Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The burden of Streptococcus suis infection in humans is increasing worldwide. In Thailand, S. suis is the second most commonly recorded zoonosis. The principal sources of human S. suis infection are pig and pork products. A detailed understanding of the epidemiological characteristics of S. suis and the burden of the disease may help improve prevention and control policy to reduce the burden of this bacterial infection. The work presented in this thesis focuses on human outbreaks of S. suis in Chiang Mai, Thailand, in humans and backyard pigs. This thesis examined the characteristics of previous outbreaks of S. suis in humans and calculated the incidence, disease burden and the associated economic burden of S. suis infection in Chiang Mai. The backyard pig system is important for S. suis transmission and this thesis examined the characteristics of the backyard pig production system in Chaing Mai and examined the prevalence and risk factor for S. suis infection in pigs. Finally, to examine transmission of S. suis, isolates collected during this study were identified and subject to molecular characterization. A retrospective analysis of surveillance data for S. suis cases in Chiang Mai between 2005 to 2014 highlighted the annual incidence rate over this ten year period of 15.52 per 1,000,000 population, 6.5 times higher than for the rest of Thailand (2.37 per 1,000,000 population). The case fatality rate was high at 10.12%. The impact on human health of S. suis infection was derived from surveillance data for the year 2013. The health burden measured in term of Disability Adjusted Life Years (DALYs) was estimated at 7.41 per 100,000 population. Most of the health burden (98.28%) was in adults aged 15-64 years. Males had 3.5 times the health burden of females. The consequences of hearing loss and deafness had significant impacts on affected individuals quality of life. The economic impact of S. suis outbreaks in Chiang Mai was between 2013 and 2014 was estimated from interview data. Most patients were covered for their health costs by the national health security scheme, with expenditure due to S. suis on average being 37,955 baht (£759) per patient. Out of pocket expenses for individuals and their families averaged 5,198 baht (£104) per patient. An epidemiological survey of backyard pig production facilities was undertaken in Chiang Mai province where there was a reported high incidence of S. suis cases in humans occurred each year. Most holdings had between one to five pigs and all holdings shared similar characteristics and management practices. The prevalence of S. suis was in pigs was 4.8% (95%CI=2.2-7.4%). Pigs living in larger spaces (≥ 1.2 m2) showed a lower risk for S. suis infection (OR = 4.35, 95% CI = 1.07-25.21). Examination of the isolates from this study revealed a diversity of serotypes. Only one isolate was identified as S. suis serotype 9. The rest did not match any common serotypes for S. suis (1, 2, 7 or 9) and known virulent strains were not identified. Twelve independent sequence profiles were determined by MLST, of which, 11 were novel. Backyard pigs were found to be commonly infected with a range of previously unidentified S. suis and may be a significant reservoir of human infection.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Actinobacillus pleuropneumoniae et Streptococcus suis sont des bactéries pathogènes entraînant des maladies porcines mortelles et des pertes économiques importantes dans l’industrie porcine mondiale. Ces bactéries sont notamment reconnues pour leur implication dans certaines maladies pulmonaires porcines, dont la pneumonie, et leurs mécanismes de pathogénicité ne sont pas parfaitement élucidés. De ce fait, nous nous sommes intéressés à l’activité de ces deux bactéries sur la barrière épithéliale de la trachée du porc, soit un modèle représentatif de la première ligne de défense des voies respiratoires supérieures du porc. Plus précisément, nous avons étudié la capacité d’A. pleuropneumoniae et de S. suis à induire une perte d’intégrité de la barrière épithéliale, à la traverser, et à induire une réponse inflammatoire. En considérant les cytokines pro-inflammatoires sécrétées par les cellules épithéliales en présence de ces bactéries pathogènes, les effets du TNF-α sur la barrière épithéliale ont également été analysés. Nous avons démontré qu’A. pleuropneumoniae, S. suis et le TNF-α sont aptes à induire des dommages importants à la barrière épithéliale et à permettre la translocation de ces bactéries pathogènes à travers cette barrière. Ces résultats suggèrent que la barrière épithéliale puisse représenter une cible thérapeutique contre les infections engendrées par les bactéries pathogènes environnantes afin de limiter leur capacité d’invasion. Pour ce faire, il serait nécessaire d’investiguer davantage les facteurs de virulence de ces bactéries contribuant à la perte d’intégrité de la barrière épithéliale des voies respiratoires supérieures du porc afin d’élaborer de potentiels thérapies ciblées inhibant leur pathogénicité

