant au phylum des Apicomplexes. Ce parasite intracellulaire obligatoire est la cause d’une pathologie sévère pour les fœtus des femmes enceintes primo-infectées ainsi que pour les personnes immunodéprimées. Son cycle de vie est complexe et comporte plusieurs étapes de prolifération et différenciation. Le stade tachyzoïte est responsable de la phase aigüe de la maladie chez les humains. Le tachyzoïte exprime des facteurs d'invasion et de virulence cruciaux pour sa survie et le détournement de la cellule hôte. L'expression de ces facteurs de virulence est hautement régulée pour permettre leur adressage correct dans des organites spécifiques appelés rhoptries et micronèmes. Cependant, peu d'informations sont connues sur les acteurs contrôlant l'expression de ces gènes de virulence. Les ApiAP2 appartiennent à une famille conservée de facteur de transcription (FT) et jouent un rôle important dans la régulation de la transcription des gènes chez les parasites apicomplexes. Des études menées au laboratoire ont révélés la capacité du FT TgAP2XI-5 à se fixer sur des promoteurs de gènes transcriptionnellement actifs durant les phases S/M du cycle cellulaire. Ce moment correspond au pic d’expression les gènes de rhoptrie et de micronème. Cependant, l'expression de TgAP2XI-5 est constitutive durant le cycle cellulaire chez le tachyzoïte. Dans le but de comprendre comment sa fonction dépendante du cycle cellulaire est régulée, nous avons identifié des potentiels partenaires d'interactions dont TgAP2X-5, un autre FT ApiAP2 dont l’expression est régulée durant les phases S/M du cycle. L'utilisation d'un système d'expression inductible ainsi que des expériences de séquençage des ARN nous ont permis de démontrer que la perte d'expression de TgAP2X-5 induit une diminution du nombre de transcrits codant pour les protéines de rhoptrie et de micronème. Alors que la perte d'expression de TgAP2X-5 n'influence pas de manière significative l'invasion et la croissance du parasite, nous observons une perte totale de virulence de la souche parasitaire in vivo. Pour mieux comprendre les mécanismes moléculaires mis en jeu, nous nous sommes demandés si la fixation de TgAP2XI-5 sur ces promoteurs cible est conservée en absence de TgAP2X-5. Par des expériences de ChIP-chip, nous avons montrés que l'absence de TgAP2X-5 conduit à une incapacité de fixation de TgAP2XI-5 sur des promoteurs de gènes de rhoptrie. L'ajout d'une copie du gène TgAP2X-5 sous son propre promoteur dans la souche mutante est capable de restaurer l'expression des protéines de rhoptrie préalablement affectée. Toutes ces expériences montrent pour la première fois une coopération des FT APiAP2 dans la régulation des gènes chez les Apicomplexes. / Toxoplasma gondii is a unicellular eukaryote belonging to the Apicomplexa phylum. It is an obligate intracellular parasite of critical importance to primarily infected pregnant women and immunosuppressed patient. Its life cycle is complex, with multiple proliferation and differentiation steps, of which tachyzoite proliferation is the most relevant to pathogenesis in humans. Tachyzoites express invasion and virulence factors that are crucial for their survival and the manipulation of host cell functions. Expression of these virulence factors is tightly regulated permitting their correct targeting in specific organelles named rhoptry and microneme. However, little is known about the factors controlling the expression of genes encoding the virulence factors. ApiAP2 are a family of conserved transcription factors (TF) that play an important role in regulating gene expression in apicomplexan parasites. Previous studies had revealed the ability of one of these TFs, TgAP2XI-5, to bind to transcriptionally active promoters of genes expressed during the S/M phase such as rhoptry and micronemes genes. However, expression of TgAP2XI-5 is constitutive during the tachyzoite cell cycle. To better understand how its function is regulated, we identified proteins interacting with TgAP2XI-5 including a cell cycle regulated ApiAP2 TF, TgAP2X-5. Using an inducible knock-down strategy and RNA-Seq, we demonstrate that the level of expression of number of rhoptry and microneme transcripts is affected by the disruption of TgAP2X-5 expression. While TgAP2X-5 disruption has mild effect on parasite growth and invasion, it leads to the strain avirulence in mice. To better understand the molecular mechanisms at stake, we investigated the binding of TgAP2XI-5 at promoters in the TgAP2X-5 mutant in a genome-wide assay. We show that disruption of TgAP2X-5 expression leads to defects in TgAP2XI-5 binding to multiple rhoptry gene promoters. Complementation of the TgAP2X-5 mutant restores the expression of rhoptry proteins previously affected. This is the first evidence of a cooperative action of ApiAP2 TF in Apicomplexa.

