Host NK cells inhibit alloreactive CD8⁺ T-cell priming in vivo through their capacity to rapidly eliminate allogeneic H-2^d DCs in draining lymph nodes. (A,B) B6 CD8^−/− mice, treated, or not, with anti-NK1.1 PK136 mAb, were injected intravenously with 10⁷ CFSE-labeled CD8⁺ T lymphocytes. Mice were then immunized with allogeneic BALB/c DCs (10⁶/mouse) 1 day after passive CD8⁺ T-cell transfer. Four days after immunization, CFSE dilution in TCR-β⁺CD8⁺ T cells was analyzed in popliteal (proximal) or inguineal (distal) lymph node cells by flow cytometry (A). (C,D) Percentage of CD8⁺ T cells (C) and CFSE low CD8⁺ T cells (D) among total popliteal lymph node cells from individual mice (3 or 4 per group). Data are representative of 3 experiments performed. (E,F) Normal C57BL/6 mice were injected with anti-NK1.1 PK136 mAb alone or together with anti-CD8–depleting mAb as indicated. Mice were immunized with a mixture of CFSE-labeled BALB/c DCs (green) and CMTMR-labeled B6 DCs (red) as in Figure 6. Lymph nodes were collected at 28 hours (E) or 72 hours (F) and processed for confocal microscopic analysis as in Figure 6. Histograms indicate the percentage of CFSE BALB/c DCs among control CMTMR B6 DCs. Data are mean plus or minus SEM of individual lymph nodes (2 or 3 mice per group) and are representative of 2 experiments performed. *P < .05. **P < .01.