Development of a DNA vaccine against hirame rhabdovirus and analysis of the expression of immune-related genes after vaccination

Intramuscular injection of Japanese flounder, Paralichthys olivaceus (average weight approximately 2 g) with 1 and 10 microg of a plasmid DNA vaccine encoding the hirame rhabdovirus (HIRRV) glycoprotein gene (pCMV-HRVg) was found to provide strong protection against HIRRV. We also conducted a real-time PCR analysis to quantify immune-related genes, e.g. MHC class Ialpha, IIalpha, IIbeta, TCR-alpha, beta1, beta2 and delta, to characterize the immune response at 1 and 7 days after DNA vaccination. In general, the copy numbers were at least 2-fold higher than those of the non-vaccinated fish. Interestingly, the gene expression of TCR beta1 and beta2 increased 1 day post-DNA vaccination, after which their copy numbers returned to levels similar to those before vaccination. These results suggest that the immune system of Japanese flounder was activated immediately after DNA immunization.