IFN-γ secreting cells after ex vivo PCV2 re-stimulation. (A) PBMC from two adult PCV2-immune animals were used as positive controls to evaluate the ability of the test to detect PCV2 specific IFN-γSC. The PBMC were re-stimulated for 24 h with PCV2-infected cell lysate, or mock cell lysate as negative control, at increasing MOI based on the titre of the PCV2 (TCID50/cell, x-axis). The IFN-γSC were measured by ELISPOT assay as described in Materials and Methods, and expressed per 106 cells. (B-D) PBMC were isolated from the piglets which had received PBS (control), PCV2 single infection, PCV2/PPV double infection and PPV single infection. The cells were re-stimulated with PCV2 or mock antigen at 1 TCID50/cell (or equivalents dilution for the mock) for 24 h, and the IFN-γSC detected by ELISPOT assay. The mean values of the groups, +/- SD, are shown for PBMC isolated before infection (0 days) (B), 7 d p.i. (C) and 21 d p.i. (D). The IFN-γSC are calculated per 106 cells.