Figure 1

Model of innate immune recognition of virus in birds. The plasma membrane receptor of TLR15 recognizes CpG-ODN derived from viruses and bacteria. Viral recognition relies on intracellular vesicles of PRR, whose ligands are dsRNA derived from viruses or virus-infected cells (TLR3), ssRNA derived from RNA viruses (TLR7), CpG-ODN (TLR21), short 5′ppp dsRNA (RIG-I), and long dsRNA (MDA5). TLR3, TLR7 and TLR21 localize mainly in the ER in the steady state and traffic to the endosome, where they engage with their ligands. The recognition triggers the downstream signal transduction to activate NF-κв or IRF3/7, finally induces interferon and inflammatory cytokine production.