Induction of viral interference by IPNV-carrier cells on target cells: AÂ cell co-culture study

•Three cell co-culture systems have been setup to study the interplay between IPNV-carrier cells and EPC cells.•The induction of an antiviral state in target EPC cells by IPNV-infected EPC cells has been demonstrated.•The establishment of an anti-VHSV state is mediated by a soluble factor.•Protection against VHSV is associated to the up-regulation of ifn and mx gene expression.

IPNV is a salmonid birnavirus that possesses the ability to establish asymptomatic persistent infections in a number of valuable fish species. The presence of IPNV may interfere with subsequent infection by other viruses. In the present study we show that an IPNV-carrier cell line (EPCIPNV) can induce an antiviral state in fresh EPC by co-cultivating both cell types in three different ways: a “droplet” culture system, a plastic chamber setup, and a transmembrane (Transwell®) system. All three cell co-culture methods were proven useful to study donor/target cell interaction. Naïve EPC cells grown in contact with EPCIPNV cells develop resistance to VHSV superinfection. The transmembrane system seems best suited to examine gene expression in donor and target cells separately. Our findings point to the conclusion that one or more soluble factors produced by the IPNV carrier culture induce the innate immune response within the target cells. This antiviral response is associated to the up-regulation of interferon (ifn) and mx gene expression in target EPC cells. To our knowledge this is the first article describing co-culture systems to study the interplay between virus-carrier cells and naive cells in fish.