In contrast, PD-1KO mice had reduced primary peak and recrudescent parasitemia compared to WT mice (note log scale on Fig. 1), < 30% of the PD-1 KO mice developed chronic infections, and recrudescent parasitemia levels in these mice were > 100-fold lower than those in the WT mice as seen previously13. Here, PDCD1 is linked to parasitic infectious disease.