Acute GVHD results in a significant reduction in the ratio of CD4⁺ Foxp3⁺ to CD4⁺ Foxp3⁻ T cells in the spleen and in GVHD target tissues. Lethally irradiated (900 cGy) Balb/c mice received transplants of TCD B6 BM alone (control) or together with 3 × 10⁵ B6 spleen cells (GVHD). Cohorts of mice (n = 6/group per time point) were then killed on days 9, 20, or 29 after transplantation. (A,B) The absolute number of CD4⁺Foxp3⁻ and CD4⁺Foxp3⁺ T cells in the spleens of control or GVHD animals is shown in panels A and B, respectively, for each time point. (C) The ratio of CD4⁺Foxp3⁻ to CD4⁺Foxp3⁺ T cells in the spleens of control and GVHD mice. Data in panels A-C are the cumulative results from 2 experiments and are presented as the mean plus or minus SEM. (D,E) Lethally irradiated (900 cGy) Balb/c mice were transplanted with TCD B6 BM alone (control) or together with 3 × 10⁵ B6 spleen cells (GVHD). Lymphocytes were isolated from the lungs or livers of control or GVHD mice (n = 2-3/group per time point) and pooled suspensions were analyzed for the proportion of CD4⁺Foxp3⁻ versus CD4⁺Foxp3⁺ T cells. The ratio of CD4⁺Foxp3⁻ to CD4⁺Foxp3⁺ T cells in the lung and liver of control and GVHD mice at the indicated time points is shown in panels D and E, respectively. Data are derived from 3 to 4 experiments per time point and are presented as the mean plus or minus SEM. Statistics: *P ≤ .05, **P < .01.