title: Innate immune response of human plasmacytoid dendritic cells to poxvirus infection is subverted by vaccinia E3 via its Z-DNA/RNA binding domain.
abstract: Plasmacytoid dendritic cells (pDCs) play important roles in antiviral innate immunity by producing type I interferon (IFN). In this study, we assess the immune responses of primary human pDCs to two poxviruses, vaccinia and myxoma virus. Vaccinia, an orthopoxvirus, was used for immunization against smallpox, a contagious human disease with high mortality. Myxoma virus, a Leporipoxvirus, causes lethal disease in rabbits, but is non-pathogenic in humans. We report that myxoma virus infection of human pDCs induces IFN-α and TNF production, whereas vaccinia infection does not. Co-infection of pDCs with myxoma virus plus vaccinia blocks myxoma induction effects. We find that heat-inactivated vaccinia (Heat-VAC; by incubating the virus at 55°C for 1 h) gains the ability to induce IFN-α and TNF in primary human pDCs. Induction of IFN-α in pDCs by myxoma virus or Heat-VAC is blocked by chloroquine, which inhibits endosomal acidification required for TLR7/9 signaling, and by inhibitors of cellular kinases PI3K and Akt. Using purified pDCs from genetic knockout mice, we demonstrate that Heat-VAC-induced type I IFN production in pDCs requires the endosomal RNA sensor TLR7 and its adaptor MyD88, transcription factor IRF7 and the type I IFN feedback loop mediated by IFNAR1. These results indicate that (i) vaccinia virus, but not myxoma virus, expresses inhibitor(s) of the poxvirus sensing pathway(s) in pDCs; and (ii) Heat-VAC infection fails to produce inhibitor(s) but rather produces novel activator(s), likely viral RNA transcripts that are sensed by the TLR7/MyD88 pathway. Using vaccinia gene deletion mutants, we show that the Z-DNA/RNA binding domain at the N-terminus of the vaccinia immunomodulatory E3 protein is an antagonist of the innate immune response of human pDCs to poxvirus infection and TLR agonists. The myxoma virus ortholog of vaccinia E3 (M029) lacks the N-terminal Z-DNA/RNA binding domain, which might contribute to the immunostimulating properties of myxoma virus.
authors.affiliation: Dermatology Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors.forename: Hua
authors.initials: H
authors.lastname: Cao
authors.forename: Peihong
authors.initials: P
authors.lastname: Dai
authors.forename: Weiyi
authors.initials: W
authors.lastname: Wang
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Jianda
authors.initials: J
authors.lastname: Yuan
authors.forename: Fangjin
authors.initials: F
authors.lastname: Wang
authors.forename: Chee-Mun
authors.initials: CM
authors.lastname: Fang
authors.forename: Paula M
authors.initials: PM
authors.lastname: Pitha
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Richard C
authors.initials: RC
authors.lastname: Condit
authors.forename: Grant
authors.initials: G
authors.lastname: McFadden
authors.forename: Taha
authors.initials: T
authors.lastname: Merghoub
authors.forename: Alan N
authors.initials: AN
authors.lastname: Houghton
authors.forename: James W
authors.initials: JW
authors.lastname: Young
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
authors.forename: Liang
authors.initials: L
authors.lastname: Deng
mesh_terms: D000818:Animals; D002738:Chloroquine / Q000494:pharmacology; D003713:Dendritic Cells / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism / Q000821:virology*; D015536:Down-Regulation; D006801:Humans; D007113:Immunity, Innate; D016898:Interferon-alpha / Q000096:biosynthesis; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D009233:Myxoma virus / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011817:Rabbits; D051199:Toll-Like Receptor 7 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D014616:Vaccinia virus / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D002738:Chloroquine; D016898:Interferon-alpha; D008562:Membrane Glycoproteins; D053594:Myeloid Differentiation Factor 88; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D016601:RNA-Binding Proteins; D051199:Toll-Like Receptor 7; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; C081374:E3L protein, Vaccinia virus; C507780:Myd88 protein, mouse; C477038:Tlr7 protein, mouse