Atlantic halibut (Hippoglossus hippoglossus L.) T-cell and cytokine response after vaccination and challenge with nodavirus

Viral encephalopathy and retinopathy (VER), caused by nodavirus, is one of the major infectious diseases affecting the marine fish farming industry, yet no effective vaccine is available. In this study, we examined the halibut immune response following administration of an experimental vaccine comprising a recombinant nodavirus capsid protein in combination with an oil adjuvant (OA). Four groups of halibut were injected with either: PBS alone, PBS plus OA, 10 mu g recCP plus OA, or 50 mu g recCP plus OA. 15 weeks later, half the fish in each group were challenged with nodavirus and the immune response investigated by analysis of: serum levels of recCP-specific halibut immunoglobulins (Igs), and mRNA transcript levels of several T-cell markers (CD3 epsilon, Lck, CD4, CD4-2, CD8 alpha and CD8 beta) and cytokines (IL-1 beta, IL-6, IL-12 beta c and IFN gamma). Additionally, the presence of nodaviral RNA2 transcripts in the brains of infected halibut was analysed. After vaccination, the level of IL-6 was consistently elevated in the spleens of fish given injections containing the OA. The combination of recCP and OA increased the expression of IL-1 beta and IFN gamma, as well as the level of recCP-specific Igs in blood plasma. Following challenge with nodavirus, IL-1 beta and IFN gamma were elevated in halibut spleens after 24 h in all groups that had received OA with or without recCP antigen. In brain, a general increase in the expression levels of all T-cell markers and IFN gamma was observed following challenge with nodavirus. The viral load at 8 weeks post-challenge was lower in the fish that received 50 mu g recCP, with 5 out of 8 individuals being negative for nodavirus. Additionally, a better correlation between these markers (apart from the CD8 markers), and the viral RNA2 was also observed in this group, suggesting that the activation of CD4 + T-cells might be important in reducing the viral load. In conclusion, this study identifies recCP as a promising candidate antigen for the future development of a vaccine against nodavirus. (C) 2013 Elsevier Ltd. All rights reserved.