Many authors claimed that a primary early source of IL-4 is needed to drive the priming of naive CD4+ T cells into differentiated Th2 type of cells (35,36). In many models of ecto- or endo-parasitic infections, it check details has been shown that IL-4 might be produced early by many cells including DCs themselves and other cells such as keratinocytes, Tγδ cells, mast cells and basophiles (37,38). Extracts from metacestodes of E. multilocularis caused a basophile degranulation as well as the secretion of histamine and of IL-13 and IL-4 (39). We expected that in the presence of endogenous IL-4, released after intraperitoneal AE-infection,

pe-DCs acted like mucosal Peyer’s patch DCs that have the feature to secrete IL-10 and TGF-β upon oral stimulus and to drive directly or indirectly the differentiation of T cells secreting TGF-β and Th2-associated cytokines (40). TGF-β-secreting pe-DCs contributed not only to the differentiation of T cell-producing Th2-associated cytokines and TGF-β but also CD4+Foxp3+ and CD8+Foxp3+ regulatory T cells (24). Next to that we found that, conversely to naive pe-DCs that increased the proliferation of naive CD4+ pe-T in the presence of Con A, pe-DCs from metacestode-infected mice decreased slightly the proliferative

response of naive CD4+ pe-T cells. These results could be explained not only by their defective accessory activity but also by the inhibitory effect of TGF-β on naive PI3K inhibitor CD4+ pe-T-cell proliferation. TGF-β was shown by others to inhibit T-cell proliferation by down-regulation of IL-2 gene transcription (41), IL-2 receptor expression (42) and the expression of co-stimulatory molecules CD80, CD86 and CD40 on APCs (43). TGF-β-secreting pe-DCs that displayed impairment in accessory activity have been qualified as tolerogenic DCs (44). Numerous works revealed the essential role of DCs in the dichotomy (Th1/Th2) of the immune response. However, besides this essential role, consolidated findings showed that DCs may act as pivotal players in the peripheral

tolerance network by active induction of T cells with immunosuppressive functions Sunitinib and regulation of T-effector cell activity. It has been reported that tolerogenic DCs present antigens to antigen-specific T cells, but fail to deliver adequate co-stimulatory signals for effector T-cell activation and proliferation. This may be manifested as T-cell death, T-cell anergy or regulatory T-cell expansion or generation. The immunosuppressive agents that are able to irreversibly block the immunostimulatory function of immature DCs favour their differentiation into stable tolerogenic DCs. Such blocked DCs are no longer responders to inflammatory stimuli (27). DCs that can induce tolerance may need to be resistant to maturation-inducing factors (45).