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Abstract: Mammalian Toll-like receptor 3 (TLR3) recognizes extracellular and intracellular viral dsRNA, and then initiates signaling cascades leading to NF-κB activation and interferon (IFN) production. To understand the roles of TLR3 in the fish immune system, TLR3 gene (JfTLR3) was identified from Japanese flounder (Paralichthys olivaceus), which consisted of 4 exons and 3 introns. Its expression in peripheral blood leukocytes increased upon stimulation with poly I:C and CpG ODN 1668. Exposure to viral hemorrhagic septicemia virus increased expression of JfTLR3 in the blood, liver, head kidney and spleen. Intracellular poly I:C stimulation in JfTLR3-overexpressing YO-K cells significantly induced IFN-inducible and NF-κB-regulated genes. NF-κB activity in JfTLR3-overexpressing YO-K cells was significantly induced by intracellular poly I:C while expression of IFN-inducible genes and NF-κB reporter activity in JfTLR3-overexpressing HINAE cells increased upon stimulation by extracellular poly I:C. These results suggest that JfTLR3 plays an important role in the induction of antiviral immune response. [Copyright &y& Elsevier]

Abstract: Toll-like receptors (TLRs) are essential for activation of the innate immune system in response to invading pathogens. TLR14, which is unique to fish, has been identified in several fish species, but its function is unclear. In this study, Japanese flounder (Paralichthys olivaceus) TLR14 gene (JfTLR14) was cloned and its expression profiles were analyzed after infection with viral hemorrhagic septicemia virus, gram-positive Streptococcus iniae and gram-negative Edwardsiella tarda. The coding region of JfTLR14 cDNA was 2,607 bp, encoding 878 amino acid residues. JfTLR14 was highly expressed in head kidney of healthy flounder. In response to infection with VHSV and S. iniae, the JfTLR14 gene was up-regulated at only 1 day post-infection (dpi). However, E. tarda infection increased JfTLR14 gene expression from 1 to 6 dpi. These results imply that JfTLR14 participates more in the immune response against E. tarda infection than in the immune responses to other pathogen infections. [ABSTRACT FROM AUTHOR]