Platelets must have CD154 for collagen-mediated CTL augmentation. (A) CD154^−/− mice were immunized subcutaneously on the flank with 10⁶ pfu Ad5-mOVA in PBS or 30 mg/mL collagen. After 14 days, spleens were harvested for lytic assays. (B) CD154^−/− mice were adoptively transferred with 3 × 10⁸ B6 platelets 4 hours before subcutaneous immunization with 10⁶ pfu Ad5-mOVA in PBS or 30 mg/mL collagen on the flank. After 14 days, spleens were harvested for lytic assays. Each panel is representative of 2 experiments of 3 mice per group.