Cellular immune reactivity of activated T lymphocyte subsets upon in vitro stimulation after Cap protein PCV2 vaccination. Levels of CD4–CD8α+ cytotoxic and CD4+CD8α+low memory T helper cells in the lymphoblast fraction of PCV2-vaccinated (PCV2-vac) and control (C) pigs upon 48-h PCV2b (A, B) and PCV2b + PHA (C, D) in vitro stimulation during the post-vaccination (PV) period. PCV2-vac pigs were vaccinated at 3 weeks of age using a PCV2a Cap protein-based subunit vaccine. Values are normalized to the corresponding medium (PCV2 stimulation) or PHA-alone (PCV2 + PHA stimulation) control samples, respectively. (*): statistically significant difference between groups (p < 0.05).