Fig. 1.

Secondary CD8 T-cell response to Listeria is CD28 dependent. Mice were infected with 5000 CFU Lm-OVA, challenged with 10⁵ CFU on day 30, and analyzed for OVA-specific splenic CD8 cells by staining with K^b/SIINFEKL tetramers 5 days later. In A, CD28^−/fl C57BL/6 mice were used, and CD28 deletion was induced by tamoxifen in oil feeding (“TM”, 2.5 mg/dose) on days 24–27; oil only served as control. In B, wt C57BL/6 mice were treated with the blocking CD28-specific mAb E18 (100 μg/dose) on days 29, 31, and 33. ***P < 0.0001