Human B10 and B10pro cells in (A) cord blood and (B) spleen and tonsil. B10 cells and B10 + B10pro cells were identified after in vitro stimulation for 5 hours and 48 hours, respectively, as in Figure 1. Representative results are shown along with graphs indicating IL-10⁺ B-cell frequencies within persons. Cells cultured with BFA alone served as negative controls for background IL-10 staining. Significant differences between means of BFA controls and individual stimuli are indicated: *P < .05; **P < .01.