Antibody and cellular immune responses of swine exposed to porcine reproductive and respiratory syndrome virus or a GP5 subunit vaccine

Developing effective vaccines against the porcine reproductive and respiratory syndrome virus (PRRSV) has proved difficult, highlighting the need for basic information on the nature of the immune response against this virus and the mechanisms of resistance that the virus employs. In this investigation our goal was to characterize the immune response against the major outer membrane protein of the virus, GP5, in pigs experimentally infected with a North Carolina isolate of PRRSV known as the NC Powell strain. In addition, we compared this response with the immune response seen after vaccination with purified recombinant GP5 (rGP5) protein. Humoral immune responses were monitored by western blot and immunofluorescence while T cell responses were monitored using proliferation assays and flow cytometry. Our results show strong humoral recognition of rGP5 protein during both natural and vaccine induced antibody responses. In addition, epitope mapping via western blot revealed that antibody responses were directed largely against the C-terminal endodomain of rGP5 protein in both experimentally infected and vaccinated pigs. We also investigated T cell responses to rGP5 protein. Our experiments revealed that T cells from vaccinated animals also responded to both rGP5 protein and inactivated NC Powell strain of PRRSV suggesting that T cells may play an important role in vaccine-induced resistance. Interestingly, we found that the inactivated NC Powell strain of PRRSV caused a strong proliferative response in naïve T cells from control animals, perhaps indicating the presence of a superantigen as a component of this highly virulent strain of PRRSV.