Modulation of early host innate immune response by a Fowlpox virus (FWPV) lateral body protein

Abstract

The avian pathogen, fowlpox virus (FWPV) has been successfully used as vaccine vector in poultry and humans but relatively little is known about its ability to modulate host antiviral immune responses in these hosts, which are replication permissive and non-permissive, respectively. FWPV is highly resistant to avian type I interferon (IFN) and able to completely block the host IFN-response. Microarray screening of host IFN-regulated gene expression in cells infected with 59 different, non-essential FWPV gene knock-out mutants revealed that FPV184 confers immunomodulatory capacity. We report that FPV184-knockout virus (FWPVΔ184) induces the cellular IFN response as early as 2 hours post-infection. The wild-type, uninduced phenotype can be rescued by transient expression of FPV184 in FWPVΔ184-infected cells. Ectopic expression of FPV184 inhibited polyI:C activation of the chicken IFN-β promoter and IFN-α activation of the chicken Mx promoter. Confocal and correlative super-resolution light and electron microscopy demonstrated that FPV184 has a functional nuclear localisation signal domain and is packaged in the lateral bodies of the virions. Taken together, these results provide a paradigm for a late poxvirus structural protein packaged in the lateral bodies and capable of supressing IFN induction early during the next round of infection.

Chicken cGAS Senses Fowlpox Virus Infection and Regulates Macrophage Effector Functions

“…The lack of IFN-I response in poxvirus infected cells is likely due to the presence of numerous virally-encoded suppressors of PRR signaling and IFN-I production ( 19 , 24 ), hence deletion of specific innate immunomodulators from the viral genome can result in a virus that stimulates host IFN-I signaling. We made use of FWPV mutants FPV012 and FPV184 ( 19 , 20 ), each deficient in single genes that are proposed immunomodulators, and both of which induce IFN-I production from infected cells ( 19 ), including HD11 cells ( Figure 6B ). In the absence of cGAS or STING the transcription of IFN-I, ISG12.2, BLB1 and CD40 by FPV184 or FPV012 was significantly lower at 24 h post infection ( Figures 6B, C ), despite robust infection of HD11 cells by all three virus strains ( Figure 6D ), indicating that FWPV is sensed in infected cells by the DNA sensing PRR cGAS and that the cGAS/STING pathway is responsible for FWPV-induced IFN-I production and MHC-II transcription.…”

“…Fowlpox WT (FP9) and mutants [FPV012 ( 19 ) and FPV184 ( 20 )] were propagated in primary chicken embryonic fibroblasts (CEFs) and grown in DMEM-F12 (Thermo Fisher Scientific, Waltham, MA, USA) containing 1% FBS and 5% P/S, and harvested 5 days later. Ten-fold dilutions of cell supernatants were prepared in serum-free DMEM-F12 and used to inoculate confluent monolayers of CEFs for 1.5 h at 37°C.…”