The establishment and partial characterization of a continuous cell line from the dorsal fin of red sea bream, Pagrus major, are described. The cell line, designated RSBF-2, has been subcultured for more than 100 passages since its initiation in November 2000. It was optimally maintained at 28 degrees C in Leibovitz L-15 medium with 10% foetal bovine serum. Propagation of RSBF-2 cells was serum dependent and exhibited low plating efficiency (<1.7%). Aside from long-term cryopreservation, the cells could also be kept at 4 degrees C for 72 days. The distribution of the chromosome number was 38-98 with a mode of 48. The RSBF-2 cell line was susceptible to red sea bream iridovirus but only produced a few rounded and refractory cells. Virus-inoculated RSBF-2 cells were then subcultured to generate a persistently infected cell line. RSBF-2 was also very sensitive to the extracellular products of Photobacterium damselae ssp. piscicida and produced significant fluorescent signals after transfection with pEGFP-C3. Analysis of mitochondrial cytochrome b gene sequences revealed 99% identity between the cell line and Pagrus major.

This study investigates the susceptibilities of the SPB cell line to fish viruses including giant seaperch iridovirus (GSIV-K1), red sea bream iridovirus (RSIV-Ku), grouper nervous necrosis virus (GNNV-K1), chum salmon reovirus (CSV) and eel herpesvirus (HVA). GSIV-K1, RSIV-Ku and CSV replicated well in SPB cells, with a significant cytopathic effect and virus production. However, the cells were HVA and GNNV refractory. To examine the ability of SPB cells to stably express foreign protein, expression vectors encoding GNNV B1 and B2 fused to enhanced green fluorescent protein (EGFP) and GSIV ORF35L fused to DsRed were constructed and introduced by transfection into SPB cells. Stable transfectants displayed different morphologies compared with SPB and with each other. EGFP-B1 was predominantly localized in the nuclei, EFPF-B2 was distributed throughout the cytoplasm and nucleus, and granular 35L-DsRed was localized with secreted vesicles. The expression of EFPF-B2 in SPB cells produced blebs on the surface, but the cells showing stable expression of EGFP, EGFP-B1 or 35L-DsRed showed normal morphologies. Results show the SPB cells and the transfected cells grow well at temperatures between 20 and 35 °C and with serum-dependent growth. SPB cells are suitable for studies on foreign protein expression and virology.