Fig. 5.

An intact +39-kb CEBPA enhancer is required for human basophil differentiation. (A) IL-3–mediated differentiation of primary human CD34⁺ cells generates both basophils and mast cells from a myeloid progenitor that may either be a basophil/mast cell progenitor (BMCP) and/or derivative of the common myeloid progenitor (CMP) population. (B) FACS analysis shows impaired differentiation of basophils and a concomitant increase in mast cells after +39-kb enhancer disruption (mean ± SD of three independent experiments). (C) Representative images of May–Giemsa stains at day 14. Arrows indicate fully differentiated, mature basophils in the left panel, whereas the arrows indicate cells with abnormal basophilic and some eosinophilic granules in the +39-kb enhancer-disrupted cultures. (D) Impaired maturation of basophils based upon morphology in May–Grünwald Giemsa stains. Student’s t test performed between control vs. both guides (**P < 0.01). (E) Previous studies have shown that ordered expression of GATA2 and CEBPA is critical for differentiation of eosinophils, basophils, and mast cells. Our GWAS follow-up study has identified enhancers that, at least partially, mediate this ordered expression pattern. Up-regulation of GATA2 is required for all three lineages. Accordingly, the rs6782812 variant in the GATA2 locus is associated with both eosinophil and basophil counts. Up-regulation of CEBPA is required only for basophil differentiation from BMCPs and/or CMPs. Accordingly, the rs78744187 variant in the CEBPA locus is associated with basophil counts and affects basophil differentiation. BMCP, basophil/mast cell progenitor; BaP, basophil progenitor; EoP, eosinophil progenitor; MCP, mast cell progenitor.