Duffy Antigen Expression in Erythroid Bone Marrow Precursor Cells of Genotypically Duffy Negative Individuals

The gene encoding the Duffy blood group protein (Fy, CD234; additional designations Duffy Antigen Receptor of Chemokines [DARC] and Atypical Chemokine Receptor 1 [ACKR1]) is characterized by a SNP in a GATA-1 transcription factor binding site associated with the erythrocyte silent (ES) phenotype. FY ES homozygous people are viewed to be highly resistant to blood stage infection with Plasmodium vivax . Increasingly, however, studies are reporting P. vivax infections in Fy-negative individuals across malarious African countries where FY ES approaches genetic fixation. This suggests that P. vivax has evolved a Fy-independent RBC invasion pathway, or that the GATA-1 SNP does not abolish Fy expression. Here, we tested the second hypothesis through binding studies to erythroid lineage cells using recombinant P. vivax Duffy binding protein, the parasite invasion ligand and Fy6-specific antibodies. We first observed variable Fy expression on circulating RBCs, irrespective of FY genotype; FY ES RBCs were periodically Fy-positive. Furthermore, during the in vitro erythroid differentiation of CD34+ cells and on ex vivo bone marrow samples, we observed Fy expression on erythroid precursor cells from FY ES people. Finally, the Fy6-specific nanobody, CA111 was used to capture Fy from the surface of FY ES RBCs. Our findings reveal that the GATA-1 SNP does not fully abolish Fy expression and provide insight on potential susceptibility of Fy-negative people to vivax malaria.