Vignette d'image

Brossard, Michel

Nom
Brossard, Michel
Affiliation principale
Identifiants
https://libra.unine.ch/handle/123456789/308

Résultat de la recherche

Filtres

1
5
5
41
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 5 sur 5
  • Publication
    Accès libre
    Splenic dendritic cells pulsed with Ixodes ricinus tick saliva prime naive CD4+T to induce Th2 cell differentiation in vitro and in vivo
    (2007)
    Mejri, Naceur
    ;
    Brossard, Michel 
    Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs) in priming naive T cells. Using an in vitro priming system, we show that DCs incubated with Ixodes ricinus tick saliva initiate the Th2 differentiation of CD4+T cells. As determined with reverse transcription–PCR, the expression of IL-4 mRNA by these cells is higher than IFN-γ mRNA. Early endogenous production of IL-4 is thought to be important during the in vitro interaction of saliva-pulsed DCs with CD4+T cells. Its neutralization with specific mAbs inhibits the development of IL-4-secreting Th2 cells. Moreover, differentiated Th2 cells proliferate only when saliva-pulsed DCs and IL-1ß are added together early in the primary culture. As demonstrated by FACS analysis, the treatment in vitro of saliva-pulsed DCs by IL-1ß enhanced the expression of B7 and mainly CD40 co-stimulatory molecules, which provide sufficient signals to stimulate sensitized CD4+T cell proliferation. On the other hand, DCs treated with tick saliva only up-regulated mostly B7-2 co-stimulator expression and this was associated with differentiation of naive CD4+T cells into Th2 type of cells. The in vitro priming system is suitable to investigate the major elements implicated in the anti-tick immune response such as naive CD4+T cells, whole DCs population and tick saliva, and it can provide the possibility to delimit further the saliva molecules, the DC subsets and the type of host cells involved in the Th2 polarization. Corresponding in vivo experiments involving subcutaneous injection of tick saliva-pulsed DCs into BALB/c mice also elicited a Th2 immune response. Ex vivo cultures of draining lymph node T cells stimulated with tick saliva produced higher IL-4 : IFN-γ ratios compared with controls, confirming the relevance obtained in the in vitro priming model. These experiments demonstrate the importance of tick saliva in priming DCs to initiate a Th2-biased immune response in vitro and in vivo.
  • Publication
    Accès libre
    Characterization of a Novel Salivary Immunosuppressive Protein from Ixodes ricinus Ticks
    (2002)
    Leboulle, Gérard
    ;
    Crippa, Mara
    ;
    Decrem, Yves
    ;
    Mejri, Naceur
    ;
    Brossard, Michel 
    ;
    Bollen, Alex
    ;
    Godfroid, Edmond
    In tick salivary glands, several genes are induced during the feeding process, leading to the expression of new proteins. These proteins are typically secreted in tick saliva and are potentially involved in the modulation of the host immune and hemostatic responses. In a previous study, the construction and the analysis of a subtractive library led to the identification of Ixodes ricinus immunosuppressor (Iris), a novel protein, differentially expressed in I. ricinus salivary glands during the blood meal. In the present study, the data strongly suggest that this protein is secreted by tick salivary glands into the saliva. In addition, Iris is also found to modulate T lymphocyte and macrophage responsiveness by inducing a Th2 type response and by inhibiting the production of pro-inflammatory cytokines. In conclusion, these results suggest that Iris is an immunosuppressor, which might play an important role in the modulation of host immune response.
  • Publication
    Accès libre
    Immunosuppressive effects of Ixodes ricinus tick saliva or salivary gland extracts on innate and acquired immune response of BALB/c mice
    (2001)
    Mejri, Naceur
    ;
    Rutti, Bernard
    ;
    Brossard, Michel 
    Saliva and salivary gland extract (SGE) of Ixodes ricinus ticks have suppressive effects on the innate immune response of BALB/c mice. Tick saliva prevents hemolysis of sheep red blood cells (SRBC) by the human alternative pathway of complement. The adaptive immune response is also modulated by tick antigens (saliva or SGE). When stimulated in vitro with increasing doses of tick antigens, the proliferation and IL-4 production of draining lymph node T cells of mice infested with nymphal ticks increase, peak and then decrease. These results indicate that immunostimulative and immunosuppressive molecules have competing effects in tick saliva or in SGE. I. ricinus saliva inhibits, in a dose-dependent manner, splenic T cell proliferation in response to concanavalin A (ConA). Tick SGE or saliva injected intraperitoneally to BALB/c mice simultaneously with SRBC systemically immunosuppress the anti-SRBC response as shown in vitro by the reduced responsiveness of sensitized splenic T cells to restimulation with SRBC. In brief some components of SGE or tick saliva reduce the responsiveness of draining lymph node T cells and of sensitized splenic T cells in vitro. The responsiveness of naive splenic T cells to ConA stimulation in vitro is also decreased by tick saliva. Modulation of host responses by tick antigens may facilitate tick feeding, transmission and the propagation of pathogens.
  • Publication
    Accès libre
    Th2 polarization of the immune response of BALB/c mice to Ixodes ricinus instars, importance of several antigens in activation of specific Th2 subpopulations
    (2001)
    Mejri, Naceur
    ;
    Franscini, Nicola
    ;
    Rutti, Bernard
    ;
    Brossard, Michel 
    BALB/c mice were infested with Ixodes ricinus larvae, nymphs or adults. Expression of IL-4 and IFN-γ mRNA in axillary and brachial draining lymph node cells were measured by competitive quantitative reverse transcription-polymerase chain reaction 9 days after the beginning of primary-infestation. IL-4 mRNA was always higher than that of IFN-γ mRNA for all tick instars. Moreover, IL-4 mRNA expression progressively increased during nymphal primary-infestation with a high burst of expression 7 days after the beginning of infestation. No evolution of IFN-γ mRNA expression was detected. Draining lymph node cells of infested BALB/c produced higher level of IL-4 than IFN-γ following in vitro restimulation with adult tick saliva, salivary gland extract (SGE) or with five selected different chromatographic fractions of SGE. Anti-tick IgG1 antibodies but no IgG2a were detected in BALB/c pluri-infested with I. ricinus nymphs, which confirmed the Th2 polarization of the immune response.