RESUMO
In this study, we described a rapid and efficient method which integrated the bioinformatic prediction and DNA vaccine technology to identify vaccine candidates against Singapore grouper iridovirus (SGIV). The 162 previously defined open reading frames (ORFs) of SGIV were subjected to extensive sequence similarity searches, as well as motif, cellular location, and domain prediction. Based on our analysis, 13 genes were chosen and cloned into the eukaryotic expression vector pcDNA 3.1. In vitro and in vivo expression of these DNA vaccine constructs was examined in Epinephelus akaara spleen cells (EAGS) and immunized fish by Western blot and RT-PCR analysis, respectively. Three weeks after the second booster, immunized fish were challenged with SGIV and the level of protection and survival was assessed. Fish vaccinated with plasmid DNA encoding viral ORF072, ORF039 and ORF036 (designated as pcDNA-72, pcDNA-39 and pcDNA-36, respectively) exhibited 66.7%, 66.7% and 58.3% relative percent survival rates, respectively, in comparison with the control fish. These three DNA vaccines induced innate immune responses, raising significantly high level of Mx expression relative to the fish vaccinated with the empty plasmid at 3 days post-vaccination. Furthermore, recombinant protein from ORF072 was also used to immunize another set of fish and similar protective effect was obtained. Taken together, our results validated the applicability of bioinformatics in genome mining, resulting in the identification of three protective antigens. The promising results obtained in the present study have prompted further testing to improve the immunogenicity of these potential DNA vaccines.
Assuntos
Antígenos Virais/imunologia , Infecções por Vírus de DNA/veterinária , Doenças dos Peixes/virologia , Iridovirus/imunologia , Perciformes/imunologia , Vacinas de DNA/imunologia , Vacinas Virais/imunologia , Animais , Antígenos Virais/genética , Distribuição de Qui-Quadrado , Biologia Computacional/métodos , Infecções por Vírus de DNA/imunologia , Infecções por Vírus de DNA/prevenção & controle , Infecções por Vírus de DNA/virologia , Doenças dos Peixes/imunologia , Doenças dos Peixes/prevenção & controle , Iridovirus/genética , Plasmídeos/genética , Distribuição Aleatória , Proteínas Recombinantes/genética , Proteínas Recombinantes/imunologia , Vacinas de DNA/genética , Vacinas Virais/genéticaRESUMO
Singapore grouper iridovirus (SGIV) is an enveloped virus causing heavy economic losses to marine fish culture. The envelope fractions of SGIV were separated from the purified virions by Triton X-100 treatment, and subjected to 1-DE-MALDI-TOF/TOF-MS/MS and LC-MALDI-TOF/TOF-MS/MS analysis. A total of 19 virus-encoded envelope proteins were identified in this study and 73.7% (13/17) of them were predicted to be membrane proteins. Three viral envelope proteins were uniquely identified by 1-DE-MALDI, whereas another ten proteins were identified only by LC-MALDI, with six proteins identified by both workflows. VP088 was chosen as a representative of proteomic identification and characterized further. VP088 was predicted to be a viral transmembrane envelope protein which contains two RGD (Arg-Gly-Asp) motifs, three transmembrane domains, and five N-glycosylation sites. VP088 gene transcript was first detected at 12 h p.i. and reached the peak at 48 h p.i. Combined with the drug inhibition assay, VP088 gene was identified as a late (L) gene. Recombinant VP088 (rVP088) was expressed in Escherichia coli, and the specific antiserum against rVP088 was raised. VP088 was proved to be a viral envelope protein by Western blot and immunoelectron microscopy (IEM). Furthermore, rVP088 can bind to a 94 kDa host cell membrane protein, suggesting that VP088 might function as an attaching protein. Neutralization assay also suggested that VP088 is involved in SGIV infection. This study will lead to a better understanding of molecular mechanisms of the iridoviral pathogenesis and virus-host interactions.
