Suppressive activity of CB-derived total CD19⁺ B cells and naive and transitional B-cell subsets partly depends on IL-10 secretion. (A) Suppressive effect of B-cell subsets on proliferation of CFSE-labeled CD4⁺ T cells in the presence or absence of IL-10 blockade. Flow cytometry histograms show CD4⁺ T cells cultured alone or with total CD19⁺ B cells, naive B cells, or transitional B cells at a 1:1 ratio in the presence or absence of a blocking mAb to both IL-10 and IL-10R simultaneously. Data represent 4 independent experiments. Bars indicate median values and upper whisker of error bar represent range. *P < .05 by nonparametric ANOVA. (B) IL-10 blockade partially reverses the suppressive effect of CB-derived B cells on CD4⁺ T-cell cytokine secretion at a 1:1 (B cell:T-cell) ratio. Supernatants were harvested from B-cell/T-cell cocultures and assayed for the presence of IL-2, IFN-γ, and TNF-α production by ELISA. Data are representative of 4 independent experiments. Bars indicate median values and ranges (upper whiskers). *P < .05 by nonparametric ANOVA.