Piscine birnavirus triggers antiviral immune response in trout red blood cells, despite not being infective [version 1; peer review: 1 approved, 1 approved with reservations]

Background: Some fish viruses, such as piscine orthoreovirus and infectious salmon anemia virus, target red blood cells (RBCs), highly replicate inside them and induce an immune response. However, the implications of RBCs in the context of birnavirus infection (i.e, infectious pancreatic necrosis virus (IPNV)) have not yet been studied. Methods: Ex vivo trout RBCs were obtained from peripheral blood, ficoll purified and exposed to IPNV in order to analyze infectivity and induced immune response using RT-qPCR, immune fluorescence imaging, flow cytometry and western-blotting techniques. Results: IPNV could not infect RBCs; however, IPNV-exposed RBCs increased the expression of the INF1-related genes ifn-1, pkr and mx genes. Moreover, conditioned media from IPNV-exposed RBCs conferred protection against IPNV infection in CHSE-214 fish cell line. Conclusions: Trout RBCs could trigger an antiviral immune response against IPNV infection despite not being infected. Fish RBCs could be considered mediators of the antiviral response and therefore targets of novel DNA vaccines and new strategies against fish viral infections. Further research is ongoing to completely understand the molecular mechanism that triggers this immune response in trout RBCs.