Our results demonstrate that antigenic strength is a key factor in the generation of IL-10 Treg in vivo, as characterized by changes in proliferative capacity, cytokine secretion, acquisition of regulatory function and protection from EAE. Administration of MBP Ac1–9[4K] i. n. limits induction of EAE in H2u mice, with higher affinity analogs Ac1–9[4A] and Ac1–9[4Y] providing greater protection 1. A TCR Tg mouse on the H2u background (Tg4) was generated in order to circumvent the limitations imposed by low T-cell precursor frequency in the WT mouse 3. As shown in Fig. 1, repeated administration of the highest affinity peptide, Ac1–9[4Y], provided ACP-196 ic50 complete protection against

the disease, while i.n. Ac1–9[4A] and Ac1–9[4K] treatment were less effective. This included a graded effect on incidence, day of onset and peak of clinical disease score that correlated with individual

peptide affinity for H-2 Au (Table 1). However, the Tg4 CD4+ T-cell repertoire is heterogeneous with respect to TCR expression whereby a proportion of the cells express endogenous α chains as a result of gene recombination 10. It follows that preferential selection of CD4+ T cells with the alternatively rearranged TCR-α genes could provide a possible explanation for tolerance induction in the Tg4 mouse model. These experiments were therefore repeated using Tg4 mice on the Rag1−/− deficient background and provided similar results (Table 1). These findings show that, similar to the WT model, the affinity of the INCB018424 concentration i.n. administered peptide for MHC also influences the effectiveness of tolerance induction in Tg4 mice as well as Tg4 Rag1−/− mice. In order to interpret the EAE protection data, we first examined the effect of i.n. peptide treatment on the extent of Tg4 cell activation in vivo using a CFSE-labeled cell transfer model. As shown in Fig. 2, administration of a single i.n. dose of MBP Ac1–9[4K], [4A] or [4Y] to mice previously injected with naïve Tg4 CFSE labeled splenocytes resulted

in their activation, albeit to varying degrees. CFSE+CD4+ T cells Dehydratase from the peptide-treated recipient mice displayed at least one round of division and up-regulated the expression of CD69 on their surface relative to PBS controls (Fig. 2A and B, respectively). Upon challenge with Ac1–9[4K], [4A] or [4Y], CFSE+CD4+ T cells proliferated with a division index, i.e. the average number of times that each responding cell had divided, of 0.11, 0.49 and 1.04, respectively, compared with that of 0.02 upon PBS challenge (Fig. 2A). The percentage of activated, CD69 expressing CFSE+CD4+ T cells (both divided and undivided) increased accordingly, with a total of around 19.8, 30.7 and 38.8% observed in Ac1–9[4K]-, [4A]- and [4Y]-treated compared with 3.3% in PBS-treated recipient mice. Thus, the ability of individual MBP Ac1–9 analogs to activate naïve Tg4 CD4+ T cells in vivo correlates with their affinity. We next investigated whether the differential effects of i.n.