A role of T cell–associated CD80 in the inhibitory effects of B7-H1/CD80 interaction. (A) WT B6 mice or CD80-KO mice were transferred intravenously with OT-I T cells. In panel B, B6 mice were transferred intravenously with WT, B7-H1-KO, or CD80-KO background OT-I T cells. In both settings, the recipient mice were injected intravenously with 0.5 mg of OVA_257-264 peptide, and treated intraperitoneally with 200 μg of 43H12 or control rat IgG on day of peptide injection and 3 days later. Splenocytes were harvested 5 days after peptide injection, and the percentage of OT-I T cells in CD8-positive population was assessed by flow cytometry. (C) B6 mice were transferred intravenously with OT-I T cells and injected intravenously with 0.5 mg of OVA_257-264 peptide. On day 3 and day 5, CD8/OVA-tetramer double-positive OT-I T cells was stained with anti-CD80 mAb and analyzed by flow cytometry (gray histogram). Nonstained background levels of the same cells are also shown (open histogram). All experiments were repeated at least 3 times, and the representative data are shown. The numbers in the histogram indicate the percentage of positively stained cells.