Further characterization of peripheral blood B cells from patients 2 and 3. Cells from a healthy control and the patients were permeabilized and stained with PerCP Cy5.5 anti-CD20, PE anti-CD79a, and FITC anti-IgM (A). The CD20⁺ cells were analyzed for expression of cytoplasmic CD79a and IgM. All of the cells were positive for CD79a, the percentage of cells positive or negative for cytoplasmic IgM is shown. Maturation and activation markers on peripheral blood B cells from a healthy control, patient 2, patient 3, and a patient with a mutation in Btk (G to C at the 1+ position of the splice donor site for intron 2) were stained with APC anti-CD19, PerCp Cy5.5 anti-CD20, PE anti-CD10, and FITC anti-20 (B). Cells that were positive for CD19 and CD20 were analyzed for expression of CD10 and CD5 (top). The percentages of B cells positive for each marker are shown. The middle and bottom panels show cells stained with PE anti-CD19, FITC anti-CD23, and APC anti-CD62L. The percentages of CD19⁺ cells that were dimly positive for CD23 are indicated. The pattern of CD62L staining is seen in the bottom panel.