Abstract
Pattern recognition receptors (PRRs) are a class of immune sensors that play a critical role in detecting and responding to several conserved patterns of microorganisms. As such, they play a major role in the maintenance of immune homeostasis and anti-microbial defense. Fundamental knowledge pertaining to the discovery of PRR functions and their ligands continue to advance the understanding of immune system and disease resistance, which led to the rational design and/or application of various PRR ligands as vaccine adjuvants. In addition, the conserved nature of many PRRs throughout the animal kingdom has enabled the utilization of the comparative genomics approach in PRR identification and the study of evolution, structural features, and functions in many animal species including avian. In the present review, we focused on PRR sensing and signaling functions in the avian species, domestic chicken, mallard, and domestic goose. In addition to summarizing recent advances in the understanding of avian PRR functions, the present review utilized a comparative biology approach to identify additional PRRs, whose functions have been well studied in mammalians but await functional characterization in avian.
Highlights
The innate immune system acts as the first line of defense against invading microorganisms and plays an important role in the establishment of anti-microbial state or shaping the adaptive immune responses
Pattern recognition receptors (PRRs) are notably classified into four families: Toll-like receptors (TLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), C-type lectin receptors (CLRs), and retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs)
Unlike low pathogenic avian influenza (LPAI)-infection, infection of goose peripheral blood mononuclear cells (PBMCs) and goslings with new gosling viral duck enteritis virus (NGVEV) resulted in a significant upregulation of goose TLR21 (goTLR21) [87]
Summary
The innate immune system acts as the first line of defense against invading microorganisms and plays an important role in the establishment of anti-microbial state or shaping the adaptive immune responses. We tended to focus on these properties of avian PRRs including TLRs, NLRs, and RLRs whose functions are characterized or yet to be defined. For those avian PRRs that await functional characterization, we extrapolated PRR functions on the basis of sequence alignments that led us to identify conserved or shared domains, motifs, and functional residues with mammalian counterparts. The present review comprehensively spans TLRs, RLRs, NLRs, and additional DNA or RNA sensors in chicken, duck, and goose, and highlights areas for further research that may enhance the understanding of PRR functions and evolution Note: goose carry one isoform each of TLR2 and TLR1
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