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

Background and Objectives Previously, a weak phenotype Am or Bm 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 Am or Bm individuals. Materials and Methods We carried out in vitro erythroid differentiation of CD34+ cells from peripheral blood of a Bm 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 CD34+ cells from this Bm 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 RUNX1 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 RUNX1 and GATA‐2 or GATA‐1.