Introduction: Currently, an in vitro immunogenicity screening system for the immunological assessment of potential porcine reproductive and respiratory syndrome virus (PRRSV) vaccine candidates is highly desired. Thus, in the present study, two genetically divergent PRRSVs were characterized in vitro and in vivo to identify an in vitro system and immunological markers that predict the host immune response.
Methods: Porcine alveolar macrophages (PAMs) and peripheral blood mononuclear cells (PBMCs) collected from PRRSV-negative pigs were used for in vitro immunological evaluation, and cellular responses to VR-2332 or FL-12 were compared with those elicited in pigs challenged with the same viruses.
Results: Compared with VR-2332 or mock infection, FL-12 induced higher levels of type I interferons and pro-inflammatory cytokines (TNF-α, IL-1α/β, IL-6, IL-8, and IL-12) in PAMs, and these elevated levels were comparable to the cytokine induction observed in PRRSV-challenged pigs. Furthermore, significantly greater numbers of activated CD4+ T cells, type I helper T cells, cytotoxic T cells and total IFN-γ+ cells were observed in FL-12-challenged pigs than in the VR-2332 or mock groups.
Conclusions: Based on the results of the current study, FL-12 induced more efficient innate and adaptive immune responses in vitro and in vivo as compared withVR-2332. Furthermore, out of the two in vitro screening systems for immunogenicity (PAMs and PBMCs), PAMs generated immune responses pattern to both PRRSVs that was similar to those elicited by these viruses in pigs. Thus, PAMs may be used as an immunogenicity screening tool for the selection of vaccine candidates against PRRSV. Finally, the induction of IFN-α, TNF-α and IL-12 in PAMs might represent vital immune markers to predict the immunogenicity of PRRSV vaccine candidates in pigs.