| 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. © 2012 Cao et al. |
| Keywords: |
signal transduction; protein kinase b; controlled study; human cell; gene deletion; genetics; interferon; nonhuman; alpha interferon; protein domain; protein function; animal cell; mouse; animal; metabolism; animals; mice; mus; dendritic cell; protein dna binding; down-regulation; drug effect; phosphatidylinositol 3 kinase; virology; rna binding protein; rna-binding proteins; biosynthesis; immunology; dendritic cells; chemistry; drug antagonism; cellular immunity; tumor necrosis factor alpha; amino terminal sequence; tumor necrosis factor-alpha; virus rna; membrane glycoproteins; membrane protein; proto-oncogene proteins c-akt; vaccinia virus; cytokine production; innate immunity; immunity, innate; immunomodulation; protein structure, tertiary; down regulation; feedback system; pathogenicity; protein tertiary structure; myeloid differentiation factor 88; alpha beta interferon receptor; myd88 protein, mouse; knockout mouse; rna transcription; virus mutant; interferon-alpha; tumor necrosis factor; virus protein; viral proteins; chloroquine; protein rna binding; poxviridae; vaccinia; variola virus; toll like receptor 9; rabbits; plasmacytoid dendritic cell; phosphatidylinositol 3-kinases; acidification; rabbit; interferon regulatory factor 7; e3l protein, vaccinia virus; mixed infection; myxoma virus; toll like receptor 7; toll-like receptor 7; orthopoxvirus; oryctolagus cuniculus; leporipoxvirus; tlr7 protein, mouse; cytokine response; myxomatosis
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