Made available in DSpace on 2015-03-26T13:47:20Z (GMT). No. of bitstreams: 1 texto completo.pdf: 198280 bytes, checksum: 2e22264df93097f0e349bfa39abd6bcd (MD5) Previous issue date: 2003-09-05 / The present work was developed with the objective to determine the efficiency of an autogenous bacterin against Streptococcus suis serotype 2 and to test route and inoculation doses. Two experiments were accomplished with 64 animals in each experiment. In the Experiment I, 32 animals were vaccinated and 32 animals received placebo, being both groups challenged at the 60 days of age. In the Experiment II, the animals were divided in four groups: NVIP - 16 animals not vaccinated and challenged by the intraperitoneal route; VIP - 16 vaccinated animals and challenged by the intraperitoneal route; NVIV - 16 animals not vaccinated and challenged by the intravenous route; and VIV - 16 vaccinated animals and challenged by the intravenous route. All the groups were challenged at the 88 days of age. In the Experiment I, it was not possible to detect significant difference in the protection, clinical signs and lesions (P>0.05) among the groups not vaccinated and vaccinated. However, the isolation of S. suis and the average of the bacterial count was higher (P <0.01) in the group not vaccinated. The results observed in Experiment II in the groups NVIV and VIV presented protection, clinical signs and lesions similar (P>0.05), and the number of animals with positive isolation of S. suis and the average of the bacterial count was higher in the group NVIV (P<0.05). The groups NVIP and VIP presented significant difference for protection, clinical signs, lesions, number of positive isolations and average of the bacterial agent count (P <0.01). The intravenous challenge route was not appropriate for that experiment type and the intraperitoneal route presented favorable aspects. The vaccine was efficient for prevention of the infection with high virulent S. suis serotype 2, protecting the animals with an efficiency of 87.5 percent. / O presente trabalho foi desenvolvido com o objetivo de determinar a eficácia de uma bacterina autógena na proteção de suínos desafiados com Streptococcus suis sorotipo 2 de alta virulência e testar vias e doses de inoculação do agente. Foram realizados dois experimentos com 64 animais em cada experimento. No Experimento I, 32 animais foram vacinados aos 21 e 45 dias de idade, através de injeção intramuscular de 2 e 3 mL da bacterina, respectivamente. Os 32 animais restantes constituíram o grupo controle não vacinado. Aos 60 dias de idade os 64 animais foram desafiados via intravenosa, na dosagem de 8,6 x 109 UFC. No experimento II, 64 animais foram divididos em dois grupos de 32 animais. Um grupo foi vacinado aos 25 (2 mL) e 50 (3 mL) dias de idade, por via intramuscular, e o outro constituiu o grupo controle não vacinado. Os animais foram desafiados aos 88 dias de idade na dosagem de 7,2 x 109 UFC. Para efeito de desafio, os animais foram divididos em quatro grupos: NVIP - 16 animais não vacinados e desafiados pela via intraperitoneal; NVIV - 16 animais não vacinados e desafiados pela via intravenosa; VIP 16 animais vacinados e desafiados pela via intraperitoneal; e VIV - 16 animais vacinados e desafiados pela via intravenosa. No Experimento I, não foi possível detectar diferença significativa na proteção, sinais clínicos e lesões (p>0.05) entre os grupos não vacinado e vacinado. Só foi possível detectar diferença significativa no número de animais com isolamento positivo do S. suis e na média da contagem de Unidades Formadoras de Colônias (UFC) de S. suis (P<0.01). Os resultados observados no Experimento II, foram: 1) os grupos NVIV e VIV apresentaram proteção, sinais clínicos e lesões similares (P>0.05), e o número de animais com isolamento positivo do S. suis e a média da contagem de colônias de S. suis foi mais elevada no grupo NVIV (P<0.01), confirmando os resultados apresentados no Experimento I; e 2) os grupos NVIP e VIP apresentaram diferenças significativas para proteção, sinais clínicos, lesões, número de isolamentos positivos e média da contagem bacteriana do agente (P<0.01). O grupo NVIP apresentou 5/16 mortes e 11/16 sobreviventes doentes, enquanto que o grupo VIP teve 14/16 sobreviventes sadios e 2/16 de sobreviventes doentes, não apresentando nenhuma morte. A temperatura retal no grupo NVIP foi, em média, 0,5o C superior à do grupo VIP (P<0.01). O escore médio dos sinais clínicos nos grupos NVIP e VIP foi de 1,10±0,10 e 0,34±0,05, respectivamente, sendo mais elevado no grupo não vacinado (P<0.05). O escore médio das lesões também foi mais elevado no grupo NVIP (0,89±0,19) em relação ao grupo VIP (0,20±0,08) (P<0.05). O isolamento do S. suis foi positivo em 9/16 animais do grupo NVIP, com média da contagem bacteriana de 295,25±91,62 UFC/mL, sendo que no grupo VIP não foi possível isolar o agente em qualquer dos animais. A proteção da vacina para os animais desafiados pela via intraperitoneal foi calculada em 87,5%. Portanto, a via de desafio utilizada influenciou nos sinais clínicos, lesões e isolamento bacteriano dos animais vacinados e não vacinados. A via intravenosa não se mostrou adequada para esse tipo de experimento e a via intraperitoneal apresentou aspectos favoráveis. Finalmente, a vacina mostrou ser eficaz na prevenção da infecção pelo S. suis sorotipo 2 de alta virulência, protegendo os animais com uma eficiência estimada de 87,5%.

