Evidence of an antimicrobial-immunomodulatory role of Atlantic salmon cathelicidins during infection with Yersinia ruckeri

• Published in: PLoS ONE
• Main Authors: Bridle, A, Nosworthy, E, Polinski, M, Nowak, B
• Format: Article in Journal/Newspaper
• Language: English
• Published: Public Library Science 2011
• Subjects: Agricultural and Veterinary Sciences; Fisheries Sciences; Fish Pests and Diseases; Atlantic salmon
• Online Access: https://doi.org/10.1371/journal.pone.0023417; http://www.ncbi.nlm.nih.gov/pubmed/21858109; http://ecite.utas.edu.au/72066

Cathelicidins are a family of antimicrobial peptides that act as effector molecules of the innate immune system with broadspectrumantimicrobial properties. These evolutionary conserved cationic host-defence peptides are integral componentsof the immune response of fish, which are generally believed to rely heavily on innate immune defences to invadingpathogens. In this study we showed that Atlantic salmon cathelicidin 1 and 2 (asCATH1 and asCATH2) stimulated peripheralblood leukocytes increasing the transcription of the chemokine interleukin-8. Further, functional differences were identifiedbetween the two cathelicidins. In the presence of serum, asCATH1 displayed greatly diminished host haemolytic activity,while the constitutively expressed asCATH2 had no haemolytic activity with or without serum. These findings support ourhypothesis that fish cathelicidins exert their primary antimicrobial action at the site of pathogen invasion such as epithelialsurfaces. Further, we hypothesise that like their mammalian counterparts in the presence of serum they act as mediators ofthe innate and adaptive immune response via the release of cytokines thus indirectly protecting against a variety ofpathogens. We highlight the importance of this immunomodulatory role from the involvement of asCATHs during aninfection with the fish pathogen Yersinia ruckeri . While we were able to demonstrate in vitro that asCATH1 and 2, possesseddirect microbicidal activity against the fish pathogen, Vibrio anguillarum , and a common gram negative bacterium, Escherichia coli , little or no bactericidal activity was found against Y. ruckeri . The contribution of either asCATH in theimmune response or as a potential virulence factor during yersiniosis is highlighted from the increased expression ofasCATH1 and 2 mRNA during an in vivo challenge with Y. ruckeri . We propose that Atlantic salmon cathelicidins participatein the interplay between the innate and adaptive immune systems via the release of cytokines enabling a more effectiveresponse to invading pathogens.