Donor CD4⁺ T-cell–derived GM-CSF promotes the activation of colonic dendritic cells. (A-E) Lethally irradiated Balb/c mice were transplanted with B6 Rag-1^−/− BM (5 × 10⁶) alone or together with 1 × 10⁶ purified CD4⁺ T cells from WT or GM-CSF^−/− mice. The gating strategy to delineate myeloid cell populations is shown in supplemental Figure 5. (A) The absolute number of donor-derived CD45.2⁺, CD4⁺ T cells, neutrophils, macrophages, and DCs in the colons of animals 21 days posttransplantation. Results are from a single experiment (n = 3-5/group). (B) The absolute number of donor-derived CD45.2⁺, CD4⁺ T cells, neutrophils, macrophages, and DCs in the colons of animals 13 days posttransplantation. (C) The percentage of donor-derived DCs that expressed CD103 and/or CD11b in the colon. Data in panels B and C are from 3 experiments (n = 9-13/group). (D) Representative histograms gated on donor CD64⁻ MHC-II⁺ CD11c⁺ cells showing expression of MHC class II, CD80, and CD86 from mice receiving either WT or GM-CSF^−/− CD4⁺ T cells compared with FMO controls. (E) Mean fluorescence intensity of MHC class II, CD80, and CD86 expression on donor CD64⁻ MHC-II⁺ CD11c⁺ dendritic cells in replicate mice. Results are from 2 experiments (n = 9-10 per group). (F) mRNA expression of Il23a in sorted donor dendritic cells obtained from pooled colon lamina propria of mice receiving either WT or GM-CSF^−/− CD4⁺ cells on days 13 to 15 posttransplant. Each data point represents pooled results from 5 animals. Data are from 3 independent groups of mice. *P < .05; ****P < .0001.