Molecular cloning, characterization and expression of goose Toll-like receptor 5

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that are vital to activation of the innate immune system in response to invading pathogens through their recognition of pathogen-associated molecular patterns (PAMPs). TLR5 is responsible for the recognition of bacterial flagellin in vertebrates. In this study, we cloned the goose TLR5 gene using rapid amplification of cDNA ends (RACE). The open reading frame (ORF) of goose TLR5 cDNA is 2583 bp in length and encodes an 860 amino acid protein. The entire coding region of the TLR5 gene was successfully amplified from genomic DNA and contained a single exon. The putative amino acid sequence of goose TLR5 consisted of a signal peptide sequence, 11 leucine-rich repeat (LRR) domains, a leucine-rich repeat C-terminal (LRR-CT) domain, a transmembrane domain and an intracellular Toll-interleukin-1 receptor (TIR) domain. The amino acid sequence of goose TLR5 shared 50.5% identity with human (Homo sapiens), 49.8% with mouse (Mus musculus) and 82.7% with chicken (Gallus gallus). The goose TLR5 gene was highly expressed in the spleen, liver and brain; moderately expressed in PBMCs, kidney, lung, heart, bone marrow, small intestine and large intestine; and minimally expressed in the cecum. HEK293 cells transfected with goose TLR5 and NF-κB-luciferase containing plasmids significantly responded to flagellin from Salmonella typhimurium indicating that it is a functional TLR5 homologue. In response to infection with S. enterica serovar Enteritidis (SE), the level of TLR5 mRNA significantly increased over the control in PBMCs at 1 d post infection (p.i.) and was slightly elevated in the spleen at 1 d or 3 d p.i. IL-6 was expressed below control levels in PBMCs but was upregulated in the spleen. In contrast to IL-6, an evident decrease in the expression level of IL-8 was observed in both PBMCs and spleens at 1 d or 3 d p.i. SE challenge also resulted in an increase in the mRNA expression of IL-18 and IFN-γ in PBMCs and the spleen. These results imply that the expression of goose TLR5 is differentially regulated in various tissues and may participate in the immune response against bacterial pathogens.