Patients with systemic lupus erythematosus (SLE) show an over-expression of Type I Interferon (IFN) responsive genes called “Interferon Signature”. We found that the B6.NZMSle1/Sle2/Sle3 (Sle1,2,3) lupus-prone mice also express an Interferon Signature compared to non autoimmune C57BL/6 mice. In vitro, myeloid dendritic cells (mDCs)(GM-CSF bone marrow-derived BMDCs) from Sle1,2,3 mice constitutively over-expressed IFN responsive genes such as IFNb, Oas-3, Mx-1, ISG-15 and CXCL10, and the members of IFN signaling pathway STAT1, STAT2, and IRF7. The Interferon Signature was similar in Sle1,2,3 BMDCs from young, pre-autoimmune mice and from mice with high titers of autoantibodies, suggesting that the Interferon Signature in mDCs precedes disease onset and it is independent from the autoantibodies. Sle1,2,3 BMDCs hyper-responded to stimulation with IFNa and the TLR7 and TLR9 agonists R848 and CpGs. We propose that this hyper-response is induced by the Interferon Signature and only partially contributes to the Signature, since oligonucleotides inhibitory for TLR7 and TLR9 only partially suppressed the constitutive Interferon Signature and pre-exposure to IFNa induced the same hyper-response in wild type BMDCs than in Sle1,2,3 BMDCs. In vivo, mDCs and with lesser extent T and B cells from young pre-diseased Sle1,2,3 mice also expressed the Interferon Signature, although they lacked the strength that BMDCs showed in vitro. Sle1,2,3 plasmacytoid DCs expressed the Interferon Signature in vitro but not in vivo, suggesting that mDCs may be more relevant before disease onset. We propose that Sle1,2,3 mice are useful tools to study the role of the Interferon Signature in lupus pathogenesis.