In the present study we investigated the IFN-ab response of mice infected with human Ads. We showed that the response is characterized by high levels of IFN-a and IFN-b, which are produced simultaneously and almost exclusively by splenic mDCs. Furthermore, the response is entirely independent of viral replication, TLR-, MyD88-, TRIF-and IRF-3-signaling, but dependent on viral escape from the endosomes, activation of the SAPK/JNK pathway and IRF-7, and subsequent IFN-ab feedback signaling. These data suggest an IFN-ab induction pathway that is different from the extracytoplasmic and cytoplasmic pathways so far described. Finally, we show that IFN-ab is a key mediator of the hypersensitivity to bacterial lipopolysaccharide, which develops, in Ad-infected mice.