COMBINED DNA IMMUNIZATION WITH THE GLYCOPROTEIN GENE OF VIRAL HEMORRHAGIC SEPTICEMIA VIRUS AND INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS INDUCES DOUBLE-SPECIFIC PROTECTIVE IMMUNITY AND NONSPECIFIC RESPONSE IN RAINBOW-TROUT

Glycoprotein (G) of viral hemorrhagic septicemia virus (VHSV) and infe ctious hematopoietic necrosis virus (IHNV) contains several neutralizi ng epitopes. However, recombinant G protein never matches intact Viral particles for immunogenicity. DNA immunization offers the possibility to deliver the antigen through the cellular machinery, thus mimicking natural infection. We constructed pCDNA_gVHS and pCDNA_glHN plasmids with the G gene of VHSV and IHNV under the control of the CMV promoter , and we tested the plasmids for the accurate G protein expression pri or to their use in fish immunization. Following intramuscular injectio n to adult rainbow trout, plasmid DNA was found inside the muscle cell s shortly after injection and was still present 45 days later. mRNA of the G protein was detected in muscle tissue extracts, and the G prote in was found within muscle cells at the site of injection. This result ed in the synthesis of high levels of specific neutralizing and protec tive antibodies. Fish injected with pCDNA_gVHS and pCDNA_glHN in combi nation responded similarly to fish receiving one recombinant plasmid. In addition to the elicitation of a strong humoral response, DNA immun ization was able to activate specialized cells of the immune system as well as nonspecific defense mechanisms, since mRNAs of MHC class II a nd Mr were strongly activated at the site of injection, (C) 1998 Acade mic Press.