Einleitung Streptococcus (S.) suis ist weltweit in Schweinepopulationen verbreitet. S. suis verursacht hohe wirtschaftliche Verluste durch das Auftreten von Meningitis, Arthritis, Serositis und Endokarditis und stellt als Zoonoseerreger gleichzeitig ein Risiko für den Menschen dar. Im Zusammenhang mit Infektionen in europäischen Schweinebetrieben werden Serotyp 2, 7 und 9 am häufigsten nachgewiesen. Die Bakteriämie spielt eine Schlüsselrolle in der invasiven S. suis Erkrankung und die Interaktion der Streptokokken mit den Immunzellen des Wirts im Blut ist entscheidend für den Ausgang der Infektion. Ziele der Untersuchung Das Ziel der vorliegenden Arbeit, war die Untersuchung der Fähigkeit von porzinen Immunzellen S. suis durch Phagozytose und reaktive Sauerstoffspezies (ROS) zu töten. Dabei wurden vor allem die Bedeutung von IgM und des Komplementsystems beleuchtet. In diesem Sinne, wurde auch die Arbeitshypothese untersucht, dass eine Modifizierung der bakteriellen Zellwand durch D-Alanylierung von Lipoteichonsäuren (LTAs) S. suis hilft, angeborene Immunfunktionen zu umgehen, wie z. B. die Opsonisierung mit Komplementfaktoren, sowie dass diese Zellwandveränderung die Interaktion von S. suis mit Leukozyten beeinflusst. Material und Methoden Die Bestimmung von ROS und dem Überleben der Streptokokken wurde in vivo im Blut zweier mit S. suis-infizierter Ferkel und in vitro in einem rekonstituierten Blutmodel durchgeführt. Die ROS-Messung erfolgte unter Zugabe von Dihydrorhodamine 123 mittels Durchflusszytometrie in Granulozyten. Verschiedene Inhibitoren wurden dabei eingesetzt: Apocynin um die NADPH Oxidase und damit die ROS-Bildung zu hemmen, Vaccinia Virus Complement Control Protein (VCP) für die Inaktivierung der Komplementkaskade und IdeSsuis um porzines IgM zu spalten. Mithilfe eines thermosensitiven Vektors wurde eine isogene Deletionsmutante des dltA Gens erstellt, um den Einfluss der D-Alanylierung von LTAs zu untersuchen. Die Sequenzierung des entsprechenden Genabschnitts und ein Southern Blot dienten der genetischen Verifizierung der Mutante. Weiterhin wurden Wachstumsverhalten, Hydrophobie und Ladung der Oberfläche sowie minimale Hemmkonzentrationen einer Reihe antimikrobieller Peptide für die dltA Mutante untersucht. Die Assoziation von Blutleukozyten mit S. suis wurde mithilfe von Far Red markierten Bakterien in der Durchflusszytometrie bestimmt. Die Zytokin-Messung erfolgte mit kommerziell erhältlichen Enzyme-linked immunosorbent assays (ELISA)-Kits. Ergebnisse S. suis Stämme der Serotypen 2, 7 und 9 zeigten sich hochsensibel gegenüber Wasserstoffperoxid. Eine Hemmung der Bildung von ROS in rekonstituierten Blutproben führte selbst in Anwesenheit einer hohen Konzentration von S. suis-spezifischen Antikörpern zu einem signifikanten Anstieg des bakteriellen Überlebens. Die Induktion von ROS durch S. suis in Granulozyten wurde durch spezifische Antikörper verstärkt und hing partiell von der Anwesenheit funktionellen Komplements ab. In der Abwesenheit von IgG reduzierte die Spaltung von IgM oder die Inaktivierung von Komplement die ROS Produktion um mehr als das Dreifache, was in einem Anstieg des bakteriellen Überlebens resultierte. Der Mechanismus von S. suis D-Alanin in seine LTAs einzulagern, erhöhte die Hydrophobie der bakteriellen Oberfläche und reduzierte die Opsonisierung mit Komplementfaktor C3b, sowie die Phagozytose durch Granulozyten in Vollblut und die Assoziation von S. suis mit Monozyten and Lymphozyten. Trotzdem wurde das Überleben der Streptokokken in Blut, welches S. suis-spezifische Antikörper enthielt, nicht signifikant durch diese Zellwandmodifikation gesteigert. Allerdings war der durch die dltA Mutante induzierte Gehalt an IL-1β im Blut signifikant geringer als der durch den Wildtyp induzierte. Hohe Antikörperspiegel verursachten einen hochsignifikanten Anstieg der Interaktion von S. suis mit Monozyten, was bei diesen zum inflammatorischen Zelltod mit einer starken Sekretion von IL-1β und TNF-α