PDCD1 and infection: These LCMV strains cause lethal immunopathology in mice deficient of the PD-1/PD-L1 axis (PD-L1 KO mice, PD-1 KO mice) during the acute phase of infection (Barber et al., 2006; Mueller et al., 2010; Frebel et al., 2012; Zinselmeyer et al., 2013; Shaabani et al., 2016).