Galectin-1 is required for maximal regulatory T cell function. (A) Phenotype of CD4⁺CD25⁻ and CD4⁺CD25⁺ T cells of wild-type and galectin-1^−/− 129P3/J mice. Dotplots showing similar percentages of CD4⁺CD25⁺ T cells in both strains of mice and expression of Foxp3 in the selected CD4⁺CD25⁻ and CD4⁺CD25⁺ T-cell populations by FACS analysis from both strain of mice. Plots are from 1 representative experiment of 3 experiments. (B) The suppressive capacity of the wild-type and galectin-1^−/− CD4⁺CD25⁺ T cells was compared by mixing the cells at different ratios with galectin-1^−/− CD4⁺CD25⁻ T cells. The cells were stimulated with anti-CD3ϵ antibody and T-cell–depleted antigen-presenting cells for 72 hours. The IC₅₀ line is represented to indicate the CD25⁺/CD25⁻ ratio that gives 50% suppression (n = 3). (C) Secretion of IL-2 as measured by CTLL cell proliferation in the supernatants harvested after 48 hours of culture. *P ≤ .038; **P ≤ .049; ***P ≤ .026. The data are the mean ± SD values of 1 representative experiment of 3 independent experiments.