Evaluation of cell-mediated immune responses against porcine circovirus type 2 (PCV2) Cap and Rep proteins after vaccination with a commercial PCV2 sub-unit vaccine

This study investigated the development of cellular immunity to Porcine circovirus type 2 (PCV2) Cap and Rep proteins in pigs vaccinated with a commercial PCV2 genotype a (PCV2a) based sub-unit vaccine, before and after a heterologous challenge with a PCV2b isolate. At three weeks of age, 20 pigs were inoculated intramuscularly with either the vaccine product (V group, n = 9) or phosphate buffered saline solution (PBS) (NV group, n = 11). Three weeks after vaccination, pigs were challenged intranasally with PCV2b (V-C and NV-C groups) or PBS (V-NC and NV-NC groups). None of the pigs developed clinical signs during the whole experiment, but all NV-C and 3/5 V-C pigs developed viraemia. Vaccination induced the development IFN-γ-secreting cells in response to the Cap protein of PCV2, which appeared three weeks post-vaccination and increased after challenge. By that time, no significant differences were detected on PCV2 antibody titres between vaccinated and non-vaccinated pigs, although there were significant differences on day 7 post-challenge. PCV2-inoculation induced a cellular response against the Rep protein. Such response was significantly reduced or even absent in PCV2-inoculated pigs that were previously vaccinated (V-C group), presumably as a result of a lower PCV2 replication in vaccinated animals compared to non-vaccinated ones.