Restricting IL-2 availability may be one means by which Treg can constrain Th17 establishment 25. Our data support this hypothesis and demonstrate a reciprocal

development of Treg and Th17 in the skin C57BL/6 mice vaccinated with Lm/CpG, indicating that IL-2, and perhaps other cytokines (rather than IL-23) may be implicated in the regulation of Th17 cells in our model. This needs to be confirmed with more experiments to define the role that multiple cytokines (i.e. IL-2, IL-12, IL-27, IL-15, IL-21, IRF4) may have in the generation and expansion of Th17 cells in our vaccination model. Our experiments intend to begin to unravel the reciprocal role of Th17 and Th1 in the Lm/CpG-vaccinated animals, and demonstrate that IL-17 is required for vaccine-associated Navitoclax cell line Ruxolitinib purchase parasite killing. IFN-γ neutralization also has a negative effect on parasite containment. Interestingly, the secretion of both IL-17 and IFN-γ appears to be linked as elimination of IL-17 decreased the expression of IFN-γ and vice versa. Although IFN-γ has proposed as a negative regulator of Th17 development, recent evidence has revealed can act synergistically to promote inflammation and disease control 18, 26–29. In any case, the fact that both IL-17 and IFN-γ are produced by

different CD4+ T-cell populations and that neutralization of the two cytokines did not result in an additive effect suggests that that their production may be sequential, or may be regulated by a shared factor (e.g. IL-27 23). The relationship of Th1 and Th17 during protective immunity remains controversial. Defining the trends that direct their interplay is impaired by the variation in inoculation routes, infection dosages, and sites of infection. New evidence further complicates this picture and points towards plasticity of Th17 and Th1 subpopulations: recent observations reveal that differentiated Th17 cells may become Th1 effectors and that Th17 cells Coproporphyrinogen III oxidase may be enhanced by the Th1 factors IFN-γ and T-bet (reviewed in 30). We intend to continue to

decipher the interplay between T-cell effector populations in our system as well as other models of leishmaniasis. The question remains on how Th17 cells control parasite growth in vaccinated animals. IL-17 is highly proinflammatory and induces expression of other inflammatory cytokines and of matrix metalloproteases important in facilitating the tissue entry of attracted leukocytes. IL-17 mediates recruitment, activation, and proliferation of neutrophils. Our data demonstrate that neutrophils migrate to the site of Lm/CpG infection concomitant with the Th17 cell expansion. It has been described that neutrophils protect C57BL/6 mice against infection, inducing killing by a mechanism that requires macrophage activation by neutrophil elastase 31.