Les parasites apicomplexes sont ubiquitaires et ont une forte incidence en médecine humaine et vétérinaire. Certains de ces parasites, comme Plasmodium falciparum, l’agent du paludisme, ou Toxoplasma gondii, l’agent de la toxoplasmose, posent des problèmes de santé publique. Les thérapies existantes montrent parfois une efficacité limitée, une forte toxicité et entraînent des résistances, d’où la nécessité de nouvelles approches plus spécifiques. Dans ce contexte, nous avons développé deux approches d’inhibition des apicomplexes : -la synthèse de biphénylimidazoazines à large spectre efficaces au micromolaire sur cinq parasites apicomplexes différents in vitro. -la synthèse d’imidazo[1,2-b]pyridazines ciblant spécifiquement une protéine kinase (CDPK1) de T. gondii et efficaces au submicromolaire sur le parasite in vitro. Une diminution de plus de 90 % de la charge parasitaire chez la souris et une innocuité à court terme font de ces imidazo[1,2-b]pyridazines de bons candidats thérapeutiques. / Apicomplexan parasites are ubiquitous and have a strong incidence in veterinary and human medicine. Some of them, like Plasmodium falciparum, causing malaria, or Toxoplasma gondii, causing toxoplasmosis, are matter of public health concern. The existing therapies may have limited efficiency, high toxicity, and may lead to resistance, highlighting the necessity of new more specific approaches. In this context, we have developed two approaches to inhibit Apicomplexa: -the synthesis of biphenylimidazoazines with broad-spectrum and efficient at the micromolar range on five different apicomplexan parasites in vitro. -the synthesis of imidazo[1,2-b]pyridazines specifically targeting a kinase protein (CDPK1) of T. gondii and efficient at the submicromolar range on the parasite in vitro. More than 90% diminution of parasite burden in mice and short term safety make these imidazo[1,2-b]pyridazines good therapeutic candidates.

Eimeria tenella est un parasite apicomplexe responsable de la coccidiose aviaire. Il s’agit de l’une des plus importantes maladies parasitaires en élevage avicole. Le génome d’E. tenella code pour 28 protéines appartenant à la famille des ROP kinases. Chez T. gondii, les ROP sont des facteurs de virulence majeurs. Elles sont secrétées dans la cellule hôte et interviennent dans le développement du parasite en détournant les fonctions cellulaires au profit du parasite et en modulant la réponse immune de l’hôte. Parmi les ROP kinases, EtROP17 est l’une des kinases identifiées en protéomique chez le sporozoïte. L'objectif de ma thèse était d'étudier les fonctions de la EtROP17 dans la pathogénicité d’E. tenella. EtROP17 est une kinase active, capable d’autophosphorylation. Son extension N-ter (NTE) est nécessaire à son activité catalytique. En outre, EtROP17 induit un arrêt du cycle cellulaire en phase G1 et bloque l'apoptose en ciblant directement la p53 de la cellule hôte. EtROP17 immunoprécipite de nombreuses protéines des filaments intermédiaires notamment la vimentine et les cytokératines, suggérant ainsi que la kinase agit sur le cytosquelette de la cellule. L’ensemble de ces résultats confirment que EtROP17 est un effecteur de la modulation de la réponse de la cellule hôte au cours de l'infection par E. tenella. / Eimeria tenella is an apicomplexan parasite. It is responsible for cecal coccidiosis which causes severe economic losses in the poultry industry. The kinome of E. tenella comprises 28 putative members of ROP kinase family which is specific to the coccidian clade. In T. gondii, ROP kinases are key virulence factors. They hijack and modulate many cellular functions and pathways, allowing the parasite’s survival and development. EtROP17 is one of the two ROP kinases, EtROP17 and EtROP25, identified in sporozoïte proteomic. The aim of my thesis was to study the functions of EtROP17 in the interaction between the parasite and the host cell. EtROP17 is an active kinase and uses a non-canonical mechanism to phosphorylate its substrate. The N-terminal extension (NTE) is essential for catalytic activity. Moreover, EtROP17 induces cell cycle arrest in G1 phase and blocks apoptosis and cell mortality by directly targeting the host cell’s p53. EtROP17 immunoprecipitates many proteins of the intermediate filaments including vimentine and cytokeratins suggesting that the kinase acts on the cell cytoskeleton. Taken together, these results support that EtROP17 is a bona fide effector for the modulation of the host cell’s response during E. tenella infection.

