PDCD1 and parasitic infectious disease: The indistinguishable kinetics of parasitemia in PD-1-/- and PD-L1-/- mice together with the LAG-3 blockade experiment support such an interpretation, since LAG-3 neutralization in PD-L1-/- mice promotes remarkable growth control and clearance of blood parasites, which in WT mice is only achieved upon co-blockade with PD-L1.