Induction of Gfi-1B during erythroid maturation of human primary cells. Expression of Gfi-1B was determined by real-time PCR and normalized using HPRT as a housekeeping gene. (A) A 2-step system of erythroid differentiation: CD34⁺ cells from PB were cultured in a serum-free medium in the presence of EPO, SCF, IL3, and DXM. After 6 days of culture, CD34 expression was lost, and nearly all the cells expressed the CD36 antigen at their surface. Cells were sorted according to the GPA expression, and CD36⁺/GPA^– cells were then induced into terminal maturation in the presence of SCF and EPO alone. (B) Up-regulation of GPA expression during erythroid differentiation. GPA level mainly increased during the late steps of maturation (RT-PCR: n = 3, each in triplicate). (C) High expression of Gfi-1B during erythroid maturation. Gfi-1B level increased at day 6 of erythroid differentiation and was higher in the CD36⁺/GPA⁺ fraction than in the CD36⁺/GPA^– one (RT-PCR: n = 3 each in triplicate). Data are expressed as mean ± SD.