Immunization of sea bream (Sparus aurata) juveniles against Photobacterium damselae subsp. piscicida by short bath: Effect on some pro-inflammatory molecules and the Mx gene expression

• We evaluated the levels of immune related genes in sea bream after vaccination head kidney leucocytes.
• We used RT-PCR to investigate the dynamic of expression of immune-related genes.
• Heat-inactivated vaccine induce an early inflammatory response in sea bream.

Cytokines are a family of proteins derived from macrophages, lymphocytes, granulocytes, mast cells and epithelial cells and can be divided into interferons (IFNs), Interleukins (ILs) and Tumor Necrosis factors (TNFs) among others. The presence of cytokines in a wide number of fish species has been proved and several molecules types have been already cloned and sequenced. In this work some proinflamatory molecules and Mx gene were detected in the liver of vaccinated sea bream juveniles with an average body weight of 5 g. The method of immunization was by short bath and three different bacterins against the marine pathogen Photobacterium damselae subsp. piscicida were designed and used to immunize fish. Five genes encoding for five different molecules were analyzed by real time PCR: IL-1β, IL Ir-2, Cox-2, Mx and TNFα. Gene expression was quantified along four days after fish immunization and results were compared among groups. Results show that the heat-inactivated vaccine stimulates the up-regulation of IL-1β, IL Ir-2, Cox-2 and TNFα genes whereas the UV-light inactivated vaccine was the unique vaccine which stimulates the expression of Mx gene. The present is a novel study that shows by the first time the effect of the inactivation process of vaccines on the expression levels of genes involved in the defense against Photobacterium damselae subsp piscicida.