Date Full Report Received03/22/2017
Date Abstract Report Received03/22/2017
Funded ByNational Pork Board
One of the challenges in developing effective vaccines for PRRSV is the limited understanding of how neutralizing antibody inhibits PRRSV replication, and how variation in PRRSV leads to escape from neutralizing antibody. In this study, we examined how genetic changes in specific virus proteins leads to increased resistance to neutralizing antibody. We identified genetic variants in PRRSV-infected pigs with high virus levels at 4-6 weeks post-infection. The predominant genetic variants were inserted into an infectious molecular clone and tested in virus neutralization assays to identify genetic changes in PRRSV that led to increased resistance to neutralizing antibody. We identified a combination of amino acid changes in both GP2/3/4 and GP5 that led to escape from neutralizing antibody. The specific amino acid changes responsible for resistance to neutralization were different in each pig, and we could not identify a single amino acid change that could predict susceptibility or resistance to neutralizing antibody. To determine how neutralizing antibody inhibits PRRSV replication, virus was incubated in the presence or absence of neutralizing antibody and PCR was used to quantify viral RNA at early steps in the virus replication cycle. Results indicated that neutralizing antibody inhibits attachment of virus to cells and also inhibits a second, post-entry step in replication that occurs between 4-8 hours after virus has entered the cell. Together, these results indicate that neutralizing antibody targets multiple virus proteins to inhibit replication at two different steps in the virus replication cycle. Multivalent vaccines designed to target these distinct steps in PRRSV replication could enhance efforts to control this important swine pathogen.