Comparison of serum neutralization and enzyme-linked immunosorbent assay on sera from porcine epidemic diarrhea virus vaccinated pigs

Background: Porcine epidemic diarrhea virus (PEDV) is an economically important pathogen of swine. Objective: Serum neutralization (SN) and enzyme-linked immunosorbent assay (ELISA) test results as well as the utility of spike proteins S1, S2, and S3 and entire nucleocapsid protein were compared. Animals and methods: Serum samples from 400 pigs vaccinated against PEDV strain SM98P were collected from 78 farms in Korea. SN test and ELISA were performed to confirm the presence of antibodies. For prokaryotic expression of partial fragments of spike protein the size and location of S1, S2, and S3, and full nucleocapsid protein, polymerase chain reaction was performed using specific primers. Results: Comparison of these results demonstrated that there was a correlation between the SN and ELISA results. Sera with higher neutralizing activity also had higher IgG titer. The antibody profiling data presented the correlation of neutralizing activity with the level of spike protein antibody. In particular, the S3 region may have an important role in neutralizing activity. Conclusions: We confirmed that the carboxy-terminal region that includes the endodomain of the S protein induced stronger neutralizing activity than the region that includes the ectodomain. Clinical relevance: The region of the S protein may have a stronger neutralizing KPEDV-9 epitope and could be useful for the evaluation of future PEDV vaccine efficacy.