T-cell responses to heterologous or primary PV infection in LCMV-immune or naive HP mice. (A) LCMV-immune mice were challenged with PV, and splenocytes were harvested at day 6 (experiment 1) or day 7 (experiments 2 and 3). Cells were stimulated with PV-specific peptides NP-38 or NP-205 or with the LCMV NP-205 peptide for 5 hours. The numbers of NP-38–specific CD8 T cells or cross-reactive LCMV/PV NP-205 CD8 T cells were counted. (B) Dot plots show the Ag-specific CD8 T cells from experiment 2 in panel A. The magnitude of the NP-205 responses is based on the numbers of NP-205–specific CD8 T cells in WT B6, whereby a strong HP response shown here is 103% of WT, a moderate response is 55% of WT, and a weak response is 7% of WT. Numbers refer to percentage of cells in designated quadrants. (C) Blood was collected from HP (n = 5) or WT (n = 5) mice day 8 after PV infection, and cells were stained with either K^bPV NP-38 or K^bPV NP-205 tetramers. The percentage of tetramer-positive cells of total CD8 T cells is shown. The horizontal bar represents the mean value.