Differential expression of the Duffy antigen receptor for chemokines according to RBC age and FY genotype

BACKGROUND: The Duffy (Fy) blood group (also known as Duffy antigen recepto r for chemokines, or DARC) may be involved in regulation of the level of ci rculating proinflammatory chemokines, and it is an obligatory receptor on R BCs for the human malaria parasite Plasmodium vivax. STUDY DESIGN AND METHODS: Because quantification of Fy expression by using RBCs of various ages will not detect acute changes associated with inflamma tory states, and because P. vivax exclusively invades reticulocytes, a flow cytometric method was developed to measure the level of surface expression of Fy. Reticulocytes and mature RBCs from persons with different genotypes (GATA-1 T-->C promoter mutation at nt -46; FY*A and FY*B in the ORF) were used. RESULTS: Expression of the Fy6 epitope, which is required for P. vivax inva sion, was 49 +/- 19 percent higher on reticulocytes than on mature RBCs, re gardless of donor genotype (p<0.0001). Fy6 levels were approximately 50 per cent lower in persons who were heterozygous for the GATA-1 promoter mutatio n and were significantly lower on reticulocytes and mature RBCs of the FY*B / FY*B genotype than on those of the FY*A/FY*A or FY*A/FY*B genotype. CONCLUSION: Fy has greater expression on reticulocytes than on mature RBCs in flow cytometry. This method may be useful in further studies of this ant igen, such as characterization of reticulocytes and RBC phenotypes across p opulations, in response to chemokine regulation, and in the context of susc eptibility to P. vivax and other parasites.