The kinetics of CD4+ and CD8+ T-cell gene expression correlate with protection in Atlantic salmon (Salmo salar L) vaccinated against infectious pancreatic necrosis.

Infectious pancreatic necrosis virus (IPNV) is a highly contagious disease causing high mortalities in juvenile salmonids. Lack of correlation between neutralizing antibodies and infecting virus suggests a likelihood of involvement of the cellular mediated immune response in vaccine protection. To elucidate the kinetics of CD4 and CD8 T-cells responses in vaccine protection, Atlantic salmon (Salmo salar L) were vaccinated with a high antigen (HiAg) or low antigen (LoAg) dose vaccine and challenged by cohabitation using a highly virulent Norwegian Sp strain. Analysis of T-cell gene expression in lymphoid organs (headkidney and spleen) showed that GATA-3 was positively correlated with increase in antibody levels when T-bet was low. Conversely, T-bet and FoxP3 were positively correlated with viral infection and negatively correlated with increase in antibody levels. Among the CD8+ T cell genes, expression of eomes and CD8α were positively correlated with increase in viral copy numbers and negatively correlated with increase in antibody levels. Up-regulation of granzyme A was highly correlated with increase in viral copy numbers in the LoAg and control groups indicating that this gene could save as a diagnostic marker of acute infection for IPNV during acute infection. In contrast, its down regulation in the HiAg which had low viral copy numbers corresponded with high antibody levels. Overall, these data show that the kinetics of CD4 and CD8 T-cell genes expression follow the same pattern as that observed in higher vertebrates. These findings suggest that functional signatures of the cellular mediated immune response could be evolutionary conserved across the vertebrate taxa and that they can effectively be used to monitor vaccine protection and infection progression of IPNV in Atlantic salmon.