Brucella est une bactérie pathogène intracellulaire responsable d'une maladie, la brucellose. Sa capacité à établir une infection chronique est due aux mécanismes qu'elle déploie pour inhiber la réponse immunitaire. Parmi les cellules infectées, les cellules dendritiques (DC) et les macrophages (MO) jouent un rôle primordial dans l'induction de la réponse immunitaire. Nous avons étudié le rôle d'un récepteur des DC, des lymphocytes T (LT), MO : CD150. Il participe à l'activation des LT et il a été montré que CD150 est capable de reconnaître des protéines de l'enveloppe bactérienne, ce qui conduit à une augmentation de son expression à la membrane des MO. Nous avons découvert que l'expression de CD150 sur les DC dérivées de moelle osseuse (BMDC) augmente en présence d'extraits membranaire de Brucella, sauf quand ces derniers proviennent d'un mutant pour Omp25 (∆omp25). L'infection de BMDC par ∆omp25 active les BMDC en termes d'expression de molécules de co-stimulation, d'ARNm pro-inflammatoires (cytokines) et de translocation de NF-κB dans le noyau. En comparant avec une souche sauvage de Brucella, l'activation par ∆omp25 est plus importante. En absence de CD150 la translocation de NF-κB dans les BMDC infectées par la souche sauvage est aussi importante que celle induite par l'infection par ∆omp25. In vivo CD150 contrôle la réplication de Brucella dans la rate de souris infectées. Nous avons démontré que CD150 est capable de lier Omp25. Nous avons identifié un nouveau mécanisme par lequel Brucella inhibe l'activation des DC : la liaison d'Omp25 à CD150. Ce récepteur joue un double rôle puisqu'il est aussi crucial dans le contrôle de la survie de Brucella in vivo. / Brucella is a pathogenic intracellular bacterium responsible for a disease, brucellosis. The ability of Brucella to establish a chronic infection is linked to the mechanism it uses to inhibit immune response. Among Brucella infected cells, dendritic cells (DC) and macrophages play a crucial role in the induction of an immune response. We studied the role of one receptor present at the DC, T cells, macrophages surface: CD150. This molecule participates at the T cell activation and it was shown recently that CD150 can recognize bacterial membrane proteins which lead to its own upregulation. We discovered that CD150 expression onto bone-marrow derived DC (BMDC) is increased when these cells are treated with Brucella membrane extracts, except when those extracts are coming from a mutant for Omp25(∆omp25), a Brucella membrane protein. BMDC infection with ∆omp25 leads to BMDC activation regarding co-stimulatory molecule expression, cytokines and chemokines secretion, pro-inflammatory mRNA expression and NF-κB translocation within the nucleus. In comparison with infection with the wild type strain, ∆omp25 induces a higher activation of BMDC. In absence of CD150, NF-κB translocation within the nucleus of infected-BMDC is the same between the wild type strain and ∆omp25. In vivo, CD150 controls Brucella replication in the spleen of infected mice, and Omp25 infection seems to trigger a higher inflammation in control mice. We finally demonstrate that CD150 binds Omp25. Here, we identified a new mechanism by which Brucella is able to inhibit DC activation: binding of Omp25 to CD150. This receptor plays a dual role since it is also required for controlling Brucella growth in mice.

Le virus de la rougeole (MV) provoque une maladie sévère chez les enfants qui induit une forte immunosuppression et peut dans certains cas infecter le système nerveux central (SNC). La protéine CD150, principal récepteur cellulaire du virus, permet l’entrée du MV en se liant à l’hémagglutinine (MV-H). L’altération fonctionnelle des cellules dendritiques (DC) étant considérée comme essentielle dans l’immunopathogénèse du MV, nous avons analysé les conséquences de l’interaction de MV-H avec les DC. Nous avons développé un modèle expérimental qui nous permet d’étudier l’interaction directe entre CD150 et MV-H hors contexte infectieux. Nos résultats montrent que cette interaction provoque une diminution de l’expression des molécules de surface CD80, CD83, CD86, et HLA-DR, de la production d’IL-12 par les DC, et de la capacité des DC à stimuler la prolifération des lymphocytes T. L’interaction CD150-MV-H a inhibé la phosphorylation des protéines kinases JNK1/2 dans les DC et les lymphocytes B (LB) induite par la stimulation de CD150 par un anticorps spécifique, mais pas celle des kinases ERK1/2. Par ailleurs MV-H seule induit la phosphorylation d’Akt via CD150 dans les DC et les LB. La liaison de CD150 par MV-H a réduit la réponse inflammatoire chez les souris transgéniques exprimant CD150 humain, ce qui confirme l’effet de l’interaction de CD150 et MV-H in vivo. Nos études ont révélé l’expression de CD150 dans les tumeurs du SNC et l’existence d’une nouvelle isoforme de CD150. Cette isoforme contient un exon supplémentaire de 83 pb et est exprimée dans les cellules lymphoïdes et les DC en plus des tumeurs du SNC. Bien que l’expression de CD150 soit uniquement intracellulaire dans les cellules tumorales, elle peut représenter un nouveau marqueur pour les tumeurs cérébrales humaines. Cette étude apporte un éclairage nouveau sur le rôle immunorégulateur de CD150 et sur la diversité de ses isoformes, et ouvre ainsi de nouvelles perspectives pour leurs applications thérapeutiques. / Measles virus (MV) causes an acute childhood disease, associated in certain cases with the infection of the central nervous system (CNS). MV induces a profound immunosuppression, resulting in high infant mortality. The major cellular receptor for MV is CD150, which binds MV hemagglutinin (MV-H). As dendritic cell (DC) dysfunction is considered to be essential for the MV immunopathogenesis, we analyzed consequences of MV-H interaction with DCs. We developed an experimental model allowing us to analyze the direct CD150-MV-H interaction in the absence of infectious context. This interaction caused the downregulation of surface expression of CD80, CD83, CD86 and HLA-DR molecules and inhibition of IL-12 production in DCs. DCs also failed to activate T cell proliferation. The CD150-MV-H interaction in DCs and B cells decreased the phosphorylation of JNK1/2, but not ERK1/2 kinases, after subsequent CD150 ligation with anti-CD150 antibodies. Moreover, MV-H by itself induced Akt phosphorylation via CD150 in DCs and B cells. Engagement of CD150 by MV-H in mice transgenic for human CD150 decreased the inflammatory reaction, contact hypersensitivity response, confirming the immunosuppressive effect of CD150-MV-H interaction in vivo. Furthermore, our studies revealed the CD150 expression in CNS tumors and identified the novel CD150 isoform, containing an additional 83bp exon expressed in lymphoid cells, DCs and CNS tumors. Although its isoforms remain intracellular in tumor cells, CD150 may represent a new marker for human brain tumors. Novel mechanism of CD150-induced immunosuppression and new CD150 isoform identified in these studies shed new light on its immunoregulatory role and CD150 isoform diversity and open perspectives for their clinical applications.

Feline morbillivirus (FeMV) is a recently discovered virus belonging to the genus Morbillivirus of the virus family Paramyxoviridae. Often, the virus has been detected in urine of cats with a history of urinary disease and has a worldwide distribution. Currently, it is unclear which receptor the virus uses to enter the target cells. Furthermore, many aspects of FeMV biology in vivo, including tissue tropism, pathogenesis, and virus excretion in the natural host remain unclear. In this study we analyzed the replication of FeMV in various cell lines. Secondly, we tested if the presence of feline SLAMF1 (Signaling Lymphocytic Activation Molecule family 1/CD150, principal entry receptor for other members of the Morbillivirus genus) improved FeMV replication efficiency in vitro. Finally, to elucidate in vivo biology in cats, as a natural host for FeMV, we experimentally infected a group of cats and monitored clinical symptoms, viremia, and excretion of the virus during the course of 56 days. Our study showed that FeMV shares some features with other morbilliviruses like the use of the SLAMF1 receptor. For the first time, experimental infection of SPF cats showed that FeMV does not induce an acute clinical disease like other morbilliviruses but can induce lesions in the kidneys, including tubulointerstitial nephritis. Further investigations are needed to confirm the site and dynamics of replication of FeMV in the urinary tract and the longer-term impact of FeMV-induced lesions on the renal function. Whether FeMV infection can result in chronic kidney disease will require the monitoring of cats over a longer period.

Measles virus (MV) causes an acute childhood disease, associated in certain cases with the infection of the central nervous system (CNS). MV induces a profound immunosuppression, resulting in high infant mortality. The major cellular receptor for MV is CD150, which binds MV hemagglutinin (MV-H). As dendritic cell (DC) dysfunction is considered to be essential for the MV immunopathogenesis, we analyzed consequences of MV-H interaction with DCs. We developed an experimental model allowing us to analyze the direct CD150-MV-H interaction in the absence of infectious context. This interaction caused the downregulation of surface expression of CD80, CD83, CD86 and HLA-DR molecules and inhibition of IL-12 production in DCs. DCs also failed to activate T cell proliferation. The CD150-MV-H interaction in DCs and B cells decreased the phosphorylation of JNK1/2, but not ERK1/2 kinases, after subsequent CD150 ligation with anti-CD150 antibodies. Moreover, MV-H by itself induced Akt phosphorylation via CD150 in DCs and B cells. Engagement of CD150 by MV-H in mice transgenic for human CD150 decreased the inflammatory reaction, contact hypersensitivity response, confirming the immunosuppressive effect of CD150-MV-H interaction in vivo. Furthermore, our studies revealed the CD150 expression in CNS tumors and identified the novel CD150 isoform, containing an additional 83bp exon expressed in lymphoid cells, DCs and CNS tumors. Although its isoforms remain intracellular in tumor cells, CD150 may represent a new marker for human brain tumors. Novel mechanism of CD150-induced immunosuppression and new CD150 isoform identified in these studies shed new light on its immunoregulatory role and CD150 isoform diversity and open perspectives for their clinical applications.