No vaccine exists against visceral leishmaniasis. To develop effective vaccines, we have previously reported protective role of live attenuated centrin gene–deleted Leishmania donovani (LdCen–/–) parasites through induction of Th1 type immune response in mice, hamsters, and dogs. In this study, we specifically explored the role of Th17 cells in LdCen–/–-induced host protection in mice. Our results showed that compared with wild-type L. donovani infection, LdCen–/– parasites induce significantly higher expression of Th17 differentiation cytokines in splenic dendritic cells. There was also induction of IL-17 and its promoting cytokines in total splenocytes and in both CD4 and CD8 T cells following immunization with LdCen–/–. Upon challenge with wild-type parasites, IL-17 and its differentiating cytokines were significantly higher in LdCen–/–-immunized mice compared with nonimmunized mice that resulted in parasite control. Alongside IL-17 induction, we observed induction of IFN-–producing Th1 cells as reported earlier. However, Th17 cells are generated before Th1 cells. Neutralization of either IL-17 or IFN- abrogated LdCen–/–-induced host protection further confirming the essential role of Th17 along with Th1 cytokines in host protection. Treatment with recombinant IL-23, which is required for stabilization and maintenance of IL-17, heightened Th17, and Tc17 responses in immunized mice splenocytes. In contrast, Th17 response was absent in immunized IL-23R–/– mice that failed to induce protection upon virulent Leishmania challenge suggesting that IL-23 plays an essential role in IL-17–mediated protection by LdCen–/– parasites. This study unveiled the role of IL-23–dependent IL-17 induction in LdCen–/– parasite-induced immunity and subsequent protection against visceral leishmaniasis.
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