DNA vaccines elicit antibody, T helper cell responses and CD8 T cell responses. Currently, little is known about the mechanism that DNA vaccines employ to induce adaptive immune responses. Prior studies have demonstrated that () and conventional dendritic cells (cDCs) play critical roles in DNA vaccine induced antibody and T cell responses. activation by double stranded (dsDNA) sensing proteins initiate the production of type I interferon (IFN),but the DC-intrinsic effect of signaling is still unclear. Here, we investigated the role of within cDCs on DNA vaccine induction of antibody and T cell responses. knockout ( ) and conditional knockout mice that lack in cDCs (), were immunized intramuscularly with a DNA vaccine that expressed influenza A nucleoprotein (pNP). Both and mice had significantly lower type I T helper (Th1) type antibody (anti-NP IgG) responses and lower frequencies of Th1 associated T cells (NP-specific IFN-γCD4 T cells) post-immunization than wild type (WT) and mice. In contrast, all mice had similar Th2-type NP-specific (IgG) antibody titers. mice developed significantly lower polyfunctional CD8 T cells than WT, and mice. These findings suggest that within cDCs mediates DNA vaccine induction of type I T helper responses including IFN-γCD4 T cells, and Th1-type IgG antibody responses. The induction of CD8 effector cell responses also require , but not within cDCs. These findings are the first to show that is required within cDCs to mediate DNA vaccine induced Th1 immune responses and provide new insight into the mechanism whereby DNA vaccines induce Th1 responses.