major-vaccinated mice. IL-6 treatment also resulted in a decrease of IFN-γ expressing CD4+CD25lo/med T cells (effector Th1 cells in our system 16) (Fig. 2B). As before, IL-6 neutralization also significantly increased the number of CD25hi IL-10+ T cells (Treg in our system 11, 16) (Supporting Information Fig. 1). These data demonstrate that vaccine-induced IL-6 modulates the development of Th17 cells in the Lm/CpG-vaccinated mice. They also suggest that Th17 cells are required for the recruitment or development of Th1 responses. To determine whether Th17 cells have a role in early parasite killing in Lm/CpG-vaccinated animals, we treated mice with anti IL-17 and/or anti IFN-γ neutralizing antibodies (or isotype

control), and examined the frequency of IL-17, IFN-γ-producing cells, and Treg during the selleck chemicals “silent” phase (wk 2). Antibody treatment decreased the frequency of CD4+ T cells in Lm/CpG-vaccinated animals, but did not significantly affect the frequency of CD4+ T cells in the dermis of L. major-vaccinated animals at wk 2 (Supporting Information Fig. 2); in this case, it is possible that the low frequency of Th1 and Th17 cells in the ears of the latter mice did not allow detecting any differences cause by treatment. As expected, parasite burden was high at wk 2 in L. major-vaccinated animals (>1.5×105 parasites per ear, Fig. 3A), and significantly reduced (fivefold) in

mice vaccinated with Lm/CpG. Neutralization of either anti IL-17 and/or anti IFN-γ did not produce an increase in parasite killing in the L. major-vaccinated group. This was expectable because the number of cytokine positive cells in these mice is very low at wk 2. In contrast, SAHA HDAC neutralization of IL-17 increased parasite burden in the ears of Lm/CpG-vaccinated mice by tenfold. Similarly, neutralization of IFN-γ or IL-17 plus IFN-γ increased parasite numbers by fivefold, suggesting that both IL-17 and IFN-γ are required for the control of parasite expansion after Lm/CpG vaccination. Differences among antibody-treated groups were not statistically significant. Parasite growth was associated

with an expansion in the number of Treg. Figure 3B shows that the absolute number of Treg significantly increased following antibody Carbachol treatments in the Lm/CpG-vaccinated group. The increased frequency of Treg may have also contributed to the expansion in parasite numbers. No additive effect was found when the two cytokines were neutralized at the same time, suggesting that the production of the cytokines may be sequential. We immunized IL-17-receptor-deficient mice (IL-17R−/−) and WT C57BL/6 with the live vaccines. As expected, WT mice vaccinated with Lm/CpG did not develop leishmaniasis, and L. major-vaccinated mice did (Fig. 4A). Disease pathology was slightly accelerated in L. major-vaccinated IL-17R−/− mice. Most importantly, IL-17R−/− mice immunized with Lm/CpG developed large lesions, further indicating that IL-17 is involved in protection.