Figure 2.

T cell deletion and functional unresponsiveness are distinct mechanisms for silencing antiviral immune responses. Naive +/+ mice, +/+ immune mice (161 d after LCMV Armstrong infection; 2 × 10⁵ PFU, i.p.), and +/+ or CD4^−/− mice infected with LCMV-t1b (2 × 10⁶ PFU, i.v.) 60 d previously were checked for the physical presence and functional responsiveness of LCMV-specific CD8 T cells. (A–H) LCMV-specific CD8 T cells were visualized using MHC class I tetramers complexed to viral peptides. Cells were costained with anti-CD8–PE, anti-CD44–FITC, and either D^b(GP33–41) or D^b(NP396–404) tetramers conjugated to allophycocyanin. The histograms show gated CD8 lymphocytes, and the percentage of CD8 cells costaining with either D^b(GP33–41) or D^b(NP396–404) are indicated in the corresponding upper right quadrant. Where not shown values are <0.2%. (I–L) Numbers of LCMV-specific IFN-γ producing cells were enumerated using single-cell cytokine ELISPOT assays. The number of splenocytes producing IFN-γ after stimulation with either GP33–41 (black bars) or NP396–404 peptides (hatched bars) are shown (± SD).