Cytopathic effects of chum salmon reovirus to salmonid epithelial, fibroblast and macrophage cell lines

The cytopathic effect (CPE) of chum salmon reovirus (CSV), an aquareovirus, was studied in three salmonid cell lines: epithelial-like CHSE-214 from Chinook salmon embryo, fibroblast-like RTG-2, and monocyte/macrophage-like RTS11, both from rainbow trout. CHSE-214 and RTG-2 supported syncytia formation with more dramatic syncytia being observed in CHSE-214 cultures, while CSV induced homotypic aggregation (HA) in RTS11. Syncytia and HA formation were blocked by cycloheximide and ribavirin but not actinomycin D, suggesting that expression of CSV genes were required for both phenomena. Cultures with syncytia underwent a decline in cell viability, which appeared to be via apoptosis, as determined by intranucleosomal fragmentation and caspase dependence assays using the pan-caspase inhibitor, zVAD-fmk. In the presence of zVAD-fmk, CHSE-214 cultures continued to form syncytia and show diminished energy metabolism, but DNA fragmentation, the loss of membrane integrity, and the release of infectious CSV were considerably blocked. These results suggest that the formation of syncytia triggers apoptosis and a leaky plasma membrane, which enhances viral release. By contrast, RTS11 cultures undergoing HA showed no loss of cell viability. The significance of HA is unclear, but the response suggests that macrophage behaviour in rainbow trout potentially could be modulated by CSV.