Study on Immunological Responses to Porcine Reproductive and Respiratory Syndrome Virus DNA Vaccines Co-expressing Modified GP5 (GP5m) and M Proteins
To enhance the immune efficiency of porcine reproductive and respiratory syndrome virus(PRRSV)DNA vaccine,the modified ORF5(ORF5m)and ORF6 genes were used as candidate genes to construct the recombinant plasmids pCI-ORF5m and pCI-ORF6 expressing GP5 and M alone,respectively,and pCI-ORF5m/ORF6 co-expressing the two proteins.Western blot analysis showed that the expressed GP5m and M proteins had good biological activities analogy to the authentic proteins and could form disulfide-linked heterodimers GP5m/M in BHK-21 cells transfected with pCI-ORF5m/ORF6.Immunological responses to the constructs were investigated in BALB/c mice and piglets.The specific detectable anti-PRRSV neutralizing antibodies were produced in the mice vaccinated with pCI-ORF5m/ORF6 at 6 weeks post primary immunization(ppi)and reached a peak titer of 1:32 at 8 weeks ppi.The specific stronger cell-mediated immune responses were also observed.In addition,the higher neutralizing antibodies and cell-mediated immune responses of the piglets vaccinated with pCI-ORF5m/ORF6 were produced when compared only with pCI-ORF5m.These data indicated an enhancement of the immunological responses of DNA vaccine co-expressing ORF5m and ORF6 and it will be a promising new vaccine for PRRSV.