Comparative innate responses induced by Toll-like receptor (TLR)7 and 21 ligands against infectious bronchitis virus infection
Date
2019-01-26
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Abstract
Toll-like receptor (TLR)7 and 21 ligands, resiquimod and cytosine-guanosine (CpG) oligonucleotides (ODNs) respectively have been used in ovo (pre-hatch) to enhance or prime an early immune response in chickens to provide protection against microbial pathogens. Yet, their protective efficacy against an infectious bronchitis virus (IBV) infection encountered post-hatch has not been evaluated. Thus, our objectives were to investigate the efficacy of resiquimod and CpG ODNs against a post-hatch IBV infection by delivering the ligands in ovo at embryo day (ED)18 and then, to determine possible mechanisms of protection. We found upregulation of interleukin (IL)-1β and interferon (IFN)-γ mRNA levels and considerable expansions of macrophage and cluster of differentiation (CD)8α+ T cell populations in lungs of chicken as early as day one post-hatch, following pre-hatch delivery of resiquimod. When the resiquimod pre-treated day-old chickens were infected with IBV, reduction in viral shedding via oral and fecal routes was observed at 3 days post-infection (dpi). Similarly, in CpG ODN pre-treated birds at 3 dpi, we found increased recruitment of macrophages, CD8α+ and CD4+ T lymphocytes in addition to up-regulation of IFN-γ and IL-1β mRNA concentrations in chicken lungs. However, only in ovo delivered CpG ODNs significantly reduced the morbidity and mortality associated with IBV infection. Overall, these studies bring us closer to understanding mechanisms behind CpG ODNs and resiquimod induced immune responses in chickens when used as stand-alone prophylactic agents in ovo.
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Keywords
In ovo; CpG oligonucleotide; resiquimod, infectious bronchitis virus; avian macrophage; CD4+ cell; CD8α+ cell; interleukin-1β; interferon-γ
Citation
De Silva Senapathi, Y. U. (2019). Comparative innate responses induced by Toll-like receptor (TLR)7 and 21 ligands against infectious bronchitis virus infection (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.