Effects of TLR agonists and viral infection on cytokine and TLR expression in Atlantic salmon (Salmo salar)

Abstract

The development of efficient and cheap vaccines against several aquatic viruses is necessary for a sustainable fish farming industry. Toll-like receptor (TLR) ligands have already been used as good adjuvants in human vaccines. With more understanding of TLR expression, function, and ligand specificity in fish, more efficient adjuvants for fish viral vaccines can be developed. In this paper, we examine all known TLRs in Atlantic salmon (Salmo salar) and demonstrate that head kidney and spleen are the main organs expressing TLRs in salmon. We also show that adherent head kidney leucocytes from salmon are able to respond to many of the known agonists for human TLRs, and that viral infection can induce up-regulation of several TLRs. These findings substantiate these receptors' role in immune responses to pathogens in salmonids making their ligands attractive as vaccine adjuvant candidates.

Aeromonas salmonicidaInfection Only Moderately Regulates Expression of Factors Contributing to Toll-Like Receptor Signaling but Massively Activates the Cellular and Humoral Branches of Innate Immunity in Rainbow Trout (Oncorhynchus mykiss)

“…Pronounced upregulation of tlr expression after infection with relevant pathogens has been documented for mammals [21,23], invertebrates [45,46], and also bony fish. Distinct sets of tlr genes showed enhanced expression in channel catfish Ictalurus punctatus [19], Atlantic salmon Salmo salar [18], and Antarctic bullhead notothen Notothenia coriiceps [20] after parasitic, bacterial, and viral infection, respectively. After infection, some of those tlr genes revealed distinctively high mRNA abundances with changes of more than 10-fold above controls.…”

“…salmonicida is the causative agent of furunculosis, a serious disease of salmonid fish inducing high mortality even after a low-dose intraperitoneal injection [13]. Pathogenic challenges induce not only the massive activation of proinflammatory mediators [14][15][16][17], but also enhanced transcription of tlr-encoding genes in fish [18][19][20] as reported previously for mammals [21][22][23]. The dominant MAMP from Gram-negative bacteria is lipopolysaccharide (LPS), known in mammals to be specifically and solely recognized by TLR4 [24].…”

Identification and characterisation of TLR18-21 genes in Atlantic salmon (Salmo salar)

“…The cells were treated with fresh complete medium alone or medium containing recombinant type I IFN (20 ng/ml), IFNg (20 ng/ ml) or IL-1b (20 ng/ml). Cytokines rather than PAMPs were used for stimulation as PAMPs do not show much effect on TLR expression [22]. The cells were collected and lysed with TRI-Reagent (SigmaeAldrich) after treatment for 4 h, 8 h, 24 h and 48 h. Total RNA extraction and cDNA synthesis were performed as described previously [21].…”

Characterization of Toll-like receptor gene expression in goldfish (Carassius auratus) during Dactylogyrus intermedius infection

“…In this study, the expression of the nine goldfish TLRs in four immune-related tissues gill, liver, spleen, head kidney and one pathogen-contacted organ tail fin during D. intermedius infection was measured using quantitative real-time PCR (RT-qPCR) for the first time. Although TLR genes are thought to be are more abundantly expressed in peripheral blood leukocytes (PBL) than other immune organs and lowest expressed in skin and gut, some receptors exhibit a more distributed expression profile (Arnemo et al, 2014;Pietretti and Wiegertjes, 2014). For the tissue specific expression analysis, we revealed their broad distribution in various organs and tissues; highest expression of almost all TLRs was detected in spleen, especially for significantly up-regulated TLRs (TLR4, 5, 20 and 22) during D. intermedius infection (Fig.…”