Noteworthy, interruption of LPS treatment, or a single LPS administration, in female NOD mice led to diabetes occurrence within a time window strikingly similar to the

delay observed upon adoptive transfer (Fig. 1C, D). Together, these data strongly this website suggested that a subset of cells present in LPS-treated donors actively controlled diabetogenic cell potential in the NOD/SCID recipients. To directly assess the contribution of Treg to the prevention of diabetes mediated by LPS we performed adoptive transfer of splenocytes depleted of these cells (Fig. 6B). While Treg are best identified by expression of Foxp3, this nuclear marker does not allow negative purification of live cells. However, most Treg are enriched in the subset of lymphocytes expressing the surface marker CD25 [51], and most CD25+ T cells

are Foxp3+ (Fig. S5). To efficiently reduce the number of Treg in the splenocyte preparations, we depleted CD25-expressing cells by mAb and complement treatment (Fig. S8A). Noteworthy, we showed above that the total frequency of CD25-expressing cells is similar in LPS-treated and healthy mice (Fig. 4), guaranteeing that depletion would be of similar efficiency in each experimental group. Depletion of CD25+ cells in splenocytes isolated from healthy donors prior to adoptive transfer did not accelerate the already rapid onset of diabetes. This finding is consistent with the reported progressive lost of Treg suppressive function in ageing NOD [4–7]. In contrast, Apoptosis inhibitor CD25+ cell depletion in splenocytes isolated from LPS-protected

animals prior to adoptive transfer dramatically precipitated diabetes in the recipient mice, as 50% of the animals were sick by 6.5 weeks after transfer (Fig. 6B). Remarkably, in this experimental group, progression of diabetes was indistinguishable from that of recipients HAS1 of total or CD25− cells prepared from healthy donors, indicating that protection in the donors was dominant and that the protective cells were readily depleted in these experiments. Similar results were obtained with donor and recipient males (Fig. S7B). We conclude that CD25+ Treg cells mediated the delay in diabetes onset in NOD/SCID female recipients of splenocytes isolated from LPS-protected animals. In turn, this result suggests that LPS treatment prevented CD25+ cell loss of regulatory function previously observed in ageing NOD mice [4–7]. In the present work we investigated the cellular mechanism at the basis of LPS-mediated prevention of spontaneous T1D in NOD mice and demonstrate a dominant regulation mediated by enhanced CD25+ Treg. The originality and power of our study rely in the comparative analysis of two modes of disease protection. Profiting from the incomplete penetrance of diabetes in NOD animals raised in SPF condition, we analysed untreated old but disease-free females and males in comparison with gender- and age-matched LPS-treated animals.