IFNG and viral infectious disease: While PD-1int CD8+ T cells elicited by acute LCMV-Armstrong viral infection remained functional (IFNγ) and downregulated PD-1 (to PD-1int) after the virus was cleared, PD-1hi-expressing CD8+ T cells displayed an exhausted phenotype in the face of chronic LCMV-clone-13 infection14.