Recombinant interferon-γ activates immune responses against Edwardsiella tarda infection in the olive flounder, Paralichthys olivaceus

Interferon gamma (IFN-γ) is a cytokine that plays a very important role in defining Th1 immune response in all vertebrates. In this study, recombinant IFN-γ (rIFN-γ) from the olive flounder (Paralichthys olivaceus) was produced in an Escherichia coli system using a pET expression vector. Stimulation of whole kidney leukocytes (immune-related cells) in vitro with the resulting rIFN-γ significantly induced the gene expression of interleukin-1β (IL-1β), signal transducer and activator of transcription 1 (STAT1), CXCL13-like chemokine (CXCL13), and IFN-γ. rIFN-γ also weakly induced the expression of IL-1β, tumor necrosis factor-α (TNF-α), CXCL13, and IFN-γ in olive flounder-derived HINAE (non-immune) cells. The effects of rIFN-γ against Edwardsiella tarda infection in vivo were assessed by intraperitoneally injecting a mixture of rIFN-γ (100 ng) and E. tarda (1 × 105 CFU/ml) into the olive flounder. The survival rate in the rIFN-γ-injected group was 60% compared to 0% in the group treated with E. tarda only, demonstrating that olive flounder IFN-γ is effective in reinforcing immune responses and preventing against edwardsiellosis.