cDC function is disrupted in GVHD, and this is specific to the MHC class II antigen presentation pathway. (Ai) B6.CD11c.OVA grafts (TCD BM ± CD3⁺ T cells) were transferred into irradiated BALB/c recipients. Ten days after transplantation, cDCs were sorted and cultured with OT-II Tg T cells. (Aii) OVA_(323-339) was added to the culture wells as positive controls for MHC class II availability. Representative data shown from one of 4 replicate experiments. Negative controls, including T cells plated with peptide alone, and B6.WT DCs + OTI/II cells were performed to confirm specificity of the assay (data not shown). (B) Same as described in panel Ai, but DCs were plated with OT-I Tg T cells. (C) CD8⁺ and CD8⁻ cDCs, from either naive (Ci) or post-transplantation animals (Cii), were sort purified and plated with OT-II T cells. Data are representative of 4 replicate experiments. (D) cDCs were further fractionated into DN or CD4⁺ subsets (non-GVHD animals) and DN only (GVHD animals). CD4⁺ cDCs were not present (NP) in the animals with GVHD and therefore could not be assessed. A total of 10⁵ of the specified cDC subset were plated with 10⁵ OT-II T cells or TEa T cells as shown. Data are representative of 3 replicate experiments. (E) A total of 5 × 10⁶ B6 TCD BM (non-GVHD) + 2 × 10⁶ CD3⁺ T cells (GVHD) were transferred into Bm1.Act-mOVA recipients, and CFSE-labeled OT-I T cells were adoptively transferred on day 7 after transplantation to measure the extent of cross-presentation by donor DCs. β₂m^−/− donor grafts were used as negative controls. Data are representative from 2 similar experiments: n = 8 in the BM only group; 9 in the BM + T group. **P = .01 to .001.