Establishment of a Novel Cell Line From the Fry of Grouper (Epinephelus coioides) for Fish Virus-Host Interactions

Continuous cell lines are useful for virus research and diagnosis. Here, a novel cell line from grouper fry (Ec-Fry) has been developed and its sensitivity to fish viruses was investigated. Mitochondrial 18S rRNA gene sequence analysis conducted after 80 generations of Ec-Fry cells verified that Ec-Fry cells originated from Epinephelus coioides. Ec-Fry cells, mainly composed of epithelioid cells, exhibited the fastest growth with 15% and 20% FBS at 28°C, but also grew well with 5% FBS. Chromosome analysis showed that the number of type chromosomes was 48. After pEGFP-N3 transfection, green fluorescence was observed in Ec-Fry cells under a fluorescence microscope. Red-spotted grouper nervous necrosis virus (RGNNV) and Singapore grouper iridovirus (SGIV) were able to propagate in Ec-Fry cells, evidenced by the obvious cytopathic effect (CPE) progression and increased production of viral proteins with the infection time. Moreover, numerous viral particles were observed in SGIV- and RGNNV-infected cells, suggesting that the infection model in Ec-Fry could be used to investigate the viral pathogenesis. Moreover, the expression levels of pro-inflammatory cytokines and interferon response-related genes were significantly elevated during SGIV or RGNNV infection in Ec-Fry cells, indicating that this infection model could also be used to explore the host immune response against fish virus infection. In addition, higher virus yields could be obtained in infected Ec-Fry cells which were cultured with FBS at a low concentration, suggesting that Ec-Fry cells were suitable for vaccine preparation in the future. Together, our findings provided a novel cell line from marine fish for virus isolation and host-virus interactions.