Innate immune activation is thought to play a central role in IBD pathogenesis because genetic polymorphisms in NOD2 and NLRP3, cytosolic innate immune receptors belonging to the NLR family, have been associated with IBD susceptibility. However, the mechanisms through which NLR mutations predispose to IBD remain unclear. The aim of this project was to dissect the functional roles of different NLRs in intestinal inflammation. Using the well-established DSS-induced colitis model as well as experimental models of IBD based on infection with Helicobacter hepaticus, we found that Nod2 expression was significantly increased at the peak of intestinal inflammation, and remained elevated throughout the resolution process. This observation suggests a possible role for Nod2 in the resolution of inflammation. Conversely, upon infection with the acute intestinal pathogen Citrobacter rodentium, Nlrp3-/- mice suffered from increased bacterial colonization as early as 3 days post infection, resulting in exacerbated intestinal inflammation and severe weight loss. Analysis of irradiation bone marrow chimeras showed that the protection required Nlrp3 activation in the non-haematopoietic compartment. Furthermore, this protective mechanism was independent of the inflammasome-associated cytokines IL-1β or IL-18. Therefore, this study implicates Nlrp3 activation in intestinal tissue cells as having a crucial role in controlling pathogenic bacterial colonization, providing a potential mechanism by which NLRP3 polymorphisms could lead to increased susceptibility to IBD.

Acute diarrhea is the second leading cause of mortality among children under 5 years of age in developing countries. The pathogens most strongly associated with diarrhea is rotavirus followed by enteric pathogens such as bacteria, helminthes and protozoan. Adequate sanitation and water supply contribute to decrease acute diarrhea incidence of most etiologic agents, although vaccination remains the most important intervention to control rotavirus acute diarrhea. This study aimed to describe environmental exposures and spatial analysis associated with acute diarrhea and enteric pathogens among rotavirus vaccinated infants from Laranjeiras, Sergipe, Brazil. The children live in an area covered by Saúde da Família National Program and were 2 to 11 months old at enrollment. All reported children were followed for 12 months. Demographic, socioeconomic and environmental data were obtained from a questionnaire, and immunization data were obtained from children vaccination card. Children stool samples were collected each month in order to run laboratory analyses. The household spatial localization was obtained by using a Global Positioning System (GPS). Spatial analysis was performed using the TerraView computer program and Kernel intensity estimation. A total of 1,113 stool samples were collected, with 80 samples associated to diarrhea episodes. Diarrhea incidence rate was 0.50 ± 0.99 episodes/child/year. Overall, we observed 5.1% of Ascaris lumbricoides infection, 3.0% of Endolimax nana infection, 2.6% of rotavirus infection and 0.9% of Giardia lamblia infection. We observed rotavirus in 3.75% of stool samples associated with diarrhea but the majority (11.25%) of known diarrhea episodes was associated with helminthes and protozoan infections. There was no influence of environmental exposures on the number of episodes of diarrhea and enteroinfecções suggesting that environmental exposures are similar for the entire study sample. We observed some changes on spatial distribution of intestinal infections and diarrhea episodes along the four evaluated trimesters, especially on the urban center and adjacent areas. In conclusion, the studied infants live equally in poor urban drainage and poor sewerage areas which probably explain the significant rates of helminthes and protozoan infections appearing in early life. The low diarrhea incidence rate in this rotavirus vaccinated population and the low number of symptomatic rotavirus infection compared to asymptomatic infections may highlight the vaccination role as an important prevention strategy of acute diarrhea among young children. / A diarreia aguda é a segunda causa de mortes em crianças menores de 5 anos em vários países em desenvolvimento, sendo a infecção pelo Rotavírus a causa mais comum, seguida das infecções por enterobactérias e enteroparasitos. Medidas de saneamento e boa qualidade da água podem diminuir a ocorrência da doença, mas em relação ao Rotavírus a vacinação específica tem papel fundamental. Este estudo teve o objetivo de conhecer as características ambientais e analisar espacialmente a diarreia aguda e as enteroinfecções em lactentes numa situação de uso ampliado da vacina contra o Rotavírus, no município de Laranjeiras/SE. Os lactentes residiam nas áreas de cobertura das Equipes de Saúde da Família, com a faixa etária entre dois e onze meses de idade e foram acompanhados durante 12 meses. Através de um questionário foram obtidos os dados demográficos, socioeconômicos e ambientais e cobertura vacinal contra rotavírus. Foram coletados mensalmente amostras de fezes para realização de exames parasitológicos, bacteriológicos e presença do rotavírus. Para a localização espacial dos domicílios foi utilizado o Sistema de Posicionamento Global (GPS). A análise espacial foi realizada no programa TerraView, utilizando-se o estimador de intensidade Kernel. Foi coletado um total de 1.113 amostras de fezes, sendo 80 associadas a episódios de diarreia. Obteve-se uma incidência média anual de episódios de diarreia de 0,50 ± 0,99/criança/ano. A presença do rotavírus ocorreu em 3,75% dos casos, enquanto que a maior parte (11,25%) das diarreias agudas com causa conhecida aconteceu na presença de infecções helmínticas e por protozoários. No total de 1113 amostras, foram encontrados: Ascaris lumbricoides (5,1%), Endolimax nana (3,0%), rotavírus (2,6%) e Giardia lamblia (0,9%). Não houve influência das condições ambientais no número de episódios de diarreia e das enteroinfecções. Ocorreram pequenas variações na distribuição espacial das enteroinfecções e dos episódios de diarreia, durante os quatro trimestres, destacando-se o centro urbano e áreas adjacentes com maior intensidade. Conclui-se que as características ambientais demonstram homogeneidade em relação às precárias condições de saneamento básico nas moradias dos lactentes, contribuindo para um significativo número de enteroparasitos, até mesmo nesta faixa etária. O baixo número de episódios de diarreia/criança/ano nesta população com ampla cobertura vacinal contra rotavírus sugere o papel da vacinação como uma importante medida de prevenção. O efeito atenuador da vacina também pode ser demonstrado pelo número de casos de infecção por rotavírus assintomáticos em maior número em comparação com os casos sintomáticos.

Les premières souches bactériennes résistantes aux antibiotiques sont connues depuis 70 ans et se sont multipliées ces dernières années posant un grave problème de santé publique. Parmi les nombreux types d’infections induites par ces bactéries, nous nous sommes intéressés aux infections intestinales qui peuvent dégénérer en maladies inflammatoires de l’intestin et cancers. Notre travail de thèse a consisté à proposer des outils thérapeutiques dans le traitement des pathologies intestinales infectieuses : des peptides antimicrobiens dérivés de la chromogranine A et des extraits de plantes de la médecine traditionnelle béninoise. La chromogranine A est une protéine libérée par les cellules nerveuses, neuroendocrines et immunitaires au cours d’un stress et maturée en peptides. Des peptides actifs contre quatre souches bactériennes pathogènes (Klebsiella oxytoca, Salmonella enterica, Shigella sonnei et Vibrio cholera non O1) ont été identifiés et l’interaction bactérie-peptide analysée. L’étude de la combinaison peptide-antibiotique montre que la cateslytine permet de réduire les doses d’antibiotiques nécessaires. Ensuite, nous avons étudié l’implication de deux peptides sur un modèle de cellules neuroendocrines, les cellules BON. La chromofungine provoque la stimulation des cellules BON en induisant un influx de calcium extracellulaire, tandis que la catestatine est capable de bloquer l’activité de la chromofungine.Après un screening des extraits de 14 plantes du Bénin, nous avons isolé deux molécules, la sinensétine et l’O-tétraméthyléther scutellaréine, responsables de l’activité antibactérienne de Chromolaena odorata contre les pathogènes étudiés. / The first bacterial strains resistant to antibiotics appeared 70 years ago and have proliferated in recent years causing a serious public health problem. Such bacteria are responsible of several types of infections including intestinal infections with chronic inflammatory bowel diseases and cancers. This work consisted of proposing new therapeutic tools in the treatment of intestinal pathologies. In this context, we have studied antimicrobial peptides derived from chromogranin A and plant extracts used in Beninese traditional medicine for the treatment of such diseases. Chromogranin A is a protein produced by nervous, endocrine and immune cells during a stress and processed to generate biologically active peptides. We identified antimicrobial peptides, active against four pathogenic bacterial strains (Klebsiella oxytoca, Salmonella enterica, Shigella sonnei and Vibrio cholera non O1) and analyzed the bacteria-peptide interactions. Moreover, the study of the peptide-antibiotic combination shows that cateslytin is useful for reducing doses of antibiotic drugs. In addition of this work, we have studied the effects of two peptides derived from chromogranin A on neuroendocrine cells with model of BON cells. Chromofungin stimules BON cells by inducing an influx of extracellular calcium, whereas catestatin is able to block chromofungin’s activity.With plant extracts, after a screening on 14 plants from Benin, our works enabled us to isolate two active molecules, sinensetin and O-tetramethylether scutellarein, responsible of the antimicrobial activity of Chromolaena odorata against the studied pathogenic strains.