Analysis of Immune Response in Yellowtail upon Vaccination with a Bivalent Vaccine of Vibrio anguillarum and Lactococcus garvieae

We inoculated yellowtail Seriola quinqueradiata with a commercial bivalent vaccine containing inactivated Vibrio anguillarum and Lactococcus garvieae to better understand the immunological responses to the vaccination. Serum samples were collected from vaccinated and control (PBS-injected) fish at 1, 3, 5, 7, 10, and 14 days post-vaccination (dpv). Compared to the controls, the serum from the vaccinated fish inhibited the proliferation of V. anguillarum from 7 dpv. However, vaccination had no effect on L. garvieae proliferation. The antibody titer against V. anguillarum obviously increased from 7 dpv, but no such increase was detected for L. garvieae. We confirmed that the protection conferred by the V. anguillarum vaccine was a result of the antibodies against the pathogen. However, humoral factors related to protection were not observed for L. garvieae. The expression of immune-related genes in the head kidney was profiled by microarray analysis. Twenty-two immune-related genes were up-regulated during the experimental period. Up-regulation of cellular immune-related genes, such as tumor necrosis factor, CC chemokine, and macrophage colony-stimulating factor receptor, was mostly observed from 1 to 3 dpv, whereas that of humoral immune-related genes was observed from 3 to 14 dpv. Notably, immunoglobulin-related genes showed continuous up-regulation during the 2-week experimental period.