A Toll-like receptor–independent antiviral response induced by double-stranded B-form DNA

Abstract

The innate immune system recognizes nucleic acids during infection or tissue damage; however, the mechanisms of intracellular recognition of DNA have not been fully elucidated. Here we show that intracellular administration of double-stranded B-form DNA (B-DNA) triggered antiviral responses including production of type I interferons and chemokines independently of Toll-like receptors or the helicase RIG-I. B-DNA activated transcription factor IRF3 and the promoter of the gene encoding interferon-beta through a signaling pathway that required the kinases TBK1 and IKKi, whereas there was substantial activation of transcription factor NF-kappaB independent of both TBK and IKKi. IPS-1, an adaptor molecule linking RIG-I and TBK1, was involved in B-DNA-induced activation of interferon-beta and NF-kappaB. B-DNA signaling by this pathway conferred resistance to viral infection in a way dependent on both TBK1 and IKKi. These results suggest that both TBK1 and IKKi are required for innate immune activation by B-DNA, which might be important in antiviral innate immunity and other DNA-associated immune disorders.

The TLR‐independent DNA recognition pathway in murine macrophages: Ligand features and molecular signature

“…-1936 Innate immunity well-defined dsDNA with blunts ends, poly(dAdT) is heterogeneous in size with random order of dA and dT bases and hence is likely to form large aggregates of partially ss and partially dsDNA (data not shown). Furthermore, ISD signaling was studied in murine macrophages [10], whereas poly(dAdT) signaling was assayed in murine embryonic fibroblasts [9]. We therefore raised the question, whether the two species of DNA would be recognized by the same receptor.…”

“…Despite ''thousands of man-years worth of DNA transfections'', it has only recently been noticed that introduction of dsDNA into the cytosol triggers a potent innate immune response, leading to the production of IL-1b, IFN-b and other cytokines [8][9][10]. IL-1b secretion is governed by the DNA sensor AIM2 that has recently been identified [11][12][13][14].…”

“…IFN-b production is regulated by the DNA-dependent activator of IFN-regulatory factors (DAI, formerly known as DLM-1/ZBP1) [15] and as-yet unknown DNA sensors [16,17]. With regard to the IFN pathway, it has been suggested that the B-conformation of DNA is stimulatory, whereas Z-DNA is not [9]. Another report suggests that the exchange of the phosphate backbone for a phosphorothioate backbone renders the DNA inert, implying that the DNA backbone is the site of recognition [10].…”

“…4B). This suggests that DNA requires at least two helical turns to be recognized by cytosolic sensors.ISD and poly(dAdT), though both meant to trigger the cytosolic DNA pathway, are likely to be of different nature and were originally identified in two distinct experimental setups [9,10]. While ISD is a Eur.…”

NF-κB and the immune response

“…However, as membrane restriction prevents TLRs from sampling the cytosol where much of the viral life cycle occurs, cytosolic PRRs provide comprehensive innate immune recognition. For example, recognition of cytoplasmic dsDNA leading to NF-kB activation and type I interferon production has also been reported, although the relevant receptor has not yet been identified (Ishii et al, 2006;Stetson and Medzhitov, 2006). This receptor(s) is predicted to be important for type I IFN production in response to viruses and intracellular pathogens, such as Listeria monocytogenes and Shigella flexneri.…”