Key role of splenic myeloid DCs in the IFN-alphabeta response to adenoviruses in vivo.

The early systemic production of interferon (IFN)-alphabeta is an
essential component of the antiviral host defense mechanisms, but
is also thought to contribute to the toxic side effects
accompanying gene therapy with adenoviral vectors. Here we
investigated the IFN-alphabeta response to human adenoviruses (Ads)
in mice. By comparing the responses of normal, myeloid (m)DC- and
plasmacytoid (p)DC-depleted mice and by measuring IFN-alphabeta
mRNA expression in different organs and cells types, we show that
in vivo, Ads elicit strong and rapid IFN-alphabeta production,
almost exclusively in splenic mDCs. Using knockout mice, various
strains of Ads (wild type, mutant and UV-inactivated) and MAP
kinase inhibitors, we demonstrate that the Ad-induced IFN-alphabeta
response does not require Toll-like receptors (TLR), known
cytosolic sensors of RNA (RIG-I/MDA-5) and DNA (DAI) recognition
and interferon regulatory factor (IRF)-3, but is dependent on viral
endosomal escape, signaling via the MAP kinase SAPK/JNK and IRF-7.
Furthermore, we show that Ads induce IFN-alphabeta and IL-6 in vivo
by distinct pathways and confirm that IFN-alphabeta positively
regulates the IL-6 response. Finally, by measuring TNF-alpha
responses to LPS in Ad-infected wild type and IFN-alphabetaR(-/-)
mice, we show that IFN-alphabeta is the key mediator of Ad-induced
hypersensitivity to LPS. These findings indicate that, like
endosomal TLR signaling in pDCs, TLR-independent virus recognition
in splenic mDCs can also produce a robust early IFN-alphabeta
response, which is responsible for the bulk of IFN-alphabeta
production induced by adenovirus in vivo. The signaling
requirements are different from known TLR-dependent or cytosolic
IFN-alphabeta induction mechanisms and suggest a novel cytosolic
viral induction pathway. The hypersensitivity to components of the
microbial flora and invading pathogens may in part explain the
toxic side effects of adenoviral gene therapy and contribute to the
pathogenesis of adenoviral disease.