Emergence of distinct CD4⁺ GM-CSF⁺ T-cell populations in the GI tract during acute GVHD. Lethally irradiated Balb/c mice were transplanted with B6 bone marrow (5 × 10⁶) plus spleen cells (adjusted to yield an αβ T-cell dose of 8 × 10⁵). (A) Representative dot plots depicting the expression of GM-CSF and IFN-γ in donor-derived (H-2K^b+, TCR-β⁺) CD4⁺ (top) or CD8⁺ (bottom) T cells isolated from indicated tissues 21 days posttransplantation. (B) The percentage of donor CD4⁺ T cells expressing GM-CSF in each tissue. (C) The percentage of donor-derived CD4⁺ T cells that were either GM-CSF⁺ IFN-γ⁻ or GM-CSF⁺ IFN-γ⁺ in each tissue. Results from panels B and C are from 2 independent experiments (n = 15). (D-F) The total number of CD4⁺ T cells (D), CD4⁺ GM-CSF⁺ IFN-γ⁻ T cells (E), and CD4⁺ GM-CSF⁺ IFN-γ⁺ T cells (F) in the colon at 7, 14, and 21 days’ posttransplantation. Data are from 2 experiments (n = 8-10 mice). (G) Representative dot plot gated on donor CD4⁺ T cells expressing GM-CSF and/or IFN-γ in the colon and mLN at 14 days’ posttransplantation. (H-I) The percentage of GM-CSF⁺ IFN-γ⁺ (H) and GM-CSF⁺ IFN-γ⁻ (I) donor CD4⁺ T cells in the indicated tissues at 7 and 14 days’ posttransplantation. Data for panels H and I are from 2 experiments (n = 9-10 mice per time point). *P < .05, **P < .01, ***P < .001, ****P < .0001. D7, day 7; D14, day 14.