Chronic Ag-stimulated day 7 secondary effector CD8+ T cells produced less IFN-γ. IFN-γ production by chronic Ag-stimulated virus-specific CD8+ T cells was defective compared with controls, after ex vivo stimulation with OVA257–264 peptide. A, Representative histogram (gated on CD8+ T cells) shows the reduction in IFN-γ production by chronic Ag-stimulated CD8+ T cells relative to single prime controls. B, Each symbol represents a single animal, pooled MFI of IFN-γ-producing cells (gated on CD8+ T cells) indicates decreased function of chronic Ag-stimulated CD8+ T cells compared with single prime controls (n = 6 mice, p < 0.001).