Fish immunization using a synthetic  double-stranded RNA Poly(I:C), an interferon inducer, offers protection against RGNNV, a fish nodavirus

Protection of Japanese flounder Paralichthys olivaceus from viral hemorrhagic septicemia (VHS) by Poly(I:C) immunization

“…The same tendency was observed in our previous experiments on Poly(I:C) immunization with rainbow trout and sevenband grouper, i.e. ELISA values representing specific antibody titers were clearly lower 21 d after immunization than 35 to 49 d after immunization (Kim et al 2009, Nishizawa et al 2009). The present results demonstrated that immunity against VHS was established in the fish injected with VHSV followed by Poly(I:C) administration, suggesting that Poly(I:C) immunization with live VHSV is protective against VHS in Japanese flounder similar to previous results with sevenband grouper and rainbow trout Poly(I:C)-immunized with live fish nodavirus and infectious hematopoietic necrosis virus (IHNV), respectively (Nishizawa et al 2009, Kim et al 2009).…”

“…ELISA values representing specific antibody titers were clearly lower 21 d after immunization than 35 to 49 d after immunization (Kim et al 2009, Nishizawa et al 2009). The present results demonstrated that immunity against VHS was established in the fish injected with VHSV followed by Poly(I:C) administration, suggesting that Poly(I:C) immunization with live VHSV is protective against VHS in Japanese flounder similar to previous results with sevenband grouper and rainbow trout Poly(I:C)-immunized with live fish nodavirus and infectious hematopoietic necrosis virus (IHNV), respectively (Nishizawa et al 2009, Kim et al 2009). Establishment of immunity determined by antibody detection ELISA was confirmed more than 6 to 7 wk after virus injection; however, immunity seems to be guaranteed even if specific antibodies in immunized fish sera are below the detectable level.…”

“…Detection of antibodies against VHSV was performed using an ELISA system according to a modification of the methods of Kim et al (2007) and Nishizawa et al (2009). Briefly, culture fluids of VHSV with 10 8.3 TCID 50 ml -1 were diluted 10-fold with distilled water, 50 µl of the fluid were loaded into ELISA plate wells, and the viral antigen was fixed by drying overnight at 37°C.…”

“…Moreover, in the antiviral state, the fish infected with the live virus are able to mount a specific protective immune response against the injected pathogenic virus. This immunization scheme has several advantages: (1) the injected Poly(I:C) does not remain in fish tissues because Poly(I:C) is unstable like other RNAs, indicating that there may be no problem using the immunized fish as food source and also that it is harmless to the fish-rearing environment; (2) neither attenuation nor inactivation of the virus is required, and high levels of immunity can be expected; (3) recombinant DNA technology is not necessary, suggesting relatively low costs for vaccine development, and it would be more acceptable to consumers who are skeptical of food products produced with recombinant DNA technology (Nishizawa et al 2009). Therefore, it is conceivable that Poly(I:C) immunization will be applicable to a wide range of fish species as well as other viruses.…”

“…A novel immunization method using polyinosinicpolycytidylic acid (Poly[I:C]), a synthetic doublestranded RNA, was devised recently and its efficacy was experimentally confirmed for infectious hematopoietic necrosis in rainbow trout and viral nervous necrosis (VNN) in sevenband grouper (Kim et al 2009, Nishizawa et al 2009). In Poly(I:C) immunization, fish are immunized with live pathogenic virus followed by Poly(I:C) administration, wherein Poly(I:C) induces a transient, non-specific antiviral state by interferon activity that enables the fish to survive the initial immunization with live virus that would otherwise be lethal.…”