Toxoplasma gondii est un protiste apicomplexe responsable de la toxoplasmose. Ce parasite intracellulaire obligatoire possède des organites sécrétoires apicaux dont les rhoptries qui contiennent des facteurs de virulence essentiels à l'invasion et à la modulation de la cellule hôte qu'il infecte. Au cours de la division cellulaire de T. gondii, les protéines de rhoptries sont synthétisées selon la même cinétique. Dans le but d'identifier de nouvelles protéines dont la fonction est potentiellement liée aux rhoptries, nous avons recherché à partir des bases de données du génome de T. gondii, les protéines présentant ce profil particulier d'expression. La localisation subcellulaire de 12 candidats a été réalisée puis une caractérisation phénotypique de quatre d'entre eux a été entreprise. Nous avons identifié une nouvelle protéase de rhoptries, DegP, essentielle à la virulence du parasite in vivo. Nous montrons que DegP contrôle la phase aigüe de l'infection en modulant la réponse immune de l'hôte contribuant ainsi à la dissémination du parasite in vivo. Nous identifions également deux protéines homologues, Claw1 et Claw2, présentant une localisation atypique à l'extrémité apicale du parasite. Notre incapacité à déléter ces gènes pourrait indiquer un rôle essentiel de ces protéines au niveau du complexe apical de T. gondii. Enfin, bien que n'étant pas reliée aux rhoptries, ce crible a permis d'identifier la première protéine associée aux jonctions des vésicules constituant le complexe membranaire interne de Toxoplasma. La délétion de cette protéine, SIP, affecte la forme du parasite, entrainant un défaut de motilité, d'invasion et de virulence in vivo. / Toxoplasma gondii is an apicomplexan protist and the causative agent of toxoplasmosis. This obligate intracellular parasite harbors apical secretory organelles such as rhoptries that contain essential virulence factors responsible of the invasion and the modulation of the infected host cell. Along the cell cycle of T. gondii, rhoptry proteins share the same timing of expression. In order to identify new proteins involve in rhoptry content, biogenesis or secretion, we screened the genome database of T. gondii to isolate proteins that present this particular profile. We obtained the subcellular localization of 12 candidates and we investigated the biological functions for 4 of them. We showed that DegP, a rhoptry protease is essential for the in vivo virulence of T. gondii. DegP controls the acute phase during infection and modulate the host immune response leading to better parasite dissemination in vivo. Also, we identified Claw1 and its paralog Claw2 that present an atypical localization at the apical end of the parasite. To date, we were unable to disrupt the genes encoding these proteins suggesting that they may have an essential function related to the apical complex in T. gondii. Finally, we also examined a ‘hit' of this screening that was not related to rhoptries and we identified SIP, the first protein associated with the transversal junctions of the inner membrane complex in T. gondii. The disruption of SIP affects the shape of the parasite leading to an aberrant motility, defect in invasion and impaired parasite virulence in mice.

Résumé confidentiel / Résumé confidentiel

Hemoparasitos do filo Apicomplexa merecem destaque devido ao impacto que podem ter na conservação da biodiversidade dos mamíferos. O presente estudo objetivou avaliar a ocorrência de agentes Piroplasmida (Cytauxzoon, Theileria e Babesia) e Hepatozoon spp., utilizando o Exame Microscópico Convencional (EMC) e a Reação em Cadeia da Polimerase (PCR), e identificar os carrapatos presentes em mamíferos silvestres destinados ao LAPAS-UFU, CETAS-GO/IBAMA e CETAS-BH/IBAMA. Obteve-se 152 amostras de sangue total e realizou-se a PCR para Hepatozoon spp., com a utilização dos primers HepF300/Hep900, Hep2F/Hep2R e HAM-1/HPFR2, e para a ordem Piroplasmida, realizou-se a PCR com auxílio dos primers BAB- 33-47/ BAB432-439, PIRO 1F/PIRO 5R. Com punção de sangue periférico, confeccionou-se 352 extensões de 123 animais. Pelo EMC, não foram observados gamontes de Hepatozoon spp., mas pela PCR obteve-se 5,2% de positividade (oito positivos). Foram obtidos quatro novos haplótipos de Hepatozoon canis e Hepatozoon felis nos mamíferos de espécies lobo-guará (Chrysocyon brachyurus), raposa-do-campo (Lycalopex vetulus), irara (Eira barbara) e onça-parda (Puma concolor). Para os piroplasmas, pelo EMC e PCR, obteve-se 34,9% (43 animais positivos) e 26,3% (40 animais positivos), respectivamente. Foram obtidos três novos haplótipos de espécies de piroplasmas, sendo