The Evasion of Antiviral Innate Immunity by Chicken DNA Viruses

Abstract

The innate immune system constitutes the first line of host defense. Viruses have evolved multiple mechanisms to escape host immune surveillance, which has been explored extensively for human DNA viruses. There is growing evidence showing the interaction between avian DNA viruses and the host innate immune system. In this review, we will survey the present knowledge of chicken DNA viruses, then describe the functions of DNA sensors in avian innate immunity, and finally discuss recent progresses in chicken DNA virus evasion from host innate immune responses.

Keywords: DNA virus; PRRs; chicken; evasion; innate immunity.

Figure 1

Chicken DNA viruses’ evasion of DNA sensor-induced antiviral innate immunity. cGAS and DDX41 localize in the cytoplasm and sense cytosolic dsDNA directly, DNA recognition induces cGAS and DDX41 activation. Upon activation, cGAS catalyzes the synthesis of the nucleotide 2'3'-cGAMP from ATP and GTP, which will be bound by STING and induce STING activation, while DDX41 interacts and activates STING directly. STING activation recruits and activates TBK1, followed by phosphorylation and nuclear translocation of transcription factor IRF7, which initiates transcription of IFN-I and pro-inflammatory cytokines. STING also activates NF-κB. TLR21, which resides in the endosome, senses CpG DNA and activates NF-κB through adaptor protein MyD88. MDV encoded proteins Meq interacts with STING and IRF7, VP23 interacts with IRF7, while RLORF4 binds the endogenous NF-κB.