CD40L-expressing CD8 T cells prime CD8α+ DC for IL-12p70 production

CD8 alpha(+) DC are implicated as the principle DC subset for cross-presentation and cross-priming of cytotoxic CD8 T cell responses. In this study, we demonstrate another unique facet of the CD8 alpha(+) DC and CD8 T cell relationship, by showing that CD8 T cells reciprocally activate CD8 alpha(+) DC, but not CD8 alpha(-) DC, for IL-12p70 production, the key Thi-promoting cytokine. This effect was observed during an antigen-specific interaction between DC and activated CD8 T cells, along with secondary TLR stimulation of DC by LPS. Activated CD8 T cells use a combination of IFN-7 and CD40L, which is rapidly up-regulated Poststimulation, to prime DC for IL-12p70 production during an antigen-specific response. Our results suggest that the interaction between CD8 alpha(+) DC and antigen-primed CD8 T cells may form an important component of Thi-mediated immunity through the induction of IL-12p70.