IgM^hi and IgM^lo TS B cells differ functionally and in their potential to differentiate. (A) Histograms of flow cytometry data demonstrating cell trace violet (CTV) dilution following 5 d of culture with CD40L + anti-IgM in IgM^hi and IgM^lo TS B cells from an HCD. (B) Scatter plots demonstrating increased proliferation of IgM^hi TS compared with IgM^lo TS B cells when stimulated with CD40L + anti-IgM for 5 d (medians, Wilcoxon test). *, P < 0.05. (C) Flow cytometry contour plots demonstrating that an IgM^hi phenotype is maintained on IgM^hi TS B cells after CpG stimulation for 5 d. (D) Scatter plots demonstrating that an IgM^hi phenotype is maintained on IgM^hi TS B cells after CpG stimulation for 5 d (mean ± SD, paired t test). **, P < 0.01. (E) Flow cytometry contour plots and scatter plots demonstrating greater up-regulation of CD45RB by IgM^hi than IgM^lo TS and naive (CD27⁻IgD⁺CD10⁻) B cell subsets at day 5 culture with CpG (mean ± SD, paired t test). *, P < 0.05; **, P < 0.01. (F) Flow cytometry contour plots and scatter plots demonstrating higher frequency of IL10 expressing cells among IgM^hi TS B cells following 6-h stimulation with PMA/ionomycin (median, Wilcoxon test). *, P < 0.05.