WT, CD28−/−, B7.1−/−, or B7.2−/− mice were immunized s.c. with B8R-peptide (10 µg/mouse) in IFA. On day seven splenocytes were harvested and stained for CD8, CD44, B8R-tetramer. Top: Representative plots of tetramer staining, gating on CD8 cells. Percentages of activated B8R-tetramer positive CD8 T cells (CD8+CD44+B8R+) are indicated. Bottom: Total numbers of B8R-tetramer positive CD8+CD44+ T cells per spleen. Results are mean number ± SEM (n=4 mice/group) from one experiment. *, p < 0.05 (wt mice vs knockout) as determined by Student’s t test. Similar results were obtained in 1 additional experiment.