Flow cytometric analysis of purified peripheral B cells from a nonallergic donor. (A) 10⁵ B cells stained with anti-CD19-PE (light black line) and its isotype control-PE (bold black line) after anti-CD19 separation. The percentage of purified CD19⁺ cells was 96.5%. (B) CD19⁺ cells after anti-IgM–selection staining with fluorescein conjugated anti-IgM (light black line) and its fluorescein-conjugated isotype control (bold black line). The percentage of purified IgM⁺ cells was 86%. (C) Shows staining of CD19 IgM-selected B cells with a biotinylated anti-IgE (2 μg/mL, HP6029) and its appropiate biotinylated isotype control in the same concentration by using streptavidin-conjugated PE as a secondary reagent. IgE⁺cells were not detectable. As a positive control, cells from an allergic donor were stained (data not shown).