**1. Introduction**

The Duffy blood group system, ISBT number 008/symbol (FY), was published for the first time in 1950 when anti-Fya was identified in a suspected hemolytic transfusion reaction in a 43-year-old patient with hemophilia who received 3 packed red blood cell (PRBC) units for treatment of spontaneous bleeding and who developed jaundice 1 day after transfusion [1, 2]. Approximately, 1 year later, anti-Fyb was discovered in a postpartum blood sample from a patient who gave birth to her third child [3].

Chromosome 1 has both FY and RH gene loci. The FY locus is located on the long arm at position 1q22-q23 where it consists of two exons distributed over 1.5 kbp of gDNA, whereas RH resides on the short arm. The Duffy system is N-glycosylated multi-pass transmembrane glycoprotein (**Figure 1**) [4] also known as the atypical chemokine receptor 1 (ACKR1, CD234). The protein is composed of 336 amino acids. There are two possible Duffy mRNAs which are translated from the Duffy antigen gene, a less abundant α form (338 amino acids) and a major β form (336 amino acids) which differ by 2 amino acids in the N-terminus. Approximately 6000–13,000 copies of the Duffy protein are found on the surface of RBCs [5].

The Duffy blood group includes six known antigens that differ by amino acid sequence. The Duffy antigen prevalence varies between racial groups.

ACKR1 (previously known as DARC) is a receptor for a variety of chemokines, including interleukin-8, monocyte chemotactic protein-1, and melanoma growth stimulatory activity. Also, this glycoprotein is a receptor for *Plasmodium vivax* and *Plasmodium knowlesi*; thus red cells with Fy(a-b-) phenotype are resistant to invasion by these malarial species. Antibodies formed against the Duffy antigens show a dosage effect and are a cause of both hemolytic transfusion reactions and hemolytic disease of fetus and newborn. The Duffy protein is also found on the endothelial cells of capillary and postcapillary venules, the epithelial cells of kidney collecting ducts, lung alveoli, and Purkinje cells of cerebellum [6].

#### **Figure 1.**

*The predicted seven-transmembrane domain structure of the Duffy protein. The amino acid change responsible for Fya/Fyb polymorphism, the mutation responsible for Fyx, and the glycosylation sites and the regions where Fy3 (and Fy6) map are indicated (reproduced with permission).*
