Host pDCs or cDCs alone are sufficient to stimulate alloreactive CD4⁺ T cells and induce GVHD. (A,B) Totals of 2 × 10⁶ BALB/c (H-2K^d+) CD4⁺ T cells were transferred to irradiated H2-Ab1^−/− mice preinjected with 2 × 10⁶ WT B cells, pDCs, or cDCs. Expansion of H-2K^d+ donor CD4⁺ T cells in the mLNs (mean ± SD;A) and cell division of CFSE-labeled donor CD4⁺ T cells in the spleens (B). (C) pDCs were injected to irradiated H2-Ab1^−/− mice. Expression levels of B220 and CD11c on I-A^b+ cells were analyzed 3 days after transfer and compared with those before transfer. (D) Aliquots of 2 × 10⁶ CFSE-labeled BALB/c CD4⁺ T cells were transferred to irradiated H2-Ab1^−/− mice preinjected with 10⁶ pDCs plus 10⁶ cDCs or 2 × 10⁶ cDCs from WT B6 mice. Cell divisions of donor CD4⁺ T cells in the spleens on day 7 are shown. (E,F) BALB/c CD4⁺ T cells were transferred as above and GVHD clinical scores (E), and pathology scores in the liver and intestine (F) on day 6 are shown as mean plus or minus SEM. (G) Lethally irradiated H2-Ab1^−/− mice preinjected with pDCs, cDCs, or B cells were injected with 2 × 10⁶ CD4⁺ T cells and 5 × 10⁶ TCD-BM from BALB/c mice. Survival after BMT is shown. Results from 2 similar experiments were combined. *P < .05 compared with B cells.