Administration of bacterial heat shock protein 70 to induce a protective innate immune response in European sea bass larvae (Dicentrarchus labrax) against Vibrio anguillarum

Abstract

We studied the use of recombinant E. coli heat-shock protein 70 (DnaK) encapsulated in alginate microparticles to protect European sea bass (Dicentrarchus labrax) larvae against Vibrio anguillarum infection. DnaK is performing a multitude of housekeeping and cytoprotective functions in prokaryotes. It stimulates the immune system of the model crustacean Artemia. The experiment was performed by feeding alginate microparticles containing a low (0.5 mg) or high (1.0 mg) dose of the recombinant DnaK, to sea bass larvae at day 7 after hatching. Simultaneously, 2 groups (n = 120) of larvae were either fed with empty alginate microparticles or were receiving no microparticles (unfed) (negative controls). Larvae were infected with V. anguillarum after 18 h of feeding. Controls experienced an acute V. anguillarum infection resulting in high mortality. DnaK could not induce protection, as the mortality in the group receiving empty microparticles was statistically the same as in the groups fed with alginate microparticles containing the low or high dose of DnaK. V. anguillarum significantly upregulated the expression of the tlr3, tlr5, il1, tnfα, cc1, cxcl8, cxcr4 and ccr9 genes. Upregulation of pro-inflammatory cytokine genes, (il1, tnfα), inflammatory chemokine genes (cc1, cxcl8) and chemokines receptor genes (cxcr4, ccr9) following bacterial infection is not uncommon in fish. However, to our knowledge, we are the first to demonstrate this in vibrio-infected axenic sea bass larvae. Although there was a significant upregulation of cas1, il1, tnfα, cc1, cxcl8, cxcr4 and ccr9 in the groups receiving DnaK, no protection against V. anguillarum was observed. We concluded that axenic European sea bass larvae receiving recombinant DnaK prior to V. anguillarum challenge were not significantly protected from V. anguillarum infection.