Analysis of B cell development in the blood and bone marrow by flow cytometry. (A) Ficoll-separated peripheral blood mononuclear cells were stained with PE-labeled anti-CD19 and FITC-labeled anti-CD20. The percentage of cells positive for CD19 and CD20 is indicated. The number of events shown is 20,000 for the healthy control and 250,000 for both the disease control (a patient with a mutation within a transcriptional regulatory element in intron 1 of BTK) and the patient. (B) Bone marrow cells were stained with PE-labeled anti-CD19 and FITC-labeled anti-CD34 or APC-labeled anti-CD19, FITC-labeled anti-TdT, and PE-labeled anti-VpreB. The percentage of cells within the lymphoid gate that fall into each of the sectors is shown. The number of events shown is 20,000 for the healthy control, 125,000 for the disease control (a patient with a mutation at the +1 donor splice site of intron 2 in BTK), and 250,000 for the patient. The peripheral blood analysis was performed on samples obtained from the p85α-deficient patient on three separate occasions. Bone marrow from the patient was obtained once and stained twice.