Molecular characterization of the Chinese isolates of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and the construction and characterization of the DNA vaccines

Abstract

The genomic regions encoding ORFs 5 and 6 of the Chinese isolates named as AV strain of PRRSV found in Guangzhou are chosen and cloned into the mammalian expression vector pcDNA3.1(+) so as to construct the DNA vaccine. The objectives of this study are to first characterize this AV strain PRRSV emerged in Guangzhou, sequences based on ORF 5 and 6 were served as reference for further phylogenetic studies on the difference with North American (VR-2332) and the European (LV) strains. Investigation further focuses on the role of DNA vaccine constructed based on AV strain PRRSV in the generation of both humoral and lymphoproliferation immune responses and the possibility of using crude bacteria as adjuvant. Immunization with plasmid encoding ORF 5 or ORF 6 of AV strain PRRSV, with or without crude bacteria as adjuvant, induced anti-ORF 5 neutralizing antibodies or ORF 6 specific antibodies in both Balb/c mice and its natural host, pigs (trial experiment). Animals vaccinated with crude bacteria conjugated with ORF 5 encoded plasmid elicited stronger (which is around 80% more) and faster antibody responses than with plasmid construct alone as measured by ELISA. In addition, the increase in the number of blood lymphocytes obtained from vaccinated mice and pigs indicates the specificity of the lymphoproliferation responses to ORF 5-envelope protein & ORF 6 matrix protein. In summary, it demonstrates that ORF 5 & 6 plasmid construct with crude bacteria as adjuvant may be a potential candidate against this regional AV strain PRRSV isolated from Guangzhou, China.