führte. Schlussfolgerung Trotz einer Vielzahl an Abwehrmechanismen von S. suis gegen oxidativen Stress, stellen Phagozytose und ROS einen sehr effektiven Mechanismus des Immunsystems dar, um die eingedrungenen Streptokokken zu töten. Die Induktion von ROS durch S. suis hängt dabei stark von der Anwesenheit spezifischer Antikörper und teilweise von aktivem Komplement ab. Die Fähigkeit von S. suis D-Alanin in seine LTAs einzulagern, verändert Eigenschaften der bakteriellen Zellwand und vermittelt dabei Schutz vor angeborenen Immunmechanismen, wie antimikrobiellen Peptiden und dem Komplementsystem, aber sie sorgt nicht für ein besseres Überleben der Streptokokken, in der Anwesenheit von spezifischen Immunglobulinen. Sie reduziert die Assoziation von S. suis mit Monozyten, was etwas in Diskrepanz zu einer 2000 postulierten modifizierten „Trojanisches Pferd“-Theorie steht. Die durch LTA D-Alanylierung gesteigerte IL 1β Sekretion im Vollblut, führt zu der Schlussfolgerung, dass S. suis durch diese Zellwandmodifikation Entzündungsprozesse im Wirt beeinflusst.:Contents 1 Introduction 2 Literature 2.1 Streptococcus suis 2.1.1 Characteristics and classification 2.1.2 Epidemiology and Pathology 2.1.3 Pathogenesis of S. suis infection 2.1.4 Cell wall modifications of S. suis 2.2 Selected aspects of the porcine blood immune system 2.2.1 Characteristics and components of porcine blood 2.2.2 Innate immunity 2.2.2.1 Cellular innate immunity in blood 2.2.2.2 Humoral innate immunity in blood 2.2.3 Adaptive immunity 2.2.3.1 Cellular adaptive immunity in blood 2.2.3.2 Humoral adaptive immunity in blood 2.3 Interaction of S. suis with the blood immune system 2.3.1 Immune evasion strategies against blood leukocytes 2.3.2 Complement evasion and S. suis cell wall modifications 3 Publications 3.1 Survival of Streptococcus suis in Porcine Blood Is Limited by the Antibody- and Complement-Dependent Oxidative Burst Response of Granulocytes 3.2 D-Alanylation of Lipoteichoic Acids in Streptococcus suis Reduces Association with Leukocytes in Porcine Blood 4 Discussion 4.1 Phagocytosis and oxidative burst in porcine blood 4.2 Interaction of S. suis with blood monocytes and lymphocytes 4.3 Conclusion 5 Zusammenfassung 6 Summary 7 References 8 Appendix 8.1 Presentations given during the development of this thesis / Introduction Streptococcus (S.) suis is a widespread pathobiont in the porcine population. It is reason for high economic losses in the swine industry by causing meningitis, arthritis, serositis, and endocarditis, but also poses a threat to human health as a zoonotic pathogen. Serotype 2, 7 and 9 play an important role in European disease cases on pig farms. Bacteremia is a hallmark of invasive S. suis infections and the interaction of the streptococci with blood immune cells is crucial for the outcome of infection. Aim of the study The objective of this thesis was to investigate the ability of porcine blood immune cells to kill S. suis by phagocytosis and oxidative burst and the importance of IgM and the complement system in the killing process. In this context, I investigated the working hypothesis that modifying its cell wall by D-alanylation of lipoteichoic acids (LTAs) aids S. suis to evade certain functions of innate immunity, like opsonization with complement components, and influences the interaction of S. suis with blood leukocytes. Materials and Methods The investigation of reactive oxygen species (ROS) and colony forming units (CFU) was performed in vivo in the blood of two S. suis-infected piglets and in vitro in a reconstituted blood model. ROS were measured by addition of dihydrorhodamine 123 and flow cytometry analysis of granulocytes. To analyze the influence of immunological components, different inhibitors were used: apocynin inhibits the NADPH oxidase and therefore the ROS production, vaccinia virus complement control protein (VCP) inhibits the complement cascade and IdeSsuis cleaves porcine IgM. To investigate the role of D-alanylation of S. suis-LTA an isogenic in-frame deletion mutant of the dltA gene, ΔdltA, was generated by using a thermosensitive shuttle vector. It was genetically verified by sequencing of the respective gene sequence and southern blotting. Phenotypical characterization included growth behavior, evaluation of surface hydrophobicity and electric charge and minimal inhibitory concentrations of a number of antimicrobial peptides. The association of blood leukocytes with S. suis was investigated by flow cytometry, using Far Red-labeled S. suis stocks. Cytokines were detected by commercially available Enzyme-linked immunosorbent assays (ELISA). Results S. suis strains of serotype 2, 7 and 9 were shown to be highly susceptible to oxidative burst intermediate hydrogen peroxide and inhibition of oxidative burst in reconstituted blood samples led to a significant increase of bacterial survival, even in the presence of high S. suis-specific antibody levels. The induction of ROS in granulocytes in response to S. suis was enhanced by specific antibodies and partially depended on the presence of functional complement. In the absence of IgG, IgM cleavage or complement inactivation both reduced the ROS production more than 3-fold and resulted in increased bacterial survival in accordance with an IgM-complement-oxidative burst axis. The mechanism of S. suis to introduce D-alanine into its LTAs increased the hydrophobicity of its surface, reduced opsonization with complement factor C3b, reduced phagocytosis by granulocytes in whole blood and association with monocytes and lymphocytes in isolated peripheral blood mononuclear cells. Nevertheless, in whole blood containing S. suis-specific antibodies, survival of the streptococci was not significantly increased by this cell wall modification, but levels of IL-1β induced by ΔdltA were significantly lower than those induced by the wt. High antibody levels caused a highly significant increase in the interaction of S. suis with monocytes in isolated PBMCs leading to an inflammatory cell death associated with the secretion of high levels of IL-1β and TNF-α. Conclusion Despite numerous described defense mechanisms of S. suis against oxidative stress, phagocytosis and ROS represent a very effective way of the porcine immune system to kill the invading streptococci. The induction of ROS by S. suis is highly dependent on the presence of specific antibodies and partially depends on active complement. The ability of S. suis to D-alanylate its LTAs changes surface properties of S. suis and provides protection from innate host defenses like antimicrobial peptides and the complement system, but does not help the bacteria to survive in the presence of specific immunoglobulins. It reduces the association with monocytes, in contradiction to a proposed “modified trojan horse theory”. The increased IL-1β production in response to S. suis, due to LTA D-alanylation, leads to the suggestion that this surface modification influences inflammatory processes is the host.:Contents 1 Introduction 2 Literature 2.1 Streptococcus suis 2.1.1 Characteristics and classification 2.1.2 Epidemiology and Pathology 2.1.3 Pathogenesis of S. suis infection 2.1.4 Cell wall modifications of S. suis 2.2 Selected aspects of the porcine blood immune system 2.2.1 Characteristics and components of porcine blood 2.2.2 Innate immunity 2.2.2.1 Cellular innate immunity in blood 2.2.2.2 Humoral innate immunity in blood 2.2.3 Adaptive immunity 2.2.3.1 Cellular adaptive immunity in blood 2.2.3.2 Humoral adaptive immunity in blood 2.3 Interaction of S. suis with the blood immune system 2.3.1 Immune evasion strategies against blood leukocytes 2.3.2 Complement evasion and S. suis cell wall modifications 3 Publications 3.1 Survival of Streptococcus suis in Porcine Blood Is Limited by the Antibody- and Complement-Dependent Oxidative Burst Response of Granulocytes 3.2 D-Alanylation of Lipoteichoic Acids in Streptococcus suis Reduces Association with Leukocytes in Porcine Blood 4 Discussion 4.1 Phagocytosis and oxidative burst in porcine blood 4.2 Interaction of S. suis with blood monocytes and lymphocytes 4.3 Conclusion 5 Zusammenfassung 6 Summary 7 References 8 Appendix 8.1 Presentations given during the development of this thesis

Streptococcus suis est un agent pathogène bactérien important qui affecte les porcelets post-sevrés et qui cause des septicémies, des méningites et des arthrites. L’infection se transmet principalement par voie respiratoire, cependant il existe une hypothèse que la voie intestinale pourrait aussi représenter une porte d’entrée pour le pathogène. Le déoxynivalénol (DON) est une mycotoxine soupçonnée depuis longtemps d’être un facteur prédisposant dans le développement de la maladie causée par S. suis, mais cela n’a encore jamais été étudié. L’objectif de cette étude est donc d’évaluer l’effet du DON sur les interactions de S. suis avec les cellules dendritiques (DCs) porcines, les macrophages alvéolaires porcins (PAMs) et les cellules épithéliales intestinales du porc (IPEC-J2). L’induction de médiateurs inflammatoires mesurée par RT-PCR ont révélé que le DON cause une diminution significative de l’expression des cytokines pro-inflammatoires (IL-6, IL-8, TNF-α) des DCs porcines et des PAMs favorisant ainsi un environnement immunosuppresseur. L’étude de l’expression du CMH-II par FACS a révélé que de faibles concentrations (≤ 1 μM) de DON augmentent significativement l’expression du CMH-II alors que de fortes concentrations (≥ 2 μM) causent plutôt une diminution significative de son expression influençant ainsi la mise en place de l’immunité adaptative. De plus, les tests de phagocytose ont révélé que de fortes concentrations (≥ 1 μM) de DON diminuent la capacité de phagocytose de S. suis par les PAMs favorisant ainsi la dissémination de la bactérie. Des tests d’adhésion et d’invasion ont révélé que le DON n’a pas d’impact sur l’adhésion de S. suis aux IPEC- J2 et que de fortes concentrations (≥ 4 μM) de DON favorisent l’invasion de S. suis dans ces cellules. Finalement, des tests ELISA ont montré que le DON (0,5, 1 et 4 μM) diminue significativement la production de cytokines pro-inflammatoires (IL-8) des IPEC-J2. / Streptococcus suis is an important bacterial pathogen that affects post-weaner piglets and causes septicemia, meningitis and arthritis. The infection is mainly transmitted by the respiratory route; however, there is a hypothesis that the intestinal tract could also represent an entry point for the pathogen. Deoxynivalenol (DON) is a mycotoxin that has long been suspected of being a predisposing factor in the development of disease caused by S. suis, but has never been studied. The objective of this study is therefore to evaluate the effect of DON on the interactions of S. suis with porcine dendritic cells (DCs), porcine alveolar macrophages (PAMs) and porcine intestinal epithelial cells (IPEC-J2). The induction of inflammatory mediators measured by RT-PCR revealed that DON causes a significant decrease in the expression of pro-inflammatory cytokines (IL-6, IL- 8, TNF-α) in porcine DCs and PAMs, thus promoting an immunosuppressive environment. The study of MHC-II expression by FACS revealed that low concentrations (≤ 1 μM) of DON significantly increase the expression of MHC-II while high concentrations (≥ 2 μM) rather cause a significant decrease in its expression, thus influencing the establishment of adaptive immunity. In addition, phagocytosis assays revealed that high concentrations (≥ 1 μM) of DON decrease the phagocytosis capacity of S. suis by PAMs, thus promoting the dissemination of the bacteria. Adhesion and invasion assays revealed that DON does not impact S. suis adhesion to IPEC-J2 and that high concentrations (≥ 4 μM) of DON promote S. suis invasion into IPEC-J2. Finally, ELISA have shown that DON (0,5, 1 et 4 μM) significantly reduce IPEC-J2’s production of pro-inflammatory cytokines (IL-8).

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal