Staining was performed on freshly isolated lymphocytes as previously described [4] . Briefly, approximately 5610 6 cells were added to the wells of a 96-well V-bottom plate and were blocked with unconjugated streptavidin (Molecular Probes) and F c block (Pharmingen) for 15 min at room temperature (RT). Following a 5-min centrifugation at 5006g, lymphocytes were labeled with a FITC-conjugated anti-CD62L antibody, (Pharmingen), an allophycocyanin-conjugated anti-CD8 antibody (Pharmingen), and tetramer for 30 min at RT. The tetramer was a PE-conjugated major histocompatibility complex (MHC) class I K b tetramer (NIH Tetramer Facility) containing the H-2K b restricted peptide VSV N 53-59 (N-RGYVYQGL-C). Sham-inoculated control animals were used to determine background levels of tetramer binding. Background was routinely less than 0.1% and was subtracted from all reported percentages.