This figure plots the CD8 T cell responses to the defined cross-reactive LCMV and PV NP313 epitopes under conditions of LCMV + PV heterologous immunity, as described in Table 1. This plots the activity in PEC CD8 T cells at day 4 post-infection. Here, the B10 series of mice is examined, and only those expressing H2d (B10.D2, like the H2d –expressing BALB/c mice (Figure 1)), show positive reactivity to the two peptides, thereby demonstrating MHC-restriction.