sequências similares à Theileria cervi em veado-catingueiro, Theileria equi em anta e Cytauxzoon felis em jaguatirica. Foram identificadas 432 espécimes, de 30 animais. Os carrapatos identificados foram: Amblyomma nodosum, A. parvum, A. ovale, A. sculptum, A. longirostre, A. dubidatum, Rhipicephalus microplus e R. sanguineus. Além disso, outros hemoparasitos foram observados em microscopia óptica, como Ehrlichia spp. em 23 animais (18,6%) e microfilárias em dois indivíduos de espécie Coendou prehensilis (ouriço-cacheiro). O conjunto de informações trazidas por este trabalho comprova a abundância de hemoparasitos que mamíferos brasileiros podem albergar. Além disso, algumas espécies de carrapatos identificados foram determinantes para inferir possíveis modos de transmissão de hemoparasitos observados nos animais. Sobre o resultado obtido pelo uso das técnicas de diagnóstico, a PCR, aliada ao sequenciamento, mostrou-se mais precisa que o EMC para identificação de espécies de hemoparasitos-alvo deste trabalho. / Haemoparasites belonging to filum Apicomplexa deserve attention because can affect the conservation of mammals’s biodiversity. This work aimed to avalue the occurencce of Piroplasmida agents (Cytauxzoon, Theileria e Babesia) e Hepatozoon spp. using Convencional Microscopic Exam (CME) and Polymerase Chain Reaction (PCR) and indetify ticks on wild mammals belonging to LAPAS-UFU, CETAS-GO/IBAMA e CETAS-BH/IBAMA. On total, this work obtained 152 total blood samples that were submited to PCR for Hepatozoon spp. with primers HepF300/Hep900, Hep2F/Hep2R e HAM-1/HPFR2, and for Piroplasmida agents, PCR was done using primers BAB- 33-47/ BAB432-439, PIRO 1F/PIRO 5R. To exam slides on optic microscope, was used peripheral samples of 123 mammals. There wasn’t observed gamonts of Hepatozoon spp. on blood slides, but on PCR was observed prevalence of 5,2% (eight positive mammals). From these, was obtained four new haplotypes of Hepatozoon spp. like similar sequence of Hepatozoon canis in maned-wolf (Chrysocyon brachyurus) and hoary fox (Lycalopex vetulus) and similar sequence of Hepatozoon felis in tayra (Eira barbara) and puma (Puma concolor). For Piroplasmida agents, the CME and PCR results were 34,9% (43 positive mammlas) and 26,3% (40 positive mammals), respectively. There was obtained three new haplotypes of Piroplasmida agents, being similar sequences of Theileria cervi in brown brocket deer (Mazama gouazoubira), similar sequence of Theileria equi in brazilian tapir (Tapirus terrestris) and similar sequence of Cytauxzoon felis in ocelot (Leopardus pardalis). There was identified 432 specimnes of ticks on 30 mammals. The species were Amblyomma nodosum, A. parvum, A. ovale, A. sculptum, A. longirostre, A. dubidatum, Rhipicephalus microplus e R. sanguineus. Besides this results, other haemoparasites were observed on optic microscope, like Ehrlichia spp. in 23 mammals (18,6%) and microfilaria in two mammals of the species Coendou prehensilis (brazilian porcupine). The information gathered by this work confirms the abundance of haemoparasites that the Brazilian mammals can harbor. In addition, some species of ticks identified were determinant to infer possible ways of transmitting hemoparasites identified in mammals. The result obtained by the use of molecular diagnostic techniques (PCR and sequencement) was more accurate than the CME for identification of hemoparasites on wild mammals of this work. / Dissertação (Mestrado)

Submitted by (edna.saturno@ufrpe.br) on 2016-08-01T16:39:12Z No. of bitstreams: 1 Antonio Tembue.pdf: 785696 bytes, checksum: 3f9e9ef8e3f1459afeea01eeed2f71fa (MD5) / Made available in DSpace on 2016-08-01T16:39:12Z (GMT). No. of bitstreams: 1 Antonio Tembue.pdf: 785696 bytes, checksum: 3f9e9ef8e3f1459afeea01eeed2f71fa (MD5) Previous issue date: 2007-05-18 / Small ruminants production is an important activity specially as a protein source, meat, leather, milk and by-products processing throughout the Brazil. However with the lack of technical support in sheep and goat production systems some parasitic disease has been related including coccidiosis. The goal of this study is describe the epidemiology of some coccidia agents in goats and sheep from Ibimirim County, Pernambuco State, Brazil. A total of 400 animals, being 319 goats and 81 sheep from different farms were studied. First a total of 400 faecal samples were evaluated to identify the eimerian species. Coccidian unsporulated the sporulate oocysts were detected in 95.3% (381/400) and 97.5% (390/400) by using the McMaster technique and aqueous solution of dichromatic (K2Cr2O7) respectively. Eight species