Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) continues to be one of the most challenging diseases in the swine industry. Given the limitations associated with PRRSV diagnostic assays including serological assays, insufficient data available on isotype-specific antibody response, and the short duration of most challenge/vaccine studies. It was recognized the need to fully elucidate the ontogeny and isotype kinetics of antibody response to PRRSV infection for a long period of time after experimental infection. The other objective of the study was to evaluate whether or not the virus type i.e., attenuated vs. wild type can influence isotype profile of antibody response.

Isotype-specific response to VR-2332 strain (wild type) and a novel modified live virus vaccine (Fostera® PRRS) strain was measured and compared with neutralizing antibody response. Interestingly, in case of the wild-type inoculated pigs, all isotype-specific assays ( IgG, IgM and IgA) provided valuable information: a) IgG response is a reliable indicator of exposure; b) IgM response can be used to detect first exposure to PRRSV; and c) IgA response pattern is very similar to neutralizing antibody response. However, diagnostic performance of these assays as measured by sensitivity and specificity need to be yet improved to be able to compete with commercial assays. Further optimization of these isotype-specific assays might be needed to increase diagnostic performance.

In case of vaccinated animals the isotype-specific response pattern was different from that of wild-type inoculated animal, specifically for IgA antibody response. Therefore future studies are needed to determine which factors affect IgA response. Other areas of future research could focus on the effect of antigen basis on isotype profile since the assays we used were nucleocapsid protein-based, even though N protein based ELISA has been reported to have the best diagnostic performance as compared to other viral protein or peptide based ELISAs. Field application of isotype-specific humoral immune-response also needs to be addressed.

In conclusion, our study was able to broaden the knowledge on PRRSV humoral immune response and demonstrated that isotype-specific serology can be utilized as a useful diagnostic tool to determine infection/immune status of pigs for PRRSV.