Changes in bcl-2 expression of CD34⁺/CD38^−/low hematopoietic precursors during overnight incubation of MPB in serum-free RPMI. Cells were analyzed using three-color immunofluorescence of CD34-tri- color, CD38-PE, and bcl-2-FITC. After membrane antigen staining with anti-CD34 and anti-CD38 antibodies, cells were permeabilized with Ortho Permeafix and stained for anti-bcl-2. Bcl-2 expression was analyzed according to CD38 antigen intensity level (regions R3, R4, and R5 in Fig 1C). Data show one representative experiment of six. (A) Bcl-2 expression before incubation, representing a bimodal histogram of bcl-2^low(MFI = 95) and bcl- 2^high (MFI = 259). (B) Bcl-2 expression in the same cells after incubation showing a single histogram of bcl- 2^high (MFI = 212).