Frequencies of PCV2-specific IFN-γ secreting cells (SC) upon PCV2 natural exposure. Levels of IFN-γ SC in PBMC of PCV2-vaccinated (PCV2-vac) and unvaccinated (C) pigs in the post-exposure (PE) period. The magnified graph highlights the profiles of the two groups before the onset of significant PCV2 viremia in the PE period. PCV2-vac pigs were vaccinated at 3 weeks of age using a PCV2a Cap protein-based subunit vaccine. PBMC were ex vivo re-stimulated for 20 h with 0.25 MOI of a whole PCV2b strain. (*): statistically significant difference between groups (p < 0.05).