Use of cell lines and primary cultures to explore the capacity of rainbow trout to be a host for frog virus 3 (FV3).

The capacity of rainbow trout, Oncorhynchus mykiss, to be a host for frog virus 3 (FV3) was evaluated at the cellular level. Cell cultures from this species were tested for their ability to express FV3 major capsid protein (MCP) gene, to develop cytopathic effect (CPE), and to produce FV3. After FV3 addition, MCP transcripts were detected in six of six cell lines and in primary macrophage cultures. CPE developed in all cell culture systems, except primary lymphocytes. For the macrophage cell line, RTS11, and primary macrophages, cell death was by apoptosis because DNA laddering and Annexin staining were detected. By contrast, markers of apoptosis did not accompany CPE in three epithelial cell lines from the gill (RTgill-W1), intestine (RTgut-GC), and liver (RTL-W1) and in two fibroblast cell lines from gonads (RTG-2) and skin (RTHDF). Therefore, FV3 was able to enter and begin replicating in several cell types. Yet, FV3 was produced in only two cell lines, RTG-2 and RTL-W1, and only modestly. Overall, these results suggest that if tissue accessibility were possible, FV3 would have the capacity to induce injury, but the ability to replicate would be limited, likely making rainbow trout a poor host for FV3.