Establishment of an IFN-γ specific reporter cell line in fish

An interferon (IFN)-γ responsive stable cell line RTG-3F7 has been developed for rainbow trout by modifying the RTG-2 cell line through transfection with a plasmid construct (pGL4.14[luc2/hygro]-PrTAP2) containing a promoter element from the IFN-γ responsive gene TAP2 linked to a luciferase reporter gene and a hygromycin resistance gene. Following transfection single clones were selected in 96 well plates using hygromycin B, and those showing specific activation after rIFN-γ stimulation were maintained. Five clones that showed the highest reporter activity to rIFN-γ were incubated with different stimuli to examine specificity. No significant induction of luciferase was observed following exposure to recombinant type I IFN, LPS, PHA or poly I:C. The cell line was responsive to rIFN-γ at concentrations between 150 pg and 20 ng ml−1. Supernatants of primary cultures of head kidney leucocytes stimulated with PHA, known to induce IFN-γ gene expression, were also used to assess the reporter activity of the stable cell line. A dose-dependent induction of the promoter activity was observed with these supernatants indicating the presence of IFN-γ. These results indicate that the stable cell line RTG-3F7 is an excellent tool for monitoring the presence of trout IFN-γ in biological samples, and in addition, enables the study of intracellular signalling pathways of IFNs, their receptor interactions, and other closely related signalling networks.