CpG ODN 1668 induce innate and adaptive immune responses in rock bream (Oplegnathus fasciatus) against rock bream iridovirus (RBIV) infection

- CpG ODN 1668 inhibited RBIV replication in rock bream.
- MyD88 and IL1β were highly expressed in CpG ODN 1668+virus-injected rock bream.
- The perforin and granzyme induced apoptosis pathway was high activated at initial time points in CpG ODN 1668+virus-injected rock bream.
- The caspase-dependent apotosis pathway was not enhanced.
- There was no significant differences between the virus- and CpG ODN 1668+virus-injected groups regarding Fas-Fas ligand and MHC class I-CD 8+ mediated immune responses.

Rock bream iridovirus (RBIV) causes severe mass mortalities in rock bream in Korea. CpG ODN 1668 showed promise as immunoprotective agents against RBIV infection in rock bream. In this study, we assessed innate/adaptive-related gene expression patterns in RBIV-infected rock bream with and without CpG ODN 1668 administration to determine important immune defense related factors that may affect fish survival. In the CpG ODN 1668+virus-injected group, virus copies were more than 7.4- to 790591-fold lower than in the virus-injected group at 4 d (8.79 × 104 and 6.58 × 105/μl, respectively), 7 d (5.30 × 102 and 2.29 × 107/μl, respectively) and 10 dpi (7.79 × 101 and 6.16 × 107/μl, respectively). Furthermore, in the CpG ODN 1668+virus-injected group, significantly higher levels of MyD88 (6 h, 1 d, 4 d and 7 dpi), IL1β (1 d, 2 d and 7 dpi) and perforin/granzyme (1 dpi) expression were observed, whereas these genes were not significantly expressed in the virus-injected group at that time points. Mx, ISG15 and PKR were significantly highly expressed at 4 d and 7 dpi and reduced when low viral loads at 10 dpi in the CpG ODN 1668+virus-injected group. Conversely, in the virus-injected group, Mx, ISG15 and PKR expression were significantly higher than the control group until 10 dpi. However, MHC class I, CD8, Fas, Fas ligand and caspases (3, 8 and 9) expression levels showed no statistically significant differences between virus- and CpG ODN 1668+virus-injected group. In summary, CpG ODN 1668 administration in fish induces innate immune response or cell death pathway, which could be a major contributing factor to effective fish control over viral transcription on 4 d to 10 dpi. Expression of MyD88, IL1β, perforin and granzyme-related immune gene response is critical factor for inhibition of RBIV replication.