TNF and infection: Lastly, having observed the marked induction of IFN-γ/TNF-α co-producing CD4+ T cells following PCV2 vaccination and also PCV2 infection, we compared the CD27 expression in PCV2-specific IFN-γ+TNF-α+CD4+ T cells from VA animals at 24 dpv (day of experimental infection), IN animals at the day of euthanasia and VI animals at both time points (Figure 6).