Aquaculture is a major production method for European sea bass (D. labrax) with the European Union (EU) as the largest producer of sea bass. Vibrio anguillarum infections may cause massive mortality in reared marine sea bass larvae and juveniles. Innate immune defence mechanisms are crucial in sea bass larvae for surviving a Vibrio infection as antigen-specific adaptive immune mechanisms are not yet functional. Therefore, prophylaxis of V. anguillarum infections by means of stimulating the larvae’s innate immune system gains interest.
Studies in aquatic animals suggested a role for ferritin in innate immune defence as they demonstrated a significant increase in ferritin gene transcript levels in several tissues upon administering microbial pathogens. At present, we examined the use of recombinant sea bass ferritin-H to protect European sea bass larvae against Vibrio anguillarum infection.
The ferritin-H gene Dlfer was cloned into pcDNA4/V5-His B. Ferritin-H was expressed in transfected COS-7 cells, purified using the ProBond™ purification kit and examined by SDS-PAGE and Western blotting using an anti-V5 FITC-labelled mouse monoclonal antibody.
Axenic sea bass larvae were fed alginate microparticles containing a high (1.0 mg) or low dose (0.5 mg) of the recombinant ferritin-H at day 7 after hatching. Simultaneously, two groups 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. Negative controls showed high mortality. V. anguillarum significantly upregulated the expression of the tlr3, tlr5, cas1, il1b, tnfα, mif, il10, cc1, cxcl8, cxcr4 and ccr9 genes. Sea bass larvae fed with recombinant ferritin-H prior to infection were not significantly protected. Gene expression points more in the direction of immuno-suppression by ferritin-H, as in humans instead of immuno-stimulation, as described for shrimp. Further research is needed to design innovative protective measures against vibrio infections in sea bass larvae.