Recovery of B cells and B-cell/T-cell ratio, B-cell subsets, and potential to produce IL-10. (A) B-cell recovery (left) and B-cell/T-cell ratio recovery (right). (B) Recovery of B-cell subsets. Percentage of transitional, naive, and memory B cells. Mean and standard error of the mean are shown, and values for 11 adult healthy volunteers (HV) are indicated. (C) Percentage of IL-10-producing B cells present early (day 90) after HSCT and in healthy volunteers (HV) was determined by stimulation of PBMCs with transfected L cells expressing CD40L for 24 hours with leukocyte activation cocktail added for the last 6 hours, followed by fixation, permeabilization, and assessment of IL-10 production by B cells, using flow cytometry. Short horizontal lines indicate the median values. IL-10 production in response to stimulation with L cells expressing CD40L was at least threefold higher than background response to nontransfected L cells. Comparison between patients and healthy volunteers were performed using a 2-tailed Mann-Whitney U test. Significant differences are indicated with ***P < .0005; **P < .005; *P < .05. NS, not significant.