| Highly pathogenic porcine reproductive and respiratory syndrome virus(HP-PRRSV) vaccine strain TJM-F92 was derived from HP-PRRSV TJ and stably contains a spontaneous continuous deletion of 120 amino acids in the Nsp2 region. Nsp2 is one of the non-structural proteins that has high immunogenicity in vivo. By using the recombinant protein GST-d120, we established an indirect enzyme-linked immunosorbent assay(d120-ELISA) for the detection and differentiation of serum antibodies against modified-live vaccine TJM-F92 from that of other PRRSV strains.At the optimized cut-off value which was calculated at an S/P of 0.25, the assay yielded a sensitivity of 90.7% and a specificity of 95.1%. Cross-reactivity tests suggested that the d120-ELISA was PRRSV-specific. Coefficient of variations of the repeatability tests were 0.77~17.02%. The comparative analysis of the results of the commercial kit and d120-ELISA describes that they have a good compliance rate when detecting non-TJM or non-inactivated vaccine sera, and the commercial kit detects TJM-F92 or inactivated vaccine positive serum as positive, while d120-ELISA detects all as negative.This application of d120-ELISA was designed to investigate the characters of antibody kinetics of GST-d120 protein and distinguish pigs with infection of wild type virus from those vaccinated with TJM-F92 vaccine on different immune states based on the clinical sera S/P values that were tested by both the d120-ELISA and IDEXX. Serum samples were collected from experimental animals and clinical animals. Results of kinetics of the antibody responses against N and GST-d120 proteins indicate that the d120-ELISA can distinguish animals infected with wild-type PRRSV TJ infection from vaccinated ones. The d120-ELISA can detect JXA1-R maternal antibodies from those vaccinated with TJM-F92, and it cannot detect antibodies against MLV JXA1-R at 14 days but at 28 days the positive rate of it is 86.7%(13/15) with high sera S/P values. In two farms where pigs were injected with inactivated vaccine, the positive rates of sera from the farm infected with PRRSV by d120-ELISA and IDEXX were 45.0%(9/20) and 100%(20/20), while the other’s were 0%(0/30) and 40%(12/30). In conclusion, the d120 ELISA can differentiate pigs infected with wild-type PRRSV or vaccinated with JXA1-R from those vaccinated with TJM-F92.The results in the study suggest that the d120-ELISA is simple for using, and suitable for differentiating animals infected with wild-type strains from those immunized with MLV TJM-F92 or inactivated vaccines and accumulate the elimination of PRRSV in the farms. |
