Comparison of host immune responses to homologous and heterologous porcine reproductive and respiratory syndrome virus (PRRSV) challenge

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is a high‐consequence animal disease worldwide. The objective of this study was to identify immune responses that are predictive of protection against heterologous PRRSV challenge. Using MLV IngelVac PRRSV vaccine, its parental strain VR2332, and K‐LI, we compared immune responses induced by a single vaccination and by experimental infection of two different PRRSV isolates. Four groups of pigs were utilized in this study in which groups 1 & 2 were vaccinated with MLV PRRSV and groups 3 & 4 were not vaccinated. 28 days post vaccination (DPV), pigs in groups 1 & 3 were challenged with VR2332, and groups 2 & 4 were challenged with K‐LI. The results shown that lung pathology score of group 1 pigs was significantly lower than that of groups 2, 3, & 4 pigs 14 DPC, confirming the vaccination‐induced homologous protection. Serum neutralizing antibody against K‐LI was detected only in group 2 pigs 14 DPC. ELISpot assay indicated that VR2332 is a stronger inducer of IFNr‐secreting PBMCs than K‐LI in all pigs, and group 2 pigs possessed more PRRSV‐specific IFNr‐secreting PBMCs. This study indicates that heterologous challenge induces a higher level of cellular immune response against PRRSV in vaccinated pigs, but only serum neutralizing antibody titer is associated with PRRSV vaccination‐induced protection against homologous and heterologous challenge.