AUTHOR=Yaacob Eamy Nursaliza , Norouzitallab Parisa , De Geest Bruno G. , Bajek Aline , Dierckens Kristof , Bossier Peter , Vanrompay Daisy 

TITLE=Recombinant DnaK Orally Administered Protects Axenic European Sea Bass Against Vibriosis

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.03162

DOI=10.3389/fimmu.2019.03162

ISSN=1664-3224

ABSTRACT=<p><italic>Vibrio anguillarum</italic> causes high mortality in European sea bass (<italic>Dicentrarchus labrax</italic>) larviculture and is a hindering factor for successful sustainable aquaculture of this commercially valuable species. Priming of the innate immune system through administration of immunostimulants has become an important approach to control disease outbreaks in marine fish larviculture. This study was conducted to evaluate immunostimulation by <italic>Escherichia coli</italic> HSP70 (DnaK) in axenic European sea bass larvae in order to protect the larvae against vibriosis. DnaK stimulates the immune response in crustaceans and juvenile fish against bacterial infections. The use of axenic fish larvae allows to study immunostimulation in the absence of an interfering microbial community. At 7 days post-hatching, larvae received a single dose of alginate encapsulated recombinant DnaK. Two non-treated control groups in which animals either received empty alginate microparticles (C1) or no alginante microparticles (C2 and C3) were included in the study. Eighteen hours later, all larvae, except the ones from group C3 (non-infected control) were challenged with <italic>V. anguillarum</italic> (10<sup>5</sup> CFU, bath infection). Mortality was daily recorded until 120 h post infection and at 18, 24, and 36 h post infection, larvae were sampled for expression of immune related genes. Results showed that <italic>V. anguillarum</italic> induced an immune response in axenic sea bass larvae but that the innate immune response was incapable to protect the larvae against deadly septicaemic disease. In addition, we showed that administration of alginate encapsulated DnaK to axenic European sea bass larvae at DAH7 resulted in a significant, DnaK dose dependent, upreglation of immune sensor, regulatory and effector genes. Significant upregulation of <italic>cxcr4, cas1</italic> and especially of <italic>hep</italic> and <italic>dic</italic> was correlated with significant higher survival rates in <italic>V. anguillarum</italic> infected larvae. In the future recombinant DnaK might perhaps be used as a novel immunostimulant in sea bass larviculture.</p>