**2. Duffy antigens**

There are six known antigens with four main phenotypes; Fy(a+b+), Fy(a−b+), Fy(a+b−), and Fy(a−b−) (**Table 1**) [5]. The most common antigens are, two polymorphic and antithetical, Fya (FY1) and Fyb (FY2) which differ by one amino acid at position 42 on the extracellular domain, with glycine resulting in Fya expression and aspartic acid resulting in Fyb expression [5, 7]. They are sensitive to destruction when RBCs are treated with proteolytic enzymes such as papain or ficin, whereas, there is no RBCs destruction with trypsin treatment [8].

Fya antigen has a prevalence of 66% in Caucasians, 10% in Blacks, and 99% in Asians. It has been identified on fetal RBCs as early as 6 weeks gestation and reaches adult levels in approximately 12 weeks after birth. Fyb has a prevalence of 83% in Caucasians, 23% in Blacks, and 18.5% in Asians. It is expressed on cord blood cells. Fy3 antigen is expressed in 100% of Caucasians, 32% of Blacks, and 99.9% of Asians. It is also expressed on cord cells and demonstrates increased expression after birth. Fy5 antigen is expressed on 32% of Blacks and 99.9% of Caucasians and Asians. It is not expressed on Rh null RBCs. Fy6 is expressed in 100% of most populations and 32% of Blacks. The Fy(a–b–) phenotype is the major phenotype in approximately 70% Blacks, but is very rarely found in other populations. This phenotype is characterized by the


#### **Table 1.**

*Duffy blood group system phenotypes and prevalence. Reproduced with permission and modification.*

**87**

*The Duffy Blood Group System*

*DOI: http://dx.doi.org/10.5772/intechopen.89952*

epitope of Duffy and Rh protein [9–12].

**3. Duffy antibodies**

absence of the Fyb antigen on RBCs and its presence on non-erythroid cells. Duffy mRNA is not detected in the bone marrow of Fy(a–b–) individuals; however, it is detected in other tissues including the colon, lung, and spleen. This unique phenotype is caused by a single amino acid substitution at position 46 in the Duffy (Fyb) gene. This mutation impairs the promotor activity in erythroid cells by disrupting the binding site for GATA1 erythroid transcription factor. Furthermore, some individuals with this phenotype do not make anti-Fyb. This is believed to be due to a mutation in the, erythroid promoter, GATA-1 binding motif. Interestingly, the same Fy(a–b–) phenotype rarely found in Caucasians is characterized by absence of Duffy antigens expression in both erythroid and non-erythroid tissues due to possibly presence of mutations which prevent formation of Duffy protein. These individuals can form anti-Fy3. The have high prevalence antigens; Fy3, Fy5, and Fy6 are conformational epitopes as opposed to specific sequence epitopes with Fy5 hypothesized to be a combined conformational

Anti-Fya and -Fyb are clinically significant RBC alloantibodies which can cause immediate and delayed hemolytic transfusion reactions (HTRs) as well as hemolytic disease of the fetus and newborn (HDFN). They often result from previous exposure such as after transfusion or pregnancy. They are not usually naturally occurring. The Duffy antibodies are predominantly of the IgG subclass whereas the IgM form is rare. The mechanism of extravascular hemolysis (EH) in both HDFN and HTR is similar. In HDFN, the mother lacks a certain red cell antigen which the fetus is positive for, thus the mother is allo-immunized (i.e., made a new antibody) during the first pregnancy. If she gets exposed to the same antigen in subsequent pregnancy (ies), the fetus (es) is/are at risk of HDFN. Similarly, if a patient lacks a certain red cell antigen but receives red cell transfusion with a unit that has such antigen, the patient is at risk for allo-immunziation after the transfusion and HTR in subsequent transfusion (s). EH is typically induced by IgG red cell antibodies. EH consists of consumption of antibody and/or C3b-bound red cells by phagocytes in the reticuloendothelial system (RES) causing a delayed hemolytic transfusion reaction (DHTR). DHTRs can be clinically significant leading to morbidity and possibly mortality. To avoid DHTR, patients with known clinically significant antibodies, receive red cell units that lack antigen (s) to their the cognate antibody (ies). The Duffy antibodies

are usually associated with a moderate DHTR and mild HDFN [13].

