Rock bream iridovirus (RBIV) is a megalocytivirus widely infected in various fish species in Korea, causing symptoms of acute inflammation and enlargement of spleen. In our previous study, RBIV induced the initial upregulation but later down-regulation of proinflammatory cytokines and IFN1 gene expression. Signal transducers and activators of transcriptions (STAT) are transcription factors involved in the regulation of immune genes including IFNs. This study was conducted to analyse the expression of STAT2. The expressional study of STAT2 gene was performed in head kidney and spleen upon RBIV infection and immune stimulants like LPS or poly I:C in vitro. Consequently, STAT2 gene expression pattern was different in head kidney and spleen as it was significantly up-regulated by LPS from 4 h to 8 h but down-regulated at 24 h while up-regulated by poly I:C at 8 h in head kidney while, in spleen, STAT2 gene expression was down regulated by LPS but significantly up-regulated by poly I:C. Upon RBIV stimulation, STAT2 gene expression was significantly down-regulated by high dose RBIV at 4 h but up-regulated at 8 h and 24 h in head kidney. In spleen cells, it was up-regulated by medium dose RBIV at 4 h and by high dose RBIV at 4 h and 8 h but down regulated later then. In vivo, STAT2 gene expression was not significantly affected by RBIV infection while significant up-regulated by vaccination at day 7 post-vaccination, indicating STAT2 gene can be involved in adaptive immune response in rock bream.

Introduction
Materials and Methods
    1. Fish
    2. Virus
    3. Quantitative real-time RT-PCR analysis
    4. STAT2 gene expressions in spleen and headkidney cells in vitro
    5. STAT2 gene expression in head kidney andspleen after intraperitoneal injection of formalinkilledRBIV or live RBIV in vivo
    6. Statistical analysis
Results
    1. STAT2 gene expression in head kidney andspleen cells stimulated by PAMPs
    2. STAT2 gene expression in head kidney andspleen cells infected with RBIV
    3. STAT1 and 3 gene expression in head kidneyand spleen injected with formalin-killed RBIV or infectedwith RBIV in vivo
Discussion

• Suhee Hong(Department of Marine Biotechnology, Gangneung-Wonju National University, Gangneung 25457, Korea) Corresponding author
• Jongwon Lim(Department of Marine Biotechnology, Gangneung-Wonju National University, Gangneung 25457, Korea)
• Jaeheon Park(Department of Marine Biotechnology, Gangneung-Wonju National University, Gangneung 25457, Korea)