Abstract
Retinoic acid-inducible gene I (RIG-I), a cytosolic pattern recognition receptor (PRR), can sense various RNA viruses, including the avian influenza virus (AIV) and infectious bursal disease virus (IBDV), and trigger the innate immune response. Previous studies have shown that mammalian RIG-I (human and mice) and waterfowl RIG-I (ducks and geese) are essential for type I interferon (IFN) synthesis during AIV infection. Like ducks, pigeons are also susceptible to infection but are ineffective propagators and disseminators of AIVs, i.e., “dead end” hosts for AIVs and even highly pathogenic avian influenza (HPAI). Consequently, we sought to identify pigeon RIG-I and investigate its roles in the detection of A/Chicken/Shandong/ZB/2007 (H9N2) (ZB07), Gansu/Tianshui (IBDV TS) and Beijing/CJ/1980 (IBDV CJ-801) strains in chicken DF-1 fibroblasts or human 293T cells. Pigeon mRNA encoding the putative pigeon RIG-I analogs was identified. The exogenous expression of enhanced green fluorescence protein (EGFP)-tagged pigeon RIG-I and caspase activation and recruitment domains (CARDs), strongly induced antiviral gene (IFN-β, Mx, and PKR) mRNA synthesis, decreased viral gene (M gene and VP2) mRNA expression, and reduced the viral titers of ZB07 and IBDV TS/CJ-801 virus strains in chicken DF-1 cells, but not in 293T cells. We also compared the antiviral abilities of RIG-I proteins from waterfowl (duck and goose) and pigeon. Our data indicated that waterfowl RIG-I are more effective in the induction of antiviral genes and the repression of ZB07 and IBDV TS/CJ-801 strain replication than pigeon RIG-I. Furthermore, chicken melanoma differentiation associated gene 5(MDA5)/ mitochondrial antiviral signaling (MAVS) silencing combined with RIG-I transfection suggested that pigeon RIG-I can restore the antiviral response in MDA5-silenced DF-1 cells but not in MAVS-silenced DF-1 cells. In conclusion, these results demonstrated that pigeon RIG-I and CARDs have a strong antiviral ability against AIV H9N2 and IBDV in chicken DF-1 cells but not in human 293T cells.
Highlights
H9N2 avian influenza virus (AIV) has been the major threat against domestic poultry in China during the last few decades [1]
Pigeon Retinoic acid-inducible gene I (RIG-I) shares 78.27% and 82.02% amino acid identity with its homologs duck and zebra finch, respectively, suggesting that pigeon RIG-I has a similar role as an RNA virus sensor in innate immunity
As an effective domain of RIG-I, caspase activation and recruitment domains (CARDs) overexpression alone is sufficient to interact with MAVS, in duck and zebra finch, respectively, suggesting that pigeon RIG-I has a similar role as an RNA virus sensor in innate immunity
Summary
H9N2 avian influenza virus (AIV) has been the major threat against domestic poultry in China during the last few decades [1]. H9N2 influenza genotype evolution has facilitated the genesis of the novel H7N9 virus, which has caused the deaths of at least 115 people [2] Another major problem in the domestic poultry industry is infectious bursal disease (IBD) caused by the infectious bursal disease virus (IBDV) characterized by acute, highly contagious, immunosuppressive disease in the young chicken [3]. Ducks and pigeons have been called the “Trojan horse” and “dead end” for susceptibility to infection; they are ineffective propagators and disseminators of the virus [4] This difference in virus resistance among waterfowl, pigeon, and chicken has been ascribed to their individual immune systems, especially their respective innate immune systems
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