**4. The Duffy glycoprotein as a receptor for chemokines**

Anti-Fya is identified more than anti-Fy3, anti-Fy5, or anti-Fyb. Fya is 20 times more immunogenic than Fyb. Some of anti-Fya can bind and activate complements [14]. Anti-Fy3 is also clinically significant antibody which can cause mild HDFN and HTRs. Serologically, it can react with enzyme treated Fy(a+) or Fy(b+) RBCs, but fails to react with Fy(a−b−) RBCs [15]. Anti-Fy4 shows lack of consistent test results. It was found to be reactive with Fy(a−b−), some Fy(a+b−), some Fy(a−b+) RBCs but shows no reaction with Fy(a+b+) RBCs [16]. Anti-Fy5 reacts with enzyme treated Fy(a+) or Fy(b+) RBCs with no reaction with Fy(a−b−) RBCs or Rh null RBCS. It has been reported in sickle cell patients with delayed HTRs in the presence of other clinically significant alloantibodies [17]. A human anti-Fy6 has not been identified [18].

The Duffy glycoprotein can bind to a variety of chemokines and is known commonly as the Duffy antigen receptor for chemokines (DARC) or more recently

#### *The Duffy Blood Group System DOI: http://dx.doi.org/10.5772/intechopen.89952*

*Human Blood Group Systems and Haemoglobinopathies*

There are six known antigens with four main phenotypes; Fy(a+b+), Fy(a−b+), Fy(a+b−), and Fy(a−b−) (**Table 1**) [5]. The most common antigens are, two polymorphic and antithetical, Fya (FY1) and Fyb (FY2) which differ by one amino acid at position 42 on the extracellular domain, with glycine resulting in Fya expression and aspartic acid resulting in Fyb expression [5, 7]. They are sensitive to destruction when RBCs are treated with proteolytic enzymes such as papain or ficin, whereas,

*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* 

Fya antigen has a prevalence of 66% in Caucasians, 10% in Blacks, and 99% in Asians. It has been identified on fetal RBCs as early as 6 weeks gestation and reaches adult levels in approximately 12 weeks after birth. Fyb has a prevalence of 83% in Caucasians, 23% in Blacks, and 18.5% in Asians. It is expressed on cord blood cells. Fy3 antigen is expressed in 100% of Caucasians, 32% of Blacks, and 99.9% of Asians. It is also expressed on cord cells and demonstrates increased expression after birth. Fy5 antigen is expressed on 32% of Blacks and 99.9% of Caucasians and Asians. It is not expressed on Rh null RBCs. Fy6 is expressed in 100% of most populations and 32% of Blacks. The Fy(a–b–) phenotype is the major phenotype in approximately 70% Blacks, but is very rarely found in other populations. This phenotype is characterized by the

**Red cell phenotype Prevalence (%) Allele Caucasians Blacks**

Fy3 100 32 Fy5 99.9 32 Fy6 100 32

Fy (a+b−) 17 9 FY\*01/FY\*01 or FY\*A/FY\*A Fy (a**−**b+) 34 22 FY\*02/FY\*02 or FY\*B/FY\*B Fy (a+b+) 49 1 FY\*A/FY\*B Fy (a**−**b−) Rare 68 FY\*/N.01–05, FY\*/N.01–02‡

*‡Nomenclature pending approval by the ISBT working party on terminology for red cell surface antigens.*

*Duffy blood group system phenotypes and prevalence. Reproduced with permission and modification.*

there is no RBCs destruction with trypsin treatment [8].

*Fy3 (and Fy6) map are indicated (reproduced with permission).*

**2. Duffy antigens**

**Figure 1.**

**86**

**Table 1.**

absence of the Fyb antigen on RBCs and its presence on non-erythroid cells. Duffy mRNA is not detected in the bone marrow of Fy(a–b–) individuals; however, it is detected in other tissues including the colon, lung, and spleen. This unique phenotype is caused by a single amino acid substitution at position 46 in the Duffy (Fyb) gene. This mutation impairs the promotor activity in erythroid cells by disrupting the binding site for GATA1 erythroid transcription factor. Furthermore, some individuals with this phenotype do not make anti-Fyb. This is believed to be due to a mutation in the, erythroid promoter, GATA-1 binding motif. Interestingly, the same Fy(a–b–) phenotype rarely found in Caucasians is characterized by absence of Duffy antigens expression in both erythroid and non-erythroid tissues due to possibly presence of mutations which prevent formation of Duffy protein. These individuals can form anti-Fy3. The have high prevalence antigens; Fy3, Fy5, and Fy6 are conformational epitopes as opposed to specific sequence epitopes with Fy5 hypothesized to be a combined conformational epitope of Duffy and Rh protein [9–12].
