The roles of IL-12 and IL-23 in CD8 T cell-mediated immunity against Listeria monocytogenes: Insights from a DC vaccination model

Listeria monocytogenes infection induces a strong inflammatory response characterized by the production of IL-12 and IFN-γ and protective immunity against this pathogen is dependent on CD8⁺ T cells (CTL). Recent studies have suggested that these inflammatory cytokines affect the rate of memory CD8⁺ T cell generation as well as the number of short-lived effector cells generated. The role of the closely related cytokine, IL-23, in this response has not been examined. We hypothesized that IL-12 and IL-23 produced by dendritic cells collectively enhance the generation and function of memory cells. To test this hypothesis, we employed a DC vaccination approach. Mice lacking IL-12 and IL-23 were vaccinated with wild-type (WT), IL-12^−/−, or IL-12/23^−/− DC and protection to Lm was monitored. Mice vaccinated with WT and IL-12^−/− DC were resistant to lethal challenge with Lm. Surprisingly, mice vaccinated with IL-12/23^−/− DC exhibited significantly reduced protection when challenged. Protection correlated with the relative size of the memory pools generated. In summary, these data indicate that IL-23 can partially compensate for the lack of IL-12 in the generation protective immunity against Lm.