PDCD1 and infection: In persistent AV [lymphocytic choriomeningitis virus (LCMV)] infections tolerance is the result of suppressive PD-L1 (CD274) signals that engage T cell expressed PD-1 (CD279) receptors, limiting effector T cell clearance and causing T cell anergy (Mueller et al., 2010; Wei et al., 2013; Penaloza-MacMaster et al., 2014).