IMMUNE-GENES EXPRESSION ANALYSIS DURING TIME COURSE AND RECOVERY PROCESS INDICATES THE MECHANISM FOR INNATE IMMUNE RESPONSE AND REPAIR AFTER AMYLOODINIOSISIN EUROPEAN SEA BASS (DICENTRARCHUS LABRAX)

Currently, there are no effective preventive measures to control Amyloodinium ocellatum(AO) dinospores/trophonts infection in Europeansea bass (ESB). A vaccine against AO is not available because specific immunogenic antigens have not been identified yet. Moreover, there is a lack of information about basic molecular mechanisms of host immune responses following AO infection.In order to investigate the innate immune response and repair mechanism during the recovery from amyloodiniosis, 26 ESB (mean weight 14g) per tank in triplicate were bath challenged for 2h with AO (3.5×106/tank; 70 dinospores/ml) under controlled conditions (26-28°Cand 34‰ salinity). As a control group (non-infected), 26 ESB per tank in triplicate were also used. The time-course of infection was determined by fresh microscopical examination of gills and histopathological evaluations. After 2 hour, fish were already infected, and at 2 days post infection (dpi) the AO trophonts burden was discrete with light clinical symptoms. During the infection, the maximum AO burden was observed at 10-12 dpi, thereafter fish started to recover even if positive to amyloodiniosis. Throughout this period the total mortality was 18 %. In control group, fish were not infected and no mortality was registered. Expression changes of innate immune genes in gills and head kidney at 2, 3, 5, 7 and 23 dpi were analysed using real-time PCR. Theresults indicated that the expression of cytokines (CC1, IL-8) and antimicrobial peptide (Hep) were strongly stimulatedand reached the peak at 5 dpi in the early infection stage, followed by a gradual reduction in the recovery stage (23 dpi), during which the levels were even lower at 23 dpi. Noticeably, the immunoglobulin (IgM) expressions were higher at 23 dpi compared to 7 dpi. These results indicated the strong correlation between igm, hepcidin and chemokine expression level. The hepcidin and chemokine CC1 might play a role in the inflammatory response during early and recovery stages. Altogether, our observations represent the first step towards understanding the molecular mechanism of theamyloodiniosispathogenesisin European sea bass.