These observations thus suggest that when limiting amounts of IL-2 exist, competition for see more this cytokine could take place between activated Treg and Tconv cells. Hence, Treg cells in our model might act by IL-2 deprivation. This hypothesis is supported by a recent mathematical model reported by Busse et al. 56 predicting that IL-2 deprivation by Treg cells occurs under conditions of limited IL-2 supply. Clear evidence of IL-2 deprivation was recently provided by Pandiyan et al. 53, who demonstrated that Treg cells “imbibe” more IL-2 than Tconv cells, particularly after activation, and this IL-2 deprivation leads to apoptosis of Tconv cells. In our model, Treg

cells are activated and express very high levels of CD25 and could thus become more efficient IL-2 consumers. Furthermore, we observed that addition of IL-2 also led to increased cell viability (data not shown). The results obtained in our work thus strongly suggest

that Treg cells mediate immunosuppression by IL-2 deprivation. However, GSK126 additional experiments are required to confirm this hypothesis. IL-2 is a molecule essential for mice survival after T. gondii infection 31, 57 and our results highlight the importance of this cytokine. It has been demonstrated that the reduced number of Treg cells during acute infection is consequence of a reduced IL-2 availability 31, and is probably related to IL-27 58, which has been shown to cooperate with IL-12 to suppress IL-2 production during acute infection 59. Our results suggest that the reduced IL-2 levels favours the competition for this cytokine between activated Treg cells and Tconv cells and that IL-2 exhaustion by activated Treg cells leads to the immunosuppression of CD4+ and CD8+ cells, but not of B lymphocytes, that do not require IL-2 for proliferation 60. These events C-X-C chemokine receptor type 7 (CXCR-7) could thus contribute to the highly inflammatory immune response that is characteristic during T. gondii infection. Analysis of Treg cells during T. gondii infection by several groups has shown a reduction of these

cells in C57BL6/J, BALB/c and in pregnant mice 30–32. We have shown herein that regardless of their reduction, Treg cells display an activated phenotype and a higher suppressive capacity, leading these cells to mediate immunosuppression. Interestingly, IL-10 does not participate as a modulator of suppression, despite the increase of IL-10-producing Treg cells. Instead, our results suggest that IL-2 deprivation is the mechanism used by Treg cells to mediate T. gondii-induced suppression. The role of Treg cells we describe herein as the mechanism controlling immunosuppression opens a new insight in the immunoregulation previously described for T. gondi infection. Six–eight-wk-old C57BL/6J (WT), and Swiss-Webster mice were bred in our animal house and maintained in microisolator cages according to the institutional guidelines. Foxp3EGFP knock-in mice (B6.