Vaccination with Recombinant Baculovirus Expressing Ranavirus Major Capsid Protein Induces Protective Immunity in Chinese Giant Salamander, Andrias davidianus

Abstract

The Chinese giant salamander iridovirus (CGSIV), belonging to the genus Ranavirus in the family Iridoviridae, is the causative agent of an emerging infectious disease causing high mortality of more than 90% and economic losses in Chinese giant salamanders in China. In this study, a recombinant baculovirus-based vaccine expressing the CGSIV major capsid protein (MCP) was developed and its protective immunity in Chinese giant salamanders was evaluated. The recombinant Autographa californica nucleopolyhedrosis virus (AcNPV), expressing CGSIV MCP, designated as AcNPV-MCP, was generated with the highest titers of 1 × 108 plaque forming units/mL (PFU/mL) and confirmed by Western blot and indirect immunofluorescence (IIF) assays. Western blot analysis revealed that the expressed MCP reacted with mouse anti-MCP monoclonal antibodies at the band of about 53 kDa. The results of IIF indicated that the MCP was expressed in the infected Spodoptera frugiperda 9 (Sf9) cells with the recombinant baculovirus, and the Chinese giant salamander muscle cells also transduced with the AcNPV-MCP. Immunization with the recombinant baculovirus of AcNPV-MCP elicited robust specific humoral immune responses detected by ELISA and neutralization assays and potent cellular immune responses in Chinese giant salamanders. Importantly, the effective immunization conferred highly protective immunity for Chinese giant salamanders against CGSIV challenge and produced a relative percent of survival rate of 84%. Thus, the recombinant baculovirus expressing CGSIV MCP can induce significant immune responses involving both humoral and cell-mediated immunity in Chinese giant salamanders and might represent a potential baculovirus based vaccine candidate for Chinese giant salamanders against CGSIV.

Protective Immunity Induced by DNA Vaccination against Ranavirus Infection in Chinese Giant Salamander Andrias davidianus

“…As demonstrated by the ELISA analysis, specific serum antibodies were detected in Chinese giant salamanders vaccinated with pcDNA-2L at 14 days post-vaccination, and the antibody level increased significantly at 21 days post-vaccination. The results were consistent with the observations in Chinese giant salamanders immunized with recombinant subunit vaccines based on the major capsid protein (a well-known immunogenic protein of the ranavirus) [ 17 , 18 ]. Similarly, adult Xenopus laevis infected with the ranavirus frog virus 3 (FV3) could generate specific anti-FV3 IgY antibodies, which neutralize the virus in vitro and provide partial passive protection to susceptible larvae [ 37 ].…”

“…For ranavirus diseases of Chinese giant salamanders, several candidate vaccines, such as an inactivated virus vaccine, a virus-like particle vaccine, and a recombinant subunit vaccine, have been developed. These vaccines conferred effective protection with a relative percentage survival of 72–84% against viral infection in laboratory trials [ 16 , 17 , 18 ]. DNA vaccines represent an attractive alternative to traditional vaccines, and they provide both humoral and cellular immunity and have various advantages including low production cost, high safety, and ease of long-term storage [ 19 ].…”