Øystein Wessel, Norwegian University of Life Sciences

Nina Askim Vatne (1), Hanne Haslene-Hox (2), Ingrid Mo (1), Marit Stormoen (1), Danica M. Sutherland (3), Terence S. Dermody (3), Espen Rimstad (1), Øystein Wessel (1) (1) Faculty of Veterinary Medicine, Norwegian University of Life Sciences (2) Department of Biotechnology and Nanomedicine, SINTEF AS, Norway (3) Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.

Virus Replication: Entry, Exit and Everything in Between

Piscine orthoreovirus-1 (PRV-1) is an important pathogen of farmed Atlantic salmon. The main target cells for PRV-1 in the infected host are erythrocytes, which are nucleated in fish. During infection of salmon, there is an initial increase in viral load in erythrocytes and plasma, followed by a decrease. To determine the nature of this virus-erythrocyte interaction, we used ex vivo assays of cultured erythrocytes to study binding and replication. Inoculation of erythrocytes with purified virus confirmed initial virus binding, as indicated by detection of viral capsid protein σ1 following a one-day incubation. After 14 days, replication was established in 10% of the cells, demonstrated by detection of nonstructural protein µNS and viral factories. In contrast, inoculation of erythrocytes with PRV-1 positive plasma collected from infected fish did not initiate viral replication. Plasma-derived PRV-1 bound extensively to the surface of erythrocytes after only 5 min incubation and was effectively internalized as monitored by surface and intracellular staining for σ1. However, the cells were not productively infected. The interaction between plasma-derived PRV-1 and erythrocytes was further studied to identify viral and cellular interaction partners, which suggested the involvement of σ1 and an unknown proteinaceous receptor. Viral proteins from plasma of infected salmon co-immunoprecipitated with immunoglobulins, suggesting that antibodies are bound to viral particles in plasma. These findings suggest that erythrocytes participate in both replication and clearance of PRV-1, highlighting dual functions for these cells in infection dynamics. This study illustrates the role of nucleated erythrocytes in viral infection of a lower vertebrate.