Despite having very similar parasitemias, vaccinated CD8+ T-cell-depleted mice had significantly lower peak clinical scores (1.2 ± 0.2 versus 2.6 ± 0.24; P = 0.004) (Fig. 6B) (P = 0.004) and were better able to maintain hemoglobin levels (lowest level 86.6 ± 6.705 g/liter versus 63.4 ± 6.35 g/liter; P = 0.036) (Fig. 6C) than the vaccinated mice that received rat Ig, suggesting that vaccine-induced CD8+ T cells contributed to pathology. This evidence concerns the gene CD8A and parasitic infectious disease.