Abstract
Toll-like receptor (TLR) 7 ligand, resiquimod, has been studied as an adjuvant and antiviral agent against several pathogens in chicken. Yet, the effectiveness of resiquimod against infectious bronchitis virus (IBV) infection has not been evaluated. In this study, we investigated the effectiveness of resiquimod delivered pre-hatch (in ovo) against IBV infection post-hatch identifying key mechanisms involved in resiquimod driven immune activation. First, we found an 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. Second, we observed that resiquimod was able to act as an adjuvant when resiquimod was delivered pre-hatch along with an inactivated IBV vaccine. Finally, when the resiquimod pretreated one-day-old chickens were infected with IBV, reduction in viral shedding via oral and fecal routes was observed at 3 days post- infection. Overall, this study shows that the pre-hatch delivered resiquimod increases cell-mediated immune responses in lungs with an advantage of reduction in IBV shedding.
Highlights
Infectious bronchitis (IB) is one of the major respiratory diseases that impacts chickens (Gallus gallus domesticus) worldwide [1,2,3]
Immunofluorescent assay performed on lung tissue obtained at day one post-hatch, revealed a significant increase in macrophage (p = 0.007, Figure 1a) and CD8α+ T (p = 0.02, Figure 1b) numbers in resiquimod pretreated chickens as compared with the PBS pretreated controls
IFN-γ, IL-1β, and iNOS mRNS Expression Levels Following In Ovo Delivery of Resiquimod
Summary
Infectious bronchitis (IB) is one of the major respiratory diseases that impacts chickens (Gallus gallus domesticus) worldwide [1,2,3]. IB remains a considerable cause of economical loss to the poultry industry [4]. Alternative strategies that aim to boost the host responses against IBV are increasingly being investigated. Toll-like receptor (TLR) ligands, a group of innate immune response modifiers have become worthy candidates that have been exploited to enhance innate immune responses in hosts against a number. Vaccines 2020, 8, 186 of pathogens [5]. TLRs are a subset of germline-encoded pattern recognition receptors found in mammals, birds, and fish. TLRs are able to recognize and bind to pathogen-associated molecular patterns (PAMPs), which are highly conserved molecular structures present in microbes
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