of Eimeria were identified: Eimeria arloingi E. ninakohlyakimovae, E. pallida, E. parva, E. intricata, E. ahsata, E. crandallis, E. faurei in goats and E. ahsata, E.crandallis, E. faurei, E. intricata, E. granulosa, E. parva and E. punctata in sheep. The other intestinal coccidia,Cryptosporidium sp oocyst was also identified in 3.7% (3/81), of sheep faeces samples by using Kinyon methodology. On the other hand a serological survey for antibodies to IgG antibodies anti- Toxoplasma gondii and Neospora caninum by Imunofluorescent antibody test were carried out. The results of serology showed the prevalence of 57% (228/400) positive samples to T. gondii, being 58.9% (188/319) and 49.4% (40/81) in goats and sheep respectively. The antibody frequencies according to the age showed that the prevalence was influenced by the age (≤4 years old) of animals in both goats and sheep. The results of imunofluorescent antibody test to Neospora caninum showed 34.3% (137/400) of positive animals, being 26.6% (85/319) in goats and 64.2% (52/81) in sheep. Serologic reactivity was associated with age only in goats (p<0, 01). In conclusion, these results indicate theexposure of small ruminants living in the study area to coccidia of genus Eimeria, Cryptosporidium, Toxoplasma and Neospora. However the frequency of infection of oocysts of Eimeria particularly Eimeria arloingi, E. ninakohlyakimovae em caprinos e Eimeria ahsata e E. crandallis age, and management practices might be consider in order decreasing the effect of these coccidia. In the other hand hygienic management practices should be adopted in these farms in order to prevent the infection of Toxoplasma gondii by the consumption of unpasteurized milk. / A caprinovinocultura é uma importante pecuária atividade, particularmente como fonte de carne, pele, leite e produtos derivados em todo o Brasil. Contudo, com a perda de assistência técnica ao sistema de produção, algumas doenças parasitárias têm sido relatadas, incluindo as coccidioses. Objetivou-se com o presente estudo contribuir no conhecimento da epidemiologia das coccidioses em pequenos ruminantes no Estado de Pernambuco. Um total de 400 animais, sendo 319 caprinos e 81 ovinos,procedentes de diferentes propriedades foram estudados. Inicialmente 400 amostras fecais foram avaliadas pelo método Gordon Whitlock através da técnica de Mc-Master para contagens de oocistos. Foi realizada a esporulação com solução de dicromato de potássio K2Cr2O7 para a identificação das de espécies de gênero Eimeria. Oocistos de coccídios não esporulados e esporulados foram detectados em 95,3% (381/400) e 97, 5% (390/400) pela técnica de McMaster e Solução aquosa de K2Cr2O7. Foram identificadas oito espécies do gênero Eimeria na espécie caprina com as seguintes freqüências relativas por ordem decrescente, Eimeria arloingi; E. ninakohlyakimovae, E. pallida, E. parva, E. intricata, E. ahsata, E. crandallis, E. faurei, enquanto nos ovinos foram encontradas a E. ahsata E.crandallis, E.faurei, E. intricata, E. granulosa, E. parva, e E. punctata. Outro coccídio intestinal, Cryptosporidium spp. oocistos também foi identificado em 3.7% (3/81) das fezes provenientes dos ovinos pelo método de Kinyon. Por outro lado foi realizado um levantamento sorológico de anticorpos IgG anti- Toxoplasma gondii e Neospora caninum através da reação de Imunofluorescencia Indireta. Os resultados revelaram a prevalência de 57% (228/400) de amostras positivas para Toxoplasma gondii, sendo 58,9% (188/319) em caprinos e 49,4% (40/81) em ovinos. A freqüência de anticorpos anti- Toxoplasma gondii foi influenciada com a idade dos animais (≤4 anos) em ambas as espécies animais. O resultado do teste de Imunofluorescencia Indireta para Neospora caninum evidenciou 34,3% (137/400) dos animais foram soropositivoss, sendo 26,6% (85/319) em caprinos e 64,2% (52/81) em ovinos. Com relação à idade, foi observada uma diferença significante somente em caprinos (p<0, 01). De acordo com os resultados obtidos, pode se concluir que os pequenos ruminantes estão expostos à infecção por coccídios de gênero Eimeria, Cryptosporidium, Toxoplasma e Neospora na área estudada. Contudo em função da freqüência de oocistos de gênero Eimeria, observada no presente estudo, particularmente Eimeria arloingi, E. ninakohlyakimovae em caprinos e Eimeria ahsata e E. crandallis em ovinos, medidas higiênico-sanitários devem ser realizadas para minimizar os efeitos produzidos porestes coccídios Não obstante, práticas higiênico-sanitárias devem ser adotadas nas criações para prevenir a infecção de Toxoplasma gondii através do consumo de leite de cabra não pasteurizado.

Toxoplasma gondii is an obligate intracellular parasite that infects virtually all warm-blooded organisms. Systemic dissemination of T. gondii in the organism can cause life-threatening infection that manifests as Toxoplasma encephalitis in immune-compromised patients. In addition, mounting evidence from epidemiological studies indicates a link between chronic Toxoplasma infection and mental disorders. To better understand the pathogenesis of toxoplasmosis, basic knowledge on the host-parasite interactions and the dissemination mechanisms are essential. Previous findings have established that, upon infection with T. gondii, dendritic cells (DCs) and microglia exhibit enhanced migration, which was termed the hypermigratory phenotype. As a result of this enhanced migration, DCs and microglia are used as vehicle cells for dissemination (‘Trojan horse’) which potentiates dissemination of T. gondii in mice. However, the precise mechanisms behind the hypermigratory phenotype remained unknown. In this thesis, we characterized host-parasite interactions upon infection with T. gondii and investigated the basic mechanisms behind the hypermigratory phenotype of T. gondii-infected DCs and microglia. In paper I, we observed that upon infection with T. gondii, DCs underwent rapid morphological changes such as loss of adhesiveness and podosomes, with integrin redistribution. These rapid morphological changes were linked to hypermotility and were induced by active invasion of T. gondii within minutes. T. gondii-infected DCs exhibited up-regulation of the C-C chemokine receptor CCR7 and chemotaxis towards the CCR7 chemotactic cue, CCL19. In paper II, we developed a 3-dimensional migration assay in a collagen matrix, which allowed us to characterize the hypermigratory phenotype in a more in vivo-like environment. The migration of T. gondii-infected DCs exhibited features consistent with integrin-independent amoeboid type of migration. T. gondii-induced hypermigration of DCs was further potentiated in the presence of CCL19 in a 3D migration assay. In paper III, we identified a parasite effector molecule, a Tg14-3-3 protein derived from parasite secretory organelles. Tg14-3-3 was sufficient to induce the hypermigratory phenotype. Transfection with Tg14-3-3-containing fractions or recombinant Tg14-3-3 protein induced the hypermigratory phenotype in primary DCs and in a microglial cell line. In addition, Tg14-3-3 localized in the parasitophorous vacuolar space and host 14-3-3 proteins were rapidly recruited around the parasitophorous vacuole. In paper IV, we found that mouse DCs dominantly express the L-type voltage-dependent calcium channel, Cav1.3. Cav1.3 was linked to the GABAergic signaling-induced hypermigratory phenotype. Pharmacological inhibition of Cav1.3 and knockdown of Cav1.3 abolished the hypermigratory phenotype in T. gondii infected DCs. Blockade of voltage-dependent calcium channels reduced the dissemination of T. gondii in a mouse model. In paper V, we showed that microglia, resident immune cells in the brain, also exhibited rapid morphological changes and hypermotility upon infection with T. gondii. However, an alternative GABA synthesis pathway was shown to be involved in the hypermigratory phenotype in microglia. In summary, this thesis describes novel host-parasite interactions, including host cell migratory responses and key molecular mechanisms that mediate the hypermigratory phenotype. The findings define a novel motility-related signaling axis in DCs. Thus, T. gondii employs GABAergic non-canonical pathways to hijack host cell migration and facilitate dissemination. We believe that these findings represent a significant step forward towards a better understanding of the pathogenesis of T. gondii infection. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>