Figure 4: Protection against plasmodium infection in IrPySpz-immunized MHC-I- -Tg mice and (MHC-I- -Tg × CS-Tg) F1 mice. (MHC-I- -Tg × CS-Tg) F1 mice were generated by crossing CS-Tg mice to MHC-I- -Tg mice. Groups (4 mice per group) of naive MHC-I- -Tg mice and MHC-I- -Tg × CS-Tg mice were immunized with 5 × 104 IrPySpz via IM injection. Protection assay was performed by challenge with 1 × 104 infectious P. yoelii sporozoites via IV injection 2 weeks after immunization. Naïve MHC-I- -Tg mice and (MHC-I- -Tg × CS-Tg) F1 mice were also challenged as infection controls. The value of parasite burden was described previously.