Blood group B gene is barely expressed in in vitro erythroid culture of B m ‐derived CD34 + cells without an erythroid cell‐specific regulatory element

Background and Objectives Previously, a weak phenotype A m or B m was assumed to be caused by a reduction of A or B gene expression in bone marrow cells, but not in mucus‐secreting cells. However, ABO expression has not been examined in erythroid progenitor cells of A m or B m individuals. Materials and Methods We carried out in vitro erythroid differentiation of CD 34 + cells from peripheral blood of a B m individual harbouring a 3·0‐kb deletion including an erythroid cell‐specific regulatory element, named the +5·8‐kb site, in intron 1 of the human ABO blood group gene. Results During the in vitro differentiation of CD 34 + cells from this B m individual into erythroid cells, B‐antigens were not detectable on the cultured cells by flow cytometric analysis, and allele‐specific RT ‐ PCR consistently detected the transcripts from the O allele, but not from the B allele. Moreover, chromatin immunoprecipitation assay demonstrated that both RUNX 1 and GATA ‐2 or GATA ‐1 were bound to the +5·8‐kb site in cultured erythroid cells expressing ABO . Conclusion It is likely that the +5·8‐kb site enhances transcription from the ABO promoter in erythroid cells through binding of RUNX 1 and GATA ‐2 or GATA ‐1.