Parmi les cinq isotypes d’anticorps présents chez l’Homme, les immunoglobulines A (IgA) prédominent dans les muqueuses. Les IgA sont produites dans le chorion sous forme majoritairement polymérique (pIgA) et sécrétées dans la lumière des muqueuses. Leur transport trans-épithélial est assuré par le récepteur aux immunoglobulines polymériques (pIgR), exprimé au pôle basal des épithéliums. Les pIgA ainsi sécrétées conservent le domaine extracellulaire du pIgR et sont appelées IgA sécrétoires (SIgA). Une fonction essentielle des SIgA intestinales est de maintenir microorganismes et antigènes alimentaires dans la lumière des muqueuses afin d’empêcher leur pénétration dans l'organisme. Néanmoins, la transcytose inverse des SIgA couplées à des bactéries a été décrite dans les plaques de Peyer où elle participe à la génération de la réponse immune contre ces bactéries. En outre, les travaux passés du laboratoire ont suggéré que le récepteur de la transferrine (CD71), surexprimé au pôle apical des entérocytes chez les patients cœliaques, interagit avec les SIgA couplées à des peptides de gliadines et permet leur transcytose inverse à travers l’épithélium intestinal. Ce travail de thèse a eu pour objectif de mieux caractériser l’interaction SIgA-CD71 dans les entérocytes humains. Dans un premier temps, nous avons utilisé la technologie CRISPR-Cas9 pour générer une lignée cellulaire intestinale humaine (Caco-2 TC7) dépourvue du récepteur CD71 (CD71KO). De manière inattendue, nous n’avons observé aucune altération de la fixation des SIgA sur les cellules Caco-2 CD71KO. Ce résultat nous a amenés à réévaluer le rôle de CD71 comme récepteur aux SIgA. Dans un second temps, nous avons vérifié et confirmé que les SIgA interagissent avec CD71, mais nous avons montré que cette interaction est indirecte. Nous avons ensuite criblé les récepteurs aux IgA déjà décrits dans la littérature et montré qu'aucun n'est responsable de la fixation des SIgA à la surface des cellules Caco-2 TC7. Ces résultats nous ont amenés à chercher le(s) autre(s) partenaire(s) du complexe SIgA-CD71. Par immunoprécipitation couplée à la spectrométrie de masse, nous avons identifié les protéines Secretory Carrier Membrane Protein 3 (SCAMP3), B-Cell Receptor-Associated Protein 31 (BCAP31) et Histocompatibility minor 13 (HM13) comme membres du complexe SIgA-CD71. En nous appuyant à nouveau sur la technologie CRIPSR-Cas9, nous avons montré qu’aucun de ses partenaires n’interagit directement avec les SIgA. Néanmoins, nos résultats suggèrent que SCAMP3 est nécessaire à l’oligomérisation de surface des complexes de fixation des SIgA. Enfin, l’internalisation des SIgA n'est pas altérée par l’absence de chacun des partenaires du complexe, suggérant que leur rôle advient durant le transport trans-épithélial des SIgA. L’ensemble de nos travaux montre que les SIgA interagissent avec l'épithélium intestinal via un complexe protéique composé d'au moins cinq membres : CD71, SCAMP3, BCAP31, HM13 et le(s) récepteur(s) inconnu(s) aux SIgA. Ces résultats complètent les travaux antérieurs sur le rôle physiopathologique des SIgA dans la maladie cœliaque et contribuent à souligner la complexité des interactions entre IgA et entérocytes. Une question importante sera d’identifier le(s) récepteur(s) aux SIgA et de déterminer le rôle des partenaires identifiés dans la transcytose inverse des SIgA par l’entérocyte. / Among the five isotypes of antibodies found in Humans, immunoglobulins A (IgA) are the most abundant in the mucosae. In the lamina propria, IgA are produced mainly as polymeric IgA (pIgA) and then secreted in the lumen. In fact, pIgA are translocated across the epithelium via the polymeric immunoglobulin receptor (pIgR), which is expressed at the basolateral side of the epithelium. Once secreted in the lumen, pIgA retain the extracellular domain of the pIgR and are called secretory IgA (SIgA). One of the main functions of intestinal SIgA is to restrain microorganisms and dietary antigens in the lumen, therefore, preventing their uptake through the epithelial barrier. However, retrotranscytosis of SIgA conjugated to bacteria has been described in Peyer’s patches where it participates to immune response. Moreover, previous works from the laboratory have suggested that transferrin receptor (CD71), which is overexpressed at the apical side of enterocytes from coeliac patients, interacts with SIgA bound to gliadin peptides and allows their retrotranscytosis across the intestinal epithelium. This thesis work aimed to further characterize the interaction between SIgA and CD71 in human enterocytes. We, first, generated a human epithelial intestinal cell line (Caco-2 TC7) devoid of CD71 expression (CD71KO) using the CRISPR/Cas9 genome editing method. Unexpectedly, flow cytometry experiments did not reveal a significant reduction of SIgA binding at the cell surface of CD71KO cells. Overall, our results indicated that CD71-SIgA interaction is indirect and may occur via additional protein partners through the assembly of a multifactorial protein complex. Therefore, we screened IgA receptors already known in the literature and showed that all are dispensable for SIgA binding at the surface of Caco-2 TC7 cells. In the effort to identify partner(s) within SIgA-CD71 complex, we set out mass spectrometry-based immunoprecipitation proteomics experiments and identified secretory carrier membrane protein 3 (SCAMP3), B-cell receptor-associated protein 31 (BCAP31) and histocompatibility minor 13 (HM13) as members of SIgA-CD71 complex. By generating knockout cell lines with the CRISPR/Cas9 system, we showed that none of these partners directly interacts with SIgA. However, our results suggest that SCAMP3 is required for the oligomerization of SIgA complexes at cell surface. Finally, we did not find any role in SIgA internalization for the different members of the complex, suggesting that they may play a role later on during SIgA retrotranscytosis. In conclusion, our work shows that SIgA interact with the intestinal epithelium via a proteic complex composed of at least five members: CD71, SCAMP3, BCAP31, HM13 and one or more unknown SIgA receptor(s). These results complement the previous works on the pathophysiologic role of SIgA in coeliac disease and underline the highly complex interaction between IgA and enterocytes. An important point to address will be to identify SIgA receptor(s) and to determine the role of the four other identified partners in SIgA retrotranscytosis across the intestinal epithelium.

Made available in DSpace on 2016-08-19T18:16:00Z (GMT). No. of bitstreams: 1 HELIANA TRINDADE MARINHO.pdf: 1186217 bytes, checksum: 54acac9509ef409a9fe2f8f198769e4f (MD5) Previous issue date: 2010-06-30 / FUNDAÇÃO DE AMPARO À PESQUISA E AO DESENVOLVIMENTO CIENTIFICO E TECNOLÓGICO DO MARANHÃO / This research aimed to study cell proliferation by Ki-67 marker and CD71 in acute leukemias, as well as establish the relationship between them and their relationship to therapeutic response. Patients were selected prospectively commencing in December 2008 and ending in November 2009 (12 months). Samples were collected from bone marrow or peripheral blood of 54 patients diagnosed with acute leukemia, from the referral hospital for cancer treatment in the state of Maranhão (northeastern Brazil) and determined the expression of Ki-67 markers and CD71 by flow cytometry. Most patients were from the northeast, followed by the central, northwest, southwest and southeast of Maranhão. No patients were in southern state. The values of Ki-67 in bone marrow and peripheral blood in the patients were higher in B-ALL than other acute leukemias. The bone marrow CD71 showed increased expression in T-ALL and peripheral blood, increased expression in AML. Was no statistical difference in Ki-67 in peripheral blood and bone marrow only in AML. A significant positive correlation between Ki-67 and CD71 in peripheral blood in B-ALL. In bone marrow, the markers showed a linear correlation in AML. No relationship was found between markers of cell proliferation and response to treatment. A continuing study of cell proliferation with a greater number of patients, coupled with other techniques of cell proliferation it is necessary to evaluate other / Esta pesquisa objetivou estudar a proliferação celular através do marcador Ki-67 e CD71 nas leucemias agudas, bem como estabelecer a relação entre eles e sua relação com a resposta terapêutica. Os pacientes foram selecionados de forma prospectiva tendo início em dezembro de 2008 e término em novembro de 2009 (12 meses). Foram coletadas amostras de medula óssea ou sangue periférico de 54 pacientes diagnosticados com leucemias agudas, provenientes do hospital de referência para tratamento oncológico no estado do Maranhão (no nordeste brasileiro), sendo determinada a expressão dos marcadores Ki-67 e CD71 por citometria de fluxo. A maior parte dos pacientes era da região nordeste, seguidos da região central, noroeste, sudoeste e sudeste do Maranhão. Não houve pacientes da região sul do estado. Os valores da expressão de Ki-67 em medula óssea e sangue periférico no total de pacientes apresentaram-se maiores na LLAB que as demais leucemias agudas. O CD71 apresentou na medula óssea uma maior expressão na LLAT e no sangue periférico, uma maior expressão na LMA. Foi observada diferença estatística na expressão de Ki-67 em sangue periférico e medula óssea apenas na LMA. Foi observada correlação positiva entre o Ki-67 e CD71 em sangue periférico na LLAB. Na medula óssea, os marcadores apresentaram correlação linear na LMA. Não foi encontrada relação entre os marcadores de proliferação celular e a resposta ao tratamento. Uma continuidade do estudo de proliferação celular com um número de pacientes maior, atrelados a outras técnicas de proliferação celular se faz necessária para avaliação de outros parâmetros como a evolução clínica, prognóstico e sobrevida dos pacientes leucêmicos em nosso estado.