The in ovo delivery of cytosine-guanosine (CpG) oligodeoxynucleotides (ODNs) protects chickens against many bacterial and viral infections, by activating the toll-like receptor (TLR)21 signaling pathway. Although the delivery of CpG ODNs in ovo at embryo day (ED) 18 has been shown to reduce infectious bronchitis virus (IBV) loads in embryonic chicken lungs pre-hatch, whether in ovo delivered CpG ODNs are capable of protecting chickens against a post-hatch challenge is unknown. Thus, our objectives were to determine the protective effect of the in ovo delivery of CpG ODNs at ED 18 against IBV infection encountered post-hatch and, then, to investigate the mechanisms of protection. We found significantly higher survival rates and reduced IBV infection in the chickens following the pre-treatment of the ED 18 eggs with CpG ODNs. At 3 days post infection (dpi), we found an increased recruitment of macrophages, cluster of differentiation (CD)8α+ and CD4+ T lymphocytes, and an up-regulation of interferon (IFN)-γ mRNA in the respiratory tract of the chickens. Overall, it may be inferred that CpG ODNs, when delivered in ovo, provide protection against IBV infection induced morbidity and mortality with an enhanced immune response.
Keywords: CD4+ cell; CD8α+ cell; CpG oligonucleotide; In ovo; avian macrophage; infectious bronchitis virus.