Figure 1. Cross-reactive epitopes in BALB/c (H2^d) mice.

A,B. After preliminary screening efforts to detect cross-reactive epitopes, BALB/c mice were inoculated with LCMV or PV as described in Table 1. At day 8 post-infection splenocytes (A) or peritoneal exudate cells (PEC) (B) were exposed to the four putative cross-reactive epitopes encoded by LCMV and by PV and defined in the text. These were tested in intracellular cytokine assays after stimulation with 1 μM peptide and gated on CD8 T cells. Solid horizontal lines mark the means of the plotted samples showing reactivity. Horizontal dashed lines show the levels of background staining without peptide. C and D show enhanced reactivity to the NP313 epitopes in mice immune to one virus and then challenged with the other at 8 days post-infection. For clarity of the figure, data for unchallenged immune controls are not plotted. However, in unchallenged LCMV-immune or PV-immune BALB/c mice, less than 0.5% of the spleen CD8 cells reacted with any of the peptides. Less than 2.5% of CD8 T cells in the PEC reacted with any of the peptides, and the number of CD8 T cells in the PEC expanded greater than 10-fold by day 8.