Résultat de la recherche
Splenic dendritic cells pulsed with Ixodes ricinus tick saliva prime naive CD4+T to induce Th2 cell differentiation in vitro and in vivo
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.
Th2 polarization of the immune response of BALB/c mice to Ixodes ricinus instars, importance of several antigens in activation of specific Th2 